Yersinia are gram-negative, rod-shaped, facultative anaerobic bacteria belonging to the group of Enterobacteriaceae. Currently, 17 species are differentiated, including Yersinia (Y.) pestis, Y. enterocolitica and Y. pseudotuberculosis which are of particular medical relevance. Among the seven known Y. enterocolitica biovars (1A, 1B, 2-5) the biovar/serotype combinations (1B/O:8; 2/O:5,27; 2/O:9; 3/O:3; 4/O:3; 5/) are responsible for most human Yersinia Enteritis cases in Europe; the majority belonging to biovars 4 (serotype O:3) and 2 (serotype O:9). Human infections are usually caused by the consumption of contaminated food products, such as pork (ground meat, uncooked sausage) and raw milk.
The highest annual numbers (incidences) of Y. enterocolitica infections in Germany are reported from the eastern federal states Thuringia, Saxony, and Saxony Anhalt, the lowest case numbers are seen in Baden-Württemberg and Bavaria. After oral ingestion of the pathogen, patients develop acute enteritis or enterocolitis after an incubation period of four to seven days. The direct and indirect detection of Y. enterocolitica in association with acute human infection is notifiable pursuant to §7 IfSG (German Infection Protection Act).
Juvenile dogs, just like children seem to be particularly susceptible to Y. enterocolitica infections. The clinical picture is characterised by diarrhoea, increased frequency of bowel movements, bloody and mucous stool, tenesmus (painful straining to defecate), as well as lethargy and anorexia. Occasionally, hepatitis may occur. In most cases, dogs become infected by ingesting raw pork meat and can excrete the pathogen for up to three weeks.
Y. enterocolitica (biovar 1A, 2- 5 /serotype O:3, O:5, O:5,27, O:8) is regularly isolated from canine faecal samples, the most common biovar/serotype combination is 4/O:3. Data on the frequency of Y. enterocolitica transmission between humans, dogs, and cats are limited; however identical serotypes have been found in all three species. It is unknown whether the infections are caused by contact with animals or by a common source of infection. However, due to the faecal-oral transmission route the likelihood of zoonotic transmission is high; as seen with other pathogens. Children, elderly persons, as well as immunosuppressed and convalescent patients are particularly susceptible.
In Germany, Y. pseudotuberculosisinfections are most frequently caused by strains of the serogroup O:1, and occasionally by strains of the groups O:2 and O:3; however, all Y. pseudotuberculosis strains must be considered as pathogenic.
The main sources of human infection are contaminated food products, especially pork products. Colitis, signs of appendicitis or Morbus Crohn-like symptoms are typical signs of disease. Y. pseudotuberculosis is regularly detected in the faeces of clinically inapparent dogs; clinical disease is relatively rare.
Increased case numbers are observed during the winter months. The clinical picture is characterised by mucous or bloody diarrhoea; occasionally, vomiting and fever may occur. In case of abscess formation, the symptoms will depend on the localisation of the abscess. Clinically apparent Y. pseudotuberculosis infections in dogs are rare – but not the excretion of the pathogen. The clinical picture in cats is characterised by anorexia, vomiting and general weakness and may be confused with feline infectious peritonitis (FIP). Pyogranulomatous lesions are frequently observed in the gastrointestinal tract, liver, and lymph nodes. Untreated infection may be fatal.