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Bluetongue is primarily a disease of sheep, and in the face of infection these animals can display clinical signs ranging from acute to subclinical^{1, 14}. Acute disease follows an incubation period of about one week, which may depend on the infectious dose of virus received.  Signs begin with pyrexia of around 40.5-42°C, and hyperaemia of the oral and nasal mucosa is seen 24-36 hours later accompanied by hypersalivation and a serous nasal discharge. The nasal discharge quickly becomes mucopurulent and potentially blood-tinged, and dries to froms a crust around the nostrils. Oedema of the head occurs, which particularly affects the lips and tongue but may also spread to include the ears and submandibular areas. In a few cases the tongue becomes severely swollen and cyanotic, lending the disease its name. Petechial haemorrhages appear on the still-hyperaemic mucosae, and areas of necrosis appear on the gums, cheeks and tongue 5-8 days after the onset of fever. Covered by a diptheritic membrane, these necrotic lesions heal slowly and contribute to inappetance, dysphagia and hypersalivation. In some cases, profuse bloody diarrhoea is seen. Erythema and petechiation of the coronary band can cause lameness, and sheep stand with an arched back, reluctant to move. In advanced disease, skeletal muscle is necrosed and contributes to rapid weight loss, along with inappetance. Animals in the late stage may also suffer torticollis. In pregnant ewes, infection with BTV may lead to abortions, foetal mummification, or the birth of stillborn or weak lambs, which may suffer congenital defects.

Bluetongue is primarily a disease of sheep, and in the face of infection these animals can display clinical signs ranging from acute to subclinical^{1, 14}. Acute disease follows an incubation period of about one week, which may depend on the infectious dose of virus received.  Signs begin with pyrexia of around 40.5-42°C, and hyperaemia of the oral and nasal mucosa is seen 24-36 hours later accompanied by hypersalivation and a serous nasal discharge. The nasal discharge quickly becomes mucopurulent and potentially blood-tinged, and dries to froms a crust around the nostrils. Oedema of the head occurs, which particularly affects the lips and tongue but may also spread to include the ears and submandibular areas. In a few cases the tongue becomes severely swollen and cyanotic, lending the disease its name. Petechial haemorrhages appear on the still-hyperaemic mucosae, and areas of necrosis appear on the gums, cheeks and tongue 5-8 days after the onset of fever. Covered by a diptheritic membrane, these necrotic lesions heal slowly and contribute to inappetance, dysphagia and hypersalivation. In some cases, profuse bloody diarrhoea is seen. Erythema and petechiation of the coronary band can cause lameness, and sheep stand with an arched back, reluctant to move. In advanced disease, skeletal muscle is necrosed and contributes to rapid weight loss, along with inappetance. Animals in the late stage may also suffer torticollis. In pregnant ewes, infection with BTV may lead to abortions, foetal mummification, or the birth of stillborn or weak lambs, which may suffer congenital defects.

Considering all cases, including those which are subclinical, mortality due to bluetongue in sheep ranges between 2% and 30%¹⁴. Death can occur up to a month after the onset of clinical signs,acutely affected sheep may be protracted. However, mild cases often recover quickly and completely. Some cases of ovine bluetongue follow a more chronic course with death occuring after a month post-infection due to exhaustion and bacterial complications.

Considering all cases, including those which are subclinical, mortality due to bluetongue in sheep ranges between 2% and 30%¹⁴. Death can occur up to a month after the onset of clinical signs, or a protracted recovery may follow acute infection. Recovery in mild cases is often much more rapid.  

Disease is most often sub-clinical in cattle despite its epidemiological significance in this species: it has been reported that only 0.01% of infected cattle show signs of bluetongue¹. Clinical signs, when seen, can include inflammation or erosions of the oral and nasal mucosae and a stiff gait. Similar signs to sheep may also occur: pyrexia, tachypnoea, lacrimation, salivation and a vesicular, ulcerative dermatitis are all possibilities. In cattle in early gestation, embryonic death and resorption can result from BTV infection.

Disease is most often sub-clinical in cattle despite its epidemiological significance in this species: it has been reported that only 0.01% of infected cattle show signs of bluetongue¹. Clinical signs, when seen, can include inflammation or erosions of the oral and nasal mucosae and a stiff gait. Similar signs to sheep may also occur: pyrexia, tachypnoea, lacrimation, salivation and an ulcerative dermatitis are all possibilities. In cattle in early gestation, embryonic death and resorption can result from BTV infection.

===Laboratory Tests===

===Laboratory Tests===