New Case of EIA Documented in NC

LENOIR, NC (August 29, 2017 by Seth Nagy)…Last week a 14-year-old female mule in Johnston County, NC contracted equine infectious anemia. This is the first new case of EIA documented in North Carolina since 2005. Equine infectious anemia, or EIA, is a bloodborne viral disease transmitted primarily by insects, particularly horse flies and deer flies. This virus can infect horses, ponies, donkeys, and mules.

The first new case of EIA was detected in North Carolina last week. This is a non -curable disease of horses, ponies, donkeys, and mules.

Besides biting flies, infection can also be spread through contaminated needles, and pregnant mares can pass the virus to her unborn foal. Although this virus is in the same family as the human immunodeficiency virus (HIV), it is not a human health concern.

The disease is most likely to be transmitted when biting fly populations are greatest – in late summer. When the horse contracts the virus, there is a 7-45 day incubation period. After the incubation period, there are three forms the disease can take – acute, chronic, or inapparent.

Acute: Severe signs of the disease display rapidly, and horses can die within 2-3 weeks. The acute form occurs so quickly that often an elevated body temperature is the only sign seen. If the horse survives, it will be infected with the virus for the rest of its life. Surviving the acute phase leads to being chronically infected or inapparent carriers.

Chronic: Horses that survive the acute infection can develop disease signs off and on. This is caused by the horse’s immune system fighting the persistent virus. Chronic issues are sudden rise in body temperature to 105° or more, decreased appetite and weight loss, swelling of the lower chest, abdomen and legs, irregular heartbeat, pinpoint-sized hemorrhages on mucous membrane, and general listlessness. Chronic EIA horses are sometimes called “swampers”. The major concern with a chronically infected horse is its ability to infect other horses through insect bites.

Inapparent: The majority of infected horses are inapparent carriers. They do not show signs of the disease. However, under times of extreme stress, some clinical signs may become apparent. These carriers are usually found only when tested for EIA. The EIA test is called the Coggins test after Dr. Leroy Coggins who developed the test in the 1970s. This test detects antibodies that the horse’s immune system develops to the virus.

Most horses, ponies, mules, and donkeys are inapparent carriers of EIA. Routine blood tests are typically the way EIA positive horses are discovered. The disease is not curable. Once infected, the animal will always shed the virus and be a potential threat to other horses. If a horse tests positive for EIA, the animal may be euthanized, but it can be kept in quarantine if the owner chooses.

There is no approved vaccine for EIA in the United States. To help prevent infection, use new sterile needles and syringes for each horse. Test all horses for EIA every year, and test any new horses that come onto your premises. Have a sound fly control program. And only participate in horse events that require a negative Coggins test.

Horse owners should also have a relationship with a veterinarian. Although there is no vaccine for EIA, there are vaccines for other horse diseases such as eastern and western equine encephalomyelitis, which is transmitted by mosquitoes, as well as tetanus and rabies.

For answers to your livestock questions, call the Caldwell County Extension Center at 828-757-1290 or visit us online anytime at

Seth Nagy is the Caldwell County Cooperative Extension Director.