African horse sickness is an acute or subacute disease of horses caused by orbivirus. It is transmitted by various biting insects. The disease affects horses severely and causes edema, hemorrhaging, and accumulation of fluids. Symptoms range from mild fever to severe respiratory distress and death. Diagnosis involves isolating the virus from blood or tissues in cell cultures or eggs. There is no cure, but control relies on vaccination, quarantining sick animals, and reducing insect vectors.