Chronic disease is characterized by weight loss, depression, weakness, edema and reduced hematocrit values, platelet counts and hemoglobin. The majority of horses infected with EIA virus do not have clinical symptoms. Federal law prohibits interstate travel of known positive animals. State control measures usually include euthanasia or permanent identification and lifelong quarantine of at least 200 yards from any other Equidae.
Transmission is mechanical when insects transfer blood from a positive horse.
The horsefly is considered a more significant vector because it transfers larger amounts of blood and virus than other vectors such as the mosquito or black fly. Other means of transmission include surgical equipment, stomach tubes, syringes and tack that has been contaminated with fresh blood. The infectivity of EIA virus in thought to diminish within hours in the environment. In order to receive and maintain this accreditation, laboratories must satisfactorily perform an initial proficiency test and annual check tests. Accredited laboratories are also required to adhere to strict federal guidelines in performing and reporting tests on individual animals.