Bluetongue and or Deer Virus Infect Virginia Cattle
Livestock Update, January 2008
Dr. Dee Whittier, Extension Veterinarian, Cattle VA-MD Regional College of Veterinary Medicine, VA Tech
The State Veterinarian’s office recently announced evidence that Virginia cattle had disease associated with a virus spread by a small biting gnat or midge. Although little death loss occurred, cattle experienced lameness and mouth sores affecting their production. Most reports of signs of the disease were in the mountain/valley regions of Virginia, especially the Shenandoah Valley.
Bluetongue is a disease that was first described in sheep. It causes sheep to have sores in their mouths and also disturbs the feet and may cause abortion. Some experts suggest that losses due to bluetongue in cattle may be greater than those in sheep. The disease is spread almost entirely by a small gnat called Culicoides.
Because bluetongue depends on the gnat, its occurrence is seasonal when the gnat is active in the late summer and fall. Once frost comes the gnats are killed and disease spread stops. The gnats also have a regional distribution and are not found in the most northern parts of the US.
A disease occurs in deer caused by a virus that is closely related to the bluetongue virus. In fact, some of the blood tests done on sheep and cattle do not distinguish between the two infections. The deer disease is called Epizootic Hemorrhagic Disease or EHD. The EHD infection causes serious disease and death in deer.
Reports of many deer deaths in areas of Virginia where cattle were observed to have lameness and mouth sores suggest that EHD infections might have been significant this past season. Diagnostic tests did not allow Virginia officials to distinguish whether the cattle were infected with EHD or bluetongue.
There is still some debate as to what effects the deer virus has on cattle. It is clear that infections can occur. It appears that the disease signs vary depending on the immune status of cattle and that previously exposed cattle may show more severe disease than others.
Reproductive effects of these viruses are always to be considered. It appears that some strains of the virus are more likely to cause abortions than others. To date abortions have not been reported in cattle showing other signs of the disease in Virginia. However, since most cows are in the early stages of pregnancy, abortions may not be very apparent.
Bluetongue is receiving much international attention, especially in Europe. Areas of Europe that had not previously diagnosed the disease have had many cases this past summer and fall. There is some suggestion that warmer temperatures there have allowed the Culicoides gnat to spread into areas where it had not previously been found.
The Virginia Office of the State Veterinarian warned veterinarians and producers to examine cattle closely that have mouth lesions. Very serious diseases such as Foot and Mouth Disease and Vesicular Stomatitis result in blisters in the mouth. For this reason it is important to examine all animals drooling excessively or showing other signs of mouth disease. Obviously if there is any suggestion that mouth blisters are present, the State Veterinarian should be contacted immediately.
Still another aspect of these viral infections is their impact on exportation of cattle. Many countries do not allow cattle to be imported if they have a positive blood test to bluetongue. Other countries limit importation to states or areas where routine testing shows the absence of bluetongue or to times of the year when gnats are not active.
While losses from the viral infections this year were not catastrophic, some producers did see losses. It can certainly be hoped that the disease will not become entrenched in Virginia and cause yearly losses.
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