CLINICAL SIGNS AND TREATMENT
Clinical signs are generally associated with sheep, and hence most descriptions of disease apply to this species. In sheep, disease can vary from subclinical to severe, including death.
The first sign is fever, and the animal may appear depressed. This is followed by hyperaemia of the oral cavity and swelling of the mucous membranes, leading to oedema of the lips, tongue and muzzle. The animal may be anorexic. There is lachrymation, serous nasal discharge, becoming mucopurulent, excessive salivation and conjunctivitis. At a later stage there may be necrosis of the epithelium of the nose and mouth. Oedema may extend to the ears and brisket, and there may be wool-break. The feet often exhibit coronitis, leading to lameness. The animal may be reluctant to stand. Torticollis may also be seen. In pregnant ewes, abortion or mummification of the fetus may occur, and at term deformed or weak lambs may be born. Paradoxically, cyanosis of the tongue, from which coloration the disease derives its name (bluetongue) is less common.In cattle, infection is usually inapparent. Where clinical disease does occur, BT is seen as a transient fever followed by hyperaemia and erosions of the nose, buccal and lingual mucosa and, rarely, the teats. Affected cattle salivate excessively and may walk with a stiff gait. Usually, less than 1% of infected cattle show clinical signs, although in the recent epizootic of BTV8 in Europe anecdotal reporting suggests that 2—3% of cattle were clinically affected, and abortion, loss in milk yield and reductions in weight gain occurred. In addition, the European strain of BTV8 has been shown to cross the placental barrier in cows infected during preg- nancy(30). The outcome of these pregnancies ranged from healthy unaffected viraemic calves to weak dying neonatal calves, and ‘dummy’ calves. BT in goats is rarely seen and when it does occur is usually mild. Certain wild ruminants, such as the North American white-tailed deer, pronghorn antelope and bighorn sheep may develop severe BT, similar to that seen in improved sheep. Lethal infections have also been described in captive South American camelids (llamas and alpacas) in Europe that developed acute respiratory distress and died within 24 hours1-26’27). Similarly, two yaks (Bos grunniens grunniens) also kept in captivity in Europe developed clinical signs. Death in one animal occurred 7 days after examination)31).
Apart from supportive treatment there is no specific therapy for BT.