Type-8 avian adenoviruses were isolated from chickens in a commerical flock suffering an outbreak of inclusion body hepatitis. Serum-neutralizing titer to this type, but not to 7 other types of avian adenovirus, was more than 4 times as high in convalescing chickens as in chickens from the flock bled 2 weeks previously, during the disease outbreak. A disease similar to that in the commercial flock and to inclusion body hepatitis as described in the literature was produced by intra-abdominal inoculation of a type-8 isolant, AMG 5 (2a), into 1-day-old specific-pathogen-free chicks. Pathologic features of the disease included necrotizing hepatitis, pancreatitis, and severe lymphoid depletion of the bursa of Fabricius, thymus, and spleen. It was concluded that type-8 avian adenoviruses were involved in the etiology of the naturally occurring outbreak of inclusion body hepatitis.

A microtiter cell-culture method was developed and used to titrate virus isolates for characterization. Virus dilutions and chicken kidney cell suspensions were dispensed into the wells of disposable microculture plates, with infectivity endpoints being determined microscopically on the fifth or sixth day, or by reading crystal-violet-stained monolayers on day 6. With this method, 37 candidate avian adenoviruses isolated from diagnostic accessions were characterized as avian adenoviruses (AAV). The criteria used for characterization were production of round-cell cytopathic effect, resistance to chloroform treatment, inhibition by 5-bromodeoxyuridine, and the presence of an antigen showing identity with a known AAV by precipitation in agar gel. Statistical anlaysis of eight replicate titrations of three AAV indicated that the titration method was highly reproducible. Use of the microculture method for titrations gave substantial savings in indicator cells, media, incubator space, culture dishes, and time.

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