In this article:
- Overview: Equine infectious anemia (EIA)
- Clinical signs and disease presentation
- Transmission of EIA
- Sample collection and paperwork
- Diagnostic options
- Interpreting test results
- Key takeaways
Overview: Equine infectious anemia (EIA)
Equine Infectious Anemia, EIA, is a blood-borne viral disease of equids caused by the Equine Infectious Anemia Virus, EIAV, a lentivirus in the Retroviridae family, making it a relative of HIV.
Once an equid is infected, the virus integrates into host macrophages and persists for life due to its ability to evade immune clearance. Given the lifelong nature of EIAV infection and the absence of a vaccine or cure, routine testing remains the most effective tool for identifying infection and prevent the spread of disease.
Annual testing for EIA, commonly referred to as the Coggins test, has long been a standard component of equine health management.
Working together with veterinarians, the Texas A&M Veterinary Medical Diagnostic Laboratory, TVMDL, offers serologic testing for equine infectious anemia, including the agar gel immunodiffusion, AGID, assay, which remains the regulatory gold standard for EIA diagnosis.
Clinical signs and disease presentation
Clinical signs of EIA vary widely. Some horses show no outward signs of disease. Others may experience acute episodes characterized by fever, weakness, anemia, jaundice, and edema. Chronic cases may show intermittent fever, weight loss, or poor performance. Importantly, clinical signs may come and go, making diagnosis challenging.
Transmission of EIA
Equine infectious anemia is a bloodborne viral disease transmitted primarily through exposure to infected blood. One of the most common routes of transmission is via blood-feeding insects, particularly horse flies and deer flies. These insects do not biologically transmit the virus but can mechanically transfer infected blood from one horse to another during interrupted feeding.
Shared needles or contaminated veterinary instruments also pose a significant transmission risk, which underscores the importance of strong biosecurity practices.
Transmission may also occur through the administration of virus contaminated blood products. This may occur despite the use of sterile equipment, such as during transfusion of infected donor blood.
Sample collection and paperwork
Suspected EIA cases require careful and accurate sample collection to ensure definitive diagnosis. For EIA serological testing, TVMDL recommends collecting at least 3 mL of unclotted blood in a plain red-top tube or a serum separator tube.
Because EIA is a federally reportable disease, sample submissions must be accompanied by clear labeling and accurate and complete paperwork. Proper and legible animal identification, including animal description and owner information, is critical for regulatory compliance.
Diagnostic options
Two primary assays are used for EIA testing:
AGID (Coggins) Test: The gold standard for EIA diagnosis. It detects EIAV-specific antibodies with high specificity.
Equine Infectious Anemia Virus (ELISA): Offers high sensitivity and rapid turnaround, making this test well suited for high-volume screening; however, any ELISA-positive sample must be confirmed by AGID testing in accordance with USDA and state regulations.
Interpreting test results
Negative test results: A negative test means no antibodies were detected. The horse is either uninfected or was exposed so recently that antibodies haven’t developed yet. After potential exposure, TVMDL recommends repeating the test at 60 days.
Positive test results: A positive test indicates exposure to EIAV. Because there is no cure or vaccine, infected horses are considered infectious for life. Regulations require that positive horses be permanently quarantined, euthanized, or transferred to an approved research facility.
Key takeaways
EIA can be prevented with routine testing and careful biosecurity practices. By performing annual tests, veterinarians help protect the equine community. Attention to accurate sample collection and proper paperwork makes a big difference in keeping testing reliable and disease under control.
The Diseases and Diagnoses podcast by TVMDL features an episode on equine infectious anemia, covering the virus, clinical signs, transmission, and diagnostic testing. Listen to the full episode on Spotify or Apple Podcasts.
For other valuable resources or guidance regarding EIA infection, visit tvmdl.tamu.edu or call the College Station laboratory at 888.646.5623 or the Canyon laboratory at 888.646.5624.