Fowl typhoid

Flocks show increased mortality, mainly in growing and laying birds. Birds are depressed, eat less, lose weight and are ruffled and dehydrated, with watery to mucoid yellowish diarrhoea pasting the vent, laboured breathing, and falling egg production, fertility and hatchability. Longer survivors become anaemic with pale, shrunken combs and wattles. At necropsy the liver is enlarged, dark and friable with a coppery bronze sheen that may appear only after air exposure, the bone marrow is dark brown and catarrhal enteritis is common; chronic cases show pericarditis and focal necrosis.

Fowl typhoid is caused by Salmonella enterica serovar Gallinarum biovar Gallinarum, a non-motile, non-flagellated Gram-negative rod of serogroup D that is adapted to birds. Birds are usually infected by mouth; the organism reaches intestinal epithelium and lymphoid tissue and, lacking flagella, enters without provoking much inflammation. Disease progression depends on its ability to survive and multiply inside macrophages of the liver and spleen, producing an acute septicaemia. As illness continues the bird becomes anaemic and the liver enlarges and turns dark and friable. The organism colonises the gut poorly, and in carrier birds it is found mostly in the liver, spleen and reproductive tract.

Chickens and turkeys are the main hosts; pheasants, quail, guinea fowl and other game birds are affected, with occasional cases in ducks, pigeons and psittacines. Growing and adult birds suffer most, and brown-egg layers are more susceptible than white-egg layers. Spread is oral through feed, water and cannibalism, and via the respiratory tract; red mites carry the organism and help it persist in houses, and rodents, wild birds and insects act as vectors. Egg transmission is less clearly important than in pullorum disease. Fowl typhoid is common in parts of Africa, Asia and Central and South America and has been eradicated from commercial flocks in many industrialised countries. Zoonotic risk is minimal.

Pullorum disease, caused by the other biovar, mainly kills chicks around 2-3 weeks old, spreads chiefly through eggs, and may show white-spot liver and spleen lesions not seen with fowl typhoid. Other septicaemias of poultry can look the same, so lesions are never pathognomonic; diagnosis requires isolating and serotyping the organism, and whole-blood plate agglutination is a flock screen that is unreliable in turkeys and ducks.

Liver, spleen, bone marrow, intestines, heart and pericardium, ovary and oviduct, blood

Stock and eggs from tested-free sources, strict biosecurity, control of rodents, wild birds and red mites; test and remove reactors or depopulate and disinfect. The live 9R vaccine reduces losses but not infection, and protection is short-lived.

Mortality ranges from under 1% to 100% depending on age, breed, strain, management and concurrent infection. Antibiotics can treat clinical cases but do not clear the flock, and multidrug resistance is increasing.