Salmonellosis (salmonellosis)

Description

Salmonella is widely extended in humans and animals. From all the Salmonella serotypes (more than 2000), the ones causing clinical disease in pigs are Salmonella choleraesuis and Salmonella typhimurium. S. choleraesuis is the specific serotype adapted to swine, and can produce a severe disease widespread in sows (fever, depression, septicemia, pneumonia, meningitis, arthritis and diarrhea), but does not affect humans. The most commonly found serotype in pigs, however, is Salmonella typhimurium which sometimes is associated with diarrhea in young pigs, and is a common source of food intoxication in humans. Pigs can be subclinical carriers of S. choleraesuis for long periods of time because the organism survives in the mesenteric lymph nodes, located in the intestine. Many of these carriers do not excrete the bacteria in feces, unless they are under stressing conditions. Some pigs might excrete the organism in feces in a continuous or intermittent way. The disease depends on the strain and the dosage, meaning there is a need for a relatively high number of organisms to produce clinical signs.

Salmonella might occur at any age, but is more frequent in growing pigs 8 weeks or older. The salmonella present in the pig’s gut can contaminate the carcass during slaughter, which is a potential risk for human health.
 

Symptoms

Sows

Clinical signs for Salmonella choleraesuis and occasionally Salmonella typhimurium may include the combination of any of the following:

• High temperature.
• Depression.
• Loss of appetite
• Ears, nose and tail congestion.
• Pneumonia.
• Coughing.
• Nervous signs (rare).
• Smelly diarrhea, which sometimes can have blood and mucus.
• Might die in the acute phase of the disease.

Lactating piglets

• The disease is not frequent in piglets due to the passive immunity of colostrum.

Weaners and growers

• Same clinical signs than sows.

 

Causes / contributing factors

• Bad hygiene.
• Crowding.
• Stress produced when moving and mixing animals.
• Barns used continuously.
• Contaminated boots and clothes.
• Mechanical transmission through feces and movement of contaminated material.
• Worms and flies.
• Feed contamination made by birds, rats and mice.
• Contamination of feed ingredients (especially animal fat). 

 

Diagnosis 

Post mortem lesions produced by Salmonella are quite typical, particularly the generalized pneumonia, the appearance of the small and large intestine mucosa, congested spleen and tiny multiple hemorrhages. However, to make a specific diagnosis, it is necessary to send to the laboratory fresh feces samples of non-treated pigs, or whenever possible, a non-treated pig (death or alive). Blood culture can also been performed. It is critical to identify the Salmonella specific strain to assess its importance.

Severe salmonella infection can be present on its own, but also can take place at the same time than classical swine fever, in countries where it is present. In those countries, it is important to make sure through serological tests and in the lab, that classical swine fever is not the main cause. (NOTE: classical swine fever normally also affects sows and piglets, and produces mummified litters and abrtions).

 

Control / Prevention

• Usually feed and water must be medicated and animals must be injected in order to reduce the infection levels.
• Some veterinarians do not agree on treating Salmonella, and only improve hygiene and decrease animal density.
• Preventive or strategic medication of feed and water can be effective. Products used depend on bacterial sensibility.
• Severity of clinical Salmonella depends on the dosage. Thus, the general objective is to obtain Salmonella levels in the environment lower than the necessary levels to produce disease. The second objective is to reduce infection transmission.
• Remember Salmonella can cause disease in humans by food intoxication. This has two implications for the producer: first, the producer must be sure all staff adopt a high personal hygiene level to avoid infection. Second, it is important that meat producers show a public image of safety and that people do not relate them with infectious outbreaks in humans. Thus, it is of paramount importance to have Salmonella under strict control.
• There are very effective live vaccines that can be used in breeding and growing/finishing areas.
• S. choleraesuis vaccines seem to give adequate protection against S. typhimurium.

Related articles

Home

Health Article

Laboratory diagnostics: Salmonella

A. Ramirez

What laboratory diagnostic methods can I use to diagnose salmonellosis? Which one should I choose according to the situation? How do I interpret the results?

Atlas of pathology