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Metz DCG, Hechinger RF. The physical soldier caste of an invasive, human-infecting flatworm is morphologically extreme and obligately sterile. Proc Natl Acad Sci U S A 2024; 121:e2400953121. [PMID: 39042696 PMCID: PMC11295071 DOI: 10.1073/pnas.2400953121] [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: 01/15/2024] [Accepted: 06/16/2024] [Indexed: 07/25/2024] Open
Abstract
We show that the globally invasive, human-infectious flatworm, Haplorchis pumilio, possesses the most physically specialized soldier caste yet documented in trematodes. Soldiers occur in colonies infecting the first intermediate host, the freshwater snail Melanoides tuberculata, and are readily distinguishable from immature and mature reproductive worms. Soldiers possess a pharynx five times absolutely larger than those of immature and mature reproductives, lack a germinal mass, and have a different developmental trajectory than reproductives, indicating that H. pumilio soldiers constitute a reproductively sterile physical caste. Neither immature nor mature reproductives showed aggression in in vitro trials, but soldiers readily attacked heterospecific trematodes that coinfect their host. Ecologically, we calculate that H. pumilio caused ~94% of the competitive deaths in the guild of trematodes infecting its host snail in its invasive range in southern California. Despite being a dominant competitor, H. pumilio soldiers did not attack conspecifics from other colonies. All prior reports documenting division of labor and a trematode soldier caste have involved soldiers that may be able to metamorphose to the reproductive stage and have been from nonhuman-infectious marine species; this study provides clear evidence for an obligately sterile trematode soldier, while extending the phenomenon of a trematode soldier caste to freshwater and to an invasive species of global public health concern.
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Affiliation(s)
- Daniel C. G. Metz
- Marine Biology Research Division, Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA92093
| | - Ryan F. Hechinger
- Marine Biology Research Division, Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA92093
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2
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Hammoud C, Mulero S, Van Bocxlaer B, Boissier J, Verschuren D, Albrecht C, Huyse T. Simultaneous genotyping of snails and infecting trematode parasites using high-throughput amplicon sequencing. Mol Ecol Resour 2021; 22:567-586. [PMID: 34435445 DOI: 10.1111/1755-0998.13492] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2020] [Revised: 07/19/2021] [Accepted: 08/18/2021] [Indexed: 01/04/2023]
Abstract
Several methodological issues currently hamper the study of entire trematode communities within populations of their intermediate snail hosts. Here we develop a new workflow using high-throughput amplicon sequencing to simultaneously genotype snail hosts and their infecting trematode parasites. We designed primers to amplify four snail and five trematode markers in a single multiplex PCR. While also applicable to other genera, we focused on medically and economically important snail genera within the superorder Hygrophila and targeted a broad taxonomic range of parasites within the class Trematoda. We tested the workflow using 417 Biomphalaria glabrata specimens experimentally infected with Schistosoma rodhaini, two strains of Schistosoma mansoni and combinations thereof. We evaluated the reliability of infection diagnostics, the robustness of the workflow, its specificity related to host and parasite identification, and the sensitivity to detect co-infections, immature infections and changes of parasite biomass during the infection process. Finally, we investigated its applicability in wild-caught snails of other genera naturally infected with a diverse range of trematodes. After stringent quality control the workflow allows the identification of snails to species level, and of trematodes to taxonomic levels ranging from family to strain. It is sensitive to detect immature infections and changes in parasite biomass described in previous experimental studies. Co-infections were successfully identified, opening the possibility to examine parasite-parasite interactions such as interspecific competition. Together, these results demonstrate that our workflow provides a powerful tool to analyse the processes shaping trematode communities within natural snail populations.
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Affiliation(s)
- Cyril Hammoud
- Limnology Unit, Department of Biology, Ghent University, Gent, Belgium.,Department of Biology, Royal Museum for Central Africa, Tervuren, Belgium
| | - Stephen Mulero
- IHPE, Univ. Montpellier, CNRS, Univ. Perpignan Via Domitia, IFREMER, Perpignan, France
| | - Bert Van Bocxlaer
- Limnology Unit, Department of Biology, Ghent University, Gent, Belgium.,Univ. Lille, UMR 8198 Evo-Eco-Paleo, CNRS, Lille, France
| | - Jérôme Boissier
- IHPE, Univ. Montpellier, CNRS, Univ. Perpignan Via Domitia, IFREMER, Perpignan, France
| | - Dirk Verschuren
- Limnology Unit, Department of Biology, Ghent University, Gent, Belgium
| | - Christian Albrecht
- Systematics & Biodiversity Lab, Department of Animal Ecology & Systematics, Justus Liebig University, Giessen, Germany
| | - Tine Huyse
- Department of Biology, Royal Museum for Central Africa, Tervuren, Belgium.,Laboratory of Biodiversity and Evolutionary Genomics, University of Leuven, Leuven, Belgium
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3
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Carpenter SA, Vannatta JT, Minchella DJ. Host exposure history and priority effects impact the development and reproduction of a dominant parasite. Int J Parasitol 2021; 51:935-943. [PMID: 34044004 DOI: 10.1016/j.ijpara.2021.03.007] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2020] [Revised: 03/12/2021] [Accepted: 03/17/2021] [Indexed: 11/16/2022]
Abstract
Within a single organism, numerous parasites often compete for space and resources. This competition, together with a parasite's ability to locate and successfully establish in a host, can contribute to the distribution and prevalence of parasites. Coinfection with trematodes in snail intermediate hosts is rarely observed in nature, partly due to varying competitive abilities among parasite taxa. Using a freshwater snail host (Biomphalaria glabrata), we studied the ability of a competitively dominant trematode, Echinostoma caproni, to establish and reproduce in a host previously infected with a less competitive trematode species, Schistosoma mansoni. Snails were exposed to S. mansoni and co-exposed to E. caproni either simultaneously or 1 week, 4 weeks, or 6 weeks post S. mansoni exposure. Over the course of infection, we monitored the competitive success of the dominant trematode through infection prevalence, parasite development time, and parasite reproductive output. Infection prevalence of E. caproni did not differ among co-exposed groups or between co-exposed and single exposed groups. However, E. caproni infections in co-exposed hosts took longer to reach maturity when the timing between co-exposures increased. All co-exposed groups had higher E. caproni reproductive output than single exposures. We show that although timing of co-exposure affects the development time of parasite transmission stages, it is not important for successful establishment. Additionally, co-exposure, but not priority effects, increases the reproductive output of the dominant parasite.
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Affiliation(s)
- S A Carpenter
- Department of Biological Sciences, Purdue University, 915 West State Street, West Lafayette, IN 47907, USA.
| | - J T Vannatta
- Department of Biological Sciences, Purdue University, 915 West State Street, West Lafayette, IN 47907, USA
| | - D J Minchella
- Department of Biological Sciences, Purdue University, 915 West State Street, West Lafayette, IN 47907, USA
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4
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Gleichsner AM, Reinhart K, Minchella DJ. Of mice and worms: are co-infections with unrelated parasite strains more damaging to definitive hosts? Int J Parasitol 2018; 48:881-885. [PMID: 30059691 DOI: 10.1016/j.ijpara.2018.05.004] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2017] [Revised: 05/24/2018] [Accepted: 05/31/2018] [Indexed: 11/29/2022]
Abstract
Intraspecific competition between co-infecting parasites can influence the amount of virulence, or damage, they do to their host. Kin selection theory dictates that infections with related parasite individuals should have lower virulence than infections with unrelated individuals, because they benefit from inclusive fitness and increased host longevity. These predictions have been tested in a variety of microparasite systems, and in larval stage macroparasites within intermediate hosts, but the influence of adult macroparasite relatedness on virulence has not been investigated in definitive hosts. This study used the human parasite Schistosoma mansoni to determine whether definitive hosts infected with related parasites experience lower virulence than hosts infected with unrelated parasites, and to compare the results from intermediate host studies in this system. The presence of unrelated parasites in an infection decreased parasite infectivity, the ability of a parasite to infect a definitive host, and total worm establishment in hosts, impacting the less virulent parasite strain more severely. Unrelated parasite co-infections had similar virulence to the more virulent of the two parasite strains. We combine these findings with complementary studies of the intermediate snail host and describe trade-offs in virulence and selection within the life cycle. Damage to the host by the dominant strain was muted by the presence of a competitor in the intermediate host, but was largely unaffected in the definitive host. Our results in this host-parasite system suggest that unrelated infections may select for higher virulence in definitive hosts while selecting for lower virulence in intermediate hosts.
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Affiliation(s)
- A M Gleichsner
- Department of Biological Sciences, Purdue University, 915 West State Street, West Lafayette, IN 47907, USA; Department of Biological Sciences, State University of New York, College at Plattsburgh, 101 Broad Street, Plattsburgh, NY 12901, USA.
| | - K Reinhart
- Department of Biological Sciences, Purdue University, 915 West State Street, West Lafayette, IN 47907, USA
| | - D J Minchella
- Department of Biological Sciences, Purdue University, 915 West State Street, West Lafayette, IN 47907, USA
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Gleichsner AM, Reinhart K, Minchella DJ. The influence of related and unrelated co-infections on parasite dynamics and virulence. Oecologia 2017; 186:555-564. [PMID: 29234885 DOI: 10.1007/s00442-017-4035-9] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2017] [Accepted: 12/03/2017] [Indexed: 01/27/2023]
Abstract
Many parasitic infections increase the morbidity and mortality of host populations. Interactions between co-infecting parasites can influence virulence, the damage done to a host. Previous studies investigating the impacts of parasite co-infection on hosts have been limited by their inability to control parasite dosage, use consistent virulence metrics, or verify co-infection status. This study used molecular tools, known infection dosage, and multiple assessments over time to test whether parasite relatedness can predict virulence in co-infections, as well as whether competitive interactions between different parasite strains within a host are predictable over time. In addition, we examined the impacts of other parasite traits, such as infectivity, as alternative predictors of virulence and competition outcomes. Hosts with single-strain (related) parasite infections were found to have lower virulence in terms of host and parasite reproduction, supporting kin selection predictions. However, these infections also resulted in higher host mortality. We argue that mortality should not be used as a measurement of virulence in parasite systems that castrate hosts. Hosts were more susceptible to mixed strain (unrelated) parasite infections, indicating that co-infections may make resistance more costly to hosts. Co-infections were dynamic, with changes in parasite dominance over the course of the infection. The more infective parasite strain appeared to suppress the less infective strain, ultimately increasing host longevity. Our findings suggest that unrelated, or more diverse, parasite infections are associated with higher virulence, but that studies must consider their methodology and possible alternative explanations beyond kin selection to understand virulence outcomes.
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Affiliation(s)
- A M Gleichsner
- Department of Biological Sciences, Purdue University, 915 West State Street, West Lafayette, IN, 47907, USA. .,Department of Biological Sciences, State University of New York, College at Plattsburgh, 101 Broad Street, Plattsburgh, NY, 12901, USA.
| | - K Reinhart
- Department of Biological Sciences, Purdue University, 915 West State Street, West Lafayette, IN, 47907, USA
| | - D J Minchella
- Department of Biological Sciences, Purdue University, 915 West State Street, West Lafayette, IN, 47907, USA
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Bakuza JS, Gillespie R, Nkwengulila G, Adam A, Kilbride E, Mable BK. Assessing S. mansoni prevalence in Biomphalaria snails in the Gombe ecosystem of western Tanzania: the importance of DNA sequence data for clarifying species identification. Parasit Vectors 2017; 10:584. [PMID: 29169384 PMCID: PMC5701381 DOI: 10.1186/s13071-017-2525-6] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2016] [Accepted: 11/06/2017] [Indexed: 01/10/2023] Open
Abstract
Background Snails are essential for the transmission and maintenance of schistosomiasis in endemic areas, as they serve as intermediate hosts for schistosome parasites. A clear understanding of the snail species present, their local distribution and infection status is therefore a prerequisite for effective control of schistosomiasis. The purpose of this study was to establish the infection status and distribution of Schistosoma mansoni in snails in the Gombe area along the shores of Lake Tanganyika in western Tanzania, using both detection of cercarial shedding and molecular approaches. Methods Snails were collected from streams located close to human settlements in Gombe National Park, as well as from nearby villages (Kiziba, Mtanga, Mwamgongo and Bugamba) and the largest town in the region (Kigoma). Snails were individually exposed to light to induce shedding of schistosome larvae, which were examined using a compound light microscope. Additionally, the internal transcribed spacer (ITS) region of the ribosomal RNA gene cluster was simultaneously amplified in both snails and their trematodes using a single polymerase chain reaction (PCR) and sequenced to confirm species identification. Results Snails morphologically identified as Biomphalaria pfeifferi were present in all streams except at Mtanga but their distribution was patchy in both time and space. Sequencing of PCR products indicated that not all snails were B. pfeifferi. None of the snails from Gombe or Bugamba shed schistosome larvae, while larvae were shed at all other sites. Overall, an infection prevalence of only 12% was observed in snails based on cercarial shedding. While 47% of the snails were PCR-positive for the 500 bp ITS fragment, which was predicted to indicate infection with S. mansoni, sequence data demonstrated that these bands are not species-specific and can be amplified from other trematode infections. In addition, a 1000 bp band was amplified in 14% of samples, which was identified as a trematode in the family Derogenidae. Conclusions The results support the previous assumption that B. pfeifferi snails may be involved in transmitting schistosomiasis in the area but suggest that the community structure of both snails and trematodes may be more complicated than previously thought. This emphasises the importance of confirming species identifications using sequencing, rather than relying only on PCR-based diagnostics or cercarial shedding. Electronic supplementary material The online version of this article (10.1186/s13071-017-2525-6) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Jared S Bakuza
- Institute of Biodiversity, Animal Health and Comparative Medicine, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, UK. .,Department of Biological Sciences, Dar es Salaam University College of Education, Dar es Salaam, Tanzania.
| | - Robert Gillespie
- Institute of Biodiversity, Animal Health and Comparative Medicine, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, UK
| | - Gamba Nkwengulila
- Department of Zoology and Wildlife Conservation, University of Dar es Salaam, Dar es Salaam, Tanzania
| | - Aileen Adam
- Institute of Biodiversity, Animal Health and Comparative Medicine, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, UK
| | - Elizabeth Kilbride
- Institute of Biodiversity, Animal Health and Comparative Medicine, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, UK
| | - Barbara K Mable
- Institute of Biodiversity, Animal Health and Comparative Medicine, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, UK
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Gurarie D, King CH, Yoon N, Li E. Refined stratified-worm-burden models that incorporate specific biological features of human and snail hosts provide better estimates of Schistosoma diagnosis, transmission, and control. Parasit Vectors 2016; 9:428. [PMID: 27492409 PMCID: PMC4973538 DOI: 10.1186/s13071-016-1681-4] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2016] [Accepted: 07/05/2016] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Schistosoma parasites sustain a complex transmission process that cycles between a definitive human host, two free-swimming larval stages, and an intermediate snail host. Multiple factors modify their transmission and affect their control, including heterogeneity in host populations and environment, the aggregated distribution of human worm burdens, and features of parasite reproduction and host snail biology. Because these factors serve to enhance local transmission, their inclusion is important in attempting accurate quantitative prediction of the outcomes of schistosomiasis control programs. However, their inclusion raises many mathematical and computational challenges. To address these, we have recently developed a tractable stratified worm burden (SWB) model that occupies an intermediate place between simpler deterministic mean worm burden models and the very computationally-intensive, autonomous agent models. METHODS To refine the accuracy of model predictions, we modified an earlier version of the SWB by incorporating factors representing essential in-host biology (parasite mating, aggregation, density-dependent fecundity, and random egg-release) into demographically structured host communities. We also revised the snail component of the transmission model to reflect a saturable form of human-to-snail transmission. The new model allowed us to realistically simulate overdispersed egg-test results observed in individual-level field data. We further developed a Bayesian-type calibration methodology that accounted for model and data uncertainties. RESULTS The new model methodology was applied to multi-year, individual-level field data on S. haematobium infections in coastal Kenya. We successfully derived age-specific estimates of worm burden distributions and worm fecundity and crowding functions for children and adults. Estimates from the new SWB model were compared with those from the older, simpler SWB with some substantial differences noted. We validated our new SWB estimates in prediction of drug treatment-based control outcomes for a typical Kenyan community. CONCLUSIONS The new version of the SWB model provides a better tool to predict the outcomes of ongoing schistosomiasis control programs. It reflects parasite features that augment and perpetuate transmission, while it also readily incorporates differences in diagnostic testing and human sub-population differences in treatment coverage. Once extended to other Schistosoma species and transmission environments, it will provide a useful and efficient tool for planning control and elimination strategies.
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Affiliation(s)
- David Gurarie
- Department of Mathematics, Applied Mathematics and Statistics, Case Western Reserve University, Cleveland, USA.,Center for Global Health and Diseases, School of Medicine, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, Ohio, USA
| | - Charles H King
- Center for Global Health and Diseases, School of Medicine, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, Ohio, USA. .,Schistosomiasis Consortium for Operational Research and Evaluation, University of Georgia, Athens, Georgia, USA.
| | - Nara Yoon
- Department of Mathematics, Applied Mathematics and Statistics, Case Western Reserve University, Cleveland, USA
| | - Emily Li
- Center for Global Health and Diseases, School of Medicine, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, Ohio, USA
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