Epizootic Hemorrhagic Disease in a Herd of Tibetan Yak (Bos grunniens)
American Association of Zoo Veterinarians Conference 2015

Kirsten S. Thomas1*, DVM; Robert Bildfell2, DVM, DACVP; Benjamin E. Alcantar Hernandez1,2, MVZ

1Wildlife Safari, Winston, OR, USA; 2College of Veterinary Medicine, Oregon State University, Corvallis, OR, USA


Epizootic hemorrhagic disease (EHD) is caused by an orbivirus that affects wild and domestic ruminants, and is most commonly diagnosed in white-tailed deer (Odocoileus virginianus).1 This virus is often transmitted by Culicoides species, or other species of biting gnats and flies. During summer 2014, an outbreak of EHD occurred in southern Oregon, affecting both white-tailed deer and black-tailed deer (Odocoileus hemionus columbianus). During this time, eight Tibetan yak (Bos grunniens) housed on a 200-acre free roaming pasture at Wildlife Safari presented with hemorrhagic disease and fever. Clinical signs in affected yak included hyperthermia, hematochezia, scleral hemorrhage, respiratory distress, hind limb ataxia, presence of a toxic line on the oral mucosa, and peracute death. Marked thrombocytopenia occurred in all affected animals. Aggressive therapy with broad spectrum antibiotics, fluids, and supportive care were attempted in each case, but all eight animals died. Gross necropsy findings included hemorrhage within the subcutis, gastrointestinal hemorrhages, and gall bladder distension. No oral lesions were noted. Histologic findings in these mortalities included widespread hemorrhage, pulmonary congestion and edema, acute myocardial necrosis, multifocal fibrinoid vasculopathy, marked cholestasis, and evidence of hemoglobinuric nephrosis. EHD was identified by PCR in five yaks tested, but virus isolation attempts were unsuccessful. As clinicopathologic findings were similar for all eight dead yak, it is assumed that all died of EHD. These findings differ from a previously recorded outbreak of EHD in Tibetan yak in Colorado,2,3 suggesting that a broader range of clinical presentation for EHD in this species should be considered.


The authors thank the Ungulate Department at Wildlife Safari for their support and assistance in caring for these animals. The authors would also like to thank North Dakota State University’s Veterinary Diagnostics Lab for their assistance in PCR identification of the EHD virus.

Literature Cited

1.  Howarth EW, Stalknecht DE, Kirkland PD. Bluetongue, epizootic hemorrhagic disease, and other orbivirus-related diseases. In: Williams ES, Baker IK (eds). Infectious Diseases of Wild Mammals. Ames, IA: Iowa State University Press; 2001:77–97.

2.  Raabis SM, Byers SR, Hann S, Callan RJ. Case report: Epizootic hemorrhagic disease in a yak. Can Vet J. 2014;55(4):369–372.

3.  Van Campen H, Davis C, Flinchum JD, Bishop JV, Schiebel A, Duncan C, Spraker T. Epizootic hemorrhagic disease in yaks (Bos grunniens). J Vet Diagn Invest. 2013;25(3):443–446.


Speaker Information
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Kirsten S. Thomas, DVM
Wildlife Safari
Winston, OR, USA

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