African horse sickness.

AHS is a noncontagious vector-borne disease of Equidae caused by Orbiviruses. Species susceptibility in decreasing order is horses, mules, donkeys, and zebras. The main vectors of AHS are culicoides. The disease is endemic in sub-Saharan Africa, but epizootics have occurred outside of this area on several occasions. The most recent outbreaks outside of the endemic area were in Spain, Morocco, and Portugal between 1987 and 1990. AHS causes mortality up to 95% and is classically divided into four clinical forms: the pulmonary, cardiac, mixed, and horse fever forms. Pathologic changes are subcutaneous and intermuscular edema and lung edema. The most consistent clinical signs include fever, nonpurulent conjunctivitis, and increased respiratory rate. Prevention and control measures include quarantines, control of insects, and vaccination. There is no treatment for AHS. Neurotropic strains of AHSV may cause retinitis and encephalitis in humans.