Yersinia are facultative, anaerobic (can grow without oxygen), pleomorphic, Gram-negative (coloured red in the so-called Gram staining), rod-shaped bacteria of the family Enterobacteraceae. The psychrophile (= liking cold) pathogens can be isolated at temperatures between 4 °C and 42 °C. Animals are considered the main reservoir of the bacteria, which are commonly found in moderate climates.
The genus Yersinia includes 14 species -- of which enteropathogenic Yersinia (Y. enterocolitica and Y. pseudotuberculosis) are obligate pathogens important from a human medicine perspective.
Yersinia pestis, the causative agent of plague, is a Gram-negative, rod-shaped bacterium found around the globe. The pathogen is responsible for the great Plague epidemics to which almost 30 % of the European population fell victim in the 13th century alone. Plague outbreaks were described in the Democratic Republic of Congo, Kenya, Madagascar, India, Vietnam, China, Malawi, Namibia, Myanmar, Zambia and several other countries in recent years.
Plague is primarily a zoonotic disease, transferred from animals (fleas) to humans. However, in the case of the mostly terminal pneumonic plague, the pathogen can be transmitted from human to human.
Bubonic Plague and Pneumonic Plague
Plague ends mostly terminally when not treated, while survivors gain life-long immunity from further infection. The most prominent form is bubonic plague, the symptoms of which are fever and painful, dark-coloured swellings of the lymph nodes in the neck, armpit and groin areas. In a good 20 % of cases, the infection takes on a septic and fatal form, which can also affect the lungs. In cases of pneumonic plague, the disease can be transmitted between humans. The disease is likely to end fatally despite the correct therapy, owing to its very short incubation period of just a few hours.
The survival of the patient depends on a rapid diagnosis, which makes molecularbiological methods that can deliver a diagnosis within hours so important upon the suspicion of an infection, in addition to isolating the culture, which can take several days. The mortality rate from pneumonic plague is far above 50 %, even with the right therapy. Other forms of plague can be treated well with antibiotics, provided the treatment is begun in time.
Laboratory workers, who are exposed to the risk of infection, are recommended to have prophylactic inoculations. Tourists should avoid travelling to regions where plague outbreaks have been reported recently, although the infection risk is usually low. Using insect repellents to protect yourself against fleas is recommended in endemic regions.