Predictive methods to define infection with equine infectious anemia virusin foals out of reactor mares

Equine infectious anemia (EIA) was diagnosed in a high percentage of horses gathered from public lands administered by the Bureau of Land Management i n the area of the confluence of the White River and the Green River in Nort heastern Utah in 1998. Twenty-three mares with foals by their sides were ga thered in this area. The twelve mares that were positive on serologic tests for EIA were euthanatized, Their foals were moved to an isolation facility where they became subjects of a prospective study. The antibodies in the f oals' serum against EIAV antigens were determined to be passive in origin, as levels declined and eventually became undetectable in official tests for EIA in all twelve foals, No evidence for the genetic material of EIA virus (EIAV) was found in sensitive reverse transcriptase-polymerase chain react ion (RT-PCR) assays of plasma samples from the foals collected at the time of separation from all test-positive adult horses, and during their 8 month s in isolation. The passively acquired antibodies against EIAV antigens wer e detected with highest sensitivity in the immunoblot test. pf the official ELISA-based test kits, the competitive ELISA (CELISA) was highest in sensi tivity, followed by the other ELISA assay (Vira-CHEK) for detection of anti bodies against the major core protein (p26) of EIAV. These results correlat ed well with those obtained in the agar gel immunodiffusion (AGID or Coggin s) test, the internationally recognized gold-standard serologic test for EI A, which also detects antibody against the p26 antigen. The least sensitive indicator for passive antibodies in these foals against EIAV was the SA-EL ISA test, which detects activity against the transmembrane protein, gp45. F rom another perspective, the SA-ELISA test was the initial serologic indica tor of lack of infection in these foals, with negative reactions a mean of greater than or equal to 101 days earlier than in AGID tests. The results c onfirm that foals of test-positive mares can be raised free of infection wi th EIAV. The data indicate that the lack of detectable EIAV-RNA in plasma o f foals with declining serum antibody titers against EIAV are excellent pre dictors for lack of infection in foals of test-positive dams.