Investigating parasite dynamics of migratory ungulates for sustaining healthy populations: Application to critically-endangered saiga antelopes Saiga tatarica

Contact between wild and domestic ungulates is increasing across rangelands, enabling disease co-transmission. Disease management is difficult given uncertainties in complex system behavior, limited empirical data, and logistical obstacles to interventions. We studied gastrointestinal nematode (GIN) transmission in a rangeland shared by both livestock and the critically-endangered migratory saiga antelope, Saiga tatarica, in order to model infection dynamics under current and plausible future scenarios of increasing livestock numbers, climate change and anti-helminth treatments. Our model was parameterised for trichostrongylid GIN – a cause of mortality and morbidity in ungulates globally - using data on observed faecal nematode egg output and host numbers and distribution. Results showed that seasonal saiga migration leads to asymmetry in parasite transmission, with the majority of GIN acquired by saigas in their autumn and winter range through prior pasture contamination from livestock. Consequently, reducing parasite burdens in livestock early in the season in these areas could disproportionately reduce cross-transmission to saigas. Early-season GIN suppression in livestock in the saiga's spring and summer range was predicted to have weaker effect on parasite transmission to saigas but reduces infections during the calving period, potentially increasing population health and resilience at this critical time. Optimally timed treatments could offset the effects of increasing livestock numbers on GIN infection pressure, while climate warming had only marginal impacts on GIN transmission under all scenarios. Our findings could support better understanding and mitigation of factors affecting saiga health and rural livelihoods. Our approach is transferable to other systems, particularly those with migratory hosts.