Studies on selected avian adenoviruses.

A virus isolate, strain B1209, was shown by morphological, physicochemical and biological studies to be an adenovirus. The virus grew and produced plaques in both chicken kidney and chick embryo cell cultures, the higher infective titres were obtained in the former cell system. B1209 also grew to a high titre in embryonated chicken eggs, causing stunting and curling of the embryos. The virus was shown to agglutinate rat RBCs and the effect of various parameters on the reaction were examined. Substances present in the chicken sera, inhibiting the HA activity of the virus with a pattern differing from that of "true" inhibition, were considered to be non-specific inhibitors. B1209 was serologically indistinguishable from chicken embryo lethal orphan (CELO) virus. Adenovirus infection was found to. be widespread in chicken flocks the incidence increasing with age to about 70-80% in birds over 60 week old. In experimentally infected chickens, neutralizing and HI antibodies appeared almost at the same time and followed the same pattern of persistence, while precipitin antibodies were detectable slightly earlier but showed a cyclic appearance in many cases. B1209 and GAL 3 strains induced a generalized infection which was not prevented by maternal antibodies in the latter experiment. No significant difference was found in the susceptibility of the very young chicks and older birds to infection but there was an earlier decline in the faecal virus titre in the latter. A delayed antibody response was evident in young chicks. The pathology of CELO virus infection by its own or in conjunctio with Mycoplasma gallisepticum was studied in a series of experiments, using various routes. Clinical signs in birds infected with virus alone consisted of depression, sneezing, coughing and gasping, This was more severe in adult birds. In gross examination, the most striking lesions were severe hyperaemia and exudation in the lungs, and varying degrees of air sacculitis, produced in aerosol experiments. In histological examinations, these lesions in the lungs corresponded to consolidation and pneumonia, and in the air sacs to exudation, oedema and epithelial hyperplasia. More severe air sacculitis, and also epithelial metaplasia in the air sacs, seen in dual infections, were considered to be the features of the synergistic effect of the virus and mycoplasma. This was also supported by the results of serological tests and mycoplasma isolation. Further studies are needed to elucidate the pathogenicity of the other strains or types of virus, and to relate the experimental data to the disease problems in the field