A survey of the presence of a new infectious bronchitis virus designated 4/91 (793B).

On the basis of virus isolation and the demonstration of specific neutralising antibody in sera, infectious bronchitis virus (IBV) 4/91 (commonly called 793B) has been shown to be present in broiler, breeder and layer flocks of chickens in many parts of western Europe and also in Thailand and Mexico. These flocks had all been vaccinated against infectious bronchitis and the need for improved methods to control this new virus, still prevalent at least four years after it was first isolated, is discussed.