Discussion

Many helminth species can infect both wild and domestic animals, but the scale of cross-transmission and its relevance to parasite control on farms is highly uncertain. In the face of this uncertainty, it is easy and common to assume that wild hosts with high parasite prevalence act as sources of infection. This presentation sets out some approaches to disentangle the complexities of host species range, spatial overlap and climatic influences on parasite transmission, to predict risks of cross-infection. Thus, bipartite networks show promise for assessing degree of overlap in helminth fauna between wild and domestic hosts where sampling effort is uneven between host species. Further, formalising empirical knowledge of factors influencing transmission within mechanistic simulation models can help to assess directions and key times of spill-over between host populations. This approach has been applied to nematodes of saiga antelopes in Kazakhstan, and diverse ungulate assemblages in Botswana. By predicting key points of transmission, rational attenuation measures can be put in place, and consequences of spill-over managed without resorting to radical and ineffective interventions. In the UK, increasing deer numbers along with the discovery of anthelmintic-resistant nematodes in deer, raise the possibility that wildlife are important vectors of drug resistance between farms; although, they might equally serve as refugia for drug-susceptible nematodes. The quantitative frameworks outlined for other systems might contribute to balanced assessments of the risks of helminth infections in wildlife for farming, and to design appropriate mitigation measures in a diverse and multi-purpose farming landscape.