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Heterogeneity in helminth infections: factors influencing aggregation in a simple host–parasite system

Published online by Cambridge University Press:  30 September 2019

Richard C. Tinsley Open the ORCID record for Richard C. Tinsley [Opens in a new window] ,
Hanna Rose Vineer ,
Rebecca Grainger-Wood  and
Eric R. Morgan
Richard C. Tinsley*
Affiliation:
School of Biological Sciences, Life Sciences Building, University of Bristol, BristolBS8 1TQ, UK
Hanna Rose Vineer
Affiliation:
School of Veterinary Sciences, University of Bristol, BristolBS40 5DU, UK
Rebecca Grainger-Wood
Affiliation:
School of Biological Sciences, Life Sciences Building, University of Bristol, BristolBS8 1TQ, UK
Eric R. Morgan
Affiliation:
School of Biological Sciences, Life Sciences Building, University of Bristol, BristolBS8 1TQ, UK
*
Author for correspondence: Richard C. Tinsley, E-mail: r.c.tinsley@bristol.ac.uk
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Abstract

The almost universally-occurring aggregated distributions of helminth burdens in host populations have major significance for parasite population ecology and evolutionary biology, but the mechanisms generating heterogeneity remain poorly understood. For the direct life cycle monogenean Discocotyle sagittata infecting rainbow trout, Oncorhynchus mykiss, variables potentially influencing aggregation can be analysed individually. This study was based at a fish farm where every host individual becomes infected by D. sagittata during each annual transmission period. Worm burdens were examined in one trout population maintained in isolation for 9 years, exposed to self-contained transmission. After this year-on-year recruitment, prevalence was 100% with intensities 10–2628, mean 576, worms per host. Parasite distribution, amongst hosts with the same age and environmental experience, was highly aggregated with variance to mean ratio 834 and negative binomial parameter, k, 0.64. The most heavily infected 20% of fish carried around 80% of the total adult parasite population. Aggregation develops within the first weeks post-infection; hosts typically carried intensities of successive age-specific cohorts that were consistent for that individual, such that heavily-infected individuals carried high numbers of all parasite age classes. Results suggest that host factors alone, operating post-infection, are sufficient to generate strongly overdispersed parasite distributions, rather than heterogeneity in exposure and initial invasion.

Keywords

Discocotyle sagittataimmune controlMonogeneaoverdispersed distributionsparasite transmission
Type
Research Article
Information
Parasitology , Volume 147 , Issue 1 , January 2020 , pp. 65 - 77
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Copyright
Copyright © Cambridge University Press 2019

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Footnotes

*

Present address: Department of Infection Biology, Institute of Infection and Global Health, University of Liverpool, Liverpool L69 3BX, UK

†

Present address: CSA Environmental, Pershore WR10 3DN, UK

‡

Present address: School of Biological Sciences, Institute for Global Food Security, Queen's University, Belfast BT9 7BL, UK

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