The Hidden Danger of Yersinia Infections: What You Need to Know

Introduction Genus Yersinia

Animals are natural hosts of yersinia, and humans are accidental hosts of yersinia infection. They are short, pleomorphic micro-aerophilic or facultatively anaerobic, Gram negative, ferments glucose, non-lactose fermenter and oxidase negative rods exhibiting bipolar staining with special stains. The genus consist of 10 species, with Yersinia pestis,  Yersinia enterocolitica and Yersinia pseudo tuberculosis being the well-known pathogens.

The genus Yersinia includes:

• Yersinia pestis, the cause of Bubonic plague.

• Yersinia pseudotuberculosis and Yersinia enterocolitica, important causes of human diarrheal diseases and others.

1. Yersinia enterocolitica:

Yersinia enterocolitica a species of the genus Yersinia, isolated from both man and animal. It is a frequent cause of bacterial gastroenteritis in children.Y.enterocolitica a bacterium that causes an infectious disease called yersiniosis. Common symptoms of yersiniosis in children are fever, abdominal pain, and diarrhea, which is often bloody. Symptoms typically develop 4to 7 days after exposure and may last 1 to 3 weeks or longer. In older children and adults, right-sided abdominal pain and fever may be predominant symptoms and may be confused with appendicitis. In a small proportion of cases, complications such as skin rash, joint pains, or spread of bacteria to the bloodstream can occur.

2. Yersinia pestis:

Yersinia pestis: the bacteria that causes the bubonic plague which in the years 541 (as the Black Death) and later in the Middle Ages decimated Europe. The effects of the plague are described in the nursery rhyme we all fall down. Y. pestis mainly infects rats and other rodents which are the prime reservoir for the bacteria. Fleas are the prime vectors carrying the bacteria from one species to another. They bite rodents infected with Y.pestis, then they bite people and so transmit the disease to them. Transmission of the plague to people can also occur from eating infected animals such as squirrels.

Virulence factors:

• Heat - stable lipopolysaccharide that have endotoxic activity and contribute to the toxaemia  of plague.

• Heat labile Fraction 1 (F1) protein capsular antigen helps the organism to resist phagocytosis and is a protective immunogen.

• The V antigen, part of the type III secretion system, is an important protective antigen. 

• Yersinia pestis also produces a plasminogen activator and fibrinolysin , which may play a critical stage of infection.

• Other proteins associated with virulence includes adhesion which are common to Yersinia enterocolitica and Yersinia pseudo tuberculosis

Pathogenesis and clinical manifestations

Y. pestis causes plague, a zoonotic disease which is transmitted from rats and other rodents to humans by infected fleas (main vectors: Xenopsylla cheopis and X. brasiliensis). Occasionally, infection occurs by inhaling the organisms in airborne droplets, or by handling infected rodents or domestic animals (e.g. cats, dogs) that harbour infected fleas. Rat flea (Xenopsylla cheopis) gets infected by biting anInfected rodent → infected rat flea bites human (accidental host) → organism migrate to regional lymphnodes from the site of bite (bubonic plaque) and gets into the blood via lymphatics (septicemic plaque), or Primary pneumonic plaque results from inhalation of infective droplets, usually from an infected coughing person.  

There are three main forms of the disease

1. Bubonic plague:

Bubonic plague: is characterized by high fever and acute lymphadenitis with painful haemorrhagic swellings called buboes, usually in the groin area. Occasionally lymph nodes in the neck or armpits are involved, depending on the site of the flea bite. There is a markedly raised white cell count with neutrophilia.

2. Pneumonic plague:

This occurs following inhalation of the organism or its spread to the lungs via the blood stream. Pulmonary infection causes severe bronchopneumonia with haemorrhaging. It is rapidly fatal unless treated at an early stage. Pneumonic plague is highly infectious and can spread quickly in conditions of poverty and overcrowding. The sputum contains large numbers of plague bacilli and is often blood stained.

3. Septicaemic plague:

This is a serious haemorrhagic condition in large numbers of Y. pestis are present in the blood. The organisms  can often be seen in peripheral blood smears. Buboes are usually absent. There is a haemorrhagic rash. Septicaemic plague is rapidly fatal.

Haw to transmission Y. pestis

The transmission of pathogen from ane host to another when the pathogen reproduced in the vector.

Laboratory diagnosis

Specimen: Lymphnode aspirate, CSF, blood. Smears: Wright’s stain, immuno-fluorescence stain, methylene blue stains, basic fuchsin stain, and Wayson’s stain to demonstrate bipolar granules.Culture: Grow on blood agar or MacConkey agar. All cultures are highly infectious and must be handled with extreme caution. Biochemical tests: Y. pestis is catalase positive and oxidase negative. Serology: Fluorescent antibody technique using Y. pestis antisera. Prognosis: Mortality rate is 50% (100% for pneumonic plaque).

Haw to Treatment Y.pestis

• Streptomycin.

• Tetracycline.

• Steptomycin plus tetracycline or chloramphenicol.

Prevention and control

Chemoprophylaxis for contacts of patients. Formalin-killed vaccine for travellers to hyper endemic areas and high risk persons. Plague is controlled by reduction of the rodent population. Other Yersinia infections are controlled by proper preparation of food and food products.

Conclusion

The genus Yersinia includes Gram-negative, facultatively anaerobic bacteria belonging to the family Enterobacteriaceae. Among them, Yersinia pestis, Yersinia enterocolitica, and Yersinia pseudotuberculosis are the most clinically significant species. These bacteria are responsible for serious human diseases such as plague (Y. pestis), gastroenteritis (Y. enterocolitica), and mesenteric lymphadenitis (Y. pseudotuberculosis). They are primarily zoonotic pathogens, transmitted from animals to humans through vectors like fleas, contaminated food, or direct contact. Understanding their pathogenesis, reservoirs, and modes of transmission is essential for effective prevention, diagnosis, and treatment of the infections they cause.