Severe Escherichia coli O111 septicaemia and polyserositis in hens at the start of lay.

Three very severe episodes of Escherichia coli infection in hens from the same farm, at the beginning of laying, are reported. They were characterized by no clinical signs, but sudden mortality, from 5 to 10%, with severe lesions of septicaemia and fibrinous polyserositis. A Gram-negative bacterium was consistently isolated in pure culture from tissues. Isolates were typed biochemically as E. coli, but they were lactose negative and non-motile. The serotyping tests typed the isolates as somatic group O111. The isolates were sensitive to enrofloxacin, amoxycil and colimycin, and partially sensitive to flumequine, all of which were used for therapy. The disease was reproduced experimentally in both specific pathogen free chickens and commercial layers by intramuscular inoculation of the E. coli, but only in some layers when inoculated by the oro-nasal route. The stress of the onset of lay seemed to be the most probable precipitating cause of the disease.