Bluetongue virus (BTV) causes a non-contagious arthropod-borne disease that affects domestic and wild ruminants.  It is primarily a disease of sheep.  The virus is transmitted by biting gnats, most often the species Culicoides variipennis.  The disease is limited to areas where the insects occur.  Infection is seasonal with disease in late summer and fall in Wyoming and surrounding states   The insect vectors feed on blood of infected animals and transfer virus at subsequent blood meals to naïve animals.  Infection is only transmitted by insects and does not go directly from animal-to-animal; in other words, bluetongue is an infectious, non-contagious disease.  Introduction of BTV to an area may occur when one or more infected animals are moved to a locality where Culicoides are endemic.  Bluetongue virus infects domestic sheep and, rarely, domestic cattle.  Bluetongue also infects wildlife species native to Wyoming.  This includes pronghorn, white-tails, mule deer and bighorn sheep.  Historically it has been responsible for large die-offs in the state, particularly in pronghorn.  A large pronghorn die-off due to BTV occurred in 2007 in Big Horn Basin along the Big Horn River and specific tributaries.

This is a reportable disease of livestock in Wyoming.  If you think this disease is active in your flock, it should be reported to the Wyoming Livestock Board.  Cases should be confirmed by laboratory testing (below).  Exposure to the virus can be established by a simple blood test (submit red top tube).  Active infection can be established by isolating the virus from blood or tissue, or by a specific polymerase chain reaction (PCR) assay

BTV and a closely related virus (epizootic hemorrhagic disease virus; EHDV) are members of the Reoviridae family in the genus Orbivirus.  There are 24 serotypes of BTV worldwide.  Five occur in the U.S.   BTV-17 is the most common member that is found in the Rocky Mountain region. This is the serotype responsible for the 2007 outbreak in Big Horn Basin,

Clinical signs in domestic sheep are lameness, depression, fever, salivation, mucopurulent nasal discharge, swollen lips and facial skin, ulcers and erosions in mucosa of the mouth, cyanosis, and swelling/redness of the coronet.  Pregnant ewes infected in the first trimester of gestation may abort.  Ewes infected in the 2^nd trimester may have lambs with teratogenic deformation or neurologic abnormalities.  When infected in the third trimester, most ewes have normal lambs due to a good immune response to the virus. Bluetongue virus causes 10-30% mortality in sheep.  In wildlife the virus causes peracute hemorrhage and death.  In cattle it occasionally causes signs similar to those seen in sheep, including abortion.  More commonly BTV causes subclinical infection in cattle.    

Samples of choice for viral isolation:

• Whole blood (in purple top tubes)

• Tissues: spleen, lung, and lymph nodes from post-mortem animals.  If an aborted fetus is found, submit the entire fetus plus fetal membranes if available. 

Samples for virus isolation are set up once a week at the WSVL.  The charge for VI  with identification by fluorescent antibody is $20.00.

Please call Dr. Nicky Bratanich 307-742-6681 ext. 161 or Jackie Cavender 307-742-6681 ext. 162 in the Virology Lab for additional information.

Dr. Nicky Bratanich DVM PhD
Virologist
Wyoming State Veterinary Laboratory
Department of Veterinary Sciences
University of Wyoming
1174 Snowy Range Road
Laramie WY 82070
Ph: 307-742-6638
Fax: 307-721-2051
abratani@uwyo.edu

11/07/2007