The clinical signs are often nonspecific and of variable severity. Clinical signs in an acute case can range from fever and decreased appetite to severe anemia and sudden death. It is often difficult to differentiate EIA from other diseases. Incubation period is a week to 60 days or longer. Additional clinical signs in an acute case can include:
Horses that survive the acute phase of the disease become chronic, in-apparent carriers. Some carriers may develop recurrent flare-ups, often following another stress – illness or strenuous work. While donkeys and mules have the ability to contract this virus, most remain non-clinical.
Samples to collect
Post Mortem Lesions
Natural transmission of EIA is by blood feeding flies (horse flies and deer flies) and is limited to relatively short distances. This virus is frequently transmitted via unclean or re-used needles and syringes, blood transfusions and contaminated instruments (IV sets, dental instruments, tattoo equipment). Mares can transmit the virus to foals in utero, and, less likely, transmission can occur via milk or semen.
There is no treatment for EIA. Because infected animals become lifelong carriers they must be permanently isolated and quarantined or euthanized.
Reducing exposure to biting flies through management practices may reduce the spread of infection. To prevent iatrogenic spread, never reuse needles, syringes or IV sets, use only new, clean needles with injectable medicines and use only licensed and approved blood products. Blood transfusions should be performed only by licensed veterinarians using donor horses tested negative for EIA and other blood-borne infections like equine piroplasmosis.
Surveillance and testing are the best methods of prevention. Since EIA control efforts began over 40 years ago the reactor rate has fallen from 4% to .004% in 2017 among tested animals. USDA recommends testing every equid annually.
There is no vaccine approved for use in the U.S.