Yersinia pseudotuberculosis

Yersinia pseudotuberculosis is a species within the family Enterobacteriaceae and the genus Yersinia. It appears as oval-shaped, short Gram-negative bacilli that are either strictly aerobic or facultatively anaerobic. This bacterium can grow at temperatures ranging from 0°C to 45°C, with an optimal growth range of 22°C to 30°C. It can survive for more than 6 months at low temperatures and thrives in environments with a pH between 4.0 and 10.0, demonstrating remarkable tolerance to both moderate acidity and alkalinity.

The genus Yersinia comprises 17 species, but only three—Yersinia enterocolitica, Yersinia pseudotuberculosis, and Yersinia pestis—are pathogenic to humans and animals. While the first two are both intestinal pathogens, they exhibit greater genetic differences at the DNA level compared to Y. pseudotuberculosis and Y. pestis. Although Y. pseudotuberculosis causes less frequent infections, its symptoms tend to be more severe than those caused by Y. enterocolitica, with serious cases typically occurring in immunocompromised individuals.

Yersinia pseudotuberculosis is a zoonotic pathogen with rodents as its natural hosts, though it can infect a wide range of animal species. It has caused outbreaks among European brown hares in Northern Europe, sheep in Australia, and farmed deer in New Zealand. The bacterium has also been isolated from healthy pigs, dogs, cats, cattle, horses, rabbits, and birds. Infection typically occurs through the ingestion of contaminated food or water, with the bacteria multiplying in the intestinal tract. Human transmission, meanwhile, is primarily linked to fecal contamination of soil, water, and fresh produce by infected animals.

The incidence of Yersinia pseudotuberculosis is seasonal, with cases peaking during winter and spiking again in April–May and June—before tapering off by June–July. Human infections with this bacterium primarily occur in Europe, North America, Russia, and Japan in the Northern Hemisphere, though overall incidence remains low across all continents. The disease can appear sporadically or in outbreaks, though most cases are reported as isolated incidents. Isolated infections are often underreported, as patients exhibiting mild clinical symptoms—such as diarrhea—are typically not tested with stool cultures. Small-scale outbreaks have been documented in Europe, while large-scale epidemics have occurred only in Canada, Finland, Russia, and Japan.

From 2001 to 2007, pathogenic Yersinia bacteria were investigated in 74 deceased non-human primates housed across 17 Japanese zoos representing 9 species. Among the 35 breeding non-human primates that died at these zoos, pathogenic Yersinia strains were isolated—19 cases involved Yersinia pseudotuberculosis. Notably, Yersinia enterocolitica serotype 7 was isolated for the first time from primates; squirrel monkeys infected with this serotype exhibited typical symptoms of Yersinia infection. PCR analysis confirmed that serotype 7 carries both the pYV and ypmA genes, firmly establishing its pathogenic potential comparable to other Yersinia serotypes.

Yersinia pseudotuberculosis has an incubation period of 2 to 20 days, with peak onset typically occurring around day 4. Symptoms of pseudotuberculosis infection usually affect the gastrointestinal tract exclusively, ranging from mild gastroenteritis to a condition resembling pseudoappendicitis. In children, small intestinal and colonic inflammation is the hallmark presentation, while in adults, terminal ileitis and mesenteric lymphadenitis are the typical clinical features—both of which are self-limiting. Notably, the appendix often appears normal, though epithelioid granulomatous lesions, coagulative necrosis, and lymphoid hyperplasia may develop near mesenteric lymph nodes and Peyer’s patches, mimicking tuberculosis. Meanwhile, the small intestine can exhibit microabscesses, cryptal hyperplasia, and shortened villi. When these granulomatous abscesses spread during systemic infection, they may eventually form lesions in organs such as the liver, spleen, lungs, kidneys, and intestines.

Yersinia pseudotuberculosis possesses an iron-scavenging system mediated by siderophores, which contributes to its virulence. Consequently, patients with iron-overload disorders such as venous congestion, hemochromatosis, liver cirrhosis, and hemolytic anemia are at a slightly higher risk of developing systemic infections.

Yersinia pseudotuberculosis shares biological characteristics with Yersinia enterocolitica and Yersinia pestis, exhibiting invasive properties and a strong tropism for lymphocytes. By encoding and secreting multiple virulence factors, it triggers varying degrees of intestinal infection in hosts, often accompanied by mesenteric lymphadenitis. In severe cases, the infection can lead to fatal outcomes and has already caused outbreaks of differing severity on multiple occasions.

Good hygiene practices are highly effective in preventing *Yersinia pseudotuberculosis* infections. Focus should be placed on strengthening rodent control efforts to prevent bacterial contamination of feed, food, and drinking water. If an outbreak occurs within a group, ensure prompt isolation and carry out thorough disinfection measures.

Antibiotics used to treat pseudotuberculosis include fluoroquinolones, aminoglycosides, ciprofloxacin, ceftriaxone, gentamicin, doxycycline, and trimethoprim-sulfamethoxazole. Fluoroquinolones are particularly effective against this condition, while other antibiotic classes show limited ability to inhibit bacterial growth. However, the use of beta-lactam antibiotics still requires further validation.

References

1. Shari Na, Zhao Liangjuan, Pang Lu, et al. PCR-Nucleic Acid Strip Assay for Detecting Yersinia pseudotuberculosis in Food [J]. Journal of Food Safety & Quality, 2018, 9(23):6107-6111.

2. Amphlett A. Far East Scarlet-Like Fever: An Overview of Epidemiology, Symptomatology, and the Role of the Superantigenic Toxin—Yersinia pseudotuberculosis-Derived Mitogen A. Open Forum Infect Dis. 2015 Dec 17;3(1):ofv202. doi: 10.1093/ofid/ofv202. PMID: 26819960; PMCID: PMC4728291.

3. Martínez-Chavarría LC, Vadyvaloo V. *Yersinia pestis* and *Yersinia pseudotuberculosis* infection: a regulatory RNA perspective. *Front Microbiol*. 2015 Sep 17;6:956. doi: 10.3389/fmicb.2015.00956. PMID: 26441890; PMCID: PMC4585118.

4. Brady MF, Yarrarapu SNS, Anjum F. Yersinia Pseudotuberculosis. [Updated April 27, 2023]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; Jan. 2023-. Available at: https://www.ncbi.nlm.nih.gov/books/NBK430717/

5. Iwata T, Hayashidani H (2011) Epidemiological Findings on Yersiniosis in Nonhuman Primates at Zoological Gardens in Japan. Jpn Agric Res Q 45(1):83-90