Fowl cholera

Often the first sign is finding dead birds. Sick birds show fever, anorexia, depression, mucus from the mouth, diarrhoea, ruffled feathers, faster breathing, fewer and smaller eggs, and a purplish comb and wattles. Chronic cases have swollen wattles, joints, foot pads and tendon sheaths, with conjunctivitis or middle-ear and meningeal infection. At necropsy acute cases show congested organs with serosal haemorrhages, enlarged liver and spleen with many small necrotic foci, pneumonia, mild ascites and pericardial oedema; chronic lesions contain caseous exudate.

Fowl cholera, or avian pasteurellosis, is caused by Pasteurella multocida, a small Gram-negative coccobacillus that shows bipolar staining. It can live as a commensal in the respiratory tract of birds and cause disease when birds are stressed or kept in poor conditions. Its polysaccharide capsule is a critical virulence factor that helps it evade host defences, and its lipopolysaccharide is a primary stimulator of the host inflammatory response. In acute and peracute disease the bacteria multiply rapidly in the liver and spleen, causing massive bacteraemia and often fatal septicaemia. Birds surviving the acute stage, or infected with low-virulence strains, develop chronic localised infections, mainly of the lungs and musculoskeletal tissues.

All bird species are susceptible, with turkeys possibly the most severely affected; chickens, ducks, geese, game birds and wild birds all suffer outbreaks, and the disease occurs worldwide. Infected birds shed bacteria in secretions from the mouth, nose and eyes that contaminate feed and water, and wild birds, rodents and cats can act as carriers. Stress, poor health and unfavourable conditions trigger disease. Sources disagree on the age at risk: WOAH describes birds older than 16 weeks as primarily affected, a University of Kentucky extension article says birds older than six weeks, and an Ethiopian study cites 40-60% mortality in newly hatched chicks. Avian isolates are not considered zoonotic.

In chickens, salmonellosis, colibacillosis and listeriosis; in turkeys, pseudotuberculosis, erysipelas and chlamydiosis can produce similar signs and lesions. Differentiation rests on isolating P. multocida, which grows readily, often in pure culture, from liver, spleen, lung, bone marrow or heart blood, or on validated PCR directly on tissue; many bipolar-staining bacteria in blood, liver or spleen smears support a presumptive diagnosis.

Blood, liver, spleen, lungs and air sacs, heart and pericardium, joints and tendon sheaths, foot pads, wattles, conjunctiva, middle ear, meninges

Thorough sanitation, rodent control and strict biosecurity. Killed bacterins protect only against strains with matching LPS; live vaccines protect more broadly but may cause pneumonitis or arthritis. Vaccinate mainly where the disease is established.

Peracute disease is one of the most virulent in poultry, with high morbidity and mortality. Antibiotics can treat it, but P. multocida is growing resistant to many drugs. Survivors may carry chronic localised infection.

Game birds · Wild birds