Among the myriad of diseases that the humanity faces, there is one, attitude to which cannot be compared to anything else. It has become something like a horror: any newly discovered fatal infection is compared with it. Dangerous political ideas and rough metal corrosion are named after it. It is commemorated in proverbs and curses. It has become the hero of many legends and stories. Classics of world literature – from Boccaccio to Camus – wrote about it. No other disease could produce such a profound impression like plague. At the time of the establishment of the science studying infectious diseases, people started to forget about the "queen" – plague, a devastating pandemic of which had inflicted terrible damage on the population of Europe. Oddly enough, neither Louis Pasteur and Robert Koch nor other luminaries of the golden age of microbiology did even try to identify the causative agent of plague. That honor fell to the next generation of microbiologists – a French Alexander Yersena and a Japanese Kitazato Shibasaburo. By participating in the fight against the plague outbreak in Hong Kong in 1894, they isolated a rod-shaped bacterium uncharacteristic of healthy people from diseased tissues and purulent materials of plague patients. After taking treatments done by Koch and Pasteur, the researchers proved that it was the causative agent of the worst infectious human disease. Originally, bacillus was attributed to the already known genus Pasteurella, but later it was isolated from some similar organisms in a separate genus named after one of the discoverers – Yersinia pestis (Orent, 2004).
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The discovery of the causative agent was not a victory over the disease, but it became a thread by pulling on which scientists from different countries would soon identify main elements of the mechanism of infection and the disease. Yersinia pestis causes three types of the deadly plague: bubonic plague developing after the bite of infected fleas when bacilli move to the lymph nodes and rapidly multiply forming tumors called bubonic; pneumonic plague, an infection when a patient coughs up blood and spreads the disease through the air; and septic plague that is spread through blood and almost always leads to death. The incubation period of plague is usually from 2 to 5 days. Once in blood, Yersinia petris is absorbed by cells’ macrophages that are specifically designed to combat alien organisms. However, a unique ability of the plague bacillus comes into play: inside the macrophage, it successfully resists digestion staying alive and even breeding. It gets into the lymph nodes where its multiplication becomes an avalanche. Large nodes (especially inguinal) swell, become hard to the touch, and are surrounded by the swollen tissue. Inside, they are filled with the pus (dead macrophages) and liquid products of the decay of tissues. This reincarnated node is called bubo and a described form of plague is called bubonic. The temperature of a patient reaches 39 degrees. Nervous system suffers. Patients are scared, anxious, can rave, and tend to run away somewhere. Coordination of movements, gait, and speech are disturbed. Bubonic plague is characterized by the development of lymphadenitis. In the field of its appearance, a patient experiences severe pain. Bubo gradually forms a dense tumor with indistinct edges that are extremely painful. The skin over the bubo initially has normal color and is hot to the touch. Then, it turns dark red with a bluish tinge and is shiny. In most cases, the disease is complicated by the DIC that is the disseminated intravascular coagulation. 10% of patients have gangrenes of feet, fingers, or skin. However, even in the absence of effective treatment a patient is not doomed. It happens that buboes spontaneously burst spilling their contents out and a slow recovery follows then (Person & Straley, 2010). More often, however, ripe bubo opens inward, i.e. into the bloodstream. Blood instantly turns into broth with bacteria that not only destroys nutrients, but also produces specific toxins. Blood pressure drops sharply (a sure sign of the beginning of the general sepsis) and the control of clotting fails. Intoxication symptoms are shivering, muscle pain, headache, confusion, and delirium. It is a septic form of plague. In this case, spontaneous recovery does not happen: a person quickly (usually within days) dies without intensive care (Emmeluth & Alcamo, 2004).
However, that's not the worst. In some patients, prior to the onset of the general sepsis plague bacillus manage to reach lungs where they cause acute pneumonia accompanied by the necrosis of tissues. A man starts coughing and sputum is soon stained with blood. Its microscopic droplets that are spread while coughing contain a huge amount of plague bacteria that enter lungs of healthy people, thus infecting them. Pneumonic plague spreads like fire. Being in the same room with a patient, it is almost impossible to avoid infection. The mortality rate among infected is 100%. Generally speaking, plague bacillus can get into a person through any mucous membranes, for example, if an invisible drop of the bacteria gets into the eye and into digestive system with food as well as in other ways. It cannot break the intact skin, but tiny sores or cracks are enough. However, the vast majority of infections come from a flea bite. The rates of deaths from the bubonic plague were 30-75%. The pulmonary form killed 90-95% of infected people. The lememia killed almost everyone and is still considered to be incurable. There can be a mild form of plague. Symptoms are swollen lymph nodes, fever, and headache. All these symptoms disappear within a week (Emmeluth & Alcamo, 2004).
The causative agent of plague is a so-called plague bacillus or Yersinia pestis – the bacteria of the genus Yersinia. It is a motile rod that does not form spores and capsules. It is characterized by the bipolar staining in a smear. It grows well on the nutrient media. It is believed that changes that occur in the body during the plague are caused by the presence of several plague bacillus’ pathogenic factors, i.e. Yersinia pestis has the endotoxin, produces the exotoxin, and pathogenicity factors (hyaluronidase, hemolysin and fibrinolysin). The plague pathogen is resistant to low temperatures, but it is quickly (within a minute) killed while boiling. It is also unstable under the influence of chemical disinfectants (Ciottone, 2006).
Today, we know that the plague bacillus can live in blood of at least 235 species of mammals belonging to eight orders, but rodents are the most common of its habitat. It inhabits various organisms of species like marmots, squirrels, rats, gerbils, voles, and prairie dogs. In animals, a disease caused by Yersinia pestis occurs in a chronic form. Another variant is that they are the carriers of the plague bacillus. Blood-sucking insects, such as fleas and ticks, exercise the transmission of plague from one rodent to another. Typically, natural foci of the plague exist in those areas where there is no man. Such centers are called primary or natural. There are also foci that exist in those places where a man lives. Here, rats and mice are the main sources of the plague bacillus. Fleas transfer Yersinia pestis from a source of infection to humans. Today, thanks to the compliance with sanitary regulations and the control of fleas as vectors of the plague, it is possible to significantly reduce the incidence. In our country, an infection caused by a plague stick is a great rarity today. However, it should not be forgotten about the causative agent of the plague and measures taken to combat it. Appearance of patients with typical symptoms of plague should be accompanied not only by their isolation, but by a whole complex of anti-epidemic measures as the agent of the plague can quickly spread in the early stages, then cause the development of the pulmonary forms, and spread from a person to a person (Duben-Engelkirk, 2006).
The diagnosis of plague is based on the epidemiological data. The first case of plague is usually particularly difficult to diagnose. Therefore, any patient who has arrived from endemic plague countries, who has an acute onset of an illness with shivering, high fever, and intoxication accompanied by lesions of lymph nodes (bubonic form), lungs (pulmonary), who has a history of hunting on marmots or foxes, of contact with rodents, sick cats, dogs, and of eating camel meat should be regarded as suspicious and be subject to isolation and testing in an infectious diseases hospital while being transferred to a strict anti-epidemic regime. At present, all the natural foci of plague are strictly recorded. A bubonic form of the plague is differentiated from tularemia, rat bite fever, cat scratch disease, suppurative lymphadenitis, and Hodgkin venereal. Tularemia bubo unlike bubo in the plague has clear contours and is not fused with the skin and nearby lymph nodes. Bubo develops slowly attaining a large size by the end of the week. Abscess, if it occurs, is revealed only during the third week of the illness. Typical clinical manifestations of the disease are very important for the diagnosis. The most important is that a person with the plague should be hospitalized in an infectious hospital. Main drugs to treat the disease are antibacterial agents. Discharge of patients who have recovered from the plague is performed after the full recovery, the relief of symptoms, and triple negative results of the bacteriological seeding. Prevention of the plague includes preventive and control measures. One of the most important points is the prompt isolation of patients with the plague or isolation of a man suspected of the disease from the surrounding people. Doctors and medical staff involved into the delivery of care to patients with the plague must wear anti-plague suits. People who are in the plague focus must be vaccinated with a special live dry vaccine. Anti-plague vaccine exists, but it cannot guarantee 100% protection. Incidence among the vaccinated is reduced by 5-10 times and the disease occurs in a milder form (Emmeluth & Alcamo, 2009).
It is considered that there are more or less effective remedies for any long-known disease in the folk medicine. Unfortunately, "recipes" of traditional cultures in the case of the outbreaks of particularly dangerous infections, especially the plague, do not support this optimistic view. A prominent Soviet microbiologist Leo Silber who led the suppression of the plague outbreak in 1930 later recalled that at the local cemetery someone regularly exposed recent plague burials. The investigation revealed that relatives of the buried did that. It turned out that according to a local legend when family members died one by one, a member of the family should have dug out the one who had died first, cut out certain parts of the internal organs (heart or liver), and eaten them. Thus, they believed that the plague would stop. Many people believed that the plague was sent down from above as a punishment for uncountable sins of the mankind. Many doctors believed that the odor could deter the plague. That is why, they poured patients with urine and smeared with feces. This way, they did everything possible to spread the disease further. Body wash during the plague was not encouraged for two reasons. First, the change of clothing was considered to be a manifestation of vanity that brought the wrath of God. Second, it was believed that after washing the skin pores opened and contaminated air got inside quicker and went outside easier, thus spreading the disease. The latter prejudice had existed in Europe until the 19th century (Orent, 2004).
The plague was raging in Europe since 1348 and to 1351. It killed approximately 60% of the Europeans. It is difficult to ascertain the exact number of deaths from the medieval sources. The mortality rate in different regions differed. According to the latest research, the number of the dead from the plague ranges between 75 and 200 million people. The name "Black Death" has recently appeared. During the epidemic and for a long time after it, the disease has been called "The Great Mortality" or "More" (Orent, 2004).
Today, a little more than 2,000 cases of the plague are registered in the world each year. The vast majority (over 90%) falls on two countries – the Democratic Republic of Congo and Madagascar (both cases involve secondary "rat" centers). Reasons are clear: extreme poverty, political instability, and as a consequence, lack of any effective public health interventions. The detection of the first cases of the terrible disease and organizing resistance to it are absolutely necessary. Today, doctors have a lot of treatment methods in order to fight the plague, for instance, it is very sensitive to antibiotics. A few days of regular injections of streptomycin or tetracycline lead to the full recovery. Intensive treatment supported by intensive care measures even saves patients with general sepsis. All of these methods allow even affluent and technologically not highly developed countries to withstand the plague. It is exemplified by Vietnam. In the 1960s during the war and American intervention, the country accounted for more than a half of all cases of the plague. However, since the 1990s, rarer sporadic outbreaks have occurred. It is flattering to think that the "queen of the disease" has been defeated forever. However, it may have just taken a break and is now preparing for its next campaign (Orent, 2004).