Salmonellosis occurs worldwide. The effects of salmonellosis death, fever, diarrhoea, nervous signs. All ages are affected (especially growers / finishers). There is a risk for human health.
- Causes of Salmonellosis >
- Effects of Salmonellosis >
- Diagnosis of Salmonellosis >
- Treatment & Control of Salmonellosis >
Causes of Salmonellosis
Salmonellosis is caused by serovars of Salmonella enterica, a bacterium which grows readily in culture. Antigenic factors present on their cell walls ('O' antigens) and on their flagellae ('H" antigens) are used to name serovars which can be subdivided by phage typing, plasmid profiling, restriction endonuclease analysis and resistance pattern and allow tracing the origin of infections.
S. enterica serovars Typhimurium, Derby, Staintpaul, Infantis, Heidelberg, Typhisuis and Choleraesuis may all occur in pigs. A common serovar is Typhimurium of which Definitive (phage) Type (DT) 104 is multi-antibiotic resistant.
Salmonella infection is oronasal and results in three types of infection:
1) septicaemia which may precede or follow enteritis;
2) enteritis with some degree of local invasion; and
3) colonisation of the intestine or its contents alone.
All may be followed by the persistence of small numbers of organisms in the gut mucosa, mesenteric lymph nodes or tonsils in clinically-normal carrier animals. Choleraesuis is a pig pathogen, infecting pig herds for long periods and causes septicaemia, while Typhimurium causes enteritis with local invasion but can cause septicaemia.
Infection is followed by the development of systemic antibodies from day 7 post-infection, peaking at 28 days post-infection and declining but still demonstrable 80 days post-infection.
Effects of Salmonellosis
Pigs are affected by invasive serovars of S. enterica (such as Choleraesuis) between weaning and 3 or 4 months of age, may be depressed, dull with weakness and even nervous signs. They often bury themselves in straw and show mauve-red cyanosis of the ears, limbs and the centre of the back., are fevered (40.6-41.7°C, 105-107°F) and die within 24-48 hours.
In the acute enteric form in younger pigs, animals pass a thin watery, yellowish diarrhoea and may be dull and fevered (40.6-41.7°C, 105-107°F). Pneumonia, weakness and nervous signs such as paralysis and tremor may occur. In severely affected cases, skin discolouration is present.
Recovered pigs may slough affected ears or tails. In the chronic enteric form affected pigs appear severely emaciated and may have intermittent fever. There is persistent diarrhoea. Typhimurium is less invasive and rarely causes death except in sucking or recently-weaned pigs.
Diarrhoea is the most prominent clinical sign although fever may occur. The diarrhoea is initially brownish (or creamy in sucking piglets) and rarely contains blood. It may contain necrotic material and sometimes has a characteristic smell.
Chronically affected animals become stunted and some develop rectal stricture. Some recovered pigs may have necrotic ear tips.
Diagnosis of Salmonellosis
Salmonellosis should be suspected where there is a history of infection on a farm and where pigs die of acute septicaemia. The presence of fever and diarrhoea suggests salmonellosis and necrotic material in the faeces also suggests salmonellosis. The isolation of the organism from the faeces in profuse culture confirms the diagnosis.
At post-mortem examination of the septicaemic form, the carcase is in good condition, there are multiple haemorrhages, enlarged haemorrhagic lymph nodes and an enlarged spleen. In the enteric form, the presence of small intestinal inflammation, enlarged mesenteric lymph nodes, necrosis of Payer's patches and typhlocolitis or rectal stricture may suggest salmonellosis.
Confirmation is by isolation of salmonellae from all parts of the carcase, especially spleen, lung, intestine and mesenteric lymph node. Small numbers of S. enterica in faeces, slurry, caecal contents, tonsil or lymph nodes suggest carriage rather than active salmonellosis.
Past infection may be confirmed by identifying serum antibody. ELISA tests using 'O' antigens may be carried out on serum and on meat juices. The Danish meat juice/serum ELISA is designed to detect a wide range of serovars using 'O' factors 1, 4, 5, 6, 7 and 12 in the LPS antigen. It is a herd test and detects exposed pigs at slaughter.
Treatment & Control of Salmonellosis
Affected animals may be injected with tetracyclines, streptomycin, apramycin, neomycin, ampicillin, amoxicillin, spectinomycin, trimethoprim:sulphonamide, enrofloxacin, danofloxacin or ceftiofur.
Tetracyclines; streptomycin; neomycin; apramycin ampicillin; amoxicillin, trimethoprim: sulphonamide, enterofloxacin, danofloxacin can be used in water for 3-5 days or until 2 days after the cessation of clinical signs.
Feed medication can be used, but inappetent animals must be treated individually. Disinfection should accompany courses of treatment. Failure to respond to antimicrobial treatment may suggest that the organism responsible is resistant to the antimicrobial used.
Isolation, the use of salmonella-free stock, the use of clean, heat-treated feed and water, rodent and fly control and netting against birds may all help prevent the introduction of salmonellosis to a farm.
Control on infected farms may require medication when disease is expected and should be accompanied by disinfection. All-in, all-out housing, couple with isolation of batches by disinfectant barriers and thorough cleaning and disinfection between batches may reduce the spread.
Vaccination is possible. Live attenuated Choleraesuis and Typhimurium vaccines have been described. Killed vaccines are also protective. Eradication of the organism has been achieved by complete depopulation, or by treatment of a whole herd, coupled with cleaning, disinfection and a 3 week empty period.
