Comparative pathogenesis of a subtype A with a subtype B avian pneumovirusin turkeys

This paper describes a study in which the pathogenesis of avian pneumovirus strains, isolated in Belgium, and belonging to the two subtypes A and B, w ere compared in 2-week-old turkeys. After oculonasal inoculation, animals w ere either observed for clinical signs or killed for pathological and virol ogical examination. Virus titration and immunofluorescence were performed o n the conjunctivae, turbinates, sinuses, upper and lower part of the trache a, lungs and air sacs, No differences were seen between the two subtypes co ncerning respiratory signs, or macroscopic and microscopic lesions in the r espiratory tract. Slight variations were found in site and extent of virus replication. First, only subtype A was able to invade the lower parts of th e respiratory tract (bronchi), whereas viral antigens were not detected in the lungs with subtype B, Secondly, the subtype A strain infected two times more epithelial cells at all levels of the upper respiratory tract compare d to subtype B, Thirdly, the amount of virus produced at different sites al ong the respiratory tract was lower in subtype B-inoculated turkeys than in subtype A-inoculated ones.