Shared Bacterial and Viral Respiratory Agents in Bighorn Sheep (Ovis canadensis), Domestic Sheep (Ovis aries), and Goats (Capra hircus) in Montana

Abstract

Transmission of infectious agents from livestock reservoirs has been hypothesized to cause respiratory disease outbreaks in bighorn sheep (Ovis canadensis), and land management policies intended to limit this transmission have proven controversial. This cross-sectional study compares the infectious agents present in multiple populations of bighorn sheep near to and distant from their interface with domestic sheep (O. aries) and domestic goat (Capra hircus) and provides critical baseline information needed for interpretations of cross-species transmission risks. Bighorn sheep and livestock shared exposure to Pasteurellaceae, viral, and endoparasite agents. In contrast, although the impact is uncertain, Mycoplasma sp. was isolated from livestock but not bighorn sheep. These results may be the result of historic cross-species transmission of agents that has resulted in a mosaic of endemic and exotic agents. Future work using longitudinal and multiple population comparisons is needed to rigorously establish the risk of outbreaks from cross-species transmission of infectious agents.

Modeling risk of pneumonia epizootics in bighorn sheep

“…Exposure to sheep or goats may occur on farms on private lands, whereas exposure on public lands likely occurs primarily on allotments, for which data exist and which agencies can more directly manage. Although risk due to private land was slightly uncertain (the 95% CRI contained 0, however the 93% CRI did not), these results provide the first empirical support for the suggestions of Miller et al (, ) and the Wild Sheep Working Group (2012) that risk of exposure to pathogens on private land should receive more focus and concern. The uncertainty of this parameter at the 95% CRI is likely due to the probably low correlation between private land and farms with domestic sheep and goats, because not every parcel of private land contains domestic Caprinae species.…”

“…As we hypothesized, greater percentage of private land in and near areas used by herds of bighorn sheep was associated with increased risk of pneumonia epizootics by >1.5‐fold per additional unit of private land. Risk associated with contact with domestic livestock on private land has not previously been quantified and tends to be neglected (Miller et al , ), perhaps because data on locations of hobby and commercial farms are generally unavailable and would be highly fluid through time. Exposure to sheep or goats may occur on farms on private lands, whereas exposure on public lands likely occurs primarily on allotments, for which data exist and which agencies can more directly manage.…”

“…We hypothesized 5 covariates were positively related to risk of pathogen transmission: proximity to number of domestic sheep and goat allotments (Singer et al b , ; Monello et al ; Epps et al ; Clifford et al ), amount of private land (Miller et al , ; Wild Sheep Working Group 2012), use of domestic sheep and goats for weed control (Miller et al , Wild Sheep Working Group 2012), a history of a pneumonia epizootic in the herd or its neighbors (Onderka and Wishart 1984, George et al , Edwards et al , Besser et al ), and close proximity to other herds (Onderka and Wishart 1984, Singer et al a , George et al , Edwards et al , Besser et al ). We hypothesized that amount of private land would be representative of risk from hobby or commercial farms with domestic sheep or goats, for which data were not available.…”

“…Identifying causes and influences of pneumonia epizootics has been the goal of extensive study; the etiology remains poorly understood, however, and the need for further research is commonly cited (Monello et al ; Cassaigne et al ; Miller et al , ). Presence of certain pathogens such as Mycoplasma ovipneumoniae and Mannheimia haemolytica are likely indicative of risk (Miller et al ; Besser et al a , b , 2013; Shanthalingam et al ). After decades of research, however, relationships between the various known and hypothesized risk factors affecting transmission, spread, and susceptibility of the pathogens that lead to pneumonia remain unclear.…”

“…Contact with feral goats also appears to result in exposure to pathogens (Rudolph et al ). Contact with sheep or goats on commercial and hobby farms or when sheep or goats are used for weed control (i.e., targeted grazing to manage noxious weeds) may result in exposure to pathogens (Miller et al , ; Wild Sheep Working Group 2012). Evidence also suggests herds of bighorn sheep are likely more interconnected than previously thought (Singer et al a , DeCesare and Pletscher 2006), and that proximity among herds may increase risk of exposure to pneumonia pathogens through such connectivity (Onderka and Wishart 1984, George et al , Edwards et al , Besser et al ).…”