Swine Salmonellosis

Clinical disease

The salmonellosis of pigs is a general disease which must be clarified by further examinations.

Salmonella can cause disease accompanied by clinical symptoms, which may become a problem that may even threaten the survival of the farm. The more the serovar is adapted to pigs, the more severe are the symptoms. In the septicaemic form of the disease, the bacteria enter the bloodstream of affected animals. The clinical signs are initially similar to those of oedema disease in piglets, but are accompanied by fever. This form affects mainly weaners but also fatteners and breeding animals. Sudden deaths may occur if the disease takes a peracute course. Acute cases are accompanied by purple discolouration of areas such as the pinnae, snout and abdominal wall. Heavy, laboured breathing suggests pulmonary involvement. Mortality can be well in excess of 20 %. In many cases, pregnant sows will abort.

Less adapted serovars usually cause only diarrhoea, mostly yellowish-grey and watery. If the production stage of post-weaners is affected, the clinical signs might be mixed up with Post Weaning Diarrhoea caused by E. coli. The chronic intestinal form is characterized by non-specific pasty or bloody diarrhoea. Other effects are chronic coughing and a higher number of runts.

Salmonella diarrhoea caused by antibiotic treatments of other diseases such as respiratory infections should be highlighted. These diarrhoea occur when animals latently infected with Salmonella are treated with an antibiotic to which the particular Salmonella strain is resistant.

Subclinical disease

In the majority of cases, Salmonella infection in pigs is asymptomatic.

Infections with S. Typhimurium and other serovars occur in most cases as a latent infection in a herd. The bacteria retreat to the intestinal lymph nodes and other organs until stressful situations prompt them to start replicating again and shedding resumes. Latent carriers therefore represent a permanent source of infection. A typical stressful situation is the sorting of pigs before slaughter, the transport to the slaughterhouse, the stay in the lairage and of course the slaughter itself. Studies have shown, that within only a few hours pigs start shedding during their stay in the waiting areas of slaughterhouses.

“A noteworthy, high prevalence of Salmonella in fecal samples (30.5%), rectal swabs (24%) and carcass swabs (9.6%) of slaughter pigs was reported by a United Kingdom study:

In contrast, other EU countries (Finland, Sweden and Norway), with special guarantees concerning Salmonella on pig carcasses (according to Regulation (EC) No 853/2004) reported a lower incidence of Salmonella in pig carcasses samples (0.02%).” (J. Campos et al., Pathogens 2019, 8, 19)

In contrast to poultry production with standardized and harmonized reporting procedures, pig production is missing yet this kind of structures. Countries apply specific national monitoring programs , based either on serology or bacteriology, if any. Additionally only 7 EU member states reported on Salmonella in sampled pig herds in 2017. However, this gives only a very incomplete overview.

In Germany for more than 16 years the Salmonella monitoring, based on the serological examination of blood samples/ meat juice on slaughter pigs, is conducted by QS Qualität und Sicherheit GmbH. Since the findings do not result in any economically relevant sanctions, the graphic shows an increase in the serologic prevalence, rather than an improvement.