Host specific infections
Infections with Salmonella pullorum usually cause very high mortality in young chickens and turkeys within the first 2 – 3 weeks of age. In adult chickens, mortality may be high but frequently there are no clinical signs. The route of infection is oral (via feed or litter) or via the navel/yolk. Also transmission via the egg appears.
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 diarrhoea around the vent. Survivors are small in size and frequently become carriers with localized infection of the ovary. These birds can continue to infect other birds. In mature chickens, chronic infections produce lesions indistinguishable from those of fowl typhoid.
The causal agent of fowl typhoid is Salmonella gallinarum. Like S. pullorum, S. gallinarum is egg-transmitted and produces lesions in chicks and poults. However, there is a much bigger tendency to spread among growing or mature flocks. Mortality in young birds is similar to that seen in S. pullorum infection but may be higher in older birds.
Clinical findings and lesions: Clinical signs and lesions in young birds are similar to those seen with S. pullorum infection. Older birds may have a fever, be pale, dehydrated, and have diarrhoea. Also the liver is swollen, brittle and often bile-stained.
Non-host specific infections
Paratyphoid Salmonellas are non-host specific (e.g. S. enteritidis and S. typhimurium). They are the cause of Salmonella-food poisoning in humans.
Paratyphoid infections can be caused by any one of the many non-host-adapted salmonellae. These salmonellae infect many types of birds, mammals, reptiles, and insects. Paratyphoid infections can be transmitted to humans via contamination of poultry products. S. enteritidis and S. typhimurium are among the most common Salmonella infections in poultry. The prevalence of other species varies widely by geographic location. Transmission usually occurs directly from infected birds, contaminated environments, or infected rodents. Infected birds remain carriers of Salmonella.
Clinical findings and lesions: Although not common, clinical signs are sometimes seen in young birds. Mortality is most often limited to the first few weeks of age. Depression, poor growth, weakness, diarrhoea and dehydration are symptoms of the disease. Lesions may include an enlarged liver with necrosis, unabsorbed yolk sac and enteritis with necrotic lesions in the mucosa. Sometimes there may be no lesions due to acute death caused by septicaemia.
As Salmonella often colonizes in the intestinal tract, this, and its contents, should be cultured. Salmonellae can spread to many tissues including ovary, spleen, liver, yolk sac, heart, heart blood, kidney, gall bladder, joint fluid/pus and the eyes. All of these can be cultured as part of a post mortem examination.
Salmonella can be controlled with the successful combination of several strategies:
Hatching eggs should be clean and disinfected or fumigated.
Day old chicks should come from Salmonella-free breeder flocks.
Salmonella negative feed should be obtained. Feed should be heat-treated or treated with acids, to avoid recontamination after production. Also attention needs to be paid to the transport of feed (e.g. no open trucks to prevent contamination via pigeon-droppings).
Drinking water should come from a clean source and ideally should be chlorinated.
Only essential equipment should be allowed into the poultry house, after acknowledging that there are no Salmonella organisms present.
Rodents, wild birds and beetles can transmit Salmonella.