Swollen head syndrome associated with E. coli and infectious bronchitis virus in the Central Valley of California.

A commercial broiler flock in the Central Valley of California experienced a sudden increase in mortality due to heavy culling. Clinical signs included a snick, swollen heads and severe depression. Necropsy and histology revealed tracheitis, rhinitis, facial cellulitis, blepharitis, episcleritis, otitis media and caseous exudate within the air spaces of cranial bones. Escherichia coli serotype O78 was isolated from all lesions. Infectious bronchitis virus (Massachusetts serotype) was isolated from trachea/nasal cavity tissue pool. Adenovirus group 1 was isolated from trachea/nasal cavity and caecal tonsil tissue pools. Serum samples were positive for infectious bronchitis using ELISA and haemagglutination inhibition tests, but negative for turkey rhinotracheitis by an ELISA using the British antigen. This case suggests that swollen head syndrome can be associated with viruses other than pneumovirus.