Epizootic hemorrhagic disease in yaks (Bos grunniens)

An epizootic of hemorrhagic disease associated with Epizootic hemorrhagic disease virus serotype 2 (EHDV-2) infections in yaks from 5 herds occurred in Colorado between August 21 and October 3, 2012. Affected yaks presented with fever, lethargy, anorexia, dyspnea, and swollen conjunctivae. Ulcerated dental pads, mucoid sanguineous nasal discharge, petechial hemorrhages in multiple organs, pulmonary edema, and serosanguinous fluid in the thorax, abdomen, and pericardial sac were observed at necropsy. Blood and tissue samples from 8 yaks with similar clinical signs and necropsy findings were positive for EHDV-2 by reverse transcription polymerase chain reaction and 5 yaks were seropositive for EHDV. Tests for malignant catarrhal fever (Ovine herpesvirus 2), Bovine viral diarrhea virus, Bovine herpesvirus 1, Foot-and-mouth disease virus, and Vesicular stomatitis virus were negative. The findings indicate that yaks are susceptible to infection with EHDV-2 and exhibit the clinical signs, and gross and histologic lesions of hemorrhagic disease observed in other ruminant species.