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Rakhshaninejad M, Zheng L, Nauwynck H. Shrimp (Penaeus vannamei) survive white spot syndrome virus infection by behavioral fever. Sci Rep 2023; 13:18034. [PMID: 37865676 PMCID: PMC10590431 DOI: 10.1038/s41598-023-45335-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2023] [Accepted: 10/18/2023] [Indexed: 10/23/2023] Open
Abstract
Both endotherms and ectotherms may raise their body temperature to limit pathogen infection. Endotherms do this by increasing their basal metabolism; this is called 'fever'. Ectotherms do this by migrating to warmer places; this is called 'behavioral fever'. White spot syndrome virus (WSSV) is the most lethal pathogen of cultured shrimp. This study examined the existence of behavioral fever in WSSV-infected Penaeus vannamei shrimp. Shrimp weighing 15 ± 0.5 g were inoculated intramuscularly with WSSV and kept in a four-compartment system (4-CS) with all the chambers at 27 °C or with a thermal gradient (27-29-31-33 °C). During the first 4 days post-inoculation, 94% of the WSSV-inoculated shrimp died in the 4-CS with a fixed temperature (27 °C), while only 28% died in the 4-CS with a temperature gradient. The inoculated animals clearly demonstrated a movement towards the warmer compartments, whereas this was not the case with the mock- and non-inoculated animals. With primary lymphoid organ cell cultures, it was demonstrated that the increase of temperature from 27-29 °C to 31-33 °C inhibits virus replication. It is concluded that behavioral fever is used by shrimp to elevate their temperature when infected with WSSV. Behavioral fever prevents WSSV infection and mortality.
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Affiliation(s)
- Mostafa Rakhshaninejad
- Laboratory of Virology, Department of Translational Physiology, Infectiology and Public Health, Faculty of Veterinary Medicine, Ghent University, Salisburylaan 133, 9820, Merelbeke, Belgium.
| | - Liping Zheng
- Laboratory of Virology, Department of Translational Physiology, Infectiology and Public Health, Faculty of Veterinary Medicine, Ghent University, Salisburylaan 133, 9820, Merelbeke, Belgium
| | - Hans Nauwynck
- Laboratory of Virology, Department of Translational Physiology, Infectiology and Public Health, Faculty of Veterinary Medicine, Ghent University, Salisburylaan 133, 9820, Merelbeke, Belgium
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2
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Forrest MJ, Halstead BJ, Grear DA, Kleeman PM, Todd BD, Miano OJ, Urquhart KD. KEEPING THE HEAT ON: WEIGHTED SURVEILLANCE FOR CHYTRID FUNGUS (BATRACHOCHYTRIUM DENDROBATIDIS) IN DIXIE VALLEY TOADS (ANAXYRUS [= BUFO] WILLIAMSI). J Wildl Dis 2023; 59:557-568. [PMID: 37486870 DOI: 10.7589/jwd-d-22-00049] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2022] [Accepted: 03/09/2023] [Indexed: 07/26/2023]
Abstract
Introduced fungal pathogens have caused declines and extinctions of naïve wildlife populations across vertebrate classes. Consequences of introduced pathogens to hosts with small ranges might be especially severe because of limited redundancy to rescue populations and lower abundance that may limit the resilience of populations to perturbations like disease introduction. As a complement to biosecurity measures to prevent the spread of pathogens, surveillance programs may enable early detection of pathogens, when management actions to limit the effects of pathogens on naïve hosts might be most beneficial. We analyzed surveillance data for the endangered and narrowly endemic Dixie Valley toad (Anaxyrus [= Bufo] williamsi) from two time periods (2011-2014 and 2019-2021) to estimate the minimum detectable prevalence of the amphibian fungal pathogen Batrachochytrium dendrobatidis (Bd). We assessed if detection efficiency could be improved by using samples from both Dixie Valley toads and co-occurring introduced American bullfrogs (Lithobates catesbeianus) and literature-derived surveillance weights. We further evaluated a weighted surveillance design to increase the efficiency of surveillance efforts for Bd within the toad's small (<6 km2) range. We found that monitoring adult and larval American bullfrogs would probably detect Bd more efficiently than monitoring Dixie Valley toads alone. Given that no Bd was detected, minimum detectable prevalence of Bd was <3% in 2011-2014, and <5% (Dixie Valley toads only) and <10% (American bullfrogs only) in 2019-2021. Optimal management for Bd depends on the mechanisms underlying its apparent absence from the range of Dixie Valley toads, but a balanced surveillance scheme that includes sampling American bullfrogs to increase the likelihood of detecting Bd, and adult Dixie Valley toads to ensure broad spatial coverage where American bullfrogs do not occur, would probably result in efficient surveillance, which might permit timely management of Bd if it is detected.
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Affiliation(s)
- Matthew J Forrest
- Scripps Institution of Oceanography, University of California San Diego, 9500 Gilman Drive, La Jolla, California 92093, USA
- Co-primary authors
| | - Brian J Halstead
- US Geological Survey, Western Ecological Research Center, Dixon Field Station, 800 Business Park Drive, Suite D, Dixon, California 95620, USA
- Co-primary authors
| | - Daniel A Grear
- US Geological Survey, National Wildlife Health Center, 6006 Schroeder Road, Madison, Wisconsin 53711, USA
| | - Patrick M Kleeman
- US Geological Survey, Western Ecological Research Center, Point Reyes Field Station, 1 Bear Valley Road, Point Reyes Station, California 94956, USA
| | - Brian D Todd
- Department of Wildlife, Fish, and Conservation Biology, University of California-Davis, One Shields Avenue, Davis, California 95616, USA
| | - Oliver J Miano
- Department of Wildlife, Fish, and Conservation Biology, University of California-Davis, One Shields Avenue, Davis, California 95616, USA
| | - Kris D Urquhart
- Nevada Department of Wildlife, 380 West B Street, Fallon, Nevada 89406, USA
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3
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Ujszegi J, Boros Z, Fodor A, Vajna B, Hettyey A. Metabolites of Xenorhabdus bacteria are potent candidates for mitigating amphibian chytridiomycosis. AMB Express 2023; 13:88. [PMID: 37615904 PMCID: PMC10449739 DOI: 10.1186/s13568-023-01585-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2023] [Accepted: 07/20/2023] [Indexed: 08/25/2023] Open
Abstract
Chytridiomycosis, caused by the chytrid fungus Batrachochytrium dendrobatidis (Bd), has caused extreme losses in amphibian biodiversity. Finding bacteria that produce metabolites with antifungal properties may turn out to be invaluable in the fight against this devastating disease. The entomopathogenic bacteria, Xenorhabdus szentirmaii and X. budapestensis produce secondary metabolites that are effective against a wide range of fungal plant pathogens. To assess whether they may also be effective against Bd, we extracted cell-free culture media (CFCM) from liquid cultures of X. szentirmaii and X. budapestensis and tested their ability to inhibit Bd growth in vitro. As a second step, using juvenile common toads (Bufo bufo) experimentally infected with Bd we also tested the in vivo antifungal efficacy of X. szentirmaii CFCM diluted to 2 and 10% (v/v), while also assessing possible malign side effects on amphibians. Results of the in vitro experiment documented highly effective growth inhibition by CFCMs of both Xenorhabdus species. The in vivo experiment showed that treatment with CFCM of X. szentirmaii applied at a dilution of 10% resulted in infection intensities reduced by ca. 73% compared to controls and to juvenile toads treated with CFCM applied at a dilution of 2%. At the same time, we detected no negative side effects of treatment with CFCM on toad survival and development. Our results clearly support the idea that metabolites of X. szentirmaii, and perhaps of several other Xenorhabdus species as well, may prove highly useful for the treatment of Bd infected amphibians.
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Affiliation(s)
- János Ujszegi
- Department of Evolutionary Ecology, Plant Protection Institute, Centre for Agricultural Research, Eötvös Loránd Research Network, Budapest, Hungary.
- Department of Systematic Zoology and Ecology, Eötvös Loránd University, Budapest, Hungary.
| | - Zsófia Boros
- Department of Evolutionary Ecology, Plant Protection Institute, Centre for Agricultural Research, Eötvös Loránd Research Network, Budapest, Hungary
- Department of Genetics, Eötvös Loránd University, Budapest, Hungary
- Department of Microbiology, Eötvös Loránd University, Budapest, Hungary
| | - András Fodor
- Department of Genetics, Eötvös Loránd University, Budapest, Hungary
| | - Balázs Vajna
- Department of Microbiology, Eötvös Loránd University, Budapest, Hungary
| | - Attila Hettyey
- Department of Evolutionary Ecology, Plant Protection Institute, Centre for Agricultural Research, Eötvös Loránd Research Network, Budapest, Hungary
- Department of Systematic Zoology and Ecology, Eötvös Loránd University, Budapest, Hungary
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4
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Adams AJ, Bushell J, Grasso RL. To treat or not to treat? Experimental pathogen exposure, treatment, and release of a threatened amphibian. Ecosphere 2022. [DOI: 10.1002/ecs2.4294] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Affiliation(s)
- Andrea J. Adams
- Resources Management and Science Division Yosemite National Park El Portal California USA
- Earth Research Institute University of California Santa Barbara California USA
| | | | - Robert L. Grasso
- Resources Management and Science Division Yosemite National Park El Portal California USA
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5
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Turner A, Heard G, Hall A, Wassens S. Age structure of amphibian populations with endemic chytridiomycosis, across climatic regions with markedly different infection risk. Ecol Evol 2022; 12:e9123. [PMID: 35898428 PMCID: PMC9309026 DOI: 10.1002/ece3.9123] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2022] [Revised: 06/05/2022] [Accepted: 06/28/2022] [Indexed: 11/30/2022] Open
Abstract
Threatening processes, such as disease, can drive major changes in population demographics of the host. Chytridiomycosis, caused by the fungal pathogen Batrachochytrium dendrobatidis (Bd), has led to the decline of at least 500 amphibian species across the globe and has been shown to truncate host age structure by lowering adult survival rates. This results in heavy reliance on annual recruitment and the inability to recover in the event of periodic recruitment failure. We used skeletochronology to determine the age structure, growth, and survival rates of populations of an endangered amphibian, Litoria raniformis, with endemic chytridiomycosis, across two climatically disparate regions in south‐eastern Australia: semi‐arid and temperate. Contrary to predictions, populations in the semi‐arid region (in which chytrid prevalence is substantially lower due to high temperatures) displayed a more truncated age structure than populations in the temperate study regions. Maximum recorded age was only two years in the semi‐arid region compared with up to four years in the temperate region. Wetland hydroperiod and average seasonal air temperature were correlated with age, and males had a slightly higher survival rate than females (0.31 for males and 0.27 for females). Despite the previously documented differences in chytrid prevalence between the two climatic regions, water availability and wetland hydroperiods appear the over‐riding determinants of the age structure and survival rates of L. raniformis. Targeted management which ensures water availability and improves survival of 1‐year‐old frogs into their second and third breeding season would reduce the impact of stochastic events on L. raniformis, and this may be true for numerous frog species susceptible to chytridiomycosis.
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Affiliation(s)
- Anna Turner
- School of Agricultural, Environmental and Veterinary Science Charles Sturt University Albury New South Wales Australia
| | - Geoffrey Heard
- Terrestrial Ecosystem Research Network The University of Queensland Indooroopily Queensland Australia
| | - Andrew Hall
- School of Agricultural, Environmental and Veterinary Science Charles Sturt University Albury New South Wales Australia
| | - Skye Wassens
- School of Agricultural, Environmental and Veterinary Science Charles Sturt University Albury New South Wales Australia
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6
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Haver M, Le Roux G, Friesen J, Loyau A, Vredenburg VT, Schmeller DS. The role of abiotic variables in an emerging global amphibian fungal disease in mountains. THE SCIENCE OF THE TOTAL ENVIRONMENT 2022; 815:152735. [PMID: 34974000 DOI: 10.1016/j.scitotenv.2021.152735] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/21/2021] [Revised: 12/23/2021] [Accepted: 12/23/2021] [Indexed: 06/14/2023]
Abstract
The emergence of the chytridiomycete fungal pathogen Batrachochytrium dendrobatidis (Bd), causing the disease chytridiomycosis, has caused collapse of amphibian communities in numerous mountain systems. The health of amphibians and of mountain freshwater habitats they inhabit is also threatened by ongoing changes in environmental and anthropogenic factors such as climate, hydrology, and pollution. Climate change is causing more extreme climatic events, shifts in ice occurrence, and changes in the timing of snowmelt and pollutant deposition cycles. All of these factors impact both pathogen and host, and disease dynamics. Here we review abiotic variables, known to control Bd occurrence and chytridiomycosis severity, and discuss how climate change may modify them. We propose two main categories of abiotic variables that may alter Bd distribution, persistence, and physiology: 1) climate and hydrology (temperature, precipitation, hydrology, ultraviolet radiation (UVR); and, 2) water chemistry (pH, salinity, pollution). For both categories, we identify topics for further research. More studies on the relationship between global change, pollution and pathogens in complex landscapes, such as mountains, are needed to allow for accurate risk assessments for freshwater ecosystems and resulting impacts on wildlife and human health. Our review emphasizes the importance of using data of higher spatiotemporal resolution and uniform abiotic metrics in order to better compare study outcomes. Fine-scale temperature variability, especially of water temperature, variability of moisture conditions and water levels, snow, ice and runoff dynamics should be assessed as abiotic variables shaping the mountain habitat of pathogen and host. A better understanding of hydroclimate and water chemistry variables, as co-factors in disease, will increase our understanding of chytridiomycosis dynamics.
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Affiliation(s)
- Marilen Haver
- Laboratoire Écologie Fonctionnelle et Environnement, Université de Toulouse, CNRS, Toulouse INP, Université Toulouse 3 - Paul Sabatier (UPS), Toulouse, France.
| | - Gaël Le Roux
- Laboratoire Écologie Fonctionnelle et Environnement, Université de Toulouse, CNRS, Toulouse INP, Université Toulouse 3 - Paul Sabatier (UPS), Toulouse, France
| | - Jan Friesen
- Environmental and Biotechnology Centre, Helmholtz Centre for Environmental Research - UFZ, Leipzig, Germany
| | - Adeline Loyau
- Laboratoire Écologie Fonctionnelle et Environnement, Université de Toulouse, CNRS, Toulouse INP, Université Toulouse 3 - Paul Sabatier (UPS), Toulouse, France; Department of Experimental Limnology, Leibniz-Institute of Freshwater Ecology and Inland Fisheries (IGB), Alte Fischerhütte 2, Stechlin D-16775, Germany
| | - Vance T Vredenburg
- Department of Biology, San Francisco State University, 1600 Holloway Ave., San Francisco, CA 94132, USA
| | - Dirk S Schmeller
- Laboratoire Écologie Fonctionnelle et Environnement, Université de Toulouse, CNRS, Toulouse INP, Université Toulouse 3 - Paul Sabatier (UPS), Toulouse, France
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7
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Alvarado-Rybak M, Acuña P, Peñafiel-Ricaurte A, Sewell TR, O'Hanlon SJ, Fisher MC, Valenzuela-Sánchez A, Cunningham AA, Azat C. Chytridiomycosis Outbreak in a Chilean Giant Frog ( Calyptocephalella gayi) Captive Breeding Program: Genomic Characterization and Pathological Findings. Front Vet Sci 2021; 8:733357. [PMID: 34631859 PMCID: PMC8497818 DOI: 10.3389/fvets.2021.733357] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2021] [Accepted: 08/27/2021] [Indexed: 11/13/2022] Open
Abstract
Emerging infectious diseases in wildlife are increasingly associated with animal mortality and species declines, but their source and genetic characterization often remains elusive. Amphibian chytridiomycosis, caused by the fungus Batrachochytrium dendrobatidis (Bd), has been associated with catastrophic and well-documented amphibian population declines and extinctions at the global scale. We used histology and whole-genome sequencing to describe the lesions caused by, and the genetic variability of, two Bd isolates obtained from a mass mortality event in a captive population of the threatened Chilean giant frog (Calyptocephalella gayi). This was the first time an association between Bd and high mortality had been detected in this charismatic and declining frog species. Pathological examinations revealed that 30 dead metamorphosed frogs presented agnathia or brachygnathia, a condition that is reported for the first time in association with chytridiomycosis. Phylogenomic analyses revealed that Bd isolates (PA1 and PA2) from captive C. gayi group with other Bd isolates (AVS2, AVS4, and AVS7) forming a single highly supported Chilean Bd clade within the global panzootic lineage of Bd (BdGPL). These findings are important to inform the strengthening of biosecurity measures to prevent the impacts of chytridiomycosis in captive breeding programs elsewhere.
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Affiliation(s)
- Mario Alvarado-Rybak
- Sustainability Research Centre & PhD Program in Conservation Medicine, Faculty of Life Sciences, Universidad Andres Bello, Santiago, Chile.,Institute of Zoology, Zoological Society of London, London, United Kingdom.,Núcleo de Ciencias Aplicadas en Ciencias Veterinarias y Agronómicas, Universidad de las Américas, Santiago, Chile
| | - Paz Acuña
- Criadero y Centro de Exhibición de la Rana Chilena Calyptocephalella gayi, Santiago, Chile
| | - Alexandra Peñafiel-Ricaurte
- Sustainability Research Centre & PhD Program in Conservation Medicine, Faculty of Life Sciences, Universidad Andres Bello, Santiago, Chile
| | - Thomas R Sewell
- Department of Infectious Disease Epidemiology, MRC Centre for Global Infectious Disease Analysis, School of Public Health, Imperial College London, London, United Kingdom
| | - Simon J O'Hanlon
- Department of Infectious Disease Epidemiology, MRC Centre for Global Infectious Disease Analysis, School of Public Health, Imperial College London, London, United Kingdom
| | - Matthew C Fisher
- Department of Infectious Disease Epidemiology, MRC Centre for Global Infectious Disease Analysis, School of Public Health, Imperial College London, London, United Kingdom
| | - Andres Valenzuela-Sánchez
- Sustainability Research Centre & PhD Program in Conservation Medicine, Faculty of Life Sciences, Universidad Andres Bello, Santiago, Chile.,ONG Ranita de Darwin, Valdivia, Chile.,Instituto de Conservación, Biodiversidad y Territorio, Facultad de Ciencias Forestales y Recursos Naturales, Universidad Austral de Chile, Valdivia, Chile
| | | | - Claudio Azat
- Sustainability Research Centre & PhD Program in Conservation Medicine, Faculty of Life Sciences, Universidad Andres Bello, Santiago, Chile
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TEMPERATURE AS A DRIVER OF THE PATHOGENICITY AND VIRULENCE OF AMPHIBIAN CHYTRID FUNGUS BATRACHOCHYTRIUM DENDROBATIDIS: A SYSTEMATIC REVIEW. J Wildl Dis 2021; 57:477-494. [PMID: 34019674 DOI: 10.7589/jwd-d-20-00105] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2020] [Accepted: 02/10/2021] [Indexed: 11/20/2022]
Abstract
Chytridiomycosis, caused by the chytrid fungus Batrachochytrium dendrobatidis (Bd), is a leading cause of global amphibian declines. Severe infections with Bd can lead to cardiac arrest, and mass deaths during epidemics have been reported. Temperature, pH, salinity, and moisture are important determinants of the survival, growth, reproduction, and pathogenicity of Bd, as well as its effect on amphibian populations. Here, we synthesize current knowledge on the role of temperature as a driver of the pathogenicity and virulence of Bd to better understand the effects of temperature on amphibian defense mechanisms against infection. This review advises on research direction and management approaches to benefit amphibian populations affected by Bd. We conclude by offering guidelines for four levels of temperature monitoring in amphibian field studies to improve consistency between studies: regional climate, habitat, microhabitat, and amphibian host.
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9
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Rahman MM, Jahan H, Rabbe MF, Chakraborty M, Salauddin M. First Detection of Batrachochytrium dendrobatidis in Wild Frogs from Bangladesh. ECOHEALTH 2021; 18:31-43. [PMID: 34028636 DOI: 10.1007/s10393-021-01522-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/03/2020] [Revised: 02/25/2021] [Accepted: 03/17/2021] [Indexed: 06/12/2023]
Abstract
Global amphibian populations are facing a novel threat, chytridiomycosis, caused by the fungus Batrachochytrium dendrobatidis (Bd), which is responsible for the severe decline of a number of species across several continents. Chytridiomycosis in Asia is a relatively recent discovery yet there have been no reports on Bd-presence in Bangladeshi amphibians. We conducted a preliminary study on 133 wild frogs from seven sites in Bangladesh between April and July 2018. Nested PCR analysis showed 20 samples (15.04%) and 50% of the tested taxa (9 species from 6 genera and 4 families) as Bd-positive. Eight of the nine species are discovered as newly infected hosts. Analysis of Bd-positive samples shows prevalence does not significantly vary among different land cover categories, although the occurrence is higher in forested areas. The prevalence rate is similar in high and low disturbed areas, but the range of occurrence is statistically higher in low disturbance areas. Maximum entropy distribution modeling indicates high probabilities of Bd occurrence in hilly and forested areas in southeast and central-north Bangladesh. The Bd-specific ITS1-5.8S-ITS2 ribosomal gene sequence from the Bd-positive samples tested is completely identical. A neighbor-joining phylogenetic tree reveals that the identified strain shares a common ancestry with strains previously discovered in different Asian regions. Our results provide the first evidence of Bd-presence in Bangladeshi amphibians, inferring that diversity is at risk. The effects of environmental and climatic factors along with quantitative PCR analysis are required to determine the infection intensity and susceptibility of amphibians in the country.
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Affiliation(s)
- Md Mokhlesur Rahman
- Department of Zoology, University of Dhaka, Dhaka, 1000, Bangladesh.
- Department of Anthropology, Durham University, South Road, Durham, DH1 3LE, UK.
| | - Hawa Jahan
- Department of Zoology, University of Dhaka, Dhaka, 1000, Bangladesh
- Division of Evolution and Genomic Sciences, FBMH, School of Biological Sciences, University of Manchester, Oxford Rd, Manchester, M13 9PT, UK
| | - Md Fazle Rabbe
- Department of Zoology, University of Dhaka, Dhaka, 1000, Bangladesh
| | | | - Md Salauddin
- Department of Geography and Environment, Jagannath University, Dhaka, 1100, Bangladesh
- Disaster Risk Management Department, Bangladesh Red Crescent Society, Red Crescent Sarak, Bara Moghbazar, Dhaka, 1217, Bangladesh
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Winter is coming-Temperature affects immune defenses and susceptibility to Batrachochytrium salamandrivorans. PLoS Pathog 2021; 17:e1009234. [PMID: 33600433 PMCID: PMC7891748 DOI: 10.1371/journal.ppat.1009234] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2020] [Accepted: 12/08/2020] [Indexed: 12/24/2022] Open
Abstract
Environmental temperature is a key factor driving various biological processes, including immune defenses and host-pathogen interactions. Here, we evaluated the effects of environmental temperature on the pathogenicity of the emerging fungal pathogen, Batrachochytrium salamandrivorans (Bsal), using controlled laboratory experiments, and measured components of host immune defense to identify regulating mechanisms. We found that adult and juvenile Notophthalmus viridescens died faster due to Bsal chytridiomycosis at 14°C than at 6 and 22°C. Pathogen replication rates, total available proteins on the skin, and microbiome composition likely drove these relationships. Temperature-dependent skin microbiome composition in our laboratory experiments matched seasonal trends in wild N. viridescens, adding validity to these results. We also found that hydrophobic peptide production after two months post-exposure to Bsal was reduced in infected animals compared to controls, perhaps due to peptide release earlier in infection or impaired granular gland function in diseased animals. Using our temperature-dependent susceptibility results, we performed a geographic analysis that revealed N. viridescens populations in the northeastern United States and southeastern Canada are at greatest risk for Bsal invasion, which shifted risk north compared to previous assessments. Our results indicate that environmental temperature will play a key role in the epidemiology of Bsal and provide evidence that temperature manipulations may be a viable disease management strategy. In 2010, a new skin-eating fungus, Batrachochytrium salamandrivorans (Bsal), was discovered killing salamanders in the Netherlands. Since then, the pathogen has spread to other European countries. Bsal is believed to be from Asia and is being translocated through the international trade of amphibians. To our knowledge, Bsal has not arrived to North America. As a proactive strategy for disease control, we evaluated how a range of environmental temperatures in North America could affect invasion risk of Bsal into a widely distributed salamander species, the eastern newt (Notophthalmus viridescens). Our results show that northeastern USA, southeastern Canada, and the higher elevations of the Appalachian Mountains have the greatest likelihood of Bsal invasion, when temperature-dependent susceptibility is included in risk analyses. Changes in eastern newt susceptibility to Bsal infection associated with temperature are likely an interaction between pathogen replication rate and host immune defenses, including changes in skin microbiome composition and the host’s ability to produce Bsal-killing proteins on the skin. Our study provides new insights into how latitude, elevation and season can impact the epidemiology of Bsal, and suggests that strategies that manipulate microclimate of newt habitats could be useful in managing Bsal outbreaks and that climate change will impact Bsal invasion probability.
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11
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Barrile GM, Chalfoun AD, Walters AW. Infection Status as the Basis for Habitat Choices in a Wild Amphibian. Am Nat 2021; 197:128-137. [PMID: 33417518 DOI: 10.1086/711927] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
AbstractAnimals challenged with disease may select specific habitat conditions that help prevent or reduce infection. Whereas preinfection avoidance of habitats with a high risk of disease exposure has been documented in both captive and free-ranging animals, evidence of switching habitats after infection to support the clearing of the infection is limited to laboratory experiments. The extent to which wild animals proximately modify habitat choices in response to infection status thus remains unclear. We investigated preinfection behavioral avoidance and postinfection habitat switching using wild, radio-tracked boreal toads (Anaxyrus boreas boreas) in a population challenged with Batrachochytrium dendrobatidis (Bd), a pathogenic fungus responsible for a catastrophic panzootic affecting hundreds of amphibian species worldwide. Boreal toads did not preemptively avoid microhabitats with conditions conducive to Bd growth. Infected individuals, however, selected warmer, more open habitats, which were associated with elevated body temperature and the subsequent clearing of infection. Our results suggest that disease can comprise an important selective pressure on animal habitat and space use. Habitat selection models, therefore, may be greatly improved by including variables that quantify infection risk and/or the infection status of individuals through time.
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12
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Grogan LF, Humphries JE, Robert J, Lanctôt CM, Nock CJ, Newell DA, McCallum HI. Immunological Aspects of Chytridiomycosis. J Fungi (Basel) 2020; 6:jof6040234. [PMID: 33086692 PMCID: PMC7712659 DOI: 10.3390/jof6040234] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2020] [Revised: 10/14/2020] [Accepted: 10/15/2020] [Indexed: 12/27/2022] Open
Abstract
Amphibians are currently the most threatened vertebrate class, with the disease chytridiomycosis being a major contributor to their global declines. Chytridiomycosis is a frequently fatal skin disease caused by the fungal pathogens Batrachochytrium dendrobatidis (Bd) and Batrachochytrium salamandrivorans (Bsal). The severity and extent of the impact of the infection caused by these pathogens across modern Amphibia are unprecedented in the history of vertebrate infectious diseases. The immune system of amphibians is thought to be largely similar to that of other jawed vertebrates, such as mammals. However, amphibian hosts are both ectothermic and water-dependent, which are characteristics favouring fungal proliferation. Although amphibians possess robust constitutive host defences, Bd/Bsal replicate within host cells once these defences have been breached. Intracellular fungal localisation may contribute to evasion of the induced innate immune response. Increasing evidence suggests that once the innate defences are surpassed, fungal virulence factors suppress the targeted adaptive immune responses whilst promoting an ineffectual inflammatory cascade, resulting in immunopathology and systemic metabolic disruption. Thus, although infections are contained within the integument, crucial homeostatic processes become compromised, leading to mortality. In this paper, we present an integrated synthesis of amphibian post-metamorphic immunological responses and the corresponding outcomes of infection with Bd, focusing on recent developments within the field and highlighting future directions.
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Affiliation(s)
- Laura F. Grogan
- Environmental Futures Research Institute and School of Environment and Science, Griffith University, Southport, QLD 4222, Australia;
- Forest Research Centre, School of Environment, Science and Engineering, Southern Cross University, Lismore, NSW 2480, Australia; (J.E.H.); (D.A.N.)
- Correspondence:
| | - Josephine E. Humphries
- Forest Research Centre, School of Environment, Science and Engineering, Southern Cross University, Lismore, NSW 2480, Australia; (J.E.H.); (D.A.N.)
| | - Jacques Robert
- University of Rochester Medical Center, Rochester, NY 14642, USA;
| | - Chantal M. Lanctôt
- Australian Rivers Institute, Griffith University, Southport, QLD 4222, Australia;
| | - Catherine J. Nock
- Southern Cross Plant Science, Southern Cross University, Lismore, NSW 2480, Australia;
| | - David A. Newell
- Forest Research Centre, School of Environment, Science and Engineering, Southern Cross University, Lismore, NSW 2480, Australia; (J.E.H.); (D.A.N.)
| | - Hamish I. McCallum
- Environmental Futures Research Institute and School of Environment and Science, Griffith University, Southport, QLD 4222, Australia;
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13
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Brannelly LA, McCallum HI, Grogan LF, Briggs CJ, Ribas MP, Hollanders M, Sasso T, Familiar López M, Newell DA, Kilpatrick AM. Mechanisms underlying host persistence following amphibian disease emergence determine appropriate management strategies. Ecol Lett 2020; 24:130-148. [PMID: 33067922 DOI: 10.1111/ele.13621] [Citation(s) in RCA: 27] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2020] [Revised: 06/18/2020] [Accepted: 09/08/2020] [Indexed: 12/19/2022]
Abstract
Emerging infectious diseases have caused many species declines, changes in communities and even extinctions. There are also many species that persist following devastating declines due to disease. The broad mechanisms that enable host persistence following declines include evolution of resistance or tolerance, changes in immunity and behaviour, compensatory recruitment, pathogen attenuation, environmental refugia, density-dependent transmission and changes in community composition. Here we examine the case of chytridiomycosis, the most important wildlife disease of the past century. We review the full breadth of mechanisms allowing host persistence, and synthesise research on host, pathogen, environmental and community factors driving persistence following chytridiomycosis-related declines and overview the current evidence and the information required to support each mechanism. We found that for most species the mechanisms facilitating persistence have not been identified. We illustrate how the mechanisms that drive long-term host population dynamics determine the most effective conservation management strategies. Therefore, understanding mechanisms of host persistence is important because many species continue to be threatened by disease, some of which will require intervention. The conceptual framework we describe is broadly applicable to other novel disease systems.
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Affiliation(s)
- Laura A Brannelly
- Veterinary BioSciences, Faculty of Veterinary and Agricultural Sciences, The University of Melbourne, Werribee, Vic, 3030, Australia
| | - Hamish I McCallum
- Environmental Futures Research Institute and School of Environment and Science, Griffith University, Nathan, Qld., 4111, Australia
| | - Laura F Grogan
- Environmental Futures Research Institute and School of Environment and Science, Griffith University, Nathan, Qld., 4111, Australia.,Forest Research Centre, School of Environment, Science and Engineering, Southern Cross University, Lismore, NSW, 2480, Australia
| | - Cheryl J Briggs
- Ecology, Evolution and Marine Biology, University of California Santa Barbara, Santa Barbara, CA, 93106, USA
| | - Maria P Ribas
- Forest Research Centre, School of Environment, Science and Engineering, Southern Cross University, Lismore, NSW, 2480, Australia.,Wildlife Conservation Medicine Research Group, Departament de Medicina i Cirurgia Animals, Universitat Autònoma de Barcelona, Bellaterra, 08193, Spain
| | - Matthijs Hollanders
- Forest Research Centre, School of Environment, Science and Engineering, Southern Cross University, Lismore, NSW, 2480, Australia
| | - Thais Sasso
- Environmental Futures Research Institute and School of Environment and Science, Griffith University, Nathan, Qld., 4111, Australia
| | - Mariel Familiar López
- School of Environment and Sciences, Griffith University, Gold Coast, Qld., 4215, Australia
| | - David A Newell
- Forest Research Centre, School of Environment, Science and Engineering, Southern Cross University, Lismore, NSW, 2480, Australia
| | - Auston M Kilpatrick
- Department of Ecology and Evolutionary Biology, University of California Santa Cruz, Santa Cruz, CA, 95064, USA
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14
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Sonn JM, Utz RM, Richards‐Zawacki CL. Effects of latitudinal, seasonal, and daily temperature variations on chytrid fungal infections in a North American frog. Ecosphere 2019. [DOI: 10.1002/ecs2.2892] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Affiliation(s)
- Julia M. Sonn
- Department of Ecology and Evolutionary Biology Tulane University New Orleans Louisiana USA
| | - Ryan M. Utz
- Falk School of Sustainability Chatham University Gibsonia Pennsylvania USA
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15
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Thermal sensitivity of innate immune response in three species of Rhinella toads. Comp Biochem Physiol A Mol Integr Physiol 2019; 237:110542. [DOI: 10.1016/j.cbpa.2019.110542] [Citation(s) in RCA: 23] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2019] [Revised: 07/01/2019] [Accepted: 08/08/2019] [Indexed: 02/07/2023]
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16
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Hettyey A, Ujszegi J, Herczeg D, Holly D, Vörös J, Schmidt BR, Bosch J. Mitigating Disease Impacts in Amphibian Populations: Capitalizing on the Thermal Optimum Mismatch Between a Pathogen and Its Host. Front Ecol Evol 2019. [DOI: 10.3389/fevo.2019.00254] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
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17
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Walls SC, Gabor CR. Integrating Behavior and Physiology Into Strategies for Amphibian Conservation. Front Ecol Evol 2019. [DOI: 10.3389/fevo.2019.00234] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
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18
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Doody KA, Ohmer ME, Cramp RL, Franklin CE. Do Frogs Infected with Batrachochytrium dendrobatidis Avoid Water While Sloughing? HERPETOLOGICA 2019. [DOI: 10.1655/d-18-00014] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Affiliation(s)
- Kathleen A. Doody
- School of Biological Sciences, The University of Queensland, St. Lucia, QLD 4072, Australia
| | - Michel E.B. Ohmer
- School of Biological Sciences, The University of Queensland, St. Lucia, QLD 4072, Australia
| | - Rebecca L. Cramp
- School of Biological Sciences, The University of Queensland, St. Lucia, QLD 4072, Australia
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19
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Muletz-Wolz CR, Fleischer RC, Lips KR. Fungal disease and temperature alter skin microbiome structure in an experimental salamander system. Mol Ecol 2019; 28:2917-2931. [PMID: 31066947 DOI: 10.1111/mec.15122] [Citation(s) in RCA: 26] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2018] [Revised: 03/27/2019] [Accepted: 04/25/2019] [Indexed: 12/29/2022]
Abstract
Pathogens compete with host microbiomes for space and resources. Their shared environment impacts pathogen-microbiome-host interactions, which can lead to variation in disease outcome. The skin microbiome of red-backed salamanders (Plethodon cinereus) can reduce infection by the pathogen Batrachochytrium dendrobatidis (Bd) at moderate infection loads, with high species richness and high abundance of competitors as putative mechanisms. However, it is unclear if the skin microbiome can reduce epizootic Bd loads across temperatures. We conducted a laboratory experiment to quantify skin microbiome and host responses (P. cinereus: n = 87) to Bd at mimicked epizootic loads across temperatures (13, 17 and 21°C). We quantified skin microbiomes using 16S rRNA gene metabarcoding and identified operational taxonomic units (OTUs) taxonomically similar to culturable bacteria known to kill Bd (anti-Bd OTUs). Prior to pathogen exposure, temperature changed the microbiome (OTU richness decreased by 12% and the abundance of anti-Bd OTUs increased by 18% per degree increase in temperature), but these changes were not predictive of disease outcome. After exposure, Bd changed the microbiome (OTU richness decreased by 0.1% and the abundance of anti-Bd OTUs increased by 0.2% per 1% increase in Bd load) and caused high host mortality across temperatures (35/45: 78%). Temperature indirectly impacted microbiome change and mortality through its direct effect on pathogen load. We did not find support for the microbiome impacting Bd load or host survival. Our research reveals complex host, pathogen, microbiome and environmental interactions to demonstrate that during epizootic events the microbiome will be unlikely to reduce pathogen invasion, even for putatively Bd-resistant species.
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Affiliation(s)
- Carly R Muletz-Wolz
- Department of Biology, University of Maryland, College Park, Maryland.,Center for Conservation Genomics, Smithsonian National Zoological Park and Conservation Biology Institute, Washington, District of Columbia
| | - Robert C Fleischer
- Center for Conservation Genomics, Smithsonian National Zoological Park and Conservation Biology Institute, Washington, District of Columbia
| | - Karen R Lips
- Department of Biology, University of Maryland, College Park, Maryland
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20
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Kohli AK, Lindauer AL, Brannelly LA, Ohmer MEB, Richards-Zawacki C, Rollins-Smith L, Voyles J. Disease and the Drying Pond: Examining Possible Links among Drought, Immune Function, and Disease Development in Amphibians. Physiol Biochem Zool 2019; 92:339-348. [PMID: 30990770 DOI: 10.1086/703137] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
Drought can heavily impact aquatic ecosystems. For amphibian species that rely on water availability for larval development, drought can have direct and indirect effects on larval survival and postmetamorphic fitness. Some amphibian species can accelerate the timing of metamorphosis to escape drying habitats through developmental plasticity. However, trade-offs associated with premature metamorphosis, such as reduced body size and altered immune function in the recently metamorphosed individual, may have downstream effects on susceptibility to disease. Here, we review the physiological mechanisms driving patterns in larval amphibian development under low water conditions. Specifically, we discuss drought-induced accelerated metamorphosis and how it may alter immune function, predisposing juvenile amphibians to infectious disease. In addition, we consider how these physiological and immunological adjustments could play out in a lethal disease system, amphibian chytridiomycosis. Last, we propose avenues for future research that adopt an ecoimmunological approach to evaluate the combined threats of drought and disease for amphibian populations.
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21
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Grogan LF, Robert J, Berger L, Skerratt LF, Scheele BC, Castley JG, Newell DA, McCallum HI. Review of the Amphibian Immune Response to Chytridiomycosis, and Future Directions. Front Immunol 2018; 9:2536. [PMID: 30473694 PMCID: PMC6237969 DOI: 10.3389/fimmu.2018.02536] [Citation(s) in RCA: 87] [Impact Index Per Article: 14.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2018] [Accepted: 10/15/2018] [Indexed: 12/27/2022] Open
Abstract
The fungal skin disease, chytridiomycosis (caused by Batrachochytrium dendrobatidis and B. salamandrivorans), has caused amphibian declines and extinctions globally since its emergence. Characterizing the host immune response to chytridiomycosis has been a focus of study with the aim of disease mitigation. However, many aspects of the innate and adaptive arms of this response are still poorly understood, likely due to the wide range of species' responses to infection. In this paper we provide an overview of expected immunological responses (with inference based on amphibian and mammalian immunology), together with a synthesis of current knowledge about these responses for the amphibian-chytridiomycosis system. We structure our review around four key immune stages: (1) the naïve immunocompetent state, (2) immune defenses that are always present (constitutive defenses), (3) mechanisms for recognition of a pathogen threat and innate immune defenses, and (4) adaptive immune responses. We also evaluate the current hot topics of immunosuppression and immunopathology in chytridiomycosis, and discuss their respective roles in pathogenesis. Our synthesis reveals that susceptibility to chytridiomycosis is likely to be multifactorial. Susceptible amphibians appear to have ineffective constitutive and innate defenses, and a late-stage response characterized by immunopathology and Bd-induced suppression of lymphocyte responses. Overall, we identify substantial gaps in current knowledge, particularly concerning the entire innate immune response (mechanisms of initial pathogen detection and possible immunoevasion by Bd, degree of activation and efficacy of the innate immune response, the unexpected absence of innate leukocyte infiltration, and the cause and role of late-stage immunopathology in pathogenesis). There are also gaps concerning most of the adaptive immune system (the relative importance of B and T cell responses for pathogen clearance, the capacity and extent of immunological memory, and specific mechanisms of pathogen-induced immunosuppression). Improving our capacity for amphibian immunological research will require selection of an appropriate Bd-susceptible model species, the development of taxon-specific affinity reagents and cell lines for functional assays, and the application of a suite of conventional and emerging immunological methods. Despite current knowledge gaps, immunological research remains a promising avenue for amphibian conservation management.
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Affiliation(s)
- Laura F Grogan
- Environmental Futures Research Institute and School of Environment and Science, Griffith University, Nathan, QLD, Australia
| | - Jacques Robert
- University of Rochester Medical Center, Rochester, NY, United States
| | - Lee Berger
- One Health Research Group, College of Public Health, Medical and Veterinary Sciences, James Cook University, Townsville, QLD, Australia.,Faculty of Veterinary and Agricultural Sciences, Melbourne Veterinary School, University of Melbourne, Werribee, VIC, Australia
| | - Lee F Skerratt
- One Health Research Group, College of Public Health, Medical and Veterinary Sciences, James Cook University, Townsville, QLD, Australia.,Faculty of Veterinary and Agricultural Sciences, Melbourne Veterinary School, University of Melbourne, Werribee, VIC, Australia
| | - Benjamin C Scheele
- Fenner School of Environment and Society, The Australian National University, Canberra, ACT, Australia.,Threatened Species Recovery Hub, National Environmental Science Program, Fenner School of Environment and Society, The Australian National University, Canberra, ACT, Australia
| | - J Guy Castley
- Environmental Futures Research Institute and School of Environment and Science, Griffith University, Nathan, QLD, Australia
| | - David A Newell
- Forest Research Centre, School of Environment, Science and Engineering, Southern Cross University, Lismore, NSW, Australia
| | - Hamish I McCallum
- Environmental Futures Research Institute and School of Environment and Science, Griffith University, Nathan, QLD, Australia
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22
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Effects of Emerging Infectious Diseases on Amphibians: A Review of Experimental Studies. DIVERSITY-BASEL 2018. [DOI: 10.3390/d10030081] [Citation(s) in RCA: 25] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Numerous factors are contributing to the loss of biodiversity. These include complex effects of multiple abiotic and biotic stressors that may drive population losses. These losses are especially illustrated by amphibians, whose populations are declining worldwide. The causes of amphibian population declines are multifaceted and context-dependent. One major factor affecting amphibian populations is emerging infectious disease. Several pathogens and their associated diseases are especially significant contributors to amphibian population declines. These include the fungi Batrachochytrium dendrobatidis and B. salamandrivorans, and ranaviruses. In this review, we assess the effects of these three pathogens on amphibian hosts as found through experimental studies. Such studies offer valuable insights to the causal factors underpinning broad patterns reported through observational studies. We summarize key findings from experimental studies in the laboratory, in mesocosms, and from the field. We also summarize experiments that explore the interactive effects of these pathogens with other contributors of amphibian population declines. Though well-designed experimental studies are critical for understanding the impacts of disease, inconsistencies in experimental methodologies limit our ability to form comparisons and conclusions. Studies of the three pathogens we focus on show that host susceptibility varies with such factors as species, host age, life history stage, population and biotic (e.g., presence of competitors, predators) and abiotic conditions (e.g., temperature, presence of contaminants), as well as the strain and dose of the pathogen, to which hosts are exposed. Our findings suggest the importance of implementing standard protocols and reporting for experimental studies of amphibian disease.
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23
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Mosher BA, Bailey LL, Muths E, Huyvaert KP. Host-pathogen metapopulation dynamics suggest high elevation refugia for boreal toads. ECOLOGICAL APPLICATIONS : A PUBLICATION OF THE ECOLOGICAL SOCIETY OF AMERICA 2018; 28:926-937. [PMID: 29430754 DOI: 10.1002/eap.1699] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/22/2017] [Revised: 12/18/2017] [Accepted: 01/02/2018] [Indexed: 06/08/2023]
Abstract
Emerging infectious diseases are an increasingly common threat to wildlife. Chytridiomycosis, caused by the fungal pathogen Batrachochytrium dendrobatidis (Bd), is an emerging infectious disease that has been linked to amphibian declines around the world. Few studies exist that explore amphibian-Bd dynamics at the landscape scale, limiting our ability to identify which factors are associated with variation in population susceptibility and to develop effective in situ disease management. Declines of boreal toads (Anaxyrus boreas boreas) in the southern Rocky Mountains are largely attributed to chytridiomycosis but variation exists in local extinction of boreal toads across this metapopulation. Using a large-scale historic data set, we explored several potential factors influencing disease dynamics in the boreal toad-Bd system: geographic isolation of populations, amphibian community richness, elevational differences, and habitat permanence. We found evidence that boreal toad extinction risk was lowest at high elevations where temperatures may be suboptimal for Bd growth and where small boreal toad populations may be below the threshold needed for efficient pathogen transmission. In addition, boreal toads were more likely to recolonize high elevation sites after local extinction, again suggesting that high elevations may provide refuge from disease for boreal toads. We illustrate a modeling framework that will be useful to natural resource managers striving to make decisions in amphibian-Bd systems. Our data suggest that in the southern Rocky Mountains high elevation sites should be prioritized for conservation initiatives like reintroductions.
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Affiliation(s)
- Brittany A Mosher
- Department of Fish, Wildlife, and Conservation Biology, Colorado State University, Fort Collins, Colorado, 80523, USA
| | - Larissa L Bailey
- Department of Fish, Wildlife, and Conservation Biology, Colorado State University, Fort Collins, Colorado, 80523, USA
| | - Erin Muths
- U.S. Geological Survey, Fort Collins Science Center, 2150 Centre Avenue, Building C, Fort Collins, Colorado, 80526, USA
| | - Kathryn P Huyvaert
- Department of Fish, Wildlife, and Conservation Biology, Colorado State University, Fort Collins, Colorado, 80523, USA
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24
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Robak MJ, Richards-Zawacki CL. Temperature-Dependent Effects of Cutaneous Bacteria on a Frog's Tolerance of Fungal Infection. Front Microbiol 2018; 9:410. [PMID: 29563909 PMCID: PMC5845872 DOI: 10.3389/fmicb.2018.00410] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2017] [Accepted: 02/21/2018] [Indexed: 11/27/2022] Open
Abstract
Defense against pathogens is one of many benefits that bacteria provide to animal hosts. A clearer understanding of how changes in the environment affect the interactions between animals and their microbial benefactors is needed in order to predict the impact and dynamics of emerging animal diseases. Due to its dramatic effects on the physiology of animals and their pathogens, temperature may be a key variable modulating the level of protection that beneficial bacteria provide to their animal hosts. Here we investigate how temperature and the makeup of the skin microbial community affect the susceptibility of amphibian hosts to infection by Batrachochytrium dendrobatidis (Bd), one of two fungal pathogens known to cause the disease chytridiomycosis. To do this, we manipulated the skin bacterial communities of susceptible hosts, northern cricket frogs (Acris crepitans), prior to exposing these animals to Bd under two different ecologically relevant temperatures. Our manipulations included one treatment where antibiotics were used to reduce the skin bacterial community, one where the bacterial community was augmented with the antifungal bacterium, Stenotrophomonas maltophilia, and one in which the frog’s skin bacterial community was left intact. We predicted that frogs with reduced skin bacterial communities would be more susceptible (i.e., less resistant to and/or tolerant of Bd infection), and frogs with skin bacterial communities augmented with the known antifungal bacterium would be less susceptible to Bd infection and chytridiomycosis. However, we also predicted that this interaction would be temperature dependent. We found a strong effect of temperature but not of skin microbial treatment on the probability and intensity of infection in Bd-exposed frogs. Whether temperature affected survival; however, it differed among our skin microbial treatment groups, with animals having more S. maltophilia on their skin surviving longer at 14 but not at 26°C. Our results suggest that temperature was the predominant factor influencing Bd’s ability to colonize the host (i.e., resistance) but that the composition of the cutaneous bacterial community was important in modulating the host’s ability to survive (i.e., tolerate) a heavy Bd infection.
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Affiliation(s)
- Matthew J Robak
- Department of Ecology and Evolutionary Biology, Tulane University, New Orleans, LA, United States
| | - Corinne L Richards-Zawacki
- Department of Ecology and Evolutionary Biology, Tulane University, New Orleans, LA, United States.,Department of Biological Sciences, University of Pittsburgh, Pittsburgh, PA, United States
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25
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Sonn JM, Berman S, Richards-Zawacki CL. The Influence of Temperature on Chytridiomycosis In Vivo. ECOHEALTH 2017; 14:762-770. [PMID: 28879516 DOI: 10.1007/s10393-017-1269-2] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/13/2016] [Revised: 06/23/2017] [Accepted: 07/11/2017] [Indexed: 06/07/2023]
Abstract
Chytridiomycosis, an amphibian disease caused by the fungal pathogen Batrachochytrium dendrobatidis (Bd), is an ideal system for studying the influence of temperature on host-pathogen relationships because both host and pathogen are ectothermic. Studies of Bd in culture suggest that optimal growth occurs between 17 and 23°C, and death of the fungus occurs above 29 or below 0°C. Amphibian immune systems, however, are also temperature dependent and often more effective at higher temperatures. We therefore hypothesized that pathogen load, probability of infection and mortality in Bd-exposed frogs would peak at a lower temperature than that at which Bd grows best in vitro. To test this, we conducted a study where Bd- and sham-exposed Northern cricket frogs (Acris crepitans) were incubated at six temperatures between 11 and 26°C. While probability of infection did not differ across temperatures, pathogen load and mortality were inversely related to temperature. Survival of infected hosts was greatest between 20 and 26°C, temperatures where Bd grows well in culture. These results demonstrate that the conditions under which a pathogen grows best in culture do not necessarily reflect patterns of pathogenicity, an important consideration for predicting the threat of this and other wildlife pathogens.
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Affiliation(s)
- Julia M Sonn
- Department of Ecology and Evolutionary Biology, Tulane University, 400 Lindy Boggs Bldg., New Orleans, LA, 70118, USA.
| | - Scott Berman
- Department of Ecology and Evolutionary Biology, Tulane University, 400 Lindy Boggs Bldg., New Orleans, LA, 70118, USA
| | - Corinne L Richards-Zawacki
- Department of Ecology and Evolutionary Biology, Tulane University, 400 Lindy Boggs Bldg., New Orleans, LA, 70118, USA
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, PA, USA
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26
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Early exposure to Batrachochytrium dendrobatidis causes profound immunosuppression in amphibians. EUR J WILDLIFE RES 2017. [DOI: 10.1007/s10344-017-1161-y] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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27
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Greenspan SE, Bower DS, Webb RJ, Roznik EA, Stevenson LA, Berger L, Marantelli G, Pike DA, Schwarzkopf L, Alford RA. Realistic heat pulses protect frogs from disease under simulated rainforest frog thermal regimes. Funct Ecol 2017. [DOI: 10.1111/1365-2435.12944] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Affiliation(s)
- Sasha E. Greenspan
- College of Science and Engineering James Cook University Townsville Qld Australia
| | - Deborah S. Bower
- College of Science and Engineering James Cook University Townsville Qld Australia
| | - Rebecca J. Webb
- One Health Research Group College of Public Health Medical and Veterinary Sciences James Cook University Douglas Qld Australia
| | | | - Lisa A. Stevenson
- College of Science and Engineering James Cook University Townsville Qld Australia
| | - Lee Berger
- One Health Research Group College of Public Health Medical and Veterinary Sciences James Cook University Douglas Qld Australia
| | | | | | - Lin Schwarzkopf
- College of Science and Engineering James Cook University Townsville Qld Australia
| | - Ross A. Alford
- College of Science and Engineering James Cook University Townsville Qld Australia
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28
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Adams AJ, Kupferberg SJ, Wilber MQ, Pessier AP, Grefsrud M, Bobzien S, Vredenburg VT, Briggs CJ. Extreme drought, host density, sex, and bullfrogs influence fungal pathogen infection in a declining lotic amphibian. Ecosphere 2017. [DOI: 10.1002/ecs2.1740] [Citation(s) in RCA: 43] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
Affiliation(s)
- Andrea J. Adams
- Department of Ecology, Evolution, and Marine Biology; University of California; Santa Barbara California 93106 USA
| | - Sarah J. Kupferberg
- Department of Integrative Biology; University of California; Berkeley California 94720 USA
| | - Mark Q. Wilber
- Department of Ecology, Evolution, and Marine Biology; University of California; Santa Barbara California 93106 USA
| | - Allan P. Pessier
- Department of Veterinary Microbiology and Pathology; College of Veterinary Medicine; Washington State University; Pullman Washington 99164 USA
| | - Marcia Grefsrud
- California Department of Fish and Wildlife; Bay Delta Region Napa California 94558 USA
| | - Steve Bobzien
- East Bay Regional Park District; Oakland California 94605 USA
| | | | - Cheryl J. Briggs
- Department of Ecology, Evolution, and Marine Biology; University of California; Santa Barbara California 93106 USA
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29
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Rakus K, Ronsmans M, Vanderplasschen A. Behavioral fever in ectothermic vertebrates. DEVELOPMENTAL AND COMPARATIVE IMMUNOLOGY 2017; 66:84-91. [PMID: 27381718 DOI: 10.1016/j.dci.2016.06.027] [Citation(s) in RCA: 51] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/06/2016] [Revised: 06/29/2016] [Accepted: 06/30/2016] [Indexed: 06/06/2023]
Abstract
Fever is an evolutionary conserved defense mechanism which is present in both endothermic and ectothermic vertebrates. Ectotherms in response to infection can increase their body temperature by moving to warmer places. This process is known as behavioral fever. In this review, we summarize the current knowledge on the mechanisms of induction of fever in mammals. We further discuss the evolutionary conserved mechanisms existing between fever of mammals and behavioral fever of ectothermic vertebrates. Finally, the experimental evidences supporting an adaptive value of behavioral fever expressed by ectothermic vertebrates are summarized.
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Affiliation(s)
- Krzysztof Rakus
- Department of Evolutionary Immunology, Institute of Zoology, Jagiellonian University, Gronostajowa 9, 30-387, Krakow, Poland.
| | - Maygane Ronsmans
- Immunology-Vaccinology, Fundamental and Applied Research for Animals & Health (FARAH), Faculty of Veterinary Medicine, University of Liège, Liège, Belgium.
| | - Alain Vanderplasschen
- Immunology-Vaccinology, Fundamental and Applied Research for Animals & Health (FARAH), Faculty of Veterinary Medicine, University of Liège, Liège, Belgium.
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30
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Longo AV, Zamudio KR. Environmental fluctuations and host skin bacteria shift survival advantage between frogs and their fungal pathogen. ISME JOURNAL 2016; 11:349-361. [PMID: 27935596 DOI: 10.1038/ismej.2016.138] [Citation(s) in RCA: 62] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/11/2016] [Revised: 08/08/2016] [Accepted: 08/15/2016] [Indexed: 12/11/2022]
Abstract
Fluctuating environments can modulate host-pathogen interactions by providing a temporary advantage to one of the interacting organisms. However, we know very little about how environmental conditions facilitate beneficial interactions between hosts and their microbial communities, resulting in individual persistence with a particular pathogen. Here, we experimentally infected Eleutherodactylus coqui frogs with the fungal pathogen Batrachochytrium dendrobatidis (Bd) under environmental conditions known to confer the survival advantage to the host during the warm-wet season, or alternatively to the pathogen during the cool-dry season. We used 16S rRNA amplicon sequencing to quantify changes in bacterial richness and phylogenetic diversity, and identified operational taxonomic units (OTUs) that became overrepresented or suppressed as a consequence of Bd infection. During the warm-wet season, frogs limited Bd infections, recruited putatively beneficial bacteria and returned to pre-infection levels of richness and phylogenetic diversity. In contrast, during the cool-dry season, Bd infections kept increasing through time, and bacterial diversity remained constant. Our findings confirm that infection outcome not only depends on abiotic factors, but also on biotic interactions between hosts and their associated bacterial communities.
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Affiliation(s)
- Ana V Longo
- Department of Ecology and Evolutionary Biology, Cornell University, Ithaca, NY 14853, USA
| | - Kelly R Zamudio
- Department of Ecology and Evolutionary Biology, Cornell University, Ithaca, NY 14853, USA
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Savage AE, Terrell KA, Gratwicke B, Mattheus NM, Augustine L, Fleischer RC. Reduced immune function predicts disease susceptibility in frogs infected with a deadly fungal pathogen. CONSERVATION PHYSIOLOGY 2016; 4:cow011. [PMID: 27293759 PMCID: PMC4834730 DOI: 10.1093/conphys/cow011] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 10/29/2015] [Revised: 02/28/2016] [Accepted: 03/16/2016] [Indexed: 06/06/2023]
Abstract
The relationship between amphibian immune function and disease susceptibility is of primary concern given current worldwide declines linked to the pathogenic fungus Batrachochytrium dendrobatidis (Bd). We experimentally infected lowland leopard frogs (Lithobates yavapaiensis) with Bd to test the hypothesis that infection causes physiological stress and stimulates humoral and cell-mediated immune function in the blood. We measured body mass, the ratio of circulating neutrophils to lymphocytes (a known indicator of physiological stress) and plasma bacterial killing ability (BKA; a measure of innate immune function). In early exposure (1-15 days post-infection), stress was elevated in Bd-positive vs. Bd-negative frogs, whereas other metrics were similar between the groups. At later stages (29-55 days post-infection), stress was increased in Bd-positive frogs with signs of chytridiomycosis compared with both Bd-positive frogs without disease signs and uninfected control frogs, which were similar to each other. Infection decreased growth during the same period, demonstrating that sustained resistance to Bd is energetically costly. Importantly, BKA was lower in Bd-positive frogs with disease than in those without signs of chytridiomycosis. However, neither group differed from Bd-negative control frogs. The low BKA values in dying frogs compared with infected individuals without disease signs suggests that complement activity might signify different immunogenetic backgrounds or gene-by-environment interactions between the host, Bd and abiotic factors. We conclude that protein complement activity might be a useful predictor of Bd susceptibility and might help to explain differential disease outcomes in natural amphibian populations.
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Affiliation(s)
| | | | | | | | - Lauren Augustine
- Center for Animal Care Sciences, Smithsonian Conservation Biology Institute, National Zoological Park, 3001 Connecticut Avenue NW, Washington, DC 20008, USA
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Roznik EA, Sapsford SJ, Pike DA, Schwarzkopf L, Alford RA. Condition-dependent reproductive effort in frogs infected by a widespread pathogen. Proc Biol Sci 2016; 282:rspb.2015.0694. [PMID: 26063847 DOI: 10.1098/rspb.2015.0694] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
To minimize the negative effects of an infection on fitness, hosts can respond adaptively by altering their reproductive effort or by adjusting their timing of reproduction. We studied effects of the pathogenic fungus Batrachochytrium dendrobatidis on the probability of calling in a stream-breeding rainforest frog (Litoria rheocola). In uninfected frogs, calling probability was relatively constant across seasons and body conditions, but in infected frogs, calling probability differed among seasons (lowest in winter, highest in summer) and was strongly and positively related to body condition. Infected frogs in poor condition were up to 40% less likely to call than uninfected frogs, whereas infected frogs in good condition were up to 30% more likely to call than uninfected frogs. Our results suggest that frogs employed a pre-existing, plastic, life-history strategy in response to infection, which may have complex evolutionary implications. If infected males in good condition reproduce at rates equal to or greater than those of uninfected males, selection on factors affecting disease susceptibility may be minimal. However, because reproductive effort in infected males is positively related to body condition, there may be selection on mechanisms that limit the negative effects of infections on hosts.
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Affiliation(s)
- Elizabeth A Roznik
- School of Marine and Tropical Biology, James Cook University, Townsville, Queensland 4811, Australia
| | - Sarah J Sapsford
- School of Marine and Tropical Biology, James Cook University, Townsville, Queensland 4811, Australia
| | - David A Pike
- School of Marine and Tropical Biology, James Cook University, Townsville, Queensland 4811, Australia
| | - Lin Schwarzkopf
- School of Marine and Tropical Biology, James Cook University, Townsville, Queensland 4811, Australia
| | - Ross A Alford
- School of Marine and Tropical Biology, James Cook University, Townsville, Queensland 4811, Australia
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Bovo RP, Andrade DV, Toledo LF, Longo AV, Rodriguez D, Haddad CFB, Zamudio KR, Becker CG. Physiological responses of Brazilian amphibians to an enzootic infection of the chytrid fungus Batrachochytrium dendrobatidis. DISEASES OF AQUATIC ORGANISMS 2016; 117:245-52. [PMID: 26758658 DOI: 10.3354/dao02940] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
Pathophysiological effects of clinical chytridiomycosis in amphibians include disorders of cutaneous osmoregulation and disruption of the ability to rehydrate, which can lead to decreased host fitness or mortality. Less attention has been given to physiological responses of hosts where enzootic infections of Batrachochytrium dendrobatidis (Bd) do not cause apparent population declines in the wild. Here, we experimentally tested whether an enzootic strain of Bd causes significant mortality and alters host water balance (evaporative water loss, EWL; skin resistance, R(s); and water uptake, WU) in individuals of 3 Brazilian amphibian species (Dendropsophus minutus, n = 19; Ischnocnema parva, n = 17; Brachycephalus pitanga, n = 15). Infections with enzootic Bd caused no significant mortality, but we found an increase in R(s) in 1 host species concomitant with a reduction in EWL. These results suggest that enzootic Bd infections can indeed cause sub-lethal effects that could lead to reduction of host fitness in Brazilian frogs and that these effects vary among species. Thus, our findings underscore the need for further assessment of physiological responses to Bd infections in different host species, even in cases of sub-clinical chytridiomycosis and long-term enzootic infections in natural populations.
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Affiliation(s)
- Rafael P Bovo
- Departamento de Zoologia, c. p. 199, Universidade Estadual Paulista, 13506-900, Rio Claro, SP, Brazil
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Becker MH, Walke JB, Cikanek S, Savage AE, Mattheus N, Santiago CN, Minbiole KPC, Harris RN, Belden LK, Gratwicke B. Composition of symbiotic bacteria predicts survival in Panamanian golden frogs infected with a lethal fungus. Proc Biol Sci 2015; 282:rspb.2014.2881. [PMID: 25788591 DOI: 10.1098/rspb.2014.2881] [Citation(s) in RCA: 103] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
Symbiotic microbes can dramatically impact host health and fitness, and recent research in a diversity of systems suggests that different symbiont community structures may result in distinct outcomes for the host. In amphibians, some symbiotic skin bacteria produce metabolites that inhibit the growth of Batrachochytrium dendrobatidis (Bd), a cutaneous fungal pathogen that has caused many amphibian population declines and extinctions. Treatment with beneficial bacteria (probiotics) prevents Bd infection in some amphibian species and creates optimism for conservation of species that are highly susceptible to chytridiomycosis, the disease caused by Bd. In a laboratory experiment, we used Bd-inhibitory bacteria from Bd-tolerant Panamanian amphibians in a probiotic development trial with Panamanian golden frogs, Atelopus zeteki, a species currently surviving only in captive assurance colonies. Approximately 30% of infected golden frogs survived Bd exposure by either clearing infection or maintaining low Bd loads, but this was not associated with probiotic treatment. Survival was instead related to initial composition of the skin bacterial community and metabolites present on the skin. These results suggest a strong link between the structure of these symbiotic microbial communities and amphibian host health in the face of Bd exposure and also suggest a new approach for developing amphibian probiotics.
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Affiliation(s)
- Matthew H Becker
- Department of Biological Sciences, Virginia Tech, Blacksburg, VA, USA
| | - Jenifer B Walke
- Department of Biological Sciences, Virginia Tech, Blacksburg, VA, USA
| | - Shawna Cikanek
- Department of Clinical Sciences, Kansas State University, Manhattan, KS, USA
| | - Anna E Savage
- Center for Conservation and Evolutionary Genetics, Smithsonian Conservation Biology Institute, National Zoological Park, Washington, DC, USA
| | - Nichole Mattheus
- Center for Conservation and Evolutionary Genetics, Smithsonian Conservation Biology Institute, National Zoological Park, Washington, DC, USA
| | | | | | - Reid N Harris
- Department of Biology, James Madison University, Harrisonburg, VA, USA
| | - Lisa K Belden
- Department of Biological Sciences, Virginia Tech, Blacksburg, VA, USA
| | - Brian Gratwicke
- Center for Species Survival, Smithsonian Conservation Biology Institute, National Zoological Park, Washington, DC, USA
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Raffel TR, Halstead NT, McMahon TA, Davis AK, Rohr JR. Temperature variability and moisture synergistically interact to exacerbate an epizootic disease. Proc Biol Sci 2015; 282:20142039. [PMID: 25567647 DOI: 10.1098/rspb.2014.2039] [Citation(s) in RCA: 67] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Climate change is altering global patterns of precipitation and temperature variability, with implications for parasitic diseases of humans and wildlife. A recent study confirmed predictions that increased temperature variability could exacerbate disease, because of lags in host acclimation following temperature shifts. However, the generality of these host acclimation effects and the potential for them to interact with other factors have yet to be tested. Here, we report similar effects of host thermal acclimation (constant versus shifted temperatures) on chytridiomycosis in red-spotted newts (Notophthalmus viridescens). Batrachochytrium dendrobatidis (Bd) growth on newts was greater following a shift to a new temperature, relative to newts already acclimated to this temperature (15°C versus 25°C). However, these acclimation effects depended on soil moisture (10, 16 and 21% water) and were only observed at the highest moisture level, which induced greatly increased Bd growth and infection-induced mortality. Acclimation effects were also greater following a decrease rather than an increase in temperature. The results are consistent with previous findings that chytridiomycosis is associated with precipitation, lower temperatures and increased temperature variability. This study highlights host acclimation as a potentially general mediator of climate-disease interactions, and the need to account for context-dependencies when testing for acclimation effects on disease.
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Affiliation(s)
- Thomas R Raffel
- Department of Biology, Oakland University, Rochester, MI, USA
| | - Neal T Halstead
- Department of Integrative Biology, University of South Florida, Tampa, FL, USA
| | | | - Andrew K Davis
- Odum School of Ecology, University of Georgia, Athens, GA, USA
| | - Jason R Rohr
- Department of Integrative Biology, University of South Florida, Tampa, FL, USA
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Short term minimum water temperatures determine levels of infection by the amphibian chytrid fungus in Alytes obstetricans tadpoles. PLoS One 2015; 10:e0120237. [PMID: 25793985 PMCID: PMC4368698 DOI: 10.1371/journal.pone.0120237] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2014] [Accepted: 02/04/2015] [Indexed: 11/19/2022] Open
Abstract
Amphibians are one of the groups of wildlife most seriously threatened by emerging infectious disease. In particular, chytridiomycosis, caused by the aquatic fungus Batrachochytrium dendrobatidis, is responsible for amphibian species declines on a worldwide scale. Population-level outcomes following the introduction of the pathogen are context dependent and mediated by a large suite of abiotic and biotic variables. In particular, studies have shown that temperature has a key role in determining infection dynamics owing to the ectothermic nature of the amphibian host and temperature-dependency of pathogen growth rates. To assess the temperature-dependent seasonality of infectious burdens in a susceptible host species, we monitored lowland populations of larval midwife toads, Alytes obstetricians, in Central Spain throughout the year. We found that infections were highly seasonal, and inversely correlated against water temperature, with the highest burdens of infection seen during the colder months. Short-term impacts of water-temperature were found, with the minimum temperatures occurring before sampling being more highly predictive of infectious burdens than were longer-term spans of temperature. Our results will be useful for selecting the optimal time for disease surveys and, more broadly, for determining the key periods to undertake disease mitigation.
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Brannelly LA, Berger L, Marrantelli G, Skerratt LF. Low humidity is a failed treatment option for chytridiomycosis in the critically endangered southern corroboree frog. WILDLIFE RESEARCH 2015. [DOI: 10.1071/wr14097] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Context
One of the major drivers of the current worldwide amphibian decline and extinction crisis is the spread of the amphibian chytrid fungus, Batrachochytrium dendrobatidis (Bd). Captive assurance colonies may be the only lifeline for some species. Current antifungal chemotherapies can be effective for clearing infection but may have detrimental side effects. The only non-chemotherapeutic treatment that has been clinically tested is heat, which is impractical for cold-adapted species. The fungus does not survive desiccation, and therefore a plausible alternative non-chemotherapeutic treatment would be a low-humidity regimen.
Aims
We tested the efficacy of a low-humidity treatment regimen for treating Bd-infected animals of the critically endangered species Pseudophryne corroboree. This species has high tolerance of dry environments, and is thus an ideal candidate for this treatment trial.
Methods
Forty frogs were exposed to 1 × 106 zoospores. At three weeks after exposure access to water was reduced to once daily for 10 days for 20 animals. Ten of these animals were also rinsed daily with the aim of removing zoospores.
Key results
The drying regimen neither increased survival nor decreased infection load, and treatment may have hastened mortality. All infected frogs died between 21 and 80 days after exposure, except one untreated frog.
Conclusions
Our results suggest that a drying regimen is not a viable treatment for chytridiomycosis. Infection may decrease the host’s ability to cope with water stress.
Implications
The failed drying treatment in P. corroboree suggests that drying is not an appropriate treatment for chytridiomycosis and treatment efforts should be focussed on chemotherapies for cold-adapted species. P. corroboree is a critically endangered species for which chytridiomycosis is the primary cause of decline, yet few experiments have been carried out on this species with regards to chytridiomycosis. All experimental information about this species and disease will benefit the management and protection of the species.
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Scheele BC, Hunter DA, Grogan LF, Berger L, Kolby JE, McFadden MS, Marantelli G, Skerratt LF, Driscoll DA. Interventions for reducing extinction risk in chytridiomycosis-threatened amphibians. CONSERVATION BIOLOGY : THE JOURNAL OF THE SOCIETY FOR CONSERVATION BIOLOGY 2014; 28:1195-1205. [PMID: 24975971 DOI: 10.1111/cobi.12322] [Citation(s) in RCA: 73] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/05/2013] [Accepted: 02/21/2014] [Indexed: 06/03/2023]
Abstract
Wildlife diseases pose an increasing threat to biodiversity and are a major management challenge. A striking example of this threat is the emergence of chytridiomycosis. Despite diagnosis of chytridiomycosis as an important driver of global amphibian declines 15 years ago, researchers have yet to devise effective large-scale management responses other than biosecurity measures to mitigate disease spread and the establishment of disease-free captive assurance colonies prior to or during disease outbreaks. We examined the development of management actions that can be implemented after an epidemic in surviving populations. We developed a conceptual framework with clear interventions to guide experimental management and applied research so that further extinctions of amphibian species threatened by chytridiomycosis might be prevented. Within our framework, there are 2 management approaches: reducing Batrachochytrium dendrobatidis (the fungus that causes chytridiomycosis) in the environment or on amphibians and increasing the capacity of populations to persist despite increased mortality from disease. The latter approach emphasizes that mitigation does not necessarily need to focus on reducing disease-associated mortality. We propose promising management actions that can be implemented and tested based on current knowledge and that include habitat manipulation, antifungal treatments, animal translocation, bioaugmentation, head starting, and selection for resistance. Case studies where these strategies are being implemented will demonstrate their potential to save critically endangered species.
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Affiliation(s)
- Ben C Scheele
- ARC Centre of Excellence for Environmental Decisions, National Environmental Research Program Environmental Decisions Hub, Fenner School of Environment and Society, Forestry Building [48], Australian National University, Canberra, ACT 0200, Australia; NSW Office of Environment and Heritage, Queanbeyan, NSW 2620, Australia.
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Amphibians acquire resistance to live and dead fungus overcoming fungal immunosuppression. Nature 2014; 511:224-7. [PMID: 25008531 DOI: 10.1038/nature13491] [Citation(s) in RCA: 166] [Impact Index Per Article: 16.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2014] [Accepted: 05/15/2014] [Indexed: 11/08/2022]
Abstract
Emerging fungal pathogens pose a greater threat to biodiversity than any other parasitic group, causing declines of many taxa, including bats, corals, bees, snakes and amphibians. Currently, there is little evidence that wild animals can acquire resistance to these pathogens. Batrachochytrium dendrobatidis is a pathogenic fungus implicated in the recent global decline of amphibians. Here we demonstrate that three species of amphibians can acquire behavioural or immunological resistance to B. dendrobatidis. Frogs learned to avoid the fungus after just one B. dendrobatidis exposure and temperature-induced clearance. In subsequent experiments in which B. dendrobatidis avoidance was prevented, the number of previous exposures was a negative predictor of B. dendrobatidis burden on frogs and B. dendrobatidis-induced mortality, and was a positive predictor of lymphocyte abundance and proliferation. These results suggest that amphibians can acquire immunity to B. dendrobatidis that overcomes pathogen-induced immunosuppression and increases their survival. Importantly, exposure to dead fungus induced a similar magnitude of acquired resistance as exposure to live fungus. Exposure of frogs to B. dendrobatidis antigens might offer a practical way to protect pathogen-naive amphibians and facilitate the reintroduction of amphibians to locations in the wild where B. dendrobatidis persists. Moreover, given the conserved nature of vertebrate immune responses to fungi and the fact that many animals are capable of learning to avoid natural enemies, these results offer hope that other wild animal taxa threatened by invasive fungi might be rescued by management approaches based on herd immunity.
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Saenz D, Hall TL, Kwiatkowski MA. Effects of urbanization on the occurrence of Batrachochytrium dendrobatidis: do urban environments provide refuge from the amphibian chytrid fungus? Urban Ecosyst 2014. [DOI: 10.1007/s11252-014-0398-4] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Ellison AR, Savage AE, DiRenzo GV, Langhammer P, Lips KR, Zamudio KR. Fighting a losing battle: vigorous immune response countered by pathogen suppression of host defenses in the chytridiomycosis-susceptible frog Atelopus zeteki. G3 (BETHESDA, MD.) 2014; 4:1275-89. [PMID: 24841130 PMCID: PMC4455776 DOI: 10.1534/g3.114.010744] [Citation(s) in RCA: 76] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/17/2014] [Accepted: 05/15/2014] [Indexed: 01/13/2023]
Abstract
The emergence of the disease chytridiomycosis caused by the chytrid fungus Batrachochytrium dendrobatidis (Bd) has been implicated in dramatic global amphibian declines. Although many species have undergone catastrophic declines and/or extinctions, others appear to be unaffected or persist at reduced frequencies after Bd outbreaks. The reasons behind this variance in disease outcomes are poorly understood: differences in host immune responses have been proposed, yet previous studies suggest a lack of robust immune responses to Bd in susceptible species. Here, we sequenced transcriptomes from clutch-mates of a highly susceptible amphibian, Atelopus zeteki, with different infection histories. We found significant changes in expression of numerous genes involved in innate and inflammatory responses in infected frogs despite high susceptibility to chytridiomycosis. We show evidence of acquired immune responses generated against Bd, including increased expression of immunoglobulins and major histocompatibility complex genes. In addition, fungal-killing genes had significantly greater expression in frogs previously exposed to Bd compared with Bd-naïve frogs, including chitinase and serine-type proteases. However, our results appear to confirm recent in vitro evidence of immune suppression by Bd, demonstrated by decreased expression of lymphocyte genes in the spleen of infected compared with control frogs. We propose susceptibility to chytridiomycosis is not due to lack of Bd-specific immune responses but instead is caused by failure of those responses to be effective. Ineffective immune pathway activation and timing of antibody production are discussed as potential mechanisms. However, in light of our findings, suppression of key immune responses by Bd is likely an important factor in the lethality of this fungus.
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Affiliation(s)
- Amy R Ellison
- Department of Ecology and Evolutionary Biology, Cornell University, Ithaca, New York 14853
| | - Anna E Savage
- Department of Ecology and Evolutionary Biology, Cornell University, Ithaca, New York 14853 Center for Conservation and Evolutionary Genetics, Smithsonian Institution, Washington, DC 20013
| | - Grace V DiRenzo
- Department of Biology, University of Maryland, College Park, Maryland 20742
| | - Penny Langhammer
- School of Life Sciences, Arizona State University, Tempe, Arizona 85287
| | - Karen R Lips
- Department of Biology, University of Maryland, College Park, Maryland 20742
| | - Kelly R Zamudio
- Department of Ecology and Evolutionary Biology, Cornell University, Ithaca, New York 14853
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Cramp RL, McPhee RK, Meyer EA, Ohmer ME, Franklin CE. First line of defence: the role of sloughing in the regulation of cutaneous microbes in frogs. CONSERVATION PHYSIOLOGY 2014; 2:cou012. [PMID: 27293633 PMCID: PMC4806747 DOI: 10.1093/conphys/cou012] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/14/2014] [Revised: 03/05/2014] [Accepted: 03/05/2014] [Indexed: 05/22/2023]
Abstract
Amphibian populations worldwide are currently experiencing unprecedented declines due to the combined effects of emerging infectious disease and climate change. The skin is the first line of defence in preventing establishment of pathogens and associated infections. Although amphibians undergo regular sloughing of the outer layer of the skin, the potential for regular sloughing to play a role in influencing cutaneous microbial populations and pathogens has been largely overlooked. In the present study, we assessed the effect of skin sloughing on cultivable cutaneous bacterial abundance in the green tree frog (Litoria caerulea). We also examined the effects of temperature and hydric environment on sloughing frequency and microbial re-establishment rates. Our data showed that cultivable cutaneous bacterial abundance was significantly reduced by sloughing events, and frogs kept at 'summer' temperatures (23-33°C) sloughed almost twice as frequently as those maintained at 'winter' temperatures (13-23°C). No effect of hydric environment on sloughing frequency was observed, but we did find that sloughing in L. caerulea appeared to be linked to ambient light cycles. Examination of the effect of sloughing on microbial recolonization indicated that at cool temperatures, an extended intermoult interval allowed microbial abundance to reach higher levels than at warmer 'summer' temperatures (when the intermoult interval was significantly reduced). Our data suggest that sloughing may significantly influence the establishment and/or maintenance of cutaneous bacterial populations (pathogenic, mutualistic and/or commensal) and this, in turn, may be affected by environmental factors, such as ambient light and temperature. These findings are likely to be important for our understanding of the ecology of skin-based pathogens, such as the amphibian chytrid fungus, Batrachochytrium dendrobatidis.
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Affiliation(s)
- Rebecca L. Cramp
- School of Biological Sciences, The University of Queensland, Brisbane, Australia
| | - Rebecca K. McPhee
- School of Biological Sciences, The University of Queensland, Brisbane, Australia
| | - Edward A. Meyer
- School of Biological Sciences, The University of Queensland, Brisbane, Australia
| | - Michel E. Ohmer
- School of Biological Sciences, The University of Queensland, Brisbane, Australia
| | - Craig E. Franklin
- School of Biological Sciences, The University of Queensland, Brisbane, Australia
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Soto-Azat C, Valenzuela-Sánchez A, Clarke BT, Busse K, Ortiz JC, Barrientos C, Cunningham AA. Is chytridiomycosis driving Darwin's frogs to extinction? PLoS One 2013; 8:e79862. [PMID: 24278196 PMCID: PMC3835940 DOI: 10.1371/journal.pone.0079862] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2013] [Accepted: 09/25/2013] [Indexed: 11/19/2022] Open
Abstract
Darwin’s frogs (Rhinoderma darwinii and R. rufum) are two species of mouth brooding frogs from Chile and Argentina that have experienced marked population declines. Rhinoderma rufum has not been found in the wild since 1980. We investigated historical and current evidence of Batrachochytrium dendrobatidis (Bd) infection in Rhinoderma spp. to determine whether chytridiomycosis is implicated in the population declines of these species. Archived and live specimens of Rhinoderma spp., sympatric amphibians and amphibians at sites where Rhinoderma sp. had recently gone extinct were examined for Bd infection using quantitative real-time PCR. Six (0.9%) of 662 archived anurans tested positive for Bd (4/289 R. darwinii; 1/266 R. rufum and 1/107 other anurans), all of which had been collected between 1970 and 1978. An overall Bd-infection prevalence of 12.5% was obtained from 797 swabs taken from 369 extant individuals of R. darwinii and 428 individuals representing 18 other species of anurans found at sites with current and recent presence of the two Rhinoderma species. In extant R. darwinii, Bd-infection prevalence (1.9%) was significantly lower than that found in other anurans (7.3%). The prevalence of infection (30%) in other amphibian species was significantly higher in sites where either Rhinoderma spp. had become extinct or was experiencing severe population declines than in sites where there had been no apparent decline (3.0%; x2 = 106.407, P<0.001). This is the first report of widespread Bd presence in Chile and our results are consistent with Rhinoderma spp. declines being due to Bd infection, although additional field and laboratory investigations are required to investigate this further.
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Affiliation(s)
- Claudio Soto-Azat
- Laboratorio de Salud de Ecosistemas, Facultad de Ecología y Recursos Naturales, Universidad Andres Bello, Santiago, Chile
- Institute of Zoology, Zoological Society of London, Regent’s Park, London, United Kingdom
- * E-mail:
| | - Andrés Valenzuela-Sánchez
- Laboratorio de Salud de Ecosistemas, Facultad de Ecología y Recursos Naturales, Universidad Andres Bello, Santiago, Chile
| | - Barry T. Clarke
- Natural History Museum, Department of Life Sciences, Cromwell Rd., London, United Kingdom
| | - Klaus Busse
- Zoologisches Forschungsmuseum Alexander Koenig, Bonn, Germany
| | - Juan Carlos Ortiz
- Departamento de Zoología, Facultad de Ciencias Naturales y Oceanográficas, Universidad de Concepción, Concepción, Chile
| | - Carlos Barrientos
- Departamento de Zoología, Facultad de Ciencias Naturales y Oceanográficas, Universidad de Concepción, Concepción, Chile
| | - Andrew A. Cunningham
- Institute of Zoology, Zoological Society of London, Regent’s Park, London, United Kingdom
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Langhammer PF, Lips KR, Burrowes PA, Tunstall T, Palmer CM, Collins JP. A fungal pathogen of amphibians, Batrachochytrium dendrobatidis, attenuates in pathogenicity with in vitro passages. PLoS One 2013; 8:e77630. [PMID: 24130895 PMCID: PMC3795048 DOI: 10.1371/journal.pone.0077630] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2013] [Accepted: 09/04/2013] [Indexed: 11/19/2022] Open
Abstract
Laboratory investigations into the amphibian chytrid fungus, Batrachochytrium dendrobatidis (Bd), have accelerated recently, given the pathogen's role in causing the global decline and extinction of amphibians. Studies in which host animals were exposed to Bd have largely assumed that lab-maintained pathogen cultures retained the infective and pathogenic properties of wild isolates. Attenuated pathogenicity is common in artificially maintained cultures of other pathogenic fungi, but to date, it is unknown whether, and to what degree, Bd might change in culture. We compared zoospore production over time in two samples of a single Bd isolate having different passage histories: one maintained in artificial media for more than six years (JEL427-P39), and one recently thawed from cryopreserved stock (JEL427-P9). In a common garden experiment, we then exposed two different amphibian species, Eleutherodactylus coqui and Atelopus zeteki, to both cultures to test whether Bd attenuates in pathogenicity with in vitro passages. The culture with the shorter passage history, JEL427-P9, had significantly greater zoospore densities over time compared to JEL427-P39. This difference in zoospore production was associated with a difference in pathogenicity for a susceptible amphibian species, indicating that fecundity may be an important virulence factor for Bd. In the 130-day experiment, Atelopus zeteki frogs exposed to the JEL427-P9 culture experienced higher average infection intensity and 100% mortality, compared with 60% mortality for frogs exposed to JEL427-P39. This effect was not observed with Eleutherodactylus coqui, which was able to clear infection. We hypothesize that the differences in phenotypic performance observed with Atelopus zeteki are rooted in changes of the Bd genome. Future investigations enabled by this study will focus on the underlying mechanisms of Bd pathogenicity.
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Affiliation(s)
- Penny F. Langhammer
- School of Life Sciences, Arizona State University, Tempe, Arizona, United States of America
| | - Karen R. Lips
- Department of Biology, University of Maryland, College Park, Maryland, United States of America
| | - Patricia A. Burrowes
- Department of Biology, University of Puerto Rico, San Juan, Puerto Rico, United States of America
| | - Tate Tunstall
- Department of Biology, University of Maryland, College Park, Maryland, United States of America
| | - Crystal M. Palmer
- School of Life Sciences, Arizona State University, Tempe, Arizona, United States of America
| | - James P. Collins
- School of Life Sciences, Arizona State University, Tempe, Arizona, United States of America
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Murray KA, Skerratt LF, Garland S, Kriticos D, McCallum H. Whether the weather drives patterns of endemic amphibian chytridiomycosis: a pathogen proliferation approach. PLoS One 2013; 8:e61061. [PMID: 23613783 PMCID: PMC3629077 DOI: 10.1371/journal.pone.0061061] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2012] [Accepted: 03/05/2013] [Indexed: 12/29/2022] Open
Abstract
The pandemic amphibian disease chytridiomycosis often exhibits strong seasonality in both prevalence and disease-associated mortality once it becomes endemic. One hypothesis that could explain this temporal pattern is that simple weather-driven pathogen proliferation (population growth) is a major driver of chytridiomycosis disease dynamics. Despite various elaborations of this hypothesis in the literature for explaining amphibian declines (e.g., the chytrid thermal-optimum hypothesis) it has not been formally tested on infection patterns in the wild. In this study we developed a simple process-based model to simulate the growth of the pathogen Batrachochytrium dendrobatidis (Bd) under varying weather conditions to provide an a priori test of a weather-linked pathogen proliferation hypothesis for endemic chytridiomycosis. We found strong support for several predictions of the proliferation hypothesis when applied to our model species, Litoria pearsoniana, sampled across multiple sites and years: the weather-driven simulations of pathogen growth potential (represented as a growth index in the 30 days prior to sampling; GI30) were positively related to both the prevalence and intensity of Bd infections, which were themselves strongly and positively correlated. In addition, a machine-learning classifier achieved ∼72% success in classifying positive qPCR results when utilising just three informative predictors 1) GI30, 2) frog body size and 3) rain on the day of sampling. Hence, while intrinsic traits of the individuals sampled (species, size, sex) and nuisance sampling variables (rainfall when sampling) influenced infection patterns obtained when sampling via qPCR, our results also strongly suggest that weather-linked pathogen proliferation plays a key role in the infection dynamics of endemic chytridiomycosis in our study system. Predictive applications of the model include surveillance design, outbreak preparedness and response, climate change scenario modelling and the interpretation of historical patterns of amphibian decline.
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Affiliation(s)
- Kris A Murray
- EcoHealth Alliance, New York, New York, United States of America.
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Davidson EW, Larsen A, Meins Palmer C. Potential influence of plant chemicals on infectivity of Batrachochytrium dendrobatidis. DISEASES OF AQUATIC ORGANISMS 2012; 101:87-93. [PMID: 23135135 DOI: 10.3354/dao02505] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
We explored whether extracts of trees frequently found associated with amphibian habitats in Australia and Arizona, USA, may be inhibitory to the fungal pathogen Batrachochytrium dendrobatidis (Bd), which has been associated with global amphibian declines. We used salamanders Ambystoma tigrinum as the model system. Salamanders acquired significantly lower loads of Bd when exposed on leaves and extracts from the river red gum Eucalyptus camaldulensis, and loads were also low in some animals exposed on extracts of 2 oak species, Quercus emoryi and Q. turbinella. Some previously infected salamanders had their pathogen loads reduced, and some were fully cured, by placing them in leaf extracts, although some animals also self cured when housed in water alone. A significant number of animals cured of Bd infections 6 mo earlier were found to be resistant to reinfection. These results suggest that plants associated with amphibian habitats should be taken into consideration when explaining the prevalence of Bd in these habitats and that some amphibians may acquire resistance to the fungus if previously cured.
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Affiliation(s)
- Elizabeth W Davidson
- School of Life Sciences, Arizona State University, Tempe, Arizona 85287-4501, USA.
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47
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Becker CG, Rodriguez D, Longo AV, Talaba AL, Zamudio KR. Disease risk in temperate amphibian populations is higher at closed-canopy sites. PLoS One 2012; 7:e48205. [PMID: 23118953 PMCID: PMC3485156 DOI: 10.1371/journal.pone.0048205] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2012] [Accepted: 09/20/2012] [Indexed: 01/11/2023] Open
Abstract
Habitat loss and chytridiomycosis (a disease caused by the chytrid fungus Batrachochytrium dendrobatidis - Bd) are major drivers of amphibian declines worldwide. Habitat loss regulates host-pathogen interactions by altering biotic and abiotic factors directly linked to both host and pathogen fitness. Therefore, studies investigating the links between natural vegetation and chytridiomycosis require integrative approaches to control for the multitude of possible interactions of biological and environmental variables in spatial epidemiology. In this study, we quantified Bd infection dynamics across a gradient of natural vegetation and microclimates, looking for causal associations between vegetation cover, multiple microclimatic variables, and pathogen prevalence and infection intensity. To minimize the effects of host diversity in our analyses, we sampled amphibian populations in the Adirondack Mountains of New York State, a region with relatively high single-host dominance. We sampled permanent ponds for anurans, focusing on populations of the habitat generalist frog Lithobates clamitans, and recorded various biotic and abiotic factors that potentially affect host-pathogen interactions: natural vegetation, canopy density, water temperature, and host population and community attributes. We screened for important explanatory variables of Bd infections and used path analyses to statistically test for the strength of cascading effects linking vegetation cover, microclimate, and Bd parameters. We found that canopy density, natural vegetation, and daily average water temperature were the best predictors of Bd. High canopy density resulted in lower water temperature, which in turn predicted higher Bd prevalence and infection intensity. Our results confirm that microclimatic shifts arising from changes in natural vegetation play an important role in Bd spatial epidemiology, with areas of closed canopy favoring Bd. Given increasing rates of anthropogenic habitat modification and the resulting declines in temperate and tropical frogs, understanding how vegetation cover and disease interact is critical for predicting Bd spread and developing appropriate management tools for wild populations.
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Affiliation(s)
- C Guilherme Becker
- Department of Ecology and Evolutionary Biology, Cornell University, Ithaca, New York, USA.
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Hauselberger KF, Alford RA. Prevalence of Batrachochytrium dendrobatidis infection is extremely low in direct-developing Australian microhylids. DISEASES OF AQUATIC ORGANISMS 2012; 100:191-200. [PMID: 22968787 DOI: 10.3354/dao02494] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
The emerging infectious disease chytridiomycosis has been implicated in declines and disappearances of amphibian populations around the world. However, susceptibility to infection and the extent of pathological effects of infection vary among hosts, and species with life histories that include parental care of direct-developing terrestrial eggs may tend to be less susceptible. We examined samples from a total of 595 individuals of 9 species of direct-developing Australian frogs in the family Microhylidae for the presence of infection by Batrachochytrium dendrobatidis (Bd). Between 1995 and 2004, 336 samples were collected; 102 of these were analysed histologically and 234 were tissues stored in alcohol, which were examined using diagnostic quantitative PCR (qPCR). Swab samples were collected from 259 frogs from 2005 to 2008 and were examined using qPCR. None of the 595 samples showed evidence of infection by Bd. If these data are regarded as a single sample representative of Australian microhylids, the upper 95% binomial confidence limit for the prevalence of infection in frogs of this family is 0.0062 (<1%). Even if only the data from the more powerful diagnostic qPCR tests are used, the upper 95% confidence limit for prevalence is 0.0075 (<1%). Our data suggest that Australian microhylids have a very low prevalence of infection by Bd in nature, and thus are either not susceptible, or are only slightly susceptible, to chytridiomycosis. This could be due solely to, or in combination with, low rates of transmission and to factors that promote resistance to infection, including ecological or behavioural characteristics, innate immune functions such as antimicrobial skin peptides, or antimicrobial symbionts in skin flora.
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Affiliation(s)
- Kim F Hauselberger
- School of Marine and Tropical Biology, James Cook University, Townsville, Queensland 4811, Australia.
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Chloramphenicol with fluid and electrolyte therapy cures terminally ill green tree frogs (Litoria caerulea) with chytridiomycosis. J Zoo Wildl Med 2012; 43:330-7. [PMID: 22779237 DOI: 10.1638/2011-0231.1] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Terminal changes in frogs infected with the amphibian fungal pathogen Batrachochytrium dendrobatidis (Bd) include epidermal degeneration leading to inhibited epidermal electrolyte transport, systemic electrolyte disturbances, and asystolic cardiac arrest. There are few reports of successful treatment of chytridiomycosis and none that include curing amphibians with severe disease. Three terminally ill green tree frogs (Litoria caerulea) with heavy Bd infections were cured using a combination of continuous shallow immersion in 20 mg/L chloramphenicol solution for 14 days, parenteral isotonic electrolyte fluid therapy for 6 days, and increased ambient temperature to 28 degrees C for 14 days. All terminally ill frogs recovered rapidly to normal activity levels and appetite within 5 days of commencing treatment. In contrast, five untreated terminally ill L. caerulea with heavy Bd infections died within 24-48 hr of becoming moribund. Subclinical infections in 15 experimentally infected L. caerulea were cured within 28 days by continuous shallow immersion in 20 mg/L chloramphenicol solution without adverse effects. This is the first known report of a clinical treatment protocol for curing terminally ill Bd-infected frogs.
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Forrest MJ, Schlaepfer MA. Nothing a hot bath won't cure: infection rates of amphibian chytrid fungus correlate negatively with water temperature under natural field settings. PLoS One 2011; 6:e28444. [PMID: 22205950 PMCID: PMC3244395 DOI: 10.1371/journal.pone.0028444] [Citation(s) in RCA: 66] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2011] [Accepted: 11/08/2011] [Indexed: 11/18/2022] Open
Abstract
Dramatic declines and extinctions of amphibian populations throughout the world have been associated with chytridiomycosis, an infectious disease caused by the pathogenic chytrid fungus Batrachochytrium dendrobatidis (Bd). Previous studies indicated that Bd prevalence correlates with cooler temperatures in the field, and laboratory experiments have demonstrated that Bd ceases growth at temperatures above 28°C. Here we investigate how small-scale variations in water temperature correlate with Bd prevalence in the wild. We sampled 221 amphibians, including 201 lowland leopard frogs (Rana [Lithobates] yavapaiensis), from 12 sites in Arizona, USA, and tested them for Bd. Amphibians were encountered in microhabitats that exhibited a wide range of water temperatures (10-50°C), including several geothermal water sources. There was a strong inverse correlation between the water temperature in which lowland leopard frogs were captured and Bd prevalence, even after taking into account the influence of year, season, and host size. In locations where Bd was known to be present, the prevalence of Bd infections dropped from 75-100% in water <15°C, to less than 10% in water >30°C. A strong inverse correlation between Bd infection status and water temperature was also observed within sites. Our findings suggest that microhabitats where water temperatures exceed 30°C provide lowland leopard frogs with significant protection from Bd, which could have important implications for disease dynamics, as well as management applications.There must be quite a few things a hot bath won't cure, but I don't know many of them--Sylvia Plath, "The Bell Jar" (1963).
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Affiliation(s)
- Matthew J Forrest
- Center for Marine Biodiversity and Conservation, Scripps Institution of Oceanography, La Jolla, California, United States of America.
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