Why can't plague bacteria be completely eradicated on the planet?

Russian scientists are developing a new generation of integrated vaccines against plague. Experts say that this dangerous, dangerous, infectious disease is coming back, the disease is still prevalent in different parts of the world. Why does 'black death' persist like that?

Bacteria spread from mice

Bubonic plague is known since ancient times. It is estimated that this dangerous dark disease spreads very quickly that killed more than two hundred million people. In the third pandemic in 1894 in Hong Kong, French bacteriologist Alexandre Yersen found a bacillus that caused plague, later named after him: Yersinia pestis .

But, unlike smallpox, plague still cannot be completely eradicated. In the old world and in the new world, there are still separate cases of this serious infection.

Picture 1 of Why can't plague bacteria be completely eradicated on the planet?
Yersinia pestis plague bacteria.

The plague bacteria circulate in burrowing populations of populations - marmots , gophers, gerbils, voles, mice as well as fleas that live on parasites. Fleas suck the host blood, the plague bacteria multiply in the flea (proventriculus) of the fleas causing obstruction of the digestive tract. Fleas are clogged, when they switch to burning new hosts, the bacteria will follow the bite into the new host body and thus the spread of bubonic plague.

People can be infected from fleas, rodents, pets and cattle. In the steppe and desert areas, plague can be transmitted from camels: sometimes people get sick when contacting or eating infected animal products. In Russia there have been cases of marmot hunters infected.

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A marmot.

After getting into the body of the hot blood host, the plague bacterium meets cells of the immune system - phagocytes are responsible for detecting dangerous bacteria and removing them from the body. To do so they 'swallow' the bacteria.

However, the bubonic plague is very well protected: it produces many pathogenic factors - molecules that prevent the efforts of the immune system in the host body of hot blood to destroy them, the bacteria The epidemic multiplies very rapidly and breaks down the phagocytosis. The bacteria are then protected from the immune system cells.

The bacteria quickly spread throughout the body through the blood stream. With pneumonic plague when an infection occurs through the respiratory tract, death can occur within a day or even hours.

With Bubonic plague , the infection is contained in lymph nodes, they increase and rupture. If treated promptly with antibiotics, this disease can be cured.

Picture 3 of Why can't plague bacteria be completely eradicated on the planet?
Bubonic plague.

How long does bacilli live?

According to paleontological data, in the third millennium BC there were people with plague. Scientists have found this bacterium's DNA in human pulp. But the bacteria itself is no longer dangerous.

Bacteria that live in bones for no more than a year and a half. Unlike anthrax bacteria - Bacillus anthracis has the ability to infect for centuries, the plague does not form spores and is susceptible to death in the air or when boiled. It can operate in cold weather for a certain period of time. Scientists saw it clearly in the epidemic in Manchuria during the years 1910-1911: in the winter on the streets there were many dead bodies.

Today, the plague cannot happen, because the doctors control and quell the epidemic in time, implement isolation measures to prevent patients, not to contact with others.

Armory of 'killer'

What causes led to the appearance of a serial killer? Genetic or environmental? There is no definitive answer. With plague bacteria too. Why is one of its strains very dangerous? In 2001, the scientific community was hoping to find answers thanks to genome decoding. However, the question is still controversial to this day.

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The first victims of Earth plague, found in Samara, Russia.

Scientists have demonstrated that, genetically, bubonic plague is related to tuberculosis. Perhaps, these two bacteria were separated several tens of thousands of years ago.

Despite the almost complete similarity of the two genomes, these two bacteria work differently.Prosthetic tuberculosis Pseudotuberculosis spreads through food, causing acute inflammation and problems with the intestines, not spread from person to person. The plague is a deadly disease.

During evolution, the bubonic plague has developed methods of molecular survival in fleas' bodies, whereby bacteria can enter the blood of warm-blooded animals, where it multiplies.

Perhaps, the external environment also plays an important role, regulating bacterial activity, including its adaptive mechanisms.

The main factor is temperature. The virulence mechanism of the bubonic plague triggers an infection process below 37 degrees Celsius. Fleas have a body temperature of 26 degrees, mice with a temperature of 38-39, so they become infected faster and die. more often. In humans, the normal temperature is still below 37 degrees.

Scientists say global warming contributes to the emergence of modern plague. We cannot completely eradicate the plague bacteria, because the ecosystem it circulates is very complicated. We will have to learn to coexist with it.

In the 1990s, scientists came up with an idea that explains why some people still survive in the 'Black Death' pandemic. Experts from the National Cancer Research Institute noted that, about 700 years ago, there was a gene mutation in the human body - CCR5 receptor on the cell membrane of the immune system - that HIV attaches to it to get into the cell. If the CCR5 receptor in the human body is turned off, the person will not have AIDS: the virus has nothing to cling to. Perhaps, this mutation has developed in survivors of the medieval pandemic. However, this has not been confirmed experimentally.

Scientists are looking for new vaccines

People living in areas with chronic plague or working with this bacterium in the laboratory must be vaccinated.

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Mouse in the laboratory.

Experts from Russia, CIS countries and China use the live plague vaccine that French scientists developed in the 1930s at the Pasteur Institute in Madagascar. Last year, 19,000 people in the Altai region of Russia were vaccinated.

Live vaccines have some limitations: the expiration date is a maximum of one year, repeated injections may not work because people are still immune. Vaccines may have side effects, such as allergies. In addition, weakened bacteria can resume activity, although such cases have not been recorded.

In the West, for a long time experts used the USP vaccine developed in the United States in the 1940s. For example, to vaccinate soldiers fighting in Vietnam. In the 1990s, the United States stopped producing this vaccine because it was not effective in the form of pneumonic plague and had side effects.

Now experts are actively developing recombinant vaccines without the limitations of live vaccines. They use different antigens - proteins produced by bacteria to fight the patient's immune system. These molecules provide immunity against plague.

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