Avian Lymphomatosis. VI. A Virus of Unusual Potency and Pathogenicity

Abstract

It is well established that avian lymphomatosis is of viral etiology. The shortcomings of viral isolates used experimentally have been that they require long incubation periods and special genetic lines of chickens, and are of low or inconsistent pathogenicity. Burmester et al. (1) demonstrated the presence of a filterable agent, designated as RPL-12 virus, in an avian lymphoid tumor. The response of line 15 chickens to graded doses of this virus demonstrated an infective range from a low of 55.5% in a low-dose lot to a high of 90.1% in a highdose lot and the average age at death in the same lots was respectively 128.2 and 55.6 days (2). The manifestations of cellular and cell-free preparations of JM lymphomatosis virus in Cornell's S-line chickens have been reported by Sevoian et al. (5,6,7,8). The response was measured by mortality, and the presence of gross lesions in the survivors during a 3-week experimental period. The mortality rarely exceeded 10% during this period, and, more often, none occurred. Therefore, virus titers of cellular preparations were expressed as the 50% infective dose and ranged