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, although it may occur in other avian species (eg, guinea fowl, quail, pheasants, sparrows, parrots, canaries, and bullfinches). Infection in mammals is rare, although there have been experimental or natural infections 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 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
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.
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 that are indistinguishable from those of fowl typhoid (see Salmonelloses: 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 USDA administered National Poultry Improvement Program.
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.
Last full review/revision March 2012 by Sherrill Davison, VMD, MS, MBA, DACPV