Equine Infectious Anemia (EIA): 25 Years and $600,000,000 Later

Owners in the United States have paid over $600 million to test for EIA since 1980. Horse owners and veterinarians in the early 1970s remember the benefits associated with using for the first time an accurate test (AGID or Coggins test) to identify carriers of EIA virus (EIAV). The risks of acquiring EIA at major racetracks and breeding farms went to zero if control guidelines were followed. In 2003 at a cost of about $50 million, 273 test-positive equids were found in the United States, a rate of 0.015%. We are evaluating current control efforts to improve the benefit/cost ratio. Estimates indicate we can offer the current or higher level of protection against EIA at considerable savings by consolidating present state programs into regional ones. The USDA has been formally requested to initiate a National State-Federal Cooperative Program that will foster such regional efforts.

Why no vaccine? Can we find the remaining reservoirs of infection? When is testing no longer required? Are our diagnostics optimal?

Our research on EIA is directed at these questions. The etiologic agent of EIA, a cousin of HIV, is an equid-specific lentivirus that causes persistent infections in equids and mutates at a high rate. Thus, EIAV poses challenges to equids that parallel those posed by HIV to humans.

Vaccine design and evaluation are high priorities in our laboratory. Our best candidates show promise; they appear to protect horses against infection and disease when exposed to our pathogenic lab strain of EIAV. Can we produce vaccines that are safe and effective against all strains of EIAV? Our current NIH grant to evaluate diversity of EIAV and its effects on vaccine efficacy addresses that question. We have collaborated with Dr. Ron Montelaro at the University of Pittsburgh on these and other basic questions on EIA since 1978.

Vaccines for EIA and HIV may be elusive because these viruses exploit a fundamental property of the immune system that limits responses to few of the many potential targets (epitopes) present on infectious agents. Although this “immunodominance” is not usually a weakness, mutable pathogens such as EIAV and HIV evade immune surveillance when these immunodominant epitopes change. Other subdominant epitopes may be more highly conserved and might stimulate broader and more effective responses that protect against infection/disease following lentiviral exposure if the immunodominance could be circumvented. The role of immunodominance in EIA is a high priority for Dr. Frank Cook, a molecular virologist on our research team.

Infection with EIAV remains an important cause of morbidity and mortality in equids in many areas of the world, and EIA serves as a valuable animal model for host responses to lentivirus infections. To date, no practical methods have been found to replace the current diagnostics based on detection of antibodies against EIAV in serologic tests in AGID and ELISA test formats. We collaborate with the USDA and diagnostic test kit manufacturers, monitor the licensed kits and suggest improvements in the routine diagnosis of EIA. We have proposed models to use existing test kits that are the basis for a new three-tier laboratory system being evaluated by the USDA.

We have the tools to eradicate EIA. If we continue to live with the infection, managing the risk will be more cost effective when regional “EIA-free” certifications are adopted.

Dr. Charles Issel, Warren Wright, Sr.-Lucille Wright Markey Chair in Equine Infectious Diseases
(859) 257-4757, cissel@uky.edu
Maxwell H. Gluck Equine Research Center, University of Kentucky.