An outbreak of bluetongue (BTV) and epizootic hemorrhagic disease viruses (EHDV) occurred in free-ranging deer in the foothills of the San Gabriel Mountains in Los Angeles County this year. The outbreak started mid to late August and continued through October. Reports from concerned citizens in the Pasadena and Altadena areas adjacent to deer habitat, including the Jet Propulsion Laboratory grounds, suggested that multiple deer were affected (> 20), deer were often found dead near streams or other water sources, there were few or no sick deer observed, and no other species were affected. The history was consistent with an outbreak of one of a group of hemorrhagic disease viruses that can affect deer. In collaboration with CDFW South Coast Region biologists and the Pasadena Humane Society, three deer associated with this mortality event were necropsied and samples were submitted to the California Animal Food and Health Safety (CAHFS) laboratory in San Bernardino. Testing at CAHFS confirmed that EHDV was the cause of death for two of the deer tested and BTV the cause of death for the third.
The Department’s Wildlife Investigations Lab (WIL) is interested in outbreaks of viral hemorrhagic diseases in California’s free-ranging deer populations. These viruses include deer adenovirus and two closely related Orbiviruses, BTV and EHDV. None of these viruses are known to affect people. Deer adenovirus was first described following a 1993 outbreak in California involving multiple counties with mortality estimates of over a thousand deer. Since first being described in California deer, deer adenovirus has subsequently been detected in association with deer mortalities in most of the Western states and may be the most important hemorrhagic disease virus affecting California’s deer. Bluetongue virus has long been recognized as a disease of both domestic ungulates like cattle, sheep, and goats, and of free-ranging ungulates like deer. Epizootic hemorrhagic disease virus is one of the most significant infectious diseases of white-tailed deer with outbreaks occurring regularly in white-tailed deer from the Northern Great Plains down to Florida, and has been associated with disease in cattle. Historically, mule deer and black-tailed deer, the deer native to California, were considered less susceptible to the Orbiviruses than white-tailed deer; however, we do see localized outbreaks of BTV and EHDV in native deer throughout California.
The Wildlife Investigations Lab would like to thank the efforts of the local citizens that reported this outbreak and the Department staff, the Pasadena Humane Society, and the California Animal Health and Food Safety labs for their efforts in determining the causes of this outbreak.
Authored by: Dr. Brandon Munk