Equine infectious anemia (EIA) is a worldwide disease of Equid, including horses, ponies, donkeys, mules, and zebras. The causative agent, EIA virus (EIAV) is a lentivirus in the family Retroviridae, subfamily Orthoretrovirinae. The disease has cyclical periods of viremia, with immune mediated damage of erythrocytes and platelets, and phagocytosis to remove altered erythrocytes and platelets. Survivors of the acute phase can become chronic with off-and-on signs, and remain carriers of the disease and with very rare exceptions, yield a positive serological test result. Virus isolation is not usually required for a diagnosis, but it can be done. EIAV can be isolated by inoculating suspect blood into a susceptible horse or onto leukocyte cultures prepared from susceptible horses. Although EIA may be suspected on the basis of clinical signs and pathological lesions, confirmation of infection requires further serological and molecularbased testing. The two most commonly used serological tests are the agar gel immunodiffusion (AGID) or enzyme-linked immunosorbent assays (ELISAs). RT-PCR appears to be an effective method of diagnosis in mules as well as horses. PCR tests can also be used to supplement or confirm serological tests, particularly when there are conflicting results or when an infection is suspected but serology is negative or equivocal. EIA is a reportable disease in the world. In countries where EIA is not present, outbreaks are contained with quarantines and movement controls, tracing of cases and surveillance. There is no vaccine or treatment for the disease.