Fatal disease due to bluetongue virus in sheep and wildlife in Wyoming
Joint Press Release - WSVL, WGFD, and WLSB
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The Wyoming Livestock Board is working with veterinarians, producers and the Wyoming State Veterinary Laboratory to address recent large-scale losses due to bluetongue virus in several sheep operations in Big Horn and Washakie counties. The outbreaks are being investigated by the Board in collaboration with veterinarians, woolgrowers, the United States Department of Agriculture, the Wyoming State Veterinary Laboratory, and Regional Veterinary Coordinators.
The outbreak of a bluetongue-like disease was first recognized in wildlife in mid-September 2007 by the Wyoming Game and Fish Department. A press release issued by the Department reported deaths in pronghorn, white-tail deer and mule deer. The role of bluetongue in the wildlife die-off was confirmed in mid-October.
Bluetongue is an infectious,
insect-borne viral disease primarily of domestic and wild ruminants. Its
distinctive name is due to blue discoloration of the mouth and lips of infected
animals. Infection is worldwide, but it is usually subclinical and mild. The
disease is transmitted by the bite of a small Culicoides midge
Lesions seen in the current outbreak include inflammation of the feet, ulcers in the mouth, and swollen lips. The cause of death in affected sheep is usually to pneumonia. When pregnant sheep are infected they sometimes abort. The death rate in sheep in the current outbreak is higher than usually experienced in Wyoming. When wildlife are affected they are usually found terminally ill or dead, often close to water sources.
Regional Veterinary Coordinator, Dr. Tim Graham, reports seeing 300 deaths in 900 affected sheep. The affected premises are along the Big Horn River or its tributaries. Losses have been equally distributed in lambs and adult ewes; affected ewes tend to be older animals. The most severely affected premise is a family farm with a range flock. Dr. Graham examined the flock and confirms that clinical signs and lesions are consistent with bluetongue. Because losses were higher than usual, and in order to rule out a dangerous foreign animal disease, Dr. Graham and United States Department of Agriculture/Animal Plant and Health Inspection Service veterinarian Dr. John Duncan investigated the episode. Blood and scabs from sick sheep were sent to the USDA's Plum Island Foreign Animal Disease Diagnostic Laboratory. The Center confirmed the presence of bluetongue virus but has yet to identify the serotype. Another sheep producer reports 200 sick in a flock of 2,500, with 10 of those 200 dead. A local veterinarian submitted samples from this case to the Wyoming State Veterinary Laboratory earlier this week and the lab detected antibodies to the virus in the blood.
Preliminary results of wildlife cases indicate that the strain of bluetongue virus in this year’s outbreak is not unusual for Wyoming. Dr. Cynthia Tate from the Wyoming Game and Fish Department notes that the stain of bluetongue virus isolated from pronghorn in the Worland area is serotype 17. This strain was responsible for the death of thousands of Wyoming pronghorn in 1976, and for hundreds of pronghorn deaths in 1984.
Livestock premises with confirmed infection have been quarantined. Bluetongue is a warm weather disease due to the insect vectors. Signs subside after the first hard frost, since the cold kills insects that transmit disease. Thus, quarantines are expected to be lifted soon. Some reports indicate that insect control may be effective at preventing disease transmission.
Although it has been years since the bluetongue virus has been isolated from a Wyoming animal, anecdotal reports indicate that the virus circulates in the state. Many old-time sheep ranchers claim to have seen it regularly, although in most years losses are small. A USDA investigation of a diseased flock in 2005 indicated that bluetongue may have been present in Johnson County that year.
There are unconfirmed reports of the disease affecting other Wyoming flocks but to date none of these reports are outside Big Horn Basin. One pronghorn and one mule deer have been diagnosed in the Sinclair and Douglas areas, respectively, but associated losses in livestock have not been reported.
The Wyoming Livestock Board
reminds producers that bluetongue is a reportable disease. Additionally, it is
important that producers who suspect the disease work with their veterinarian
and the state veterinarian to establish whether bluetongue is involved.
Bluetongue can mimic some very dangerous diseases so a full diagnostic work-up
is prudent. Typically this involves submitted blood
Contact information:
Wildlife losses: Contact Dr. Cynthia Tate or WGFD biologists
Sheep losses: WSVL and Dr. Walt
Cook
11/07/2007