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| EIA Explained
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Equine Infectious Anemia (EIA) is a disease that threatens the world’s horse, donkey, and mule populations. Despite testing and measures to eradicate the equine infectious anemia virus, EIAV, more than 500 new cases are identified each year in the U.S. There is no cure for EIA. Although most infected horses show no symptoms, they remain contagious for life, endangering the health of other horses. For this reason, the United States Department of Agriculture (USDA; www.USDA.gov) and state animal health regulatory agencies require euthanasia or strict lifelong quarantine for horses testing positive for EIAV. Equine infectious anemia is a potentially fatal viral disease. EIAV reproduces in white blood cells that circulate throughout the body. The immune system, via antibodies, may attack and destroy red blood cells leading to anemia. Inflammation associated with the viral infection may damage vital organs, such as the bone marrow, liver, heart, and kidney. Secondary infections, e.g., pneumonia, may occur due to subsequent immunosupression. EIAV-infected horses may die from the direct effects of the virus or from secondary infections. EIA GENERALLY HAS THREE FORMS: Back to Top 1) Acute: Seen within 1-4 weeks after the horse’s first exposure to the virus, this phase is the most detrimental. It may be difficult to accurately diagnose acutely infected horses, as antibodies are not immediately produced and anemia is not present at this stage. However, the virus is active, multiplying and damaging the immune system and other organ systems. 2) Chronic: If the horse survives the acute phase, a subacute or chronic phase may occur. The classic signs of EIA such as fever, depression, weight loss, anemia, and petechial (pinpoint sized) hemorrhages on the mucous membranes are most likely seen in this phase. Repeated flare-ups of clinical signs often occur. Such episodes are seen with a new proliferation of the virus in the blood stream during periods of stress or the administration of corticosteroids. 3) Inapparent: Over time, the periodic episodes decrease in severity and frequency. Within a one-year period many horses begin to control the infection and show no clinical signs. These inapparent carriers are infected for life and may be a source of infection for other horses
EIAV is transmitted by blood or by passage across the placenta in the pregnant mare directly to the foal. Blood transmission can occur via blood-sucking insects, such as horse flies, deer flies, and mosquitoes. The virus is carried in the residual blood on the insect’s mouthparts as it travels from one horse to the next. Transmission may also occur via blood transfusion, or blood-contaminated needles and instruments. The virus may also be found in semen and milk. EIA is also known as “swamp fever” because the disease has been associated with warm, wet regions, but the disease is not limited by geography. States reporting the highest incidence of EIA include: Arkansas, Oklahoma, Louisiana, Texas, Florida, Tennessee, Mississippi, Georgia, Michigan, and Alabama.*
EIA may be difficult to diagnose because the symptoms are not specific and may vary from horse to horse. Signs may include one or more of the following: THE COGGINS (AGID) AND C-ELISA TESTS Back to Top The only way to accurately determine whether a horse is infected with the EIA virus is by identifying antibodies in the blood via agar gel immunodiffusion (AGID) or competitive enzyme linked immunoadsorbent assay (C-ELISA) tests. The AGID method is considered the “gold-standard” and is commonly known as the Coggins test. This test was developed many years ago by veterinary researcher, Dr. Leroy Coggins. A negative Coggins test means there are no detectable antibodies at the time of testing. A positive test indicates the horse is infected and a carrier of the virus. C-ELISA tests offer the advantage of rapid results. However, false-positive results are more common with the C-ELISA tests, and positive results should be verified by a standard Coggins (AGID) test. Foals may be false positive due to maternal antibodies passed via colostrum for as long as 6 months with either test. The USDA requires horses imported from foreign countries have a negative Coggins test. Within the U.S., each state drafts its own specific requirements regarding EIAV and the movement of horses interstate, intrastate, and in change of ownership. Learn what is required in your state and states you will be visiting. Be aware that laboratory results take time, and plan to have your horse tested in time to get results before you must transport your horse. By law, EIA is a reportable disease. All positive cases must be filed with the state veterinarians and the federal Animal and Plant Health Inspection Service (APHIS; www.aphis.usda.gov). RISK FACTORS Back to Top There are management and geographic factors that put horses at greater risk for contracting EIA. These include:
There is no effective treatment for EIA. There is no vaccine to prevent it. There is no cure. However, good management can reduce the potential of infection. The following guidelines will help: DIFFICULT CHOICE Back to Top If your horse tests positive for EIAV, your options are extremely limited. Federal and state health agencies, as well as the American Association of Equine Practitioners, support euthanasia as the most prudent, albeit emotionally difficult, option. Lifelong quarantine in a screened stall is another, less acceptable, alternative. EIAV-positive horses will always pose an unnecessary health risk to other horses, whether or not they show signs of illness. Even in the best management situations, blood-sucking insects cannot be totally controlled or eliminated. The only way to eradicate the disease is to eliminate the carriers. Horses testing positive for EIAV are required by law to be permanently identified via branding or tattooing and to be quarantined. Transportation and housing are severely restricted. You should contact your state animal health agency for specific requirements. Owners who choose quarantine must post signs clearly stating: “Quarantined: Equine Infectious Anemia” or “Swamp Fever.” Horses should be quarantined at least 200 yards away from all other animals. CONTINUED VIGILANCE Back to Top Stopping the spread of EIAV is everyone’s responsibility. If you suspect a horse has EIAV, call your veterinarian or state animal health agency immediately. They can assess the animal and initiate the required tests. Owner compliance with EIAV testing and the destruction of known carrier animals has aided in a marked decline in EIA cases in the last 20 years. Today less than 1 percent of the 1 million horses tested annually are found to be carriers. But with an estimated 6.6 million horses in the U.S., more widespread screening is needed. Even backyard horses that never leave the property will benefit. By having your horse tested, you will be doing yourself and the entire equine industry a favor. The cost is minimal and the price well worth the peace of mind. For more information contact your veterinarian, the American Association of Equine Practitioners (AAEP; www.aaep.org), or the Animal Plant Health Inspection Service (APHIS). Bayer HealthCare LLC, Animal Health Division Shawnee Mission, Kansas 66201 © 2003 Bayer HealthCare LLC
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© 2002 Bayer Corporation |
Bayer Corporation, Animal Health,