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The causative agent of plague, and all about it: distribution, sources, routes of transmission, diagnosis, etc.

The plague Bacillus, the causative agent of plague

The causative agent of plague is the plague Bacillus – and remains a potential threat to many people.

Although large-scale outbreaks of the disease no longer exists, and the millions of victims left in the past, even today when the modern level of medicine is celebrated every year 2-3 thousand occasions. The death rate dropped considerably, but still hovers around 5-10%. Therefore, Microbiology is continuing to study this pathogen.

What is the causative agent of plague?

For a long time the cause of the plague remained a mystery for people. Were put forward different versions, but it took a while to understand this question.

An additional complexity was the presence of several forms of the disease. Symptoms of bubonic plague differ significantly from pulmonary, which they have long been taken for different diseases.

Only in 1894 by bacteriologist Alexander Yersin, an employee of the Pasteur Institute, identified the causative agent of plague, linking various forms of this disease.

Later these researches allowed to determine the life path of this bacterium, its properties, mechanisms of spread and methods of struggle.

The plague Bacillus is a gram-negative bacterium, a member of the family of enterobacteria. Its biological name is associated with the discoverer – Yersinis pestis. Today there are many strains that have partially different properties, the structure of the cell, virulence and toxicity.

The plague Bacillus is not too sustainable to the environment. It is rapidly killed by boiling and can withstand only about half an hour when heated to 50 degrees, a well destroyed by most disinfectants and are relatively easily cured with antibiotics. At the same time, it can a long time to remain viable in carcasses, pus, sputum and other fluids of infected people and infected food, especially milk. Relatively resistant to freezing.

Distribution, and transmission of plague

To the end to defeat the plague Bacillus is not yet possible due to the presence of a large number of natural foci. This zooantroponoznyh infection in nature affects many animals, primarily rodents such as marmots, gerbils, gophers, rabbits, rats and mice of various kinds. When eating sick animals can be infected with wild predators such as foxes, and also some Pets: rabbits, camels, rarely cats.

footnote a Carrier of this pathogen – blood-sucking insects, primarily fleas, but also they may become some species of ticks.

Once in the body of the insect, the bacterium causes the formation of a dense tube in the esophagus, which after a bite, the blood enters the stomach of the flea, and srygivaniya out with the plague Bacillus. Hungry flea continues to seek new source of food, moving from host to host.

Laboratory tests have shown that it infected flea can infect an average of 11 owners.

The spread of plague in natural foci contributes to the overcrowding of animals, so often reservoirs of infection localized in the colonies of rodents and their places of dense residence.

The way of transmission

This disease is not a single pathway. There are several possible options:

  • Alimentary. It is the transmission via blood-sucking insects is the main way of distribution. Medieval epidemics contributed to the high number of rats and fleas in cities. Today this way of infection for humans is not major, but still, is often the cause of infection.
  • From sick animals. Contact with their blood, meat, hides often leads to the transfer person. At risk include hunters, people working on farms. Dangerous eating the meat of infected animals, which has not been properly heat-treated and infected dairy products.
  • Airborne droplets. Patients with bubonic plague not too contagious, unlike the plague in the pneumonic form. With coughing and breathing, they emit into the environment a large number of bacteria. Thus infected people are also sick with the plague in the pneumonic form.
  • From a sick person. In humans, patients with bubonic plague threat are separable pus and ulcers as well as other secretions and bodily fluids. A healthy person can become infected after contact with them if on the skin or mucous membrane there is even a small damage. It is also possible to transfer over other items infected with plague Bacillus, butthis happens rarely.
The researchers of plague while there is no consensus about what path was the key. There are versions that at different times and in different regions has varied, the main way of spreading.

Epidemiological situation

Even today, there is no continent (except Australia and Antarctica) where there would be natural reservoirs of Yersinia pestis. More likely to find them in the steppe and the Hague areas, the vast plains where good feel rodents, as well as hot tropical regions.

Officially active sources of the disease are recorded in many countries: China, Kazakhstan, Russia, USA, Peru, Tanzania, China, Mongolia, Vietnam, and India.

In these countries recorded a more or less regular outbreaks. Over the last 25 years the incidence of this disease was noted in 24 countries.

In Russia the situation with the plague is quite complex. Extensive land borders with Kazakhstan, China and Mongolia and the regular migration of rodents it is much worse. In areas unfavorable from the viewpoint of epidemiology, there are about 20 thousand people. Natural foci are located in the Astrakhan region, on Altai, in Dagestan, Karachay-Cherkess and Kabardino-Balkar republics.

For a long time Russia did not have outbreaks of the disease, but more recently, in July 2016, Altai went to the hospital the child with bubonic plague. The spread of this outbreak was not received, but does not exclude the replays in the future, because extensive colonies of ground squirrels serve as permanent reservoirs of infection. And, despite the ban and public awareness, many local people hunt these animals, putting themselves at risk.

The last major outbreak of plague was noted in Madagascar in 2014. It was involved 119 patients, 40 of whom died.

Forms and manifestations of plague

The plague is no single path of development that has confused medieval doctors. Classic bubonic and pneumonic plague have completely different properties and different symptoms. Because of this for a long time believed that this variety of the disease.

And only modern Microbiology helped to establish the truth: the plague pathogen in both cases is the same, changing only the way of hitting the body.

There are three forms of this disease:

  • Bubonic. About 90% of cases occur in this form. The route of infection is through insect bites or contact with pathogens in the blood in a different way. On the site of the flea bite in a few days, a small vesicle filled with fluid. The average incubation period is 4-5 days, in some cases, it can vary from 1 to 12. Significantly enlarged lymph nodes, most often inguinal, closest to the flea bites. In their place are formed fistula or ulcer, at the same time increase other lymph nodes. Appear common symptoms: fever, intoxication, painful arousal, the blood pressure decreases on the background of tachycardia. Often develop sepsis. Bubonic plague without going heavier has a favorable prognosis with timely beginning of treatment, but in 5-10% of cases recovery is possible. With adequate therapy the percentage of recovery reaches 95%.
  • Pulmonary. Can be either primary, when infected through the lungs, and secondary, developing in the bubonic form. The symptoms – cough, hemoptysis, shortness of breath, lack of air, temperature up to 40-41 degrees. Tongue thickly coated with white bloom, possible nausea and vomiting. Primary pneumonic plague is one of the most short – lived- symptoms may appear already on the first day, the secondary develops gradually.
  • Septic. Also can be primary and secondary. Without treatment, death occurs in 2-3 days. Primary septicemic plague develops relatively rarely in contact with the pathogen directly into the blood. Secondary is a relatively frequent complication of bubonic. Symptoms: high, 40-42, temperature, muscle pain, headache, nausea, vomiting, bleeding, subcutaneous hemorrhage, gangrene, chills, septic shock.

Despite these different properties, all forms of plague are caused by the same pathogen – the plague Bacillus. Therefore, diagnostic methods in all cases are the same.

Diagnostic method

The plague Bacillus is a well studied microorganism, and it is possible to find effective and accurate methods of diagnosis. At the same time, yet there is no analysis which would give a fast and simultaneously an accurate result. In most cases, cases, they are used to confirm already of the diagnosis, and examination of potentially infected people.

A major role in the diagnosis of plague still plays inspection and survey.

The doctor draws attention to the typical symptoms of the plague – the size, shape, tenderness, consistency of lymph nodes and General condition. For more information, the doctor may do a lumbar puncture, which revealed a large amount of pus rich in bacteria.

Also necessary for the production of a correct diagnosis of information gives history collection. Doctor it is important to find out, could people at least theoretically have the contact with the agent. Risk factors – the living or recent visits to the regionswith natural foci, contact with rodents and so on.

Often use the following methods of diagnosis:

  • Microscopy smears from mucous membranes, and separable ulcers or biopsy. It can be found a large number of bipolar bacteria oval.
  • Bacterial inoculation. Doing this analysis on the same biological material. It gives a more accurate result, but requires more time.
  • Determination of the presence of antigens for Yersinia pestis. They appear some time after the onset of the disease, therefore, does not always give the result at an early stage.
  • Allergopharma. A positive result confirms that people in the past suffered plague. Also confirms the presence of a formed immunity after vaccination.
  • Plague bacteriophage. It is a drug that reacts selectively with the plague Bacillus. The reaction of the blood of a patient with diagnostic bacteriophage confirms the diagnosis.
  • Biological sample. Specially prepared blood serum is administered to laboratory animals, most commonly laboratory mice and Guinea pigs. If positive symptoms, and the animal dies on day 3-9.
  • Luminescent-serological diagnosis. Used if there is suspicion of plague and to get the result after a few hours, but its accuracy can be not big enough.
With a quick result gives the fluorescent-serological analysis, and reaction with a specific plague with bacteriophage. They give quite a large number of false positives, but have a high sensitivity.

These properties allow the use of rapid methods for mass diagnosis. It is required to determine carriers and infected in the incubation period among people having contact with the patient.

The formation of the immune system

Plague is one of the most contagious diseases. Natural immunity or resistance in this bacteria is not. Even the disease does not give protection, because they are determined only relative immunity, which protects against recurrence. The second time the plague is transferred just as hard as the first time.

Considerable difficulties arose in the search for a cure. A proven method of accelerating the formation of specific immunity with the introduction of serum – in this case, to no avail. Thus prepared, the drug only prolongs the disease, but did not increase the percentage of recovery.

The first effective vaccine was received in 1934. It is possible to prevent onset of the disease.

To date, there is also no vaccine that provides lifelong protection. The used scheme provides protection throughout the year. After that it is repeated if necessary. But even in this case, vaccine efficacy is around 70%, although vaccinated people carry the disease easier.

Because the probability of Contracting plague is relatively low, vaccination is not mandatory, even in the regions where there are natural foci. They are required by the people belonging to the risk groups: hunters, agricultural workers and farms, biologists, and medical workers. Where there are no lesions, vaccinations are prescribed only to people working with cultures of Yersinia pestis.

Treatment of plague

The plague Bacillus is susceptible to antibiotics, so after their invention in the therapy of fracture occurred. The first experience of application of streptomycin in 1947 turned out to be extremely successful – all patients recovered. Without antibiotics to achieve such a result could not be anyone.

Now the most effective antibiotics remains streptomycin, and tetracycline drugs and some others. Typically, they are used in the treatment of strains of plague that are resistant to streptomycin.

In addition, when the active treatment is symptomatic and intoxication therapy needed to rid the body of waste products of the bacteria. An important part of therapy is prevention of complications. The transition into secondary bubonic or septicemic form is significantly worsens the prognosis.

Overall, the plague Bacillus now well-studied and is no longer in such danger as before. But the disease remains difficult and prone to the formation of epidemics, therefore, its study and control has been addressed by many experts.

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