Wild ruminants as reservoirs of domestic livestock gastrointestinal nematodes

Authors: BARONE, CARLY - Non ARS Employee; WIT, JANNEKE - University Of Calgary; GILLEARD, JOHN - University Of Calgary; HOBERG, ERIC - University Of Wisconsin; Zarlenga, Dante

Submitted to: Veterinary Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/27/2020
Publication Date: 1/28/2020
Citation: Barone, C.D., Wit, J., Gilleard, J.S., Hoberg, E.P., Zarlenga, D.S. 2020. Wild ruminants as reservoirs of domestic livestock gastrointestinal nematodes. Veterinary Parasitology. https://doi.org/10.1016/j.vetpar.2020.109041.
DOI: https://doi.org/10.1016/j.vetpar.2020.109041

Interpretive Summary: Gastrointestinal nematode (GIN) infections have a major impact on the production characteristics of grazing ruminants. Anthelmintics initially provided high efficacy management of these infections; however, misuse and overuse have resulted in widespread drug resistance. Wild cervids such as deer, caribou, elk, and pronghorn are also ruminants that acquired GIN infections by grazing on pastures contaminated with infective larvae. Thus, transmission of GIN among domestic and wild ruminant host species can interfere with efforts to manage GIN infections on farms. To assess the extent to which co-grazing wildlife are infected with the major species of cattle GIN, we acquired more than 550 wildlife-derived, fecal samples from 25 states and examined them for nematode eggs. Those positive for nematodes were further analyzed by molecular methods including sequencing to ascertain the species. Results showed that the three most devastating nematodes of cattle i.e., Ostertagia, Trichostrongylus and Haemonchus were present in 90%, 66% and 26% of the wildlife samples analyzed. Results indicate that on-farm management approaches must account for wildlife that can act as a reservoir to propagate GIN infections. This study will enlighten both scientists and producer groups to the importance of surrounding environment in developing future management schemes to control GIN infections.

Technical Abstract: 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 many 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. 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. All samples were cultured to third stage larvae and nematode DNA was isolated and PCR amplified. Among the 576 samples received, 33% (188 samples) were positive for nematode DNA, among which half (89 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, 13% 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 66% 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 spread of anthelmintic resistance.