Yersinia enterocolitica of the small intestine

Yersinia enterocolitica is a class of Gram-negative bacilli widely distributed in nature and closely linked to human health. Over 40 countries have reported human infections caused by this bacterium, with Europe and Japan being the most affected regions. In recent years, foodborne outbreaks associated with Yersinia enterocolitica have occurred from time to time, leading the pathogenic strain to be classified as a significant foodborne pathogen. The World Health Organization (WHO) collectively refers to diseases caused by Yersinia species—excluding Yersinia pestis—as yersiniosis. Beyond causing intestinal symptoms such as fever and diarrhea, Yersinia enterocolitica can also lead to extraintestinal infections, affecting the cardiovascular, respiratory, and musculoskeletal systems, often resulting in persistent sequelae that warrant attention. In the 1980s, China experienced two notable outbreaks of Yersinia enterocolitica infections among humans and piglets. Moreover, it has been found that more than 40 animal species—including livestock, poultry, rodents, reptiles, and aquatic animals—are susceptible to this bacterium. Among these, pigs, cattle, and rodents are particularly relevant to human infections. According to testing data from Suzhou Xishan Bio, a third-party laboratory in China, collected between 2020 and 2023, the detection rate of Yersinia enterocolitica in laboratory animals remained at 0%. This suggests that, while infection with Yersinia enterocolitica is not commonly observed in domestic laboratory animals, it still requires careful monitoring and vigilance.

Currently, nearly all domestic animals have been found to be naturally infected with Y. pestis. Among them, pigs, cattle, cats, and dogs can serve as healthy carriers, posing a serious threat to humans. Pigs exhibit the highest carriage rate, with their tonsils and tongues often yielding higher isolation rates compared to the cecum or feces. To date, over 20 species of rodents have been identified as carriers of Y. pestis, among which house mice and field mice are considered potential reservoirs of the bacterium. The carrier rate in rodents ranges from 5.2% to 10%, while in China, the prevalence among local rodent populations is between 2.46% and 4.77%. Notably, studies have reported that rodents inhabiting slaughterhouses can carry the bacteria at rates as high as 35.2%, suggesting that these rodents likely play a significant role in the secondary contamination of pigs and pork products after slaughtering.

This disease typically causes asymptomatic, latent infections in animals. Diarrheal symptoms or nodular lesions in the liver have occasionally been observed in infected pigs, dogs, cats, sheep, monkeys, and other species—but such cases are generally quite rare.

Outbreaks have been reported in pigs. The incubation period lasts 2 to 3 days, and at the onset of the disease, pigs typically exhibit anorexia, with body temperatures soaring to 40–41°C, accompanied by watery diarrhea—ranging from several episodes daily to more than ten—and, in severe cases, even fecal incontinence around the anus. Later stages often involve a drop in body temperature, refusal to eat, reduced urine output, and cyanosis of the skin. Without timely fluid replacement therapy, piglets frequently succumb to dehydration and shock, while adult pigs usually recover successfully. The illness typically lasts about one week, though in some cases it may extend up to two weeks. Post-mortem examinations reveal catarrhal gastroenteritis as the primary pathological change.

There was once an outbreak among sheep, primarily characterized by suppurative bronchopneumonia and suppurative dermatitis. Affected sheep exhibited elevated body temperature, coughing, and difficulty breathing, along with pus-filled, necrotic lesions on the skin of their mouths and ears. Post-mortem examination revealed fluid accumulation in the thoracic cavity, as well as congested and swollen lungs covered with fibrinous exudates. Additionally, the pericardium was thickened, and the myocardium showed signs of hemorrhage. Both adult and young sheep could be affected, though lambs had a significantly higher incidence and mortality rate.

Japanese scholar Maruemon Yama (1997) successfully conducted oral infection experiments on monkeys, inducing symptoms and tissue lesions similar to those observed in humans. He concluded that while Yersinia infections affect both the jejunum and colon, the primary site of infection is the ileum. The infection is acquired orally: first, the bacteria multiply within Peyer’s patches, after which they localize and adhere to the intestinal mucus—depending on their serotype and the virulence plasmids they carry. Outer membrane proteins facilitate this adhesion and enhance resistance to phagocytosis, enabling the bacteria to survive despite the host cell’s defensive mechanisms. In some cases, they even manage to penetrate the intestinal epithelium, entering lymphatic tissues (causing mesenteric inflammation) and subsequently infecting cells within the monocyte lineage. Ultimately, the bacteria may enter the bloodstream, leading to septicemia.

Since Yersinia enterocolitica is widely distributed in nature and has numerous sources of infection, there are still many epidemiological questions that need to be clarified. Therefore, completely controlling this disease remains challenging at present, and only general preventive measures can be implemented. It is essential to maintain good environmental hygiene and carry out thorough disinfection, strengthen sanitary supervision of meat products, and actively engage in rodent, fly, and cockroach control efforts. Additionally, any sick animals should be promptly isolated and treated to prevent their excrement from contaminating feed, food, and drinking water.

To treat this disease, streptomycin, chloramphenicol, tetracycline, or sulfonamide drugs can be used.

References

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