Bluetongue is caused by Bluetongue virus, which is transmitted between animals by biting midges (Culicoides). It affects sheep most often, but can infect any of the ruminants. Bluetongue is becoming more of a problem as the vector is adapting to the cooler climates of Europe and is bringing the virus with it. Bluetongue is not a contagious disease but can be spread via surgical equipment and needles. The virus is also found in semen and can be transmitted between animals at the time of mating. Cattle are less commonly affected than sheep but can still be infected by the virus. Virus can be found in the blood 4 days after the cow is infected with the virus, and can be ingested by biting midges ready to be transmitted to other animals.
- Usually no clinical signs are seen in cattle
- Changes in white blood cell levels and rectal temperature may be observed
- Mild redness, vesicles or ulcers in the mouth or on the skin may rarely be observed
- Skin may develop thickened folds, especially in the neck area
- Bulls may become temporarily infertile
- Severe breaks in the hooves may develop weeks after infection, and this is usually followed by foot rot
- Calves born to infected dams may have developmental abnormalities, particularly involving the brain
Treatment and Control
There is no treatment for Bluetongue infection, but antibiotics may be used if there is suspicion of bacterial infection secondary to the primary viral infection. Disinfection of housing will not prevent disease transmission, as the mode of transmission is by midge vectors, not by direct contact. Use of synthetic pyrethroids or organophosphates are useful in getting rid of midges. Moving animals into barns away from the midges, especially in the evening when midges are most active, can reduce the risk of infection.