THE PATHOGENESIS OF EQUINE INFECTIOUS ANEMIA AND ISOLATION OF THE VIRUS FROM HORSES INFECTED BY NATURAL TRANSMISSION FROM ASYMPTOMATIC CARRIERS

The horizontal and vertical transmission of equine infectious anemia virus (EIAV) by asymptomatic or inapparent carrier horses was demonstrated during a field study using the agar gel immunodiffusion (AGID) test for EIA. The presence of the disease in the newly infected horses was substantiated by clinical pathology and histopathology. The clinical form of the disease in new recipients was unpredictable. Clinical signs in acute EIA were pyrexia, anorexia, ataxia, edema, lymphadenopathy, and cachexia. Clinically, a normochromic normocytic anemia, intravascular hemolysis, hypoalbuminemia, hyperfibrinogenemia, and hypergammaglobulinemia were demonstrated. Circulating IgG was shown to be elevated. Anemia, liver damage, and general debilitation was indicated by elevated sorbitol dehydrogenase (SDH), ornithine carbamyl transferase (OCT), glutamic pyruvate transaminase (GPT), and glutamic oxaloacetic transaminase (GOT) in the plasma. Histopathology indicated a lymphoid infiltration and proliferation attended by a parenchymal degeneration in the liver, kidney, and lung. A secondary bacterial infection was indicated by the presence of acute purulent fibrinous pneumonia. The clinical signs, pathology, and histopathology observed in horse dying of acute EIA were consistent with those described in the literature. An acute experimental case of EIA was presented for comparison. A new inapparent carrier was shown to exhibit no observable clinical signs other than an elevated IgG level and a positive AGID test. A discussion of the epizootiology of EIA was presented. It was also shown that AGID precipitating antibody acquired passively from an asymptomatic carrier mare via the colostrum was not detectable in the foal at 6 months of age indicating the absence of EIAV infection. A wild type (WT) strain of EIAV was isolated from the serum of a horse dying of acute EIA by adaptation to equine dermis (E. Derm) cell culture providing evidence of the presence of the virus in the horse and potential for transmission. Infection of the E. Derm cells by EIAV was verified by testing viral antigens precipitated from cell culture fluids with polyethylene glycol 6000 using a modification of the AGID test for EIA