Epidemiology of Fowl Cholera in Free Range Broilers

Fowl cholera, caused by Pasteurella multocida, remains a major problem of poultry worldwide. In the current report, we describe an outbreak in free range organic broilers. In addition to culturing samples from dead broilers, we attempted to isolate P. multocida from feral cats trapped on the farm. The isolates were identified by PCR as P. multocida and then serotyped using the Heddleston scheme and genotyped using both a multilocus sequence typing (MLST) method and an enterobacterial repetitive intergenic consensus (ERIC)-PCR method. A total of 123 isolates of P. multocida were recovered from 12 broilers. All 123 isolates were examined by ERIC-PCR, and only one pattern was identified. A subset of seven broiler isolates were examined by MLST and all were typed as sequence type (ST) 20. A total of 28 isolates of P. multocida were recovered from 17 cats, and five ERIC-PCR genotypes were identified, with one genotype (E-1, shared by 19 isolates) being the same as the ERIC-PCR pattern associated with the broilers. One representative cat strain for each ERIC-PCR pattern was subjected to MLST. The cat isolate with the same ERIC-PCR genotype as the broiler isolates was confirmed as having the same MLST result, ST 20. The other five cat ERIC-PCR patterns were allocated to four STs: E-2 and E-5 to ST 265, E-3 to ST 30, E-4 to ST 20, and E-6 to ST 264. Both genotyping methods confirmed that isolates of P. multocida were common between the feral cats and the chickens. It was not clear whether the strain was transmitted from the cats to the chicken or whether the cats obtained the strain preying on chicken. The study has shown that cats can harbor P. multocida strains with the same genotype found in chickens affected with fowl cholera.