Three outbreaks of colibacillosis have occurred in chicks during the quarantine period after importation to Japan. All three were derived from three different countries without epidemiological relevance. Some birds from each infected flock were examined pathologically and bacteriologically. The characteristic histological finding common to all three cases was severe bacterial meningitis in the central nervous system. Pericarditis, perihepatitis, and omphalitis with bacterial colonies were also observed. The bacterial colonies observed histologically were immunohistochemically positive for Escherichia coli (E. coli) antigens. E. coli was isolated from the organ samples of each outbreak. At least two E. coli isolates were serotyped as O18 and O161, which differed from the popular serotypes in Japan. These results suggest that avian pathogenic E. coli of uncommon serotypes can be imported from outside countries by infected chicks. Colibacillosis should be included in the differential diagnosis when meningitis is histologically observed in chicks.

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