An outbreak of bluetongue this fall has killed more than 300 sheep in Montana’s Big Horn Basin and led to sickness in hundreds of other sheep.
The virus also killed pronghorn antelope, white-tailed deer and mule deer in the Big Horn Basin as well as antelope and mule deer in the Cody, Wyo., Sinclair, Wyo., and Douglas, Wyo., areas. The disease is also present in southern Montana.
Effects Still Present After Freeze
Sheep owners are urged to contact their veterinarian if they notice symptoms of bluetongue in their flocks, says Don Montgomery, director of the Wyoming State Veterinary Laboratory (WSVL) director Don Montgomery.
The lab is managed by the University of Wyoming’s College of Agriculture.
“We may see additional losses due to abortion, particularly in sheep but possibly in cattle. This could occur even after a hard freeze kills the midge vector,” Montgomery says. “Bluetongue crosses the placenta and causes fetal malformations. We are most likely to see this in the Big Horn Basin along the affected drainages.”
UW Department of Veterinary Sciences Prof. Donald O’Toole says it has been an unusual year for bluetongue in Wyoming.
“We don’t usually see high death loss like we have this fall,” O’Toole says. “If woolgrowers see an outbreak of lameness or sore mouths in their flocks, they should work with their veterinarian to establish whether it is bluetongue rather than orf or other common diseases of sheep.”
Orf (a.k.a. “soremouth” and “pox”) is a highly contagious disease of sheep and goats caused by a parapoxvirus.
Lesions seen in the current outbreak include inflammation of the feet, crusting around the nose and mouth, and swollen lips. Bluetongue’s distinctive name is due to blue discoloration of the mouth and lips of infected animals. The cause of death in affected sheep is usually pneumonia.
Where It Comes From
The disease is transmitted by a small Culicoides biting midge, commonly called “no-see-ums.”
The outbreaks in wildlife and sheep in the Big Horn Basin are being investigated by the Wyoming Livestock Board (WLSB) the WSVL, area veterinarians, woolgrowers, U.S. Department of Agriculture (USDA), and Wyoming Game and Fish Department (G&F).
The outbreak of a bluetongue-like disease was first recognized in wildlife in mid-September. By Nov. 8, the WSVL had confirmed infection in sheep on seven ranches in the Worland, Otto, Basin and Greybull areas. Lambs and adult ewes have died, with deaths tending to occur among older ewes.
Big Horn Basin veterinarian Tim Graham reported that about 300 of 900 affected sheep in one range flock died from the infection.
Another sheep producer reported 200 sick in a flock of 2,500, with 10 of those 200 dead. A local veterinarian submitted samples from this case to the WSVL and the lab detected antibodies to the virus in the blood.
Livestock premises with confirmed infection have been quarantined.
O’Toole says treatment is symptomatic.
“It involves support and nursing care,” he says. “Because the mouth is so sore, sheep are reluctant to eat. Valuable animals may have to be fed by a stomach tube, which producers in the Big Horn Basin are doing. Animals need to be given shade and access to water, and they need time to recover.”
Antibiotics aren’t used to directly treat bluetongue since it’s a virus, but sometimes antibiotics are given to reduce secondary infections, he says.
Preliminary results of wildlife cases indicate the strain of bluetongue virus in this year’s outbreak is not unusual for Wyoming.
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 coronetregnant. Ewes infected in the first trimester of gestation may abort. Ewes infected in the second 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.