Role of route of exposure, age, sex, and type of chicken on the pathogenicity of avian reovirus strain 81-176.

Chickens were evaluated by age, sex, and type for susceptibility to reovirus strain 81-176 inoculated subcutaneously. Chicks were most susceptible to the lethal effects of reovirus infection at hatching, after which resistance increased rapidly. By 1 week of age, mortality was negligible, but chicks were still susceptible to the less lethal effects of the virus. Mortality rates of males and females were equal. Leghorn and broiler-type chicks did not differ appreciably in their response to viral inoculation. An effort was made to find a more "natural" means of exposure to reovirus than parenteral inoculation. Neither oral nor aerosol exposure was as effective as subcutaneous inoculation. Attempts to transmit reovirus to susceptible hatching chicks, starting when they were in ovo (19 days of incubation), also failed. Decreased weight gain proved to be a valid criterion for judging reovirus infection. Reovirus infection lowered the mean values of body weights, and the standard deviations were substantially greater, indicating an unevenness in size of the affected chickens.