Molecular epidemiology of two fowl cholera outbreaks on a free-range Chicken layer farm

Two outbreaks of fowl cholera on a multi-age free range egg farm were investigated. The outbreaks occurred in 1994 and 2002. A total of 22 strains of P. multocida were available for study – 11 from the 1994 outbreak and 11 from the 2002 outbreak. Lesions typical of acute fowl cholera were seen in the 1994 outbreak, whereas both acute and chronic FC occurred in the 2002 outbreak. The isolates were examined in an extended phenotypic typing methodology, by a P. multocida-specific PCR, by the Heddleston somatic serotyping scheme and by restriction endonuclease analysis (REA) typing using the enzyme HpaII. All 22 strains had the same phenotypic properties, all were confirmed as P. multocida by PCR, all were Hedddleston serovar 4, and all had the same REA pattern. Our results indicate that these two outbreaks were caused by the same clone of P. multocida – despite the eight year time period between the outbreaks