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Twenty flocks of web-footed birds (Pekin and Muscovy ducks and geese) and eight flocks of chickens
raised under intensive management were examined for the presence of carriers of Pasteurella
multocida. Five hundred and seventy-eight web-footed birds and 240 chickens from healthy flocks, as
well as from flocks affected by fowl cholera, were investigated. A total of 135 isolates (80 from healthy
flocks and 55 from flocks affected by fowl cholera) were obtained from the pharyngeal and cloacal
mucosae after mouse passage (134 isolates) and culture in selective medium (one isolate). Thirty-five
percent (7/20) of the flocks of web-footed birds and 38% (3/8) of chicken flocks had birds carrying P.
multocida in the pharynx and/or cloaca. Birds from flocks affected by fowl cholera carried P. multocida
at a significantly higher prevalence in the mucosa of the cloaca (P < 0.001) compared with the pharynx,
while the opposite was observed in birds from healthy flocks. Extended phenotypic characterization
confirmed the presence of P. multocida ssp. multocida, P. multocida ssp. septica and P. multocida ssp.
gallicida in the flocks examined. P. multocida ssp. gallicida was exclusively isolated from Pekin ducks,
while P. multocida ssp. multocida and P. multocida ssp. septica were obtained from chickens as well as
web-footed birds. Each flock was shown to be infected by a single phenotypic clone, but some clones
were found in more than one flock. A different clone was found in each of four outbreaks of fowl
cholera on one of the farms in the preceding 2 years. Two genotypic and phenotypic clones each of P.
multocida ssp. multocida and P. multocida ssp. septica were found. This observation indicated that
outbreaks are usually clonal and that elimination of P. multocida from infected farms is possible. The
results suggest that healthy poultry, in addition to convalescent carriers, may also be carriers of P.
multocida. However, the virulence of P. multocida isolates and resistance of carriers to clinical infection
needs to be examined. This is the first report of isolation of P. multocida from the cloacal mucosa of
apparently healthy domestic poultry. Sampling of the cloaca appeared to be more sensitive for
detecting carriers of P. multocida. Although selective medium was used only to a limited extent, the
results suggested that mouse inoculation was a more efficient method of isolating P. multocida from
poultry than the use of selective media. |
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