Pullorum disease

Chicks and poults from infected eggs sicken and die within the first weeks: they huddle near heat, are weak, eat poorly, grow slowly, chirp shrilly and pass chalky white droppings that paste the vent. Deaths peak at two to three weeks of age. Older birds may show no signs or only reduced egg production and hatchability. At necropsy newly hatched chicks have peritonitis, general congestion and an inflamed unabsorbed yolk sac; longer infections produce necrotic caecal cores and small necrotic foci in liver, lungs and other organs. Adult carriers may have misshapen, discoloured, shrunken ovarian follicles on fibrous stalks.

Pullorum disease is caused by Salmonella enterica subspecies enterica serovar Gallinarum biovar Pullorum, a bacterium adapted to birds. Unlike most salmonellae it is non-flagellated and non-motile; loss of flagellar genes helps it avoid immune detection, and it colonises the gut poorly. After invasion, free bacteria and infected phagocytes move to lymphoid tissue, and the organism survives and multiplies inside macrophages of the liver and spleen, producing septicaemia in young chicks. In birds that survive it persists mainly in the ovary and oviduct, so carrier hens infect their eggs and the chicks that hatch from them.

Chickens are the natural host, but turkeys, quail, guinea fowl, pheasants, ducks, pigeons and other birds can be infected. The disease is widespread in developing countries and has been eradicated from commercial poultry in Western Europe, the United States, Canada, Australia and Japan, though it persists in backyard flocks, game birds and wild birds, which can carry it. Transmission through the egg is a major route; within flocks it also spreads by contact, cannibalism, wounds and faecal contamination of feed, water and litter. Antimicrobial resistance in these strains is increasing. It is a WOAH-listed disease, reportable in the United States, and carries minimal zoonotic risk.

Fowl typhoid, caused by biovar Gallinarum, affects mainly growing and adult birds and gives an enlarged, friable liver with a coppery-bronze sheen and dark bone marrow. Other causes of septicaemia produce lesions that are not clearly distinct. Confirmation therefore requires isolation and serological identification of the organism; flock agglutination tests show infection but are unreliable in turkeys and ducks.

Liver, spleen, yolk sac, caeca, lungs, peritoneum, ovary and oviduct

Source chicks and hatching eggs from tested pullorum-free breeder flocks (NPIP in the US), blood-test breeding stock and confirm reactors by culture, and apply strict hatchery and farm biosecurity.

Losses concentrate in chicks aged 2-3 weeks; older birds are often mildly affected. Drugs may cut deaths but do not eliminate infection, recovered birds tend to remain carriers, and flock treatment is not considered feasible.

Game birds