Wild ruminants as reservoirs of domestic livestock gastrointestinal nematodes.

Gastrointestinal nematode (GIN) infections in cattle cause appetite suppression which leads to poor feed conversion, reduced weight gain and reduced milk production. Overuse and exclusive reliance on anthelmintic drugs has resulted in widespread resistance in many parasitic nematode species infecting livestock making control increasingly difficult. Wild ruminants are competent hosts of a number of nematode species that typically infect and are best adapted for cattle, sheep, and goats. Thus, the potential exists for wild ruminants to act as reservoirs in the translocation of domestic GIN, including those carrying anthelmintic resistance mutations as well as susceptible genotypes. The potential for parasite exchange is heightened by interfaces or ecotones between managed and wild rangelands, and by perturbations linked to climate warming that can increasingly alter the distributions of wild ungulates and their interactions with domestic and free-ranging ruminants. To investigate the extent to which wild ruminants harbour parasites capable of infecting domestic ruminants we first performed an epidemiological study of feces from wildlife hosts that spanned 16 states and included white-tailed deer (85 % of the samples), pronghorn, elk, mule deer, bighorn sheep, moose, cattle, and caribou across the United States. All samples were cultured to third stage larvae and nematode DNA was isolated and PCR amplified. Among the 548 wild ruminant samples received, 33 % (181 samples) were positive for nematode DNA, among which half (84 samples) contained DNA from GIN species commonly found in cattle. DNA from cattle GIN species was detected in 46 % of samples from the Northeast, 42 % from the Southeast, 10 % from the Midwest, 0 % from the Southwest and 11 % from the West. Deep amplicon sequencing of the ITS-2 rDNA indicated that Ostertagia and Trichostrongylus were present in 90 % and 69 % of the nematode DNA positive samples, respectively, whereas Haemonchus, Cooperia and Oesophagostomum were present in 26 %, 2 % and 10 % of the samples, respectively. These data clearly show that wild ruminants commonly harbour multiple parasite species whose primary hosts are domestic cattle, and suggest that further work is warranted to investigate their specific roles in the management of anthelmintic resistance.