Identification and Epizootiology of Infectious Bronchitis in a Closed Flock

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Abstract
A strain of infectious bronchitis (IB) was isolated from chickens with respira-tory symptoms at the US Regional Poultry Research Laboratory. The virus was identified as IB on symptoms, histopathology, lesions in embryos and lack of lesions on the chorioallantoic membrane, hemagglutination with trypsin-modified virus, and lack of Newcastle disease virus hemagglutination inhibition. Serum-virus neutralization tests conducted in embryos indicated it to be related to the Iowa 97 strain of Hofstad. A flock study suggests that the virus has been maintained in the unisolated breeding stock as an inapparent infection. Periodically there is a break in the quarantine, and the disease occurs in more mature birds in the isolated area.