Bluetongue: how to spot and report the disease

Clinical signs

Infection with bluetongue can significantly compromise livestock welfare, both in terms of unpleasant symptoms and a potentially high mortality rate. The severity of disease varies among different species, with symptoms being most severe in sheep, resulting in deaths, weight loss and disruption in wool growth. In highly susceptible sheep, morbidity can be as high as 100%. Mortality averages from 2 to 30%, but can be as high as 70%. Cattle often have a higher infection rate than sheep and demonstration and severity of clinical signs varies depending on the strain of virus.

Animals can recover from the disease. Such animals become immune to the strain with which they were infected and, after around 60 days, they stop shedding virus into the bloodstream, meaning they no longer pose a risk in terms of onward infection of the midge population. However, there are long terms impacts on productivity and fertility.

If you keep livestock, you must continue to keep a close watch for, and report any suspicion of bluetongue disease in your animals.

In sheep

Sheep are more likely to show obvious clinical signs of bluetongue than cattle if they become infected. Signs of bluetongue in sheep include:

• ulcers or sores in the mouth and nose
• discharge from the eyes or nose and drooling from mouth
• swelling of the lips, tongue, head and neck, and the coronary band (where the skin of the leg meets the horn of the foot)

Other clinical signs include:

• red skin, as a result of blood collecting beneath the surface
• fever
• lameness
• breathing problems
• abortion
• death

In cattle

Signs of the disease include:

• lethargy
• crusty erosions around the nostrils and muzzle
• redness of the mouth, eyes, nose
• reddening of the skin above the hoof
• nasal discharge
• reddening and erosions on the teats
• fever
• milk drop
• not eating
• abortion

Adult cattle may serve as a source of virus for several weeks while displaying little or no clinical signs of disease, and are often the preferred host for insect vectors.

In calves

Calves can become infected with bluetongue (BTV-8) before birth if the mother is infected while pregnant. Signs of infection include:

• calves born small, weak, deformed or blind
• death of calves within a few days of birth
• abortions

Livestock keepers and vets should consider bluetongue as a possible cause for calves showing these signs.

Photos of clinical signs

We have published some photos of clinical signs of bluetongue disease on Flickr.