[Pathogenesis of equine infectious anemia (with reference to similar chronic viral infection)].

1. Equine infectious anemia (EIA) is an immunologically-medicated disease. Immune complexes formed in blood and tissues are responsible for most symptoms and lesions (anemia, splenomegaly, lymphadenopathy, glomerulonephritis, etc.). In addition, a state of cellular hypersensitivity of the delayed type is involved in the pathogenesis. 2. Periodical attacks of pyrexia and clinical illness in the presence of immunity are caused by antigenically-modified variants of virus. By means of immunosuppressive treatments similar relapses of fever associated with the appearance of new virus variants can be also provoked during longlasting asymptomatic periods. 3. The mechanisms responsible for the lifelong persistence of virus are not fully elucidated. Obviously of prime importance is the viral antigenic drift allowing the virus to escape from humoral and cellular immune reaction. Finally, however, a state of cell-mediated immunity ensuring protection against homologous and heterologous virus strains may be reached. 4. Pathogenetic analogies and differences existing between EIA and other chronic viral infections of animals are recorded.