Epizootic hemorrhagic disease (EHD), a disease caused by virus of the genus Orbivirus, is having a significant impact in deer this year in the United States (US). Although mainly infecting white-tail deer, EHD may be seen in mule and black-tailed deer, elk, bighorn sheep, pronghorn antelope, sheep and cattle. EHD is not transmissible to humans. Two serotypes, EHDV-1 and EHDV-2, known to be endemic in some areas in the United States (US) cause sporadic epidemics. Since 2006, disease associated with a third serotype, EHDV-6, has been seen. In 2012, all three serotypes were detected in the US; 2012 is the first year with a major outbreak for EHDV-6. Deer mortalities, numbering in the hundreds, were reported in some states. Significant numbers of deer deaths were reported in Pennsylvania, West Virginia, North Carolina, Nebraska, Colorado, Missouri and Indiana. Speculation is that drought conditions in many states have intensified breeding conditions for biting midges of the genus Culicoides. The main EHD vector is considered to be C. variipennis, but EHD has also been recovered from mosquitoes and gnats. Freezing conditions impact biting midges, so as fall approaches, the vector impact should lessen. EHDV cattle infections are generally subclinical; however, an unusual feature in 2012 is the appearance of some severe clinical presentations in cattle, yak (Colorado) and even one bison herd. In states, including Nebraska, Colorado, Iowa and South Dakota, clinically ill animals have been reported. In cattle, the clinical signs can include fever, oral ulcers, salivation, lameness (coronitis) and even weight loss. In pregnant cattle, fetal resorption may occur or, depending on the stage of gestation at time of infection, fetal hydranencephaly may develop. The clinical signs of EHD in cattle are similar to clinical signs of Foot and Mouth Disease, Bluetongue and Vesicular Stomatitis. Due to these presentation similarities, please call your local CDFA District Office to report cattle with these clinical signs so that appropriate sampling and testing may be obtained.
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