ANIMAL HEALTH: Dealing with bluetongue

Endemic to South Africa, the bluetongue virus now occurs worldwide and is on the increase. The disease, which is spread by midges, affects ruminants, mainly sheep, explains Roelof Bezuidenhout.

- Roelof Bezuidenhout

Bluetongue (BT) was first described in South Africa during the 1800s after the importation of Merino sheep. It has probably always been endemic in antelope and other game.

Indigenous sheep breeds, cattle and antelope are frequently infected, but rarely show clinical signs, whereas improved European sheep breeds are most susceptible, according to research.

Caused by the bluetongue virus (BTV), the disease occurs throughout the country during the summer rainy season when the biting midges that carry the virus are active in vleis, pans, rivers and around dams, particularly between sunset and sunrise.

PREVENTION

There are more than 20 different strains of BTV, with no crossimmunity between them, so they must all be included in the vaccine.

Many farmers choose not to vaccinate; they take the obvious risk of being hit hard, but hope there won’t be too many midges around.