Equine infectious anemia is a viral disease of horses. It is usually spread through blood transfer caused by large biting insects such as horseflies and deerflies. The disease causes immune suppression. Horses infected with EIA may develop acute symptoms and die or they may have slowly progressing symptoms and live for many years.

The positive horse was tested for EIA, as required prior to attending an exhibition. Current Minnesota rules require all horses be negative to an EIA test within 12 months of importation or exhibition to limit possible exposure to other horses. Because there is no vaccine or treatment for EIA, an infected horse will always be a reservoir for spread of the disease.