Etiology and Transmission
Infections with Salmonella Pullorum usually cause very high mortality (potentially approaching 100%) in young chickens and turkeys within the first 2–3 wk of age. In adult chickens, mortality may be high but frequently there are no clinical signs. Pullorum disease was once common but has been eradicated from most commercial chicken stock in the USA, although it may be seen in other avian species (eg, guinea fowl, quail, pheasants, sparrows, parrots, canaries, and bullfinches) and in small backyard or hobby flocks. Infection in mammals is rare, although experimental or natural infections have been reported (chimpanzees, rabbits, guinea pigs, chinchillas, pigs, kittens, foxes, dogs, swine, mink, cows, and wild rats).
Transmission can be vertical (transovarian) but also occurs via direct or indirect contact with infected birds (respiratory or fecal) or contaminated feed, water, or litter. Infection transmitted via egg or hatchery contamination usually results in death during the first few days of life up to 2–3 wk of age. Transmission between farms is due to poor biosecurity.
Clinical Findings and Lesions
The disease may be seen in all age groups, but birds <4 wk old are most commonly affected. Birds may die in the hatchery shortly after hatching. Affected birds huddle near a heat source, are anorectic, appear weak, and have whitish fecal pasting around the vent (diarrhea). Survivors are small in size and frequently become asymptomatic carriers with localized infection of the ovary. Some of the eggs laid by such hens hatch and produce infected progeny.
There may be no lesions due to an acute septicemia and death. Lesions in young birds usually include unabsorbed yolk sacs and classic gray nodules in the liver, spleen, lungs, heart, gizzard, and intestine. Firm, cheesy material in the ceca (cecal cores) and raised plaques in the mucosa of the lower intestine are sometimes seen. Occasionally, synovitis is prominent. Adult carriers usually have no gross lesions but may have nodular pericarditis; fibrinous peritonitis; or hemorrhagic, atrophic, regressing ovarian follicles with caseous contents. In mature chickens, chronic infections produce lesions indistinguishable from those of fowl typhoid (see Fowl Typhoid).
Lesions may be highly suggestive, but diagnosis should be confirmed by isolation, identification, and serotyping of S Pullorum. Infections in mature birds can be identified by serologic tests, followed by necropsy evaluation complemented by microbiologic culture and typing for confirmation. Official testing recommendations for flocks in the USA are outlined in the National Poultry Improvement Plan.
Treatment and Control
Treatment of infected flocks to alleviate the perpetuation of the carrier state is not recommended. Control is based on routine serologic testing of breeding stock to assure freedom from infection. In addition, management and biosecurity measures should be taken to reduce the introduction of S Pullorum from feed, water, wild birds, rodents, insects, or people. Birds should be purchased from sources free of S Pullorum.
Last full review/revision August 2013 by Sherrill Davison, VMD, MS, MBA, DACPV