THE EPIDEMIOLOGY OF FOWL CHOLERA : V. FURTHER FIELD OBSERVATIONS OF THE SPONTANEOUS DISEASE

An investigation of endemic fowl cholera, the common form of the disease in this locality, has been made at a poultry farm in Belle Meade, N. J. The focus or reservoir of P. avicida proved to be the healthy pullets which had become carriers the previous year and which were selected as the breeding stock for the ensuing season. From these carriers, the organisms spread and gave rise during the winter months to the various forms of infection, including the carrier state, localized upper respiratory disease, and typical cholera. Strains of P. avicida were in general very similar and of the "blue" colony type. They were all of the same low degree of virulence; no differences were demonstrable between a) "carrier" and "autopsy" strains, b) strains where the infection was spreading and severe, and strains where disease was rare, and c) "autumn" and "winter" strains. In general, a relatively high carrier rate was accompanied by a high mortality rate, although in one instance, a community with high carrier incidence plus a probable high degree of host resistance suffered but little fatal infection. An attempt was made to reduce the amount of cholera by the removal of carriers. The results of this measure indicate that such a procedure is both effective and practical.