Pathogenicity of a Viral Strain (RPL12) Causing Avian Visceral Lymphomatosis and Related Neoplasms. III. Influence of Host Age and Route of Inoculation

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Abstract
Seven experiments were conducted, with 6,200 White Leghorn chickens of inbred line 151, on the disease response of chickens to strain RPL12 virus, to study the influence of age of the chicken at the time of inoculation, the route of inoculation, or other methods of exposure. Chickens inoculated at 1 day of age with moderately large doses of virus died primarily of erythroblastosis, and the sensitivity to this response decreased with the various routes in the following order: intramedullary, intravenous, intraperitoneal, intracerebral, intramuscular, and subcutaneous. The 2 natural routes, oral and nasal, caused a much lower response than any of the parenteral routes, and most of the mortality was due to visceral lymphomatosis. Age of the chicken at the time of inoculation had a profound effect on the magnitude of the response obtained. Sensitivity of chickens to large doses, given intravenously and resulting primarily in erythroblastosis, increased slightly or not at all for the first 2 to 3 weeks of life, then decreased at a uniform rate until the chickens were at least 12 weeks of age. A more rapid decrease in sensitivity with no delay was obtained when large doses were inoculated intraperitoneally. Sensitivity of chickens to small doses, given intravenously and resulting primarily in visceral lymphomatosis, decreased uniformly from the 1st day and at a rate similar to that obtained with large doses given intravenously. Sensitivity of chickens given large doses by the oral and nasal routes, which resulted primarily in visceral lymphomatosis, decreased rapidly during the first 2 to 3 weeks of life, after which the decrease was much slower. Certain RPL12 virus preparations caused a high incidence of osteopetrosis when intravenous inoculations were made at 1 day of age. This response decreased rapidly with an increase in age at inoculation, so that the percent of chickens with osteopetrosis, inoculated at 3 weeks of age, was only one tenth that of chickens inoculated at 1 day of age.