Gastrointestinal nematodes represent a major problem for livestock production across the globe, one that has intensified with the rapid and repeated evolution of multi-drug resistance (Wit et al., 2021). Understanding parasite exposure and how resistance is maintained over time are therefore of key importance for defining efficient management strategies. To date, the role wildlife play in these dynamics has been poorly studied. The work of Beaumelle et al. examine this essential question by studying the transmission dynamics of nematodes at the environmental interface between transhumant sheep and wild ungulates, more specifically with ibex (Capra ibex) that allochronically share alpine pastures when sheep are brought to graze in summer. By collecting fresh fecal material from both species and using a metabarcoding approach based on ITS-2 sequences, the authors characterise the nemabiome in each ungulate species and demonstrate that the two host species share a large portion of their parasite diversity. More importantly, by focusing on a gene (β-tubulin isotype 1) associated with resistance to a commonly used anthelmintic drug (benzimidazole), they demonstrate that both species carry resistant nematode strains, but that the diversity of strains, and particularly susceptible strains, is much higher in ibex. A key feature of the sampling design is that fecal material from both species was collected before seasonal transmission between the ungulate species could occur. Therefore, their results demonstrate that ibex are able to maintain resistant strains over long periods of time and therefore may be major nematode reservoirs for sheep infection. This important conclusion raises a series of key questions. How are resistant genotypes maintained in untreated ibex hosts? Is the cost of resistance so weak that they can coexist with susceptible strains in the absence of drug treatment or does anthelminthic contamination of the pastures maintain resistant genotypes directly in wild hosts? This work also opens several interesting perspectives: For example, what additional resistant parasites may be maintained by these wildlife hosts? What role do other wild ungulate species play in the evolution of nematode communities in transhumant sheep? An expansion of this work to the larger community of wild ungulates using alpine pastures, and an evaluation of the degree to which wild species are exposed to anthelminthic drugs released by grazing livestock into the environment is now required to understand the deeper consequences of drug treatment for shaping parasite communities and their cascading impacts for wildlife conservation, and the development of efficient and sustainable management strategies for pastoral livestock. 

References

Beaumelle et al. Cross-transmission of resistant gastrointestinal nematodes between wildlife and transhumant sheep. bioRxiv, ver. 5 peer-reviewed and recommended by Peer Community in Zoology. https://doi.org/10.1101/2023.07.21.550073

Wit, J., Dilks, C.M., Andersen, E.C., 2021. Complementary Approaches with Free-living and Parasitic Nematodes to Understanding Anthelmintic Resistance. Trends Parasitol. 37, 240–250. https://doi.org/10.1016/j.pt.2020.11.008