The bacterium Yersinia pestis (also called Pasteurelle pestis) is the causative agent of the dangerous infectious disease plague. There are several forms of plague, bubonic plague, pneumonic plague, plague sepsis, skin plague, abortive plague, and plague meningitis. Except for cutaneous plague, all are very dangerous and are often fatal if untreated. Even among treated patients today, between 10 to 15 percent still die from the disease.
What is Yersinia pestis?
The plague bacterium Yersinia pestis belongs to the Enterobacteriaceae family. It received its name from the Swiss physician and explorer Alexandre Yersin, who researched plague and discovered the pathogen in 1894. He was also the first to recognize that Yersina pestis is transmitted primarily by rats and mice or by rat fleas and insects. Plague is not easy to diagnose initially. Often the first symptoms are mistaken for malaria, typhus, and typhus before the plague bumps become visible. The plague bacterium is isolated from blood, pus or the sputum of the sick person and either stained and viewed under a microscope or grown in a culture. In addition, a test with special antigens is also in use.
Occurrence, distribution, and characteristics
The history of plague is a tale of horror. Plague epidemics have been reported as far back as ancient times. The first surviving plague wave occurred in the 6th century. Its outbreak probably began in Egypt, spread from there across North Africa and the entire Mediterranean region, and particularly affected the Byzantine Empire. It is not known how many people fell victim to it, but it probably affected almost half of all the people living in the region at the time. Whole families were wiped out, hardly anyone dared to leave the house, the fields remained uncultivated, and famine broke out. The second great plague wave shook the same region again in the 8th century. In the 14th century, the “Black Death” then made its way throughout Europe. This time it probably came with traders from Asia, especially from China. This plague epidemic also greatly decimated the population and probably claimed millions of lives. Into the 18th century and on the edges of Europe even into the 20th century, the plague occurred every now and then thereafter. The last major plague outbreak occurred at the end of the 19th and beginning of the 20th century in Central Asia, where it probably claimed the lives of 12 million people. One of the reasons the plague bacterium is so dangerous is that it can be transmitted in a number of ways. Usually, infection begins when a rat flea bites a plague-infected rat and then infects other rats. Thus, a large rat die-off begins and the fleas, now unable to find hosts, also spread to mice, squirrels, other rodents and their hunters, and also to humans. Not only rat fleas spread the plague, but also human fleas and many insects such as mosquitoes, lice, ants and spiders can transmit it. In addition, infection occurs through direct contact with infected tissue, with objects, or through droplet infection from person to person. The incubation period is about 7 days for bubonic plague and only a few hours to 2 days for pneumonic plague. After that, the disease breaks out with high fever, chills, headache and aching limbs, nausea, diarrhea, and vomiting. It is not until 24 hours later that the first pus-filled bumps appear due to swelling of the lymph nodes. In pneumonic plague, there is severe shortness of breath, coughing, and black and bloody sputum. In plague sepsis or plague meningitis, patients often die before the first visible symptoms appear.
Diseases and symptoms
But even today, especially in Asia but also in Africa and North America, there are still cases of plague. Between 1000 and 2000 cases of the disease are registered annually, according to WHO, and the number of unreported cases is high. However, improved hygienic conditions, effective quarantine measures and effective treatment methods have been able to prevent larger epidemics. The plague pathogen is still dangerous, and in the slums and shantytowns of the world, illnesses occur again and again. Although there are now vaccines against the plague, they are comparatively ineffective due to extreme genetic changes in the pathogens and have severe side effects. For this reason, they are only used in exceptional cases.However, there is the possibility of chemoprophylaxis for all people who have to travel to plague areas. The plague pathogen also poses a great danger as a possible biological weapon. The WHO lists the bacterium yersinia pestis, just like the pathogens of Ebola, anthrax, cholera and smallpox, among the “dirty weapons” that could be used by terrorist groups or in wars. Today, plague is treated with effective antibiotics. The drugs of first choice are streptomycin, tetracyclines and quinolones. In addition, the severe symptoms of the disease are alleviated and, if possible, the fever is reduced. Patients are strictly isolated to minimize the great risk of infection. If the patient survives a plague illness, then there is lifelong immunity to this specific pathogen.
