Occurrence of Lymphomatosis in Chickens Free of Resistance-Inducing Factor (RIF) Virus

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Abstract
Neural, visceral, and ocular lymphomatosis occurred between 15 and 40 weeks of age in 29% of 75 uninoculated isolated chickens hatched from groups of dams which did not shed resistance-inducing factor (RIF) virus in their eggs. RIF virus infection was not present in this flock, since attempts to isolate virus (at 3 and 40 weeks) or demonstrate acquired antibody (on 7 occasions through 40 weeks) were negative in all birds. Tissue homogenates from each of 4 leukotic or paralyzed RIF-free birds induced neural or visceral lymphomatosis or both in 13-75% of RIF-free chicks within 10 weeks of intraperitoneal inoculation at one day of age. Uninoculated control chicks remained free of leukotic lesions. Leukotic lesions in birds with non-RIF leukemia were composed of small lymphocytes, while lesions in RIF-inoculated leukotic birds were usually characterized by anaplastic cells. These data have shown that not all lymphomatosis is caused by RIF-positive virus strains, and suggests that neural, visceral, and ocular lymphomatosis may be induced in chickens by a non-RIF transmissible agent.