Further studies on vertical transmission and persistence of Salmonella enterica serovar Enteritidis phage type 4 in chickens

One-week-old commercial layers were infected orally with 10(8) colony formi ng units of Salmonella enterica serovar Enteritidis phage type 4. No mortal ity was observed. The inoculated organism was isolated in decreasing viable numbers from a number of tissues, particularly the spleen, liver and caeca . Organisms present in the spleen were primarily localized within macrophag es. No Salmonella Enteritidis organisms were isolated between 10 and 24 wee ks of age, when the experiment was terminated after several weeks of lay. W hen two groups of adult hens, housed with males, were infected, contaminate d eggs were found within 2 weeks of infection in one of the experiments onl y. Progeny hatched from these eggs showed no mortality unless they were inf ected artificially with the S. Enteritidis strain. In this case, the percen tage mortality fell as the hatches progressed, indicating increasing immuni ty to infection. The faecal excretion of the inoculated phage type 4 strain by infected but healthy progeny was followed. Although most birds ceased t o excrete by 11 to 12 weeks of age, a small number of the birds continued t o excrete until they themselves came into lay. The small numbers of birds i n which this occurred indicates that tolerance to infection does not occur readily following infection of hens laying fertile eggs or in progeny birds infected before or within hours of hatching. Birds infected when they were less than 24 h old remained persistently infected until they were well int o lay. However, control birds infected when 1 week old, on this occasion, s howed a high level of excretion until the birds began to lay at 18 weeks. I nbred lines of chickens showing differences in their susceptibility to syst emic salmonellosis did not show significant differences in the extent to wh ich S. Enteritidis localized in the organs of the reproductive tract or in the number of infected eggs produced.