Salmonellosis

Presentation depends on serovar and species. Chicks and poults under a week old show depression, ruffled feathers, huddling, white diarrhoea and pasted vents. Calves with S. Dublin, mainly at 2-6 weeks old, are dull, feverish and anorexic with bloody, mucoid diarrhoea, sometimes pneumonia or gangrene of the extremities, and dehydrate fast; S. Dublin also causes abortion in cows. Pigs with S. Choleraesuis may die suddenly or show fever, cough, laboured breathing and bluish extremities. Adults with enteric disease have fever, then profuse watery diarrhoea with blood, mucus or fibrin, and falling milk yield. At necropsy the lower ileum, caecum and colon have fibrinonecrotic, haemorrhagic mucosa.

Salmonellosis is caused by Gram-negative bacteria of the genus Salmonella, almost always serovars of S. enterica subspecies enterica; more than 2600 serovars exist. Most infect many species, but some are host-adapted (S. Dublin in cattle, S. Choleraesuis in pigs) or host-specific (S. Abortusovis in sheep, S. Gallinarum in poultry), and these tend to cause septicaemia. Swallowed bacteria attach to the gut lining, trigger membrane ruffling that pulls them into enterocytes, and multiply there and in lymphoid tissue, provoking intense inflammation that destroys the mucosa of the lower ileum, caecum and colon. If they survive inside macrophages and reach the blood, they can settle in the meninges, pregnant uterus, joints and limb extremities.

All domestic animal species can be affected, and young, pregnant and lactating animals are most susceptible. The disease occurs in every country, and non-typhoidal infections are most common where pigs, calves and poultry are reared intensively. Transmission is mainly faecal-oral through contaminated feed, water and environment; rodents and wild birds help spread it. Many animals, especially pigs and poultry, carry and shed the bacteria continuously or intermittently without illness, spreading it within and between herds and contaminating meat, eggs and milk. Transport, crowding, feed deprivation and calving increase risk. Salmonellosis is one of the most common and costly food-borne zoonoses, and farm workers and veterinarians can also be infected by direct contact.

In young birds, Pullorum disease, fowl typhoid and E. coli septicaemia look alike, and Salmonella arthritis in birds can be mistaken for other synovitis. Septicaemic disease in pigs may mimic classical swine fever (hog cholera). In calves and weaned pigs, colibacillosis resembles it but strikes younger animals, and acute enteric salmonellosis in calves resembles coccidiosis. Ovine abortion from S. Abortusovis must be separated from Chlamydia abortus, Campylobacter, Coxiella burnetii and Brucella ovis.

Small intestine (ileum), caecum, colon, intestinal lymphoid tissue, blood, lungs, uterus and fetus, joints, meninges, limb extremities, gall bladder

Buy stock from salmonella-free sources and isolate newcomers; protect feed and water from rodents and birds; clean maternity areas and disinfect buildings; reduce stress; live or inactivated vaccines exist for some species and serovars.

Septicaemic neonates can die within 24-48 hours and outbreak mortality may reach 100% (MSD); calves die quickly without timely treatment. Clinical cure is achievable, but bacteriological cure is difficult and survivors may stay carriers.