The genus Yersinia includes 11 species, of which 3 are notable for causing human diseases: Yersinia pestis, Yersinia enterocolitica, and Yersinia pseudotuberculosis. Yersinioses are zoonotic infection with the human being the incidental hosts who do no contribute to the life cycle for the pathogen.
Y. enterocolitica have been isolated from a variety of animals with pigs being the most common source. The pathogen can spread from one pig to another in a herd. The bug can contaminate pork products including neck trimmings, tongue, tonsils and can spread to other meat cuts during slaughter.
Yersinia is classified according to their phenotype and serotype. Phenotypically, these bugs are divided into 6 bio groups out of which 5 (1B and 2-5) are regarded as pathogens. Based on serotyping, this pathogen is classified into more than 57 O serogroups. However, only a few of these are associated pathogenic. The pathogenic serotypes are O:3 (biogroup 4), O:5,27 (biogroup 2 and 3), O:8 (biogroup 1B), and O:9 (biogroup 2). The most common serogroup isolated from humans in European countries is O:3 followed by O:9. In the United States, serogroup O:8 is more prevalent.
Infection is transferred predominantly through the fecal-oral route. Pork consumption especially undercooked or raw pork products are responsible for yersiniosis. Outbreaks have also been reported in Norway and New Zealand from untreated drinking water contaminated with this pathogen. There are case reports of infection being transferred from an infected household pet and through transfused blood products.
The pathogen passes into the stomach, traverses the gut wall, and localized in lymphoid tissue and mesenteric lymph nodes. The bacteria has a 70 kilodalton virulent plasmid known as pYV that is present in pathogen species of Yersinia including enterocolitica, pestis, and pseudotuberculosis. The bacteria also produce ureases that metabolized urea and forms ammonia to protect itself from the harsh acidic environment of the stomach. The bacteria also produce Ail (attachment invasion focus) and YadA, that confers resistance to complement-mediated opsonization and prevents phagocytosis. The bacteria also contains Yops (Yersinia outer membrane proteins) that arrests phagocytosis by block secretion of mediators including TNF-alpha and IL-8. Certain strains produce yersiniabactin that is an iron-binding agent that can effectively bind iron in a depleted state. This further allows the bacteria to thrive and grow.
The pathogenesis of reactive arthritis is likely due to an immune response that is primarily to Yersinia antigens that cross-reacts with host antigens. The host may have HLA-B27 positivity making them susceptible to reactive arthritis. The other common post-infectious sequela is erythema nodosum.
Yersinia infections can present with enterocolitis, pseudoappendicitis, reactive arthritis, sepsis, pharyngitis, myocarditis, mesenteric adenitis or dermatitis. Clinically the infection can manifest in 2 ways:
This condition manifest as diarrhea, abdominal pain, nausea, vomiting, and fever. The duration of diarrhea can range from 12 to 22 days. Yersiniosis is difficult to distinguish from other causes of acute diarrhea given the similar presentation. The localization of pain to right lower quadrant may be a diagnostic clue for yersiniosis. Bloody diarrhea is more frequently observed in children compared to adults. Sepsis has been described in infants and patients who are immunocompromised or in iron overload state with an overall 50 percent fatality rate.
Following the acute infection, the bacteria may continue to shed in stool for a median of 40 days (range 17 to 116 days).
Acute yersiniosis can mimic appendicitis and present with right lower quadrant abdominal pain, fever, vomiting, elevated white blood count, and diarrhea. Patients taken for surgery demonstrate inflammation of the terminal ileum and mesenteric lymph node with a normal appendix.
The blood work is usually unremarkable, but in severe cases of diarrhea, one may observe hypernatremia and hypokalemia. A stool culture is the best way to make a diagnosis of Yersinia. Blood cultures are usually negative. Other studies depend on the organ system involved. Imaging studies (e.g., ultrasound or CT scan) are often required to determine if the patient has appendicitis or pseudoappendicitis. Diagnosis may also be obtained from positive cultures obtained from mesenteric lymph nodes, pharyngeal exudates, peritoneal fluid, or blood.
Serologic tests including enzyme-linked immunosorbent assays (ELISA) and immunoblotting to detect IgG, IgA and IgM are used in Japan and Europe but not very commonly used in the US. Polymerase chain reaction and immunofluorescence assays have been developed but not widely used.
The treatment of Yersinia is supportive care with hydration and nutritional support. The drugs of choice are the aminoglycosides or trimethoprim-sulfamethoxazole. Other effective agents include tetracycline (not in children), quinolones and cephalosporins. Sometimes surgery is required to drain an abdominal abscess, and surgical exploration is warranted if appendicitis cannot be ruled out. It is important to note that in many cases, pseudoappendicitis and appendicitis cannot be differentiated on a clinical exam or even with imaging. Thus, some patients undergo surgery for removal of an appendix. In such scenarios, the appendix is found to be normal, but there is localized mesenteric adenitis, which is confirmed by the pathologist. Antimotility agents should be avoided in patients with diarrhea, as they may worsen the infection. Antibiotics should be used only in selected patients such as the elderly, immunocompromised individuals or patients with diabetes. Children may need admission for dehydration or sepsis. Most patients are anorexic and may require an overnight admission for intravenous (IV) hydration. In some cases, patients are admitted because it is not possible to rule out appendicitis.
The preventive measures include handwashing after exposure to an exposed animal, safe food processing, avoiding raw consumption of pork and products, routine water treatment and disinfection, and screening for the pathogen in blood and blood products.
Diagnosis depends on a detailed history, detailed physical examination and supportive laboratory and radiological findings. Diseases that can present in a similar include:
Yersiniosis generally has a favorable outcome. A study from the United States reported only 1.2% (18 deaths out of 1373 patients) diagnosed with Yersiniosis. In another study from Norway, only 2 deaths were reported from 458 patient diagnosed with yersiniosis.
Complications related to Yersiniosis include:
Patients presenting with appendicitis needs evaluation by general surgery for surgical exploration to evaluate the etiology.
Patients should be counseled regarding hydration and electrolyte intake if they have uncomplicated diarrhea that can be observed.
Education including proper food processing, handwashing, and avoidance of raw pork products should be done to prevent infection.
Care should be sought immediately if the patient develops severe symptoms/complications including fever, bloody bowel movements, abdominal distension, toxic appearance, decreased urinary output, among others.
Yersinia enterocolitica is a gram-negative bacillus shaped bacterium that causes a zoonotic disease called yersiniosis. The infection is manifested as acute diarrhea, mesenteric adenitis, terminal ileitis, and pseudoappendicitis. In rare cases, it can even cause sepsis. Since the majority of patients with yersinia infection present to the emergency department, nurses and emergency dept physicians should be aware of the presentation, diagnosis and management. While most patients do improve with hydration, some may require antibiotics. The key to prevention is to educate the patients on the importance of hand washing and maintenance of personal hygiene.
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