Systematic Veterinary Virology

SYMPTOMS

• Bluetongue is clinically manifested as two syndromes:
  • vascular affection of several organ systems particularly oral and buccal mucosa and 
  • a reproductive syndrome. 
• Sheep are commonly seen with clinical disease, but other domestic ruminants such as cattle and goats only rarely show clinical signs
• Sheep
  • The clinical signs of BT are variable and not all strains of BTV that infect sheep cause clinical disease. The first clinical sign is the rise in temperature to 41.6-41.7o C. Within 24 hours of the initial rise in temperature, excessive salivation and frothing at the mouth develop and are associated with hyperemia and swelling of the buccal and nasal mucosa followed by erosions and ulcerations. By 4 to 7 days in severe cases, extensive ulcerations may be covered by gray necrotic tissue on the dental pad and dorsal surface of the tongue. Hyperemia is also observed around the coronary bands of the hooves. The hooves are tender and varying degrees of lameness are also observed. In more severe cases, the animals stand with an arched back. Sloughing of hooves is common at this stage. Animals that recover may have a dark line in the wall of the hoof. The lesions in the mouth, the reluctance to move, and the necrosis of striated musculature lead to weakness, depression, and rapid weight loss. These can result in prostration and eventual death in severely affected animals. Sheep that recover from severe infections may have a break in the wool 3 to 4 weeks after the fever has subsided. This can lead to partial or complete shedding of wool. The reproductive form of the disease varies greatly.  Signs include abortions, stillbirths, and weak  “dummy lamb” live births.
• Cattle: Bluetongue virus infection in cattle usually does not cause any clinical sign of disease. Clinical signs consist of
  • mild hyperemia in the buccal cavity and around the coronary band; 
  • vesicular lesions, which lead to ulcerations, in the buccal mucosa;
  • erect hair over the cervical and dorsal thoracic areas; and
  • hyperesthesia.
  • In addition, the dermis becomes thickened with prominent folds apparent in the cervical areas, and a dry crusty exudate leads to matting of hair in affected areas. These lesions may persist for 10 to 20 days. Similar lesions have been reported on teats of cattle with clinical BT. Hoof lesions may be associated with lameness.
  • BTV is both abortigenic and teratogenic in cattle experimentally, but not observed commonly in field conditions.  Early embryonic loss and decreased reproductive efficiency are the more frequently seen manifestations of the disease in cattle and can severely affect calf/milk production.
• Goats
  • Bluetongue infection of goats is an inapparent infection similar to that described for cattle.