A Coggins test is a serological blood test used in horses to detect the presence of antibodies to Equine Infectious Anemia (EIA), a potentially fatal viral disease caused by a lentivirus in the same family as HIV. The test was developed by Dr. Leroy Coggins in the early 1970s, and his name has become the colloquial term for both the test and the official EIA test certificate it generates.
EIA has no approved vaccine and no cure. Infected horses may show acute signs (fever, anemia, weakness, edema) or remain as asymptomatic carriers capable of transmitting the virus to other horses via blood-feeding insects, primarily horseflies and deerflies. Because carriers show no clinical signs yet remain infectious for life, blood testing is the only way to identify them.
Legal Requirements
A negative Coggins test result is legally required for interstate transport of horses in the United States under USDA regulations, and individually by most states for intrastate movement to shows, competitions, trail rides, sales, or boarding facilities. Most equine events require a negative result dated within 12 months (some within 6 months). The official test uses the agar gel immunodiffusion (AGID) method; a competitive ELISA (cELISA) is approved as a screening test. Testing is performed by accredited veterinarians who collect a blood sample and submit it to a USDA-approved laboratory. Results are documented on a federally-approved certificate issued in the horse’s name and with identifying markings.
What a Positive Result Means
A horse that tests positive for EIA antibodies must by law be permanently identified (lip tattoo or microchip), quarantined from other horses, or euthanized. Sale of an EIA-positive horse without disclosure is a federal offense. The horse cannot be moved across state lines. Positive horses are reported to USDA APHIS, which maintains a national EIA database.
Further Reading: USDA APHIS Equine Infectious Anemia program.