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Visna viruses isolated from persistently infected sheep were antigenically distinct from the plaque-purified virus used for inoculation. The selection of antigenic variants under antibody pressure, thought to occur in vivo, was reproduced in sheep cell cultures inoculated with plaque-purified visna virus and maintained in antibody. Antigenic shift may be a mechanism for persistence of virus in slow or recurrent viral infections.
Narayan et al. (Fri,) studied this question.