1
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Keegan SP, Pedersen AB, Fenton A. The impact of within-host coinfection interactions on between-host parasite transmission dynamics varies with spatial scale. Proc Biol Sci 2024; 291:20240103. [PMID: 38628126 PMCID: PMC11021925 DOI: 10.1098/rspb.2024.0103] [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: 01/14/2024] [Accepted: 03/18/2024] [Indexed: 04/19/2024] Open
Abstract
Within-host interactions among coinfecting parasites can have major consequences for individual infection risk and disease severity. However, the impact of these within-host interactions on between-host parasite transmission, and the spatial scales over which they occur, remain unknown. We developed and apply a novel spatially explicit analysis to parasite infection data from a wild wood mouse (Apodemus sylvaticus) population. We previously demonstrated a strong within-host negative interaction between two wood mouse gastrointestinal parasites, the nematode Heligmosomoides polygyrus and the coccidian Eimeria hungaryensis, using drug-treatment experiments. Here, we show this negative within-host interaction can significantly alter the between-host transmission dynamics of E. hungaryensis, but only within spatially restricted neighbourhoods around each host. However, for the closely related species E. apionodes, which experiments show does not interact strongly with H. polygyrus, we did not find any effect on transmission over any spatial scale. Our results demonstrate that the effects of within-host coinfection interactions can ripple out beyond each host to alter the transmission dynamics of the parasites, but only over local scales that likely reflect the spatial dimension of transmission. Hence there may be knock-on consequences of drug treatments impacting the transmission of non-target parasites, altering infection risks even for non-treated individuals in the wider neighbourhood.
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Affiliation(s)
- Shaun P. Keegan
- Department of Evolution, Ecology and Behaviour, Institute of Infection, Veterinary and Ecological Sciences, University of Liverpool, Liverpool L69 7ZB, UK
| | - Amy B. Pedersen
- Institute of Ecology and Evolution, School of Biological Sciences, University of Edinburgh, Edinburgh EH9 3FL, UK
| | - Andy Fenton
- Department of Evolution, Ecology and Behaviour, Institute of Infection, Veterinary and Ecological Sciences, University of Liverpool, Liverpool L69 7ZB, UK
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2
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Dujon AM, Jeanjean J, Vincze O, Giraudeau M, Lemaître J, Pujol P, Ujvari B, Thomas F. Cancer hygiene hypothesis: A test from wild captive mammals. Ecol Evol 2023; 13:e10547. [PMID: 37745791 PMCID: PMC10515881 DOI: 10.1002/ece3.10547] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2023] [Revised: 08/31/2023] [Accepted: 09/04/2023] [Indexed: 09/26/2023] Open
Abstract
The hygiene hypothesis, according to which the recent reduction of exposure to infectious agents in the human species would be the origin of various diseases, including autoimmune diseases and cancer, has often been proposed but not properly tested on animals. Here, we evaluated the relevance of this hypothesis to cancer risk in mammals in an original way, namely by using information on zoo mammals. We predicted that a higher richness of parasitic cohorts in the species' natural habitat would result in a greater occurrence of evolutionary mismatch due to the reduction of parasites in captive conditions. This, in turn, could contribute to an increased risk of developing lethal cancers. Using a comparative analysis of 112 mammalian species, we explored the potential relationship between cancer risk and parasite species richness using generalized phylogenetic least squares regressions to relate parasite species richness to cancer risk data. We found no strong evidence that parasite species richness increased cancer risk in zoo mammals for any of the parasite groups we tested. Without constituting definitive proof of the irrelevance of the hygienic hypothesis, our comparative study using zoo mammals does not support it, at least with respect to cancer risks.
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Affiliation(s)
- Antoine M. Dujon
- Geelong, School of Life and Environmental Sciences, Centre for Integrative EcologyDeakin UniversityWaurn PondsVictoriaAustralia
- CREEC/CANECEV (CREES), MIVEGEC, IRD 224–CNRS 5290–Université de MontpellierMontpellierFrance
| | - Jérémy Jeanjean
- CREEC/CANECEV (CREES), MIVEGEC, IRD 224–CNRS 5290–Université de MontpellierMontpellierFrance
| | - Orsolya Vincze
- Institute of Aquatic Ecology, Centre for Ecological ResearchDebrecenHungary
- Evolutionary Ecology Group, Hungarian Department of Biology and EcologyBabes‐Bolyai UniversityCluj‐NapocaRomania
- Littoral, Environnement et Sociétés (LIENSs), UMR 7266 CNRS‐La Rochelle UniversitéLa RochelleFrance
| | - Mathieu Giraudeau
- Littoral, Environnement et Sociétés (LIENSs), UMR 7266 CNRS‐La Rochelle UniversitéLa RochelleFrance
| | - Jean‐François Lemaître
- CNRS, UMR 5558, Laboratoire de Biométrie et Biologie EvolutiveUniversité de LyonVilleurbanneFrance
- Laboratory of Rare Human Circulating Cells (LCCRH)University Hospital of MontpellierMontpellierFrance
| | - Pascal Pujol
- CREEC/CANECEV (CREES), MIVEGEC, IRD 224–CNRS 5290–Université de MontpellierMontpellierFrance
- Centre Hospitalier Universitaire Arnaud de VilleneuveMontpellierFrance
| | - Beata Ujvari
- Geelong, School of Life and Environmental Sciences, Centre for Integrative EcologyDeakin UniversityWaurn PondsVictoriaAustralia
- CREEC/CANECEV (CREES), MIVEGEC, IRD 224–CNRS 5290–Université de MontpellierMontpellierFrance
| | - Frédéric Thomas
- CREEC/CANECEV (CREES), MIVEGEC, IRD 224–CNRS 5290–Université de MontpellierMontpellierFrance
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3
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Kirk D, O’Connor MI, Mordecai EA. Scaling effects of temperature on parasitism from individuals to populations. J Anim Ecol 2022; 91:2087-2102. [PMID: 35900837 PMCID: PMC9532350 DOI: 10.1111/1365-2656.13786] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2022] [Accepted: 07/15/2022] [Indexed: 11/27/2022]
Abstract
Parasitism is expected to change in a warmer future, but whether warming leads to substantial increases in parasitism remains unclear. Understanding how warming effects on parasitism in individual hosts (e.g. parasite load) translate to effects on population-level parasitism (e.g. prevalence, R0 ) remains a major knowledge gap. We conducted a literature review and identified 24 host-parasite systems that had information on the temperature dependence of parasitism at both individual host and host population levels: 13 vector-borne systems and 11 environmentally transmitted systems. We found a strong positive correlation between the thermal optima of individual- and population-level parasitism, although several of the environmentally transmitted systems exhibited thermal optima >5°C apart between individual and population levels. Parasitism thermal optima were close to vector performance thermal optima in vector-borne systems but not hosts in environmentally transmitted systems, suggesting these thermal mismatches may be more common in certain types of host-parasite systems. We also adapted and simulated simple models for both types of transmission modes and found the same pattern across the two modes: thermal optima were more strongly correlated across scales when there were more traits linking individual- to population-level processes. Generally, our results suggest that information on the temperature dependence, and specifically the thermal optimum, at either the individual or population level should provide a useful-although not quantitatively exact-baseline for predicting temperature dependence at the other level, especially in vector-borne parasite systems. Environmentally transmitted parasitism may operate by a different set of rules, in which temperature dependence is decoupled in some systems, requiring the need for trait-based studies of temperature dependence at individual and population levels.
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Affiliation(s)
- Devin Kirk
- Department of Biology, Stanford University, Stanford, USA
- Department of Zoology, University of British Columbia, Vancouver, Canada
| | - Mary I. O’Connor
- Department of Zoology, University of British Columbia, Vancouver, Canada
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4
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Jones RP, Ponomarenko A. Roles for Pathogen Interference in Influenza Vaccination, with Implications to Vaccine Effectiveness (VE) and Attribution of Influenza Deaths. Infect Dis Rep 2022; 14:710-758. [PMID: 36286197 PMCID: PMC9602062 DOI: 10.3390/idr14050076] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/07/2022] [Revised: 09/15/2022] [Accepted: 09/15/2022] [Indexed: 08/29/2023] Open
Abstract
Pathogen interference is the ability of one pathogen to alter the course and clinical outcomes of infection by another. With up to 3000 species of human pathogens the potential combinations are vast. These combinations operate within further immune complexity induced by infection with multiple persistent pathogens, and by the role which the human microbiome plays in maintaining health, immune function, and resistance to infection. All the above are further complicated by malnutrition in children and the elderly. Influenza vaccination offers a measure of protection for elderly individuals subsequently infected with influenza. However, all vaccines induce both specific and non-specific effects. The specific effects involve stimulation of humoral and cellular immunity, while the nonspecific effects are far more nuanced including changes in gene expression patterns and production of small RNAs which contribute to pathogen interference. Little is known about the outcomes of vaccinated elderly not subsequently infected with influenza but infected with multiple other non-influenza winter pathogens. In this review we propose that in certain years the specific antigen mix in the seasonal influenza vaccine inadvertently increases the risk of infection from other non-influenza pathogens. The possibility that vaccination could upset the pathogen balance, and that the timing of vaccination relative to the pathogen balance was critical to success, was proposed in 2010 but was seemingly ignored. Persons vaccinated early in the winter are more likely to experience higher pathogen interference. Implications to the estimation of vaccine effectiveness and influenza deaths are discussed.
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Affiliation(s)
- Rodney P Jones
- Healthcare Analysis and Forecasting, Wantage OX12 0NE, UK
| | - Andrey Ponomarenko
- Department of Biophysics, Informatics and Medical Instrumentation, Odessa National Medical University, Valikhovsky Lane 2, 65082 Odessa, Ukraine
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5
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Sweeny AR, Corripio-Miyar Y, Bal X, Hayward AD, Pilkington JG, McNeilly TN, Nussey DH, Kenyon F. Longitudinal dynamics of co-infecting gastrointestinal parasites in a wild sheep population. Parasitology 2022; 149:1-12. [PMID: 35264257 PMCID: PMC10090596 DOI: 10.1017/s0031182021001980] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2021] [Revised: 10/09/2021] [Accepted: 11/01/2021] [Indexed: 11/07/2022]
Abstract
Within-year variation in infection is a ubiquitous feature of natural populations, but is determined by a complex interplay of environmental, parasitological and host factors. At the same time, co-infection is the norm in the wild. Longitudinal dynamics of co-infecting parasites may therefore be further complicated by covariation across multiple parasites. Here, we used fecal parasite egg and oocyst counts collected repeatedly from individually marked wild Soay sheep to investigate seasonal dynamics of six gastrointestinal parasite groups. Prevalence and abundance tended to be higher in spring and summer, and abundance was higher in lambs compared to adults. We found that within-year variation in highly prevalent strongyle nematode counts was dependent on adult reproductive status, where reproductive ewes had distinct dynamics compared to males and barren ewes. For similarly prevalent coccidia we found an overall peak in oocyst counts in spring but no differences among males, barren and pregnant ewes. Using multivariate mixed-effects models, we further show that apparent positive correlation between strongyle and coccidia counts was driven by short-term within-individual changes in both counts rather than long-term among-individual covariation. Overall, these results demonstrate that seasonality varies across demographic and parasite groups and highlight the value of investigating co-infection dynamics over time.
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Affiliation(s)
- Amy R. Sweeny
- Institute of Evolutionary Biology, University of Edinburgh, Edinburgh, UK
| | | | - Xavier Bal
- Institute of Evolutionary Biology, University of Edinburgh, Edinburgh, UK
| | | | - Jill G. Pilkington
- Institute of Evolutionary Biology, University of Edinburgh, Edinburgh, UK
| | | | - Daniel H. Nussey
- Institute of Evolutionary Biology, University of Edinburgh, Edinburgh, UK
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6
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Rovenolt FH, Tate AT. The Impact of Coinfection Dynamics on Host Competition and Coexistence. Am Nat 2022; 199:91-107. [DOI: 10.1086/717180] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
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7
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Bielby J, Price SJ, Monsalve-CarcaÑo C, Bosch J. Host contribution to parasite persistence is consistent between parasites and over time, but varies spatially. ECOLOGICAL APPLICATIONS : A PUBLICATION OF THE ECOLOGICAL SOCIETY OF AMERICA 2021; 31:e02256. [PMID: 33164249 DOI: 10.1002/eap.2256] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/30/2020] [Revised: 06/11/2020] [Accepted: 08/16/2020] [Indexed: 06/11/2023]
Abstract
Most parasites and pathogens infect multiple hosts, but a great deal of variation exists in the role of those hosts in persistence of infection. Understanding which hosts are most important in maintaining parasites can provide a clearer target for infection control. Recently developed empirical and theoretical approaches provide a way to quantify the relative contribution of hosts within a community and place them in a multi-host framework to better direct control efforts. Amphibians provide a framework for better understanding multi-host-multi-parasite dynamics. Two well-studied amphibian parasites, Batrachochytrium dendrobatidis (Bd) and Ranavirus, infect multiple host species and exhibit a great deal of heterogeneity in how they affect hosts. We used these two parasites and a community of five amphibian species to investigate the relative importance of hosts in parasite persistence, and how any patterns varied spatially and temporally. At two sites (Lake Ercina and Lake Lloroza in the Picos de Europa National Park, Spain) we collected data on the prevalence and shedding rate of parasite infection for both Bd and Ranavirus, and the abundance of each species' life stages. We used these data to parameterize a recently developed modeling framework, which was used to quantify the relative contribution of each host to the community reproductive number, R0 . By comparing each host-category over time and between sites we were able to identify consistencies in which host was responsible for the maintenance of these two parasites. Within a site one species consistently contributed the most to the persistence of both parasites. This consistency did not transfer between sites, the maintenance host species being different for each. At one site (Ercina), life stages of the common midwife toad, Alytes obstetricans, acted as the maintenance host for both Bd and Ranavirus. In contrast, at the second site, Lloroza, the alpine newt, Ichthyosaura alpestris, fulfilled that role. A single host species was responsible for infection persistence of both parasites at each lake. Attempts to control the infection levels and impacts of multiple parasites can benefit from a community epidemiology approach, and provide clarity on which hosts are the foci of mitigation efforts. However, at a small spatial scale, the target host may vary according to the physical qualities of those sites and the demographics of the host community.
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Affiliation(s)
- Jon Bielby
- School of Natural Sciences and Psychology, Liverpool John Moores University, James Parsons Building, Byrom Street, Liverpool, L3 3AF, United Kingdom
| | - Stephen J Price
- UCL Genetics Institute, Darwin Building, Gower Street, London, WC1E 6BT, United Kingdom
- Institute of Zoology, Zoological Society of London, Regents Park, London, NW1 4RY, United Kingdom
| | | | - Jaime Bosch
- Museo Nacional de Ciencias Naturales, CSIC, José Gutiérrez Abascal 2, Madrid, 28006, Spain
- Research Unit of Biodiversity (CSIC, UO, PA), Oviedo University-Campus Mieres, Mieres, Spain
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8
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Vanalli C, Mari L, Righetto L, Casagrandi R, Gatto M, Cattadori IM. Within-host mechanisms of immune regulation explain the contrasting dynamics of two helminth species in both single and dual infections. PLoS Comput Biol 2020; 16:e1008438. [PMID: 33226981 PMCID: PMC7721179 DOI: 10.1371/journal.pcbi.1008438] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2020] [Revised: 12/07/2020] [Accepted: 10/12/2020] [Indexed: 11/18/2022] Open
Abstract
Variation in the intensity and duration of infections is often driven by variation in the network and strength of host immune responses. While many of the immune mechanisms and components are known for parasitic helminths, how these relationships change from single to multiple infections and impact helminth dynamics remains largely unclear. Here, we used laboratory data from a rabbit-helminth system and developed a within-host model of infection to investigate different scenarios of immune regulation in rabbits infected with one or two helminth species. Model selection suggests that the immunological pathways activated against Trichostrongylus retortaeformis and Graphidium strigosum are similar. However, differences in the strength of these immune signals lead to the contrasting dynamics of infections, where the first parasite is rapidly cleared and the latter persists with high intensities. In addition to the reactions identified in single infections, rabbits with both helminths also activate new pathways that asymmetrically affect the dynamics of the two species. These new signals alter the intensities but not the general trend of the infections. The type of interactions described can be expected in many other host-helminth systems. Our immune framework is flexible enough to capture different mechanisms and their complexity, and provides essential insights to the understanding of multi-helminth infections.
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Affiliation(s)
- Chiara Vanalli
- Center for Infectious Disease Dynamics and Department of Biology, The Pennsylvania State University, University Park, Pennsylvania, USA
| | - Lorenzo Mari
- Dipartimento di Elettronica, Informazione e Bioingegneria, Politecnico di Milano, Milano, Italy
| | - Lorenzo Righetto
- Dipartimento di Elettronica, Informazione e Bioingegneria, Politecnico di Milano, Milano, Italy
| | - Renato Casagrandi
- Dipartimento di Elettronica, Informazione e Bioingegneria, Politecnico di Milano, Milano, Italy
| | - Marino Gatto
- Dipartimento di Elettronica, Informazione e Bioingegneria, Politecnico di Milano, Milano, Italy
| | - Isabella M. Cattadori
- Center for Infectious Disease Dynamics and Department of Biology, The Pennsylvania State University, University Park, Pennsylvania, USA
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9
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Fountain-Jones NM, Packer C, Jacquot M, Blanchet FG, Terio K, Craft ME. Endemic infection can shape exposure to novel pathogens: Pathogen co-occurrence networks in the Serengeti lions. Ecol Lett 2019; 22:904-913. [PMID: 30861289 PMCID: PMC7163671 DOI: 10.1111/ele.13250] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2018] [Revised: 11/12/2018] [Accepted: 02/11/2019] [Indexed: 11/30/2022]
Abstract
Pathogens are embedded in a complex network of microparasites that can collectively or individually alter disease dynamics and outcomes. Endemic pathogens that infect an individual in the first years of life, for example, can either facilitate or compete with subsequent pathogens thereby exacerbating or ameliorating morbidity and mortality. Pathogen associations are ubiquitous but poorly understood, particularly in wild populations. We report here on 10 years of serological and molecular data in African lions, leveraging comprehensive demographic and behavioural data to test if endemic pathogens shape subsequent infection by epidemic pathogens. We combine network and community ecology approaches to assess broad network structure and characterise associations between pathogens across spatial and temporal scales. We found significant non‐random structure in the lion‐pathogen co‐occurrence network and identified both positive and negative associations between endemic and epidemic pathogens. Our results provide novel insights on the complex associations underlying pathogen co‐occurrence networks.
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Affiliation(s)
- Nicholas M Fountain-Jones
- Department of Veterinary Population Medicine, University of Minnesota, 1365 Gortner Avenue, St Paul, MN, 55108, USA
| | - Craig Packer
- Department of Ecology Evolution and Behavior, University of Minnesota, St Paul, MN, 55408, USA
| | - Maude Jacquot
- INRA, UMR346 EPIA, Epidémiologie des maladies Animales et zoonotiques, 63122, Saint-Genès-Champanelle, France
| | - F Guillaume Blanchet
- Département de biologie, Université de Sherbrooke, 2500 Boulevard Université, Sherbrooke, QC, Canada, J1K 2R1
| | - Karen Terio
- Zoological Pathology Program, University of Illinois, Urbana-Champaign, IL, USA
| | - Meggan E Craft
- Department of Veterinary Population Medicine, University of Minnesota, 1365 Gortner Avenue, St Paul, MN, 55108, USA
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10
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Lello J, McClure SJ, Tyrrell K, Viney ME. Predicting the effects of parasite co-infection across species boundaries. Proc Biol Sci 2019. [PMID: 29540516 PMCID: PMC5879626 DOI: 10.1098/rspb.2017.2610] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
It is normal for hosts to be co-infected by parasites. Interactions among co-infecting species can have profound consequences, including changing parasite transmission dynamics, altering disease severity and confounding attempts at parasite control. Despite the importance of co-infection, there is currently no way to predict how different parasite species may interact with one another, nor the consequences of those interactions. Here, we demonstrate a method that enables such prediction by identifying two nematode parasite groups based on taxonomy and characteristics of the parasitological niche. From an understanding of the interactions between the two defined groups in one host system (wild rabbits), we predict how two different nematode species, from the same defined groups, will interact in co-infections in a different host system (sheep), and then we test this experimentally. We show that, as predicted, in co-infections, the blood-feeding nematode Haemonchus contortus suppresses aspects of the sheep immune response, thereby facilitating the establishment and/or survival of the nematode Trichostrongylus colubriformis; and that the T. colubriformis-induced immune response negatively affects H. contortus This work is, to our knowledge, the first to use empirical data from one host system to successfully predict the specific outcome of a different co-infection in a second host species. The study therefore takes the first step in defining a practical framework for predicting interspecific parasite interactions in other animal systems.
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Affiliation(s)
- Joanne Lello
- School of Biosciences, Cardiff University, Cardiff CF10 3AX, UK .,Department of Biodiversity and Molecular Ecology, Research and Innovation Centre, Fondazione Edmund Mach, S. Michele all'Adige, Trentino 38010, Italy.,Division of Animal, Food and Health Sciences, CSIRO, Armidale, New South Wales 2350, Australia
| | - Susan J McClure
- Division of Animal, Food and Health Sciences, CSIRO, Armidale, New South Wales 2350, Australia
| | - Kerri Tyrrell
- Division of Animal, Food and Health Sciences, CSIRO, Armidale, New South Wales 2350, Australia
| | - Mark E Viney
- School of Biological Sciences, University of Bristol, Bristol BS8 1TQ, UK
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11
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Abstract
AbstractCompetition between parasite species or genotypes can play an important role in the establishment of parasites in new host populations. Here, we investigate a mechanism by which a rare parasite is unable to establish itself in a host population if a common resident parasite is already present (a ‘priority effect’). We develop a simple epidemiological model and show that a rare parasite genotype is unable to invade if coinfecting parasite genotypes inhibit each other's transmission more than expected from simple resource partitioning. This is because a rare parasite is more likely to be in multiply-infected hosts than the common genotype, and hence more likely to pay the cost of reduced transmission. Experiments competing interfering clones of bacteriophage infecting a bacterium support the model prediction that the clones are unable to invade each other from rare. We briefly discuss the implications of these results for host-parasite ecology and (co)evolution.
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12
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Henrichs B, Oosthuizen MC, Troskie M, Gorsich E, Gondhalekar C, Beechler BR, Ezenwa VO, Jolles AE. Within guild co-infections influence parasite community membership: a longitudinal study in African Buffalo. J Anim Ecol 2016; 85:1025-34. [PMID: 27084785 DOI: 10.1111/1365-2656.12535] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2015] [Accepted: 04/04/2016] [Indexed: 11/26/2022]
Abstract
Experimental studies in laboratory settings have demonstrated a critical role of parasite interactions in shaping parasite communities. The sum of these interactions can produce diverse effects on individual hosts as well as influence disease emergence and persistence at the population level. A predictive framework for the effects of parasite interactions in the wild remains elusive, largely because of limited longitudinal or experimental data on parasite communities of free-ranging hosts. This 4-year study followed a community of haemoparasites in free-ranging African buffalo (Syncerus caffer). We detected infection by 11 haemoparasite species using PCR-based diagnostic techniques, and analyzed drivers of infection patterns using generalized linear mixed models to understand the role of host characteristics and season on infection likelihood. We tested for (i) effects of co-infection by other haemoparasites (within guild) and (ii) effects of parasites infecting different tissue types (across guild). We found that within guild co-infections were the strongest predictors of haemoparasite infections in the buffalo; but that seasonal and host characteristics also had important effects. In contrast, the evidence for across-guild effects of parasites utilizing different tissue on haemoparasite infection was weak. These results provide a nuanced view of the role of co-infections in determining haemoparasite infection patterns in free living mammalian hosts. Our findings suggest a role for interactions among parasites infecting a single tissue type in determining infection patterns.
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Affiliation(s)
- Brian Henrichs
- Department of Integrative Biology, Oregon State University, Corvallis, OR, 97331, USA
| | - Marinda C Oosthuizen
- Department of Veterinary Tropical Diseases, Faculty of Veterinary Sciences, University of Pretoria, Onderstepoort, 0110, South Africa
| | - Milana Troskie
- Department of Veterinary Tropical Diseases, Faculty of Veterinary Sciences, University of Pretoria, Onderstepoort, 0110, South Africa
| | - Erin Gorsich
- Department of Biology, Colorado State University, Fort Collins, CO, 80523, USA
| | - Carmen Gondhalekar
- Department of Integrative Biology, Oregon State University, Corvallis, OR, 97331, USA
| | - Brianna R Beechler
- Department of Biomedical Sciences, Oregon State University, Corvallis, OR, 97331, USA
| | - Vanessa O Ezenwa
- Department of Infectious Diseases, University of Georgia, Athens, GA, 30602, USA.,Odum School of Ecology, University of Georgia, Athens, GA, 30602, USA
| | - Anna E Jolles
- Department of Integrative Biology, Oregon State University, Corvallis, OR, 97331, USA.,Department of Biomedical Sciences, Oregon State University, Corvallis, OR, 97331, USA
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13
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Diuk-Wasser MA, Vannier E, Krause PJ. Coinfection by Ixodes Tick-Borne Pathogens: Ecological, Epidemiological, and Clinical Consequences. Trends Parasitol 2015; 32:30-42. [PMID: 26613664 DOI: 10.1016/j.pt.2015.09.008] [Citation(s) in RCA: 227] [Impact Index Per Article: 25.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2015] [Revised: 09/25/2015] [Accepted: 09/28/2015] [Indexed: 12/13/2022]
Abstract
Ixodes ticks maintain a large and diverse array of human pathogens in the enzootic cycle, including Borrelia burgdorferi and Babesia microti. Despite the poor ecological fitness of B. microti, babesiosis has recently emerged in areas endemic for Lyme disease. Studies in ticks, reservoir hosts, and humans indicate that coinfection with B. burgdorferi and B. microti is common, promotes transmission and emergence of B. microti in the enzootic cycle, and causes greater disease severity and duration in humans. These interdisciplinary studies may serve as a paradigm for the study of other vector-borne coinfections. Identifying ecological drivers of pathogen emergence and host factors that fuel disease severity in coinfected individuals will help guide the design of effective preventative and therapeutic strategies.
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Affiliation(s)
| | - Edouard Vannier
- Tufts Medical Center and Tufts University School of Medicine, Boston, MA, USA
| | - Peter J Krause
- Yale School of Public Health and Yale School of Medicine, New Haven, CT, USA.
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14
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Vaumourin E, Vourc'h G, Gasqui P, Vayssier-Taussat M. The importance of multiparasitism: examining the consequences of co-infections for human and animal health. Parasit Vectors 2015; 8:545. [PMID: 26482351 PMCID: PMC4617890 DOI: 10.1186/s13071-015-1167-9] [Citation(s) in RCA: 113] [Impact Index Per Article: 12.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2015] [Accepted: 10/14/2015] [Indexed: 11/23/2022] Open
Abstract
Most parasites co-occur with other parasites, although the importance of such multiparasitism has only recently been recognised. Co-infections may result when hosts are independently infected by different parasites at the same time or when interactions among parasite species facilitate co-occurrence. Such interactions can have important repercussions on human or animal health because they can alter host susceptibility, infection duration, transmission risks, and clinical symptoms. These interactions may be synergistic or antagonistic and thus produce diverse effects in infected humans and animals. Interactions among parasites strongly influence parasite dynamics and therefore play a major role in structuring parasite populations (both within and among hosts) as well as host populations. However, several methodological challenges remain when it comes to detecting parasite interactions. The goal of this review is to summarise current knowledge on the causes and consequences of multiparasitism and to discuss the different methods and tools that researchers have developed to study the factors that lead to multiparasitism. It also identifies new research directions to pursue.
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Affiliation(s)
- Elise Vaumourin
- UR346 Animal Epidemiology Research Unit, INRA, Saint Genès Champanelle, France. .,USC BIPAR, INRA-ANSES-ENVA, Maisons-Alfort, France.
| | - Gwenaël Vourc'h
- UR346 Animal Epidemiology Research Unit, INRA, Saint Genès Champanelle, France.
| | - Patrick Gasqui
- UR346 Animal Epidemiology Research Unit, INRA, Saint Genès Champanelle, France.
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Pearsonema plica (Capillaria plica) infection and associated urinary bladder pathology in red foxes (Vulpes vulpes) from Bosnia and Herzegovina. Parasitol Res 2015; 114:1933-8. [PMID: 25687525 DOI: 10.1007/s00436-015-4382-6] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2015] [Accepted: 02/05/2015] [Indexed: 01/09/2023]
Abstract
Pearsonema plica is a widely distributed nematode parasite that occurs in the urinary tract of various domestic and wild carnivores. The aim of this study was to investigate the occurrence and geographical distribution of P. plica and associated urinary bladder pathology in 112 red foxes (70 males, 42 females; 87 adults >1 year, 25 juveniles <1 year) from six different geographical regions in Bosnia and Herzegovina. The urinary bladders of the red foxes were subjected to gross examination and histopathology. Urine content (n = 40) and mucosal smears (n = 71) of the urinary bladders were examined microscopically for the presence of P. plica. Overall, adults and eggs of P. plica were detected in 65 (58.0 %; 95% CI 48.9-67.2%) of the foxes. Out of the positive foxes, 42 were males (64.6%) and 23 females (35.3%). According to age, 49 adults (75.3%) and 16 juveniles (24.6%) were positive. There were no statistically significant differences in the infection prevalence between the geographical regions (p = 0.701), sex (p = 0.693), or age (p = 0.646) of the host. Also, no significant differences in the prevalence of parasites in urine content (48.7%; 20/41) and mucosal smears (63.3%; 45/71) were observed (p = 0.165). Eosinophilic cystitis characterized with mild to severe infiltrates of eosinophils in the propria of the bladder mucosa accompanied by hyperemia and edema was observed in 36 examined foxes, 24 of which were P. plica positive. Parasites attached and embedded into the mucosa and free in the lumen were recorded in both cystitis positive and negative foxes. Beside clear numerical differences, the influence of P. plica infection on the occurrence of cystitis was not significant (p = 0.309). The results of this study give the first insight into the distribution of P. plica infection among the red fox population in Bosnia and Herzegovina. Observed microscopic changes may contribute toward a better understanding of pathology caused by this widely distributed parasite in free-ranging red foxes.
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16
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Buhnerkempe MG, Roberts MG, Dobson AP, Heesterbeek H, Hudson PJ, Lloyd-Smith JO. Eight challenges in modelling disease ecology in multi-host, multi-agent systems. Epidemics 2014; 10:26-30. [PMID: 25843378 DOI: 10.1016/j.epidem.2014.10.001] [Citation(s) in RCA: 56] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2014] [Revised: 10/14/2014] [Accepted: 10/15/2014] [Indexed: 12/23/2022] Open
Abstract
Many disease systems exhibit complexities not captured by current theoretical and empirical work. In particular, systems with multiple host species and multiple infectious agents (i.e., multi-host, multi-agent systems) require novel methods to extend the wealth of knowledge acquired studying primarily single-host, single-agent systems. We outline eight challenges in multi-host, multi-agent systems that could substantively increase our knowledge of the drivers and broader ecosystem effects of infectious disease dynamics.
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Affiliation(s)
- Michael G Buhnerkempe
- Department of Ecology and Evolutionary Biology, University of California-Los Angeles, Los Angeles, CA, USA; Fogarty International Center, National Institutes of Health, Bethesda, MD, USA.
| | - Mick G Roberts
- Institute of Natural & Mathematical Sciences, New Zealand Institute for Advanced Study and Infectious Disease Research Centre, Massey University, Auckland, New Zealand
| | - Andrew P Dobson
- Department of Ecology and Evolutionary Biology, Princeton University, Princeton, NJ, USA; Santa Fe Institute, Santa Fe, NM, USA
| | - Hans Heesterbeek
- Faculty of Veterinary Medicine, University of Utrecht, Utrecht, Netherlands
| | - Peter J Hudson
- Fogarty International Center, National Institutes of Health, Bethesda, MD, USA; Center for Infectious Disease Dynamics, Pennsylvania State University, University Park, PA, USA; The Huck Institute for Life Sciences, Pennsylvania State University, University Park, PA, USA
| | - James O Lloyd-Smith
- Department of Ecology and Evolutionary Biology, University of California-Los Angeles, Los Angeles, CA, USA; Fogarty International Center, National Institutes of Health, Bethesda, MD, USA
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17
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Cizauskas CA, Turner WC, Wagner B, Küsters M, Vance RE, Getz WM. Gastrointestinal helminths may affect host susceptibility to anthrax through seasonal immune trade-offs. BMC Ecol 2014; 14:27. [PMID: 25388877 PMCID: PMC4247756 DOI: 10.1186/s12898-014-0027-3] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2014] [Accepted: 10/03/2014] [Indexed: 12/05/2022] Open
Abstract
Background Most vertebrates experience coinfections, and many pathogen-pathogen interactions occur indirectly through the host immune system. These interactions are particularly strong in mixed micro-macroparasite infections because of immunomodulatory effects of helminth parasites. While these trade-offs have been examined extensively in laboratory animals, few studies have examined them in natural systems. Additionally, many wildlife pathogens fluctuate seasonally, at least partly due to seasonal host immune changes. We therefore examined seasonality of immune resource allocation, pathogen abundance and exposure, and interactions between infections and immunity in plains zebra (Equus quagga) in Etosha National Park (ENP), Namibia, a system with strongly seasonal patterns of gastrointestinal (GI) helminth infection intensity and concurrent anthrax outbreaks. Both pathogens are environmentally transmitted, and helminth seasonality is driven by environmental pressures on free living life stages. The reasons behind anthrax seasonality are currently not understood, though anthrax is less likely directly driven by environmental factors. Results We measured a complex, interacting set of variables and found evidence that GI helminth infection intensities, eosinophil counts, IgE and IgGb antibody titers, and possibly IL-4 cytokine signaling were increased in wetter seasons, and that ectoparasite infestations and possibly IFN-γ cytokine signaling were increased in drier seasons. Monocyte counts and anti-anthrax antibody titers were negatively associated with wet season eosinophilia, and monocytes were negatively correlated with IgGb and IgE titers. Taken together, this supports the hypothesis that ENP wet seasons are characterized by immune resource allocation toward Th-2 type responses, while Th1-type immunity may prevail in drier seasons, and that hosts may experience Th1-Th2 trade-offs. We found evidence that this Th2-type resource allocation is likely driven by GI parasite infections, and that these trade-offs may render hosts less capable of concurrently mounting effective Th1-type immune responses against anthrax. Conclusions This study is one of the first to examine laboratory-demonstrated Th1-Th2 trade-offs in a natural system. It provides evidence that seasonally bound pathogens may affect, through immunology, transmission dynamics of pathogens that might otherwise not be seasonally distributed. It suggests that, by manipulating the internal host ecosystem, GI parasites may influence the external ecosystem by affecting the dynamics of another environmentally transmitted pathogen. Electronic supplementary material The online version of this article (doi:10.1186/s12898-014-0027-3) contains supplementary material, which is available to authorized users.
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18
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Comparative community-level associations of helminth infections and microparasite shedding in wild long-tailed macaques in Bali, Indonesia. Parasitology 2014; 142:480-9. [PMID: 25249163 DOI: 10.1017/s0031182014001462] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Helminthes have the capacity to modulate host immunity, leading to positive interactions with coinfecting microparasites. This phenomenon has been primarily studied during coinfections with a narrow range of geo-helminthes and intracellular microparasites in human populations or under laboratory conditions. Far less is known regarding differences in coinfection dynamics between helminth types, the range of microparasites that might be affected or the overall community-level effects of helminth infections on microparasites in wild systems. Here, we analysed the presence/absence and abundance patterns of enteric parasites in long-tailed macaques (Macaca fascicularis) on the island of Bali, Indonesia, to assess whether naturally occurring helminth infections were associated with increased shedding of the most common intracellular (Cryptosporidium spp., Isospora spp.) and extracellular (Entamoeba spp., Giardia spp.) microparasites. We also comparatively assessed the statistical correlations of different helminth taxa with microparasite shedding to determine if there were consistent relationships between the specific helminth taxa and microparasites. Helminth infections were associated with increased shedding of both intracellular and extracellular microparasites. Platyhelminthes repeatedly displayed strong positive correlations with several microparasites; while nematodes did not. Our results indicate that helminthes can influence microparasite community shedding dynamics under wild conditions, but that trends may be driven by a narrow range of helminthes.
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Cattadori IM, Wagner BR, Wodzinski LA, Pathak AK, Poole A. Infections do not predict shedding in co-infections with two helminths from a natural system. Ecology 2014; 95:1684-92. [PMID: 25039232 DOI: 10.1890/13-1538.1] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Given the health and economic burden associated with the widespread occurrence of co-infections in humans and agricultural animals, understanding how coinfections contribute to host heterogeneity to infection and transmission is critical if we are to assess risk of infection based on host characteristics. Here, we examine whether host heterogeneity to infection leads to similar heterogeneity in transmission in a population of rabbits single and co-infected with two helminths and monitored monthly for eight years. Compared to single infections, co-infected rabbits carried higher Trichostrongylus retortaeformis intensities, shorter worms with fewer eggs in utero, and shed similar numbers of parasite eggs. In contrast, the same co-infected rabbits harbored fewer Graphidium strigosum with longer bodies and more eggs in utero, and shed more eggs of this helminth. A positive density-dependent relationship between fecundity and intensity was found for T. retortaeformis but not G. strigosum in co-infected rabbits. Juvenile rabbits contributed to most of the infection and shedding of T. retortaeformis, while adult hosts were more important for G. strigosum dynamics of infection and transmission, and this pattern was consistent in single and co-infected individuals. This host-parasite system suggests that we cannot predict the pattern of parasite shedding during co-infections based on intensity of infection alone. We suggest that a mismatching between susceptibility and infectiousness should be expected in helminth coinfections and should not be overlooked.
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20
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The reliability of observational approaches for detecting interspecific parasite interactions: comparison with experimental results. Int J Parasitol 2014; 44:437-45. [DOI: 10.1016/j.ijpara.2014.03.001] [Citation(s) in RCA: 64] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2013] [Revised: 02/27/2014] [Accepted: 03/02/2014] [Indexed: 11/22/2022]
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Jaiswal N, Upadhyay SK, Malhotra A, Malhotra SK. Ecological morphotaxometry of trematodes of garfish (Teleostomi: Belonidae) from Gangetic riverine ecosystem in India. III. Principal component analysis in the dynamics of Cephalogonimus yamunii (Upadhyay, Jaiswal, Malhotra and Malhotra, 2012). J Parasit Dis 2014; 38:153-62. [PMID: 24808643 DOI: 10.1007/s12639-012-0200-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2012] [Accepted: 10/25/2012] [Indexed: 11/24/2022] Open
Abstract
The attributes of multivariate analyses were applied to infer peculiarity in distribution dynamics of Cephalogonimus yamunii Upadhyay et al. (J Parasit, 2012) in Xenentodon cancilla under influence of interionic interactions amongst hydrobiological factors. Non-parametric Mann-Whitney's Test χ(2) statistic was significant for the effect of Dissolved Oxygen and magnesium. The temperature optimum 23-27 °C was concluded for expression of peak prevalence and mean intensity during change in water temperature between autumn and winter periods. The dominant Ist component (PC1 (p) ) from Principal Component Analysis of monthwise response of infection data by C. yamunii in X. cancilla was further confirmed by Scree Plot of Eigenvalues and Factor Loadings Plot to identify the critical impact of hardness of water on infection prevalence and mean intensity. The findings of larger PC1 (p) positive coefficients comprehensively substantiated predominating hardness factor, under the influence of enhanced Dissolved Oxygen and optimum thermal effect. Therefore, the role of multifactorial etiology is a definite possibility.
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Affiliation(s)
- Neeshma Jaiswal
- Parasitology Laboratory, Department of Zoology, University of Allahabad, Allahabad, 211002 UP India
| | - Sushil K Upadhyay
- Parasitology Laboratory, Department of Zoology, University of Allahabad, Allahabad, 211002 UP India
| | - Anshu Malhotra
- Parasitology Laboratory, Department of Zoology, University of Allahabad, Allahabad, 211002 UP India ; Department of Neurological Surgery, D-4108, Medical Center North, Vanderbilt University Medical Center, Nashville, TN 37232 USA
| | - Sandeep K Malhotra
- Parasitology Laboratory, Department of Zoology, University of Allahabad, Allahabad, 211002 UP India
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22
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Ryder JJ, Hoare MJ, Pastok D, Bottery M, Boots M, Fenton A, Atkinson D, Knell RJ, Hurst GDD. Disease epidemiology in arthropods is altered by the presence of nonprotective symbionts. Am Nat 2014; 183:E89-104. [PMID: 24561609 DOI: 10.1086/674827] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
Inherited microbial symbionts can modulate host susceptibility to natural enemy attack. A wider range of symbionts influence host population demography without altering individual susceptibility, and it has been suggested that these may modify host disease risk through altering the rate of exposure to natural enemies. We present the first test of this thesis, specifically testing whether male-killing symbionts alter the epidemiology of a sexually transmitted infection (STI) carried by its host. STIs are typically expected to show female-biased epidemics, and we first present a simple model which indicates that male-biased STI epidemics may occur where symbionts create female-biased population sex ratios. We then examined the dynamics of a STI in the ladybird beetle Adalia bipunctata, which is also host to a male-killing bacterium. We present evidence that male-biased epidemics of the STI are observed in natural populations when the male-killer is common. Laboratory experiments did not support a role for differential susceptibility of male and female hosts to the STI, nor a protective role for the symbiont, in creating this bias. We conclude that the range of symbionts likely to alter parasite epidemiology will be much wider than previously envisaged, because it will additionally include those that impact host demography alone.
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Affiliation(s)
- Jonathan J Ryder
- Institute of Integrative Biology, University of Liverpool, Crown Street, Liverpool L69 7ZB, United Kingdom
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23
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Abstract
Co-infection of individual hosts by multiple parasite species is a pattern that is very commonly observed in natural populations. Understanding the processes that generate these patterns poses a challenge. For example, it is difficult to discern the relative roles of exposure and susceptibility in generating the mixture and density of parasites within hosts. Yet discern them we must, if we are to design and deliver successful medical interventions for co-infected populations. Here, we synthesise an emergent understanding of how processes operate and interact to generate patterns of co-infection. We consider within-host communities (or infracommunities) generally, that is including not only classical parasites but also the microbiota that are so abundant on mucosal surfaces and which are increasingly understood to be so influential on host biology. We focus on communities that include a helminth, but we expect similar inferences to pertain to other taxa. We suggest that, thanks to recent research at both the within-host (e.g. immunological) and between-host (e.g. epidemiological) scales, researchers are poised to reveal the processes that generate the observed distribution of parasite communities among hosts. Progress will be facilitated by using new technologies as well as statistical and experimental tools to test competing hypotheses about processes that might generate patterns in co-infection data. By understanding the multiple interactions that underlie patterns of co-infection, we will be able to understand and intelligently predict how a suite of co-infections (and thus the host that bears them) will together respond to medical interventions as well as other environmental changes. The challenge for us all is to become scholars of co-infections.
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Affiliation(s)
- Mark E Viney
- School of Biological Sciences, University of Bristol, Woodland Road, UK.
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Randall J, Cable J, Guschina IA, Harwood JL, Lello J. Endemic infection reduces transmission potential of an epidemic parasite during co-infection. Proc Biol Sci 2013; 280:20131500. [PMID: 23966641 DOI: 10.1098/rspb.2013.1500] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Endemic, low-virulence parasitic infections are common in nature. Such infections may deplete host resources, which in turn could affect the reproduction of other parasites during co-infection. We aimed to determine whether the reproduction, and therefore transmission potential, of an epidemic parasite was limited by energy costs imposed on the host by an endemic infection. Total lipids, triacylglycerols (TAG) and polar lipids were measured in cockroaches (Blattella germanica) that were fed ad libitum, starved or infected with an endemic parasite, Gregarina blattarum. Reproductive output of an epidemic parasite, Steinernema carpocapsae, was then assessed by counting the number of infective stages emerging from these three host groups. We found both starvation and gregarine infection reduced cockroach lipids, mainly through depletion of TAG. Further, both starvation and G. blattarum infection resulted in reduced emergence of nematode transmission stages. This is, to our knowledge, the first study to demonstrate directly that host resource depletion caused by endemic infection could affect epidemic disease transmission. In view of the ubiquity of endemic infections in nature, future studies of epidemic transmission should take greater account of endemic co-infections.
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Affiliation(s)
- J Randall
- School of Biosciences, Cardiff University, Cardiff CF10 3AX, UK.
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25
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Slater HC, Gambhir M, Parham PE, Michael E. Modelling co-infection with malaria and lymphatic filariasis. PLoS Comput Biol 2013; 9:e1003096. [PMID: 23785271 PMCID: PMC3681634 DOI: 10.1371/journal.pcbi.1003096] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2012] [Accepted: 04/27/2013] [Indexed: 10/26/2022] Open
Abstract
Malaria and lymphatic filariasis (LF) continue to cause a considerable public health burden globally and are co-endemic in many regions of sub-Saharan Africa. These infections are transmitted by the same mosquito species which raises important questions about optimal vector control strategies in co-endemic regions, as well as the effect of the presence of each infection on endemicity of the other; there is currently little consensus on the latter. The need for comprehensive modelling studies to address such questions is therefore significant, yet very few have been undertaken to date despite the recognised explanatory power of reliable dynamic mathematical models. Here, we develop a malaria-LF co-infection modelling framework that accounts for two key interactions between these infections, namely the increase in vector mortality as LF mosquito prevalence increases and the antagonistic Th1/Th2 immune response that occurs in co-infected hosts. We consider the crucial interplay between these interactions on the resulting endemic prevalence when introducing each infection in regions where the other is already endemic (e.g. due to regional environmental change), and the associated timescale for such changes, as well as effects on the basic reproduction number R₀ of each disease. We also highlight potential perverse effects of vector controls on human infection prevalence in co-endemic regions, noting that understanding such effects is critical in designing optimal integrated control programmes. Hence, as well as highlighting where better data are required to more reliably address such questions, we provide an important framework that will form the basis of future scenario analysis tools used to plan and inform policy decisions on intervention measures in different transmission settings.
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Affiliation(s)
- Hannah C. Slater
- Department of Infectious Disease Epidemiology, Imperial College London, London, United Kingdom
| | - Manoj Gambhir
- MRC Centre for Outbreak Analysis and Modelling, Department of Infectious Disease Epidemiology, Imperial College London, London, United Kingdom
| | - Paul E. Parham
- Grantham Institute for Climate Change, Department of Infectious Disease Epidemiology, Imperial College London, London, United Kingdom
| | - Edwin Michael
- Department of Biological Sciences, University of Notre Dame, Notre Dame, Indiana, United States of America
- * E-mail:
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Hoverman JT, Hoye BJ, Johnson PTJ. Does timing matter? How priority effects influence the outcome of parasite interactions within hosts. Oecologia 2013; 173:1471-80. [DOI: 10.1007/s00442-013-2692-x] [Citation(s) in RCA: 74] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2012] [Accepted: 05/16/2013] [Indexed: 11/29/2022]
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Yakob L, Williams GM, Gray DJ, Halton K, Solon JA, Clements ACA. Slaving and release in co-infection control. Parasit Vectors 2013; 6:157. [PMID: 23721567 PMCID: PMC3691829 DOI: 10.1186/1756-3305-6-157] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2013] [Accepted: 05/23/2013] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Animal and human infection with multiple parasite species is the norm rather than the exception, and empirical studies and animal models have provided evidence for a diverse range of interactions among parasites. We demonstrate how an optimal control strategy should be tailored to the pathogen community and tempered by species-level knowledge of drug sensitivity with use of a simple epidemiological model of gastro-intestinal nematodes. METHODS We construct a fully mechanistic model of macroparasite co-infection and use it to explore a range of control scenarios involving chemotherapy as well as improvements to sanitation. RESULTS Scenarios are presented whereby control not only releases a more resistant parasite from antagonistic interactions, but risks increasing co-infection rates, exacerbating the burden of disease. In contrast, synergisms between species result in their becoming epidemiologically slaved within hosts, presenting a novel opportunity for controlling drug resistant parasites by targeting co-circulating species. CONCLUSIONS Understanding the effects on control of multi-parasite species interactions, and vice versa, is of increasing urgency in the advent of integrated mass intervention programmes.
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Affiliation(s)
- Laith Yakob
- Infectious Disease Epidemiology Unit, School of Population Health, University of Queensland, Herston, Brisbane, QLD 4006, Australia.
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Dances with worms: the ecological and evolutionary impacts of deworming on coinfecting pathogens. Parasitology 2013; 140:1119-32. [PMID: 23714427 PMCID: PMC3695730 DOI: 10.1017/s0031182013000590] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Parasitic helminths are ubiquitous in most host, including human, populations. Helminths
often alter the likelihood of infection and disease progression of coinfecting
microparasitic pathogens (viruses, bacteria, protozoa), and there is great interest in
incorporating deworming into control programmes for many major diseases (e.g. HIV,
tuberculosis, malaria). However, such calls are controversial; studies show the
consequences of deworming for the severity and spread of pathogens to be highly variable.
Hence, the benefits of deworming, although clear for reducing the morbidity due to
helminth infection per se, are unclear regarding the outcome of
coinfections and comorbidities. I develop a theoretical framework to explore how helminth
coinfection with other pathogens affects host mortality and pathogen spread and evolution
under different interspecific parasite interactions. In all cases the outcomes of
coinfection are highly context-dependent, depending on the mechanism of helminth-pathogen
interaction and the quantitative level of helminth infection, with the effects of
deworming potentially switching from beneficial to detrimental depending on helminth
burden. Such context-dependency may explain some of the variation in the benefits of
deworming seen between studies, and highlights the need for obtaining a quantitative
understanding of parasite interactions across realistic helminth infection ranges.
However, despite this complexity, this framework reveals predictable patterns in the
effects of helminths that may aid the development of more effective, integrated management
strategies to combat pathogens in this coinfected world.
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Joseph MB, Mihaljevic JR, Arellano AL, Kueneman JG, Preston DL, Cross PC, Johnson PTJ. Taming wildlife disease: bridging the gap between science and management. J Appl Ecol 2013; 50:702-712. [PMID: 32336775 PMCID: PMC7166616 DOI: 10.1111/1365-2664.12084] [Citation(s) in RCA: 64] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2012] [Accepted: 03/04/2013] [Indexed: 01/16/2023]
Abstract
Parasites and pathogens of wildlife can threaten biodiversity, infect humans and domestic animals, and cause significant economic losses, providing incentives to manage wildlife diseases. Recent insights from disease ecology have helped transform our understanding of infectious disease dynamics and yielded new strategies to better manage wildlife diseases. Simultaneously, wildlife disease management (WDM) presents opportunities for large‐scale empirical tests of disease ecology theory in diverse natural systems. To assess whether the potential complementarity between WDM and disease ecology theory has been realized, we evaluate the extent to which specific concepts in disease ecology theory have been explicitly applied in peer‐reviewed WDM literature. While only half of WDM articles published in the past decade incorporated disease ecology theory, theory has been incorporated with increasing frequency over the past 40 years. Contrary to expectations, articles authored by academics were no more likely to apply disease ecology theory, but articles that explain unsuccessful management often do so in terms of theory. Some theoretical concepts such as density‐dependent transmission have been commonly applied, whereas emerging concepts such as pathogen evolutionary responses to management, biodiversity–disease relationships and within‐host parasite interactions have not yet been fully integrated as management considerations. Synthesis and applications. Theory‐based disease management can meet the needs of both academics and managers by testing disease ecology theory and improving disease interventions. Theoretical concepts that have received limited attention to date in wildlife disease management could provide a basis for improving management and advancing disease ecology in the future.
Theory‐based disease management can meet the needs of both academics and managers by testing disease ecology theory and improving disease interventions. Theoretical concepts that have received limited attention to date in wildlife disease management could provide a basis for improving management and advancing disease ecology in the future.
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Affiliation(s)
- Maxwell B Joseph
- Department of Ecology and Evolutionary Biology University of Colorado CB 334 Boulder CO 80309 USA
| | - Joseph R Mihaljevic
- Department of Ecology and Evolutionary Biology University of Colorado CB 334 Boulder CO 80309 USA
| | - Ana Lisette Arellano
- Department of Ecology and Evolutionary Biology University of Colorado CB 334 Boulder CO 80309 USA
| | - Jordan G Kueneman
- Department of Ecology and Evolutionary Biology University of Colorado CB 334 Boulder CO 80309 USA
| | - Daniel L Preston
- Department of Ecology and Evolutionary Biology University of Colorado CB 334 Boulder CO 80309 USA
| | - Paul C Cross
- Northern Rocky Mountain Science Center U. S. Geological Survey 2327 University Way, Suite 2 Bozeman MT 59715 USA
| | - Pieter T J Johnson
- Department of Ecology and Evolutionary Biology University of Colorado CB 334 Boulder CO 80309 USA
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Chung E, Petit E, Antonovics J, Pedersen AB, Hood ME. Variation in resistance to multiple pathogen species: anther smuts of Silene uniflora. Ecol Evol 2012; 2:2304-14. [PMID: 23139888 PMCID: PMC3488680 DOI: 10.1002/ece3.346] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2012] [Revised: 07/10/2012] [Accepted: 07/14/2012] [Indexed: 11/10/2022] Open
Abstract
The occurrence of multiple pathogen species on a shared host species is unexpected when they exploit the same micro-niche within the host individual. One explanation for such observations is the presence of pathogen-specific resistances segregating within the host population into sites that are differentially occupied by the competing pathogens. This study used experimental inoculations to test whether specific resistances may contribute to the maintenance of two species of anther-smut fungi, Microbotryum silenes-inflatae and Microbotryum lagerheimii, in natural populations of Silene uniflora in England and Wales. Overall, resistance to the two pathogens was strongly positively correlated among host populations and to a lesser degree among host families within populations. A few instances of specific resistance were also observed and confirmed by replicated inoculations. The results suggest that selection for resistance to one pathogen may protect the host from the emergence via host shifts of related pathogen species, and conversely that co-occurrence of two species of pathogens may be dependent on the presence of host genotypes susceptible to both.
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Affiliation(s)
- Erin Chung
- Department of Biology, Amherst College Amherst, Massachusetts
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31
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Basáñez MG, McCarthy JS, French MD, Yang GJ, Walker M, Gambhir M, Prichard RK, Churcher TS. A research agenda for helminth diseases of humans: modelling for control and elimination. PLoS Negl Trop Dis 2012; 6:e1548. [PMID: 22545162 PMCID: PMC3335861 DOI: 10.1371/journal.pntd.0001548] [Citation(s) in RCA: 76] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
Abstract
Mathematical modelling of helminth infections has the potential to inform policy and guide research for the control and elimination of human helminthiases. However, this potential, unlike in other parasitic and infectious diseases, has yet to be realised. To place contemporary efforts in a historical context, a summary of the development of mathematical models for helminthiases is presented. These efforts are discussed according to the role that models can play in furthering our understanding of parasite population biology and transmission dynamics, and the effect on such dynamics of control interventions, as well as in enabling estimation of directly unobservable parameters, exploration of transmission breakpoints, and investigation of evolutionary outcomes of control. The Disease Reference Group on Helminth Infections (DRG4), established in 2009 by the Special Programme for Research and Training in Tropical Diseases (TDR), was given the mandate to review helminthiases research and identify research priorities and gaps. A research and development agenda for helminthiasis modelling is proposed based on identified gaps that need to be addressed for models to become useful decision tools that can support research and control operations effectively. This agenda includes the use of models to estimate the impact of large-scale interventions on infection incidence; the design of sampling protocols for the monitoring and evaluation of integrated control programmes; the modelling of co-infections; the investigation of the dynamical relationship between infection and morbidity indicators; the improvement of analytical methods for the quantification of anthelmintic efficacy and resistance; the determination of programme endpoints; the linking of dynamical helminth models with helminth geostatistical mapping; and the investigation of the impact of climate change on human helminthiases. It is concluded that modelling should be embedded in helminth research, and in the planning, evaluation, and surveillance of interventions from the outset. Modellers should be essential members of interdisciplinary teams, propitiating a continuous dialogue with end users and stakeholders to reflect public health needs in the terrain, discuss the scope and limitations of models, and update biological assumptions and model outputs regularly. It is highlighted that to reach these goals, a collaborative framework must be developed for the collation, annotation, and sharing of databases from large-scale anthelmintic control programmes, and that helminth modellers should join efforts to tackle key questions in helminth epidemiology and control through the sharing of such databases, and by using diverse, yet complementary, modelling approaches.
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Affiliation(s)
- María-Gloria Basáñez
- Department of Infectious Disease Epidemiology, School of Public Health, Faculty of Medicine (St Mary's campus), Imperial College London, London, UK.
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32
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Paradigm lost: how parasite control may alter pattern and process in human helminthiases. Trends Parasitol 2012; 28:161-71. [DOI: 10.1016/j.pt.2012.02.004] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2011] [Revised: 02/07/2012] [Accepted: 02/07/2012] [Indexed: 11/22/2022]
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Mideo N, Acosta-Serrano A, Aebischer T, Brown MJF, Fenton A, Friman VP, Restif O, Reece SE, Webster JP, Brown SP. Life in cells, hosts, and vectors: parasite evolution across scales. INFECTION GENETICS AND EVOLUTION 2012; 13:344-7. [PMID: 22465537 DOI: 10.1016/j.meegid.2012.03.016] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/13/2012] [Revised: 03/14/2012] [Accepted: 03/17/2012] [Indexed: 12/13/2022]
Abstract
Parasite evolution is increasingly being recognized as one of the most important issues in applied evolutionary biology. Understanding how parasites maximize fitness whilst facing the diverse challenges of living in cells, hosts, and vectors, is central to disease control and offers a novel testing ground for evolutionary theory. The Centre for Immunity, Infection, and Evolution at the University of Edinburgh recently held a symposium to address the question "How do parasites maximise fitness across a range of biological scales?" The symposium brought together researchers whose work looks across scales and environments to understand why and how parasites 'do what they do', tying together mechanism, evolutionary explanations, and public health implications. With a broad range of speakers, our aim was to define and encourage more holistic approaches to studying parasite evolution. Here, we present a synthesis of the current state of affairs in parasite evolution, the research presented at the symposium, and insights gained through our discussions. We demonstrate that such interdisciplinary approaches are possible and identify key areas for future progress.
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Affiliation(s)
- Nicole Mideo
- Centre for Immunity, Infection & Evolution, School of Biological Sciences, University of Edinburgh, Edinburgh EH9 3JT, United Kingdom.
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ALLEN LJS, BROWN VL, JONSSON CB, KLEIN SL, LAVERTY SM, MAGWEDERE K, OWEN JC, VAN DEN DRIESSCHE P. Mathematical Modeling of Viral Zoonoses in Wildlife. NATURAL RESOURCE MODELING 2012; 25:5-51. [PMID: 22639490 PMCID: PMC3358807 DOI: 10.1111/j.1939-7445.2011.00104.x] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
Zoonoses are a worldwide public health concern, accounting for approximately 75% of human infectious diseases. In addition, zoonoses adversely affect agricultural production and wildlife. We review some mathematical models developed for the study of viral zoonoses in wildlife and identify areas where further modeling efforts are needed.
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Affiliation(s)
- L. J. S. ALLEN
- Department of Mathematics and Statistics, Texas Tech University, Lubbock, TX 79409, E‐mail:
| | - V. L. BROWN
- Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, MI 48109
| | - C. B. JONSSON
- Center for Predictive Medicine for Biodefense and Emerging Infectious Disease, University of Louisville, Louisville, KY 40202
| | - S. L. KLEIN
- W. Harry Feinstone Department of Molecular Microbiology and Immunology, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD 21205
| | - S. M. LAVERTY
- Department of Mathematics, University of Utah, Salt Lake City, UT 84112
| | - K. MAGWEDERE
- Division of Veterinary Public Health, Directorate of Veterinary Services, Mariental, Namibia, Africa
| | - J. C. OWEN
- Departments of Fisheries and Wildlife and Large Animal Clinical Sciences, Michigan State University, East Lansing, MI 48824
| | - P. VAN DEN DRIESSCHE
- Department of Mathematics and Statistics, University of Victoria, Victoria, BC, Canada V8W 3R4
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Abstract
Little is known about the viruses infecting most species. Even in groups as well-studied as Drosophila, only a handful of viruses have been well-characterized. A viral metagenomic approach was used to explore viral diversity in 83 wild-caught Drosophila innubila, a mushroom feeding member of the quinaria group. A single fly that was injected with, and died from, Drosophila C Virus (DCV) was added to the sample as a control. Two-thirds of reads in the infected sample had DCV as the best BLAST hit, suggesting that the protocol developed is highly sensitive. In addition to the DCV hits, several sequences had Oryctes rhinoceros Nudivirus, a double-stranded DNA virus, as a best BLAST hit. The virus associated with these sequences was termed Drosophila innubila Nudivirus (DiNV). PCR screens of natural populations showed that DiNV was both common and widespread taxonomically and geographically. Electron microscopy confirms the presence of virions in fly fecal material similar in structure to other described Nudiviruses. In 2 species, D. innubila and D. falleni, the virus is associated with a severe (∼80-90%) loss of fecundity and significantly decreased lifespan.
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Affiliation(s)
- Robert L Unckless
- Department of Biology, University of Rochester, Rochester, New York, United States of America.
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Ezenwa VO, Jolles AE. From host immunity to pathogen invasion: the effects of helminth coinfection on the dynamics of microparasites. Integr Comp Biol 2011; 51:540-51. [PMID: 21727178 DOI: 10.1093/icb/icr058] [Citation(s) in RCA: 109] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Concurrent infections with multiple parasites are ubiquitous in nature. Coinfecting parasites can interact with one another in a variety of ways, including through the host's immune system via mechanisms such as immune trade-offs and immunosuppression. These within-host immune processes mediating interactions among parasites have been described in detail, but how they scale up to determine disease dynamic patterns at the population level is only beginning to be explored. In this review, we use helminth-microparasite coinfection as a model for examining how within-host immunological effects may influence the ecological outcome of microparasitic diseases, with a specific focus on disease invasion. The current literature on coinfection between helminths and major microparasitic diseases includes many studies documenting the effects of helminths on individual host responses to microparasites. In many cases, the observed host responses map directly onto parameters relevant for quantifying disease dynamics; however, there have been few attempts at integrating data on individual-level effects into theoretical models to extrapolate from the individual to the population level. Moreover, there is considerable variability in the particular combination of disease parameters affected by helminths across different microparasite systems. We develop a conceptual framework identifying some potential sources of such variability: Pathogen persistence and severity, and resource availability to hosts. We also generate testable hypotheses regarding diseases and the environmental contexts when the effects of helminths on microparasite dynamics should be most pronounced. Finally, we use a case study of helminth and mycobacterial coinfection in the African buffalo to illustrate both progress and challenges in understanding the population-level consequences of within-host immunological interactions, and conclude with suggestions for future research that will help improve our understanding of the effects of coinfection on dynamics of infectious diseases.
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Affiliation(s)
- Vanessa O Ezenwa
- Odum School of Ecology, University of Georgia, Athens, GA 30602, USA.
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Johnson PTJ, Buller ID. Parasite competition hidden by correlated coinfection: using surveys and experiments to understand parasite interactions. Ecology 2011; 92:535-41. [PMID: 21608460 DOI: 10.1890/10-0570.1] [Citation(s) in RCA: 74] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Within most free-living species exists a cryptic community of interacting parasites. By combining multiscale field data with manipulative experiments, we evaluated patterns of parasite coinfection in amphibian hosts and their underlying mechanisms. Surveys of 86 wetlands and 1273 hosts revealed positive correlations between two pathogenic trematodes (Ribeiroia ondatrae and Echinostoma trivolvis) both between wetlands and within individual hosts. In infection and coinfection experiments, Ribeiroia caused greater pathology than Echinostoma, including high host mortality (24%) and severe limb malformations (75%). No interactive effects were noted for host pathology, but both parasites decreased the per capita persistence of one another by 17-36%. Thus, in spite of consistently positive associations from field data, these parasites negatively affected the persistence of one another, likely via cross immunity (apparent competition). These findings underscore the danger of inferring parasite interactions from coinfection patterns and emphasize the potential disconnect between within-host processes (e.g., competition) and between-host processes (e.g., exposure and transmission). Here, correlated coinfections likely resulted from similarities in the parasites' host requirements and heterogeneity in host susceptibility or exposure. Understanding complex interactions among parasites depends critically on the scale under consideration, highlighting the importance of combining coinfection field studies with mechanistic experiments.
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Ezenwa V, Etienne R, Luikart G, Beja‐Pereira A, Jolles A. Hidden Consequences of Living in a Wormy World: Nematode‐Induced Immune Suppression Facilitates Tuberculosis Invasion in African Buffalo. Am Nat 2010; 176:613-24. [DOI: 10.1086/656496] [Citation(s) in RCA: 174] [Impact Index Per Article: 12.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022]
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39
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Applying predator-prey theory to modelling immune-mediated, within-host interspecific parasite interactions. Parasitology 2010; 137:1027-38. [PMID: 20152061 DOI: 10.1017/s0031182009991788] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
Predator-prey models are often applied to the interactions between host immunity and parasite growth. A key component of these models is the immune system's functional response, the relationship between immune activity and parasite load. Typically, models assume a simple, linear functional response. However, based on the mechanistic interactions between parasites and immunity we argue that alternative forms are more likely, resulting in very different predictions, ranging from parasite exclusion to chronic infection. By extending this framework to consider multiple infections we show that combinations of parasites eliciting different functional responses greatly affect community stability. Indeed, some parasites may stabilize other species that would be unstable if infecting alone. Therefore hosts' immune systems may have adapted to tolerate certain parasites, rather than clear them and risk erratic parasite dynamics. We urge for more detailed empirical information relating immune activity to parasite load to enable better predictions of the dynamic consequences of immune-mediated interspecific interactions within parasite communities.
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Parasite zoonoses and climate change: molecular tools for tracking shifting boundaries. Trends Parasitol 2009; 25:285-91. [PMID: 19428303 DOI: 10.1016/j.pt.2009.03.007] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2008] [Revised: 02/19/2009] [Accepted: 03/05/2009] [Indexed: 11/21/2022]
Abstract
For human, domestic animal and wildlife health, key effects of directional climate change include the risk of the altered occurrence of infectious diseases. Many parasite zoonoses have high potential for vulnerability to the new climate, in part because their free-living life-cycle stages and ectothermic hosts are directly exposed to climatic conditions. For these zoonoses, climate change can shift boundaries for ecosystem components and processes integral to parasite transmission and persistence, and these shifts can impact host health. Vulnerable boundaries include those for spatial distributions, host-parasite assemblages, demographic rates, life-cycle phenologies, associations within ecosystems, virulence, and patterns of infection and disease. This review describes these boundary shifts and how molecular techniques can be applied to defining the new boundaries.
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Optimality analysis of Th1/Th2 immune responses during microparasite-macroparasite co-infection, with epidemiological feedbacks. Parasitology 2008; 135:841-53. [PMID: 18442426 DOI: 10.1017/s0031182008000310] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Individuals are typically co-infected by a diverse community of microparasites (e.g. viruses or protozoa) and macroparasites (e.g. helminths). Vertebrates respond to these parasites differently, typically mounting T helper type 1 (Th1) responses against microparasites and Th2 responses against macroparasites. These two responses may be antagonistic such that hosts face a 'decision' of how to allocate potentially limiting resources. Such decisions at the individual host level will influence parasite abundance at the population level which, in turn, will feed back upon the individual level. We take a first step towards a complete theoretical framework by placing an analysis of optimal immune responses under microparasite-macroparasite co-infection within an epidemiological framework. We show that the optimal immune allocation is quantitatively sensitive to the shape of the trade-off curve and qualitatively sensitive to life-history traits of the host, microparasite and macroparasite. This model represents an important first step in placing optimality models of the immune response to co-infection into an epidemiological framework. Ultimately, however, a more complete framework is needed to bring together the optimal strategy at the individual level and the population-level consequences of those responses, before we can truly understand the evolution of host immune responses under parasite co-infection.
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