Researchers: The Stigma of EIA is Misplaced

Equine infectious anemia (EIA), also known as swamp fever, is a viral infection/disease of equids that has been largely controlled in the United States through application of Coggins testing since the early 1970s. In many areas of the country, especially where testing for antibodies to EIA virus (EIAV) has occurred in a high proportion of the population at regular intervals, the chance of finding test-positive horses approaches zero. In other areas of the country where annual testing has not been the tradition, EIA has been found in recent years on a number of specific premises or in free-roaming populations at rates exceeding 30%. This article is written to help horse owners understand the risks associated with not testing for EIA, to help put the risk of acquiring EIA in its proper perspective, and to promulgate recommendations for the more effective control of EIA at the national level. Yesterday and Today Although each year about 300 new EIA test-positive horses are discovered in the United States, most are without overt clinical signs of the disease. Strains of EIAV that were associated with severe clinical disease, including rapid progression to death, were relatively common before testing was widely used. Today the vast majority of horses found positive on the approved serologic tests for EIA are "inapparent carriers" of EIAV. As EIAV induces persistent infections, these carriers are infected for life and have EIAV in their blood at all times. The level of EIAV in these individuals might be low today, but EIAV mutates at a high rate and has the potential to increase its replication at any time. Thus, we recommend the application of the same controls for the movement of all test-positive horses, regardless of their clinical status. Today control of EIA depends on horse owners testing their equine charges to identify the carriers of EIAV. Most states have some regulations/rules/laws concerning EIA, at least requiring testing of horses coming from another state. Regulations imposed on the maintenance and movement of test-positive horses usually discourage the owners from keeping them. For example, test-positive horses should be segregated from other horses by at least 200 yards (440 yards by law in Arkansas) or segregated by 200 yards and isolated within a stall screened to exclude biting insects (enforced by several states). Few states have permitted the establishment of quarantine farms for accumulation of EIAV carriers; none have actively encouraged them.