Generalists at the interface: Nematode transmission between wild and domestic ungulates.

Josephine G. Walker,Eric R. Morgan

doi:10.1016/j.ijppaw.2014.08.001

Josephine G. Walker, Eric R. Morgan

Open Access

https://doi.org/10.1016/j.ijppaw.2014.08.001

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Abstract

Many parasitic nematode species are generalists capable of infecting multiple host species. The complex life cycle of nematodes, involving partial development outside of the host, facilitates transmission of these parasites between host species even when there is no direct contact between hosts. Infective nematode larvae persist in the environment, and where grazing or water sources are shared ingestion of parasite larvae deposited by different host species is likely. In this paper we examine the extent to which nematode parasite species have been observed in sympatric wild and domestic ungulates. First, using existing host-parasite databases, we describe expected overlap of 412 nematode species between 76 wild and 8 domestic ungulate host species. Our results indicate that host-specific parasites make up less than half of the nematode parasites infecting any particular ungulate host species. For wild host species, between 14% (for common warthog) and 76% (for mouflon) of parasitic nematode species are shared with domestic species. For domestic host species, between 42% (for horse) and 77% (for llamas/alpacas) of parasitic nematode species are shared with wild species. We also present an index of liability to describe the risk of cross-boundary parasites to each host species. We then examine specific examples from the literature in which transmission of nematode parasites between domestic and wild ungulates is described. However, there are many limitations in the existing data due to geographical bias and certain host species being studied more frequently than others. Although we demonstrate that many species of parasitic nematode are found in both wild and domestic hosts, little work has been done to demonstrate whether transmission is occurring between species or whether similar strains circulate separately. Additional research on cross-species transmission, including the use of models and of genetic methods to define strains, will provide evidence to answer this question.

Highlights

Many parasitic nematode species are generalists capable of infecting multiple host species
In this paper we examine the extent to which nematode parasite species have been observed in sympatric wild and domestic ungulates globally
We reviewed known host–parasite associations in wild and domestic ungulates to determine the extent of overlap between nematode parasites in different host species

Summary

Introduction

Many parasitic nematode species are generalists capable of infecting multiple host species. In this paper we examine the extent to which nematode parasite species have been observed in sympatric wild and domestic ungulates. We examine specific examples from the literature in which transmission of nematode parasites between domestic and wild ungulates is described. The seminal example of population-level impacts of nematodes is the regulation of population cycles in red grouse by Trichostrongylus tenuis (Hudson et al, 1998). These accounts, while primarily descriptive, do include limited examples of a clinical or ecological perspective. While there has been much recent work on ecological theory related to host– parasite interactions, this is only beginning to be applied to the interface between wild and domestic ruminants (Hoberg et al, 2008)

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