Pathogenesis of Salmonella enteritidis phage type four after experimental infection of young chickens.

White leghorn specific-pathogen-free chickens were inoculated orally with Salmonella enteritidis phage type 4 at the age of one day (group 1) and four weeks (group 2). From 3 h until 4 weeks post inoculation (pi), birds were sacrificed. Gross lesions were recorded and different sites of the intestine and visceral organs were collected for bacteriological and histopathological examination. Clinical disease and mortality were only observed in group 1. Mortality was 8%. The birds were depressed, had diarrhoea and an indurated yolk sac. Infection of the liver and the heart was present within 12 h pi in both groups. The percentage of infected organs was very high and similar in both groups during the first week pi. Thereafter the isolation rate of Salmonella was declining faster in group 2. The crop, the proventriculus, the lower intestinal tract and the bursa of Fabricius were the predilective sites of isolation in both groups. Most prevalent lesions were serous typhlitis, omphalitis and polyserositis. Histopathology revealed inflammation in the intestines and visceral organs. In some birds granulomatous nodules were present in the caeca. Antibodies were detected from 18 and 5 days pi in group 1 and 2, respectively. Granulomatous nodules were typical of infection with this strain of S. enteritidis phage type 4. These granulomatous nodules together with the retained yolk sac possibly are a source of Salmonella organisms that may account for intermittent faecal shedding by carrier birds.