Tuberculosis, Plague and Cholera: How Epidemics Affect Humanity

What is an epidemic?

Epidemic - the progressive spread of an infectious disease among humans,

significantly exceeding the level of morbidity usually registered in a given territory and capable of causing an emergency.

In everyday life, the universal epidemiologicalthe threshold is considered to be the disease of 5% of the inhabitants of the territory or sometimes 5% of any social group. However, many health agencies calculate their own epidemic thresholds for common diseases based on the average rate of that disease over many years.

The branch of medicine that studies epidemics and methods of combating them is epidemiology. She studies epidemics of both infectious and noncommunicable diseases.

What is an epidemic process?

The epidemic process is continuoustransmission of the disease (in the case of an infectious disease - the causative agent of the infection) in the population. In other words, three factors (or conditions) are necessary for the emergence of an epidemic process:

  • the source of the causative agent of an infectious process or the cause of a non-infectious disease;
  • transmission mechanisms;
  • people susceptible to the disease (or in general living organisms: animals, plants).

The occurrence and course of epidemics are influenced by howprocesses occurring in natural conditions (natural focus, epizootics, etc.), and social factors (communal improvement, living conditions, health care, etc.).

Human-only sources of infections are anthroponoses, the sources of which are both man and animals, - anthropozoonoses.

For all infectious diseases from the momentinfection before the first visible signs of the disease appear, a certain time passes, called the incubation period. The duration of this period for various infections is not the same - from several hours to several years.

Mechanisms of transmission of the causative agent of infection

Depending on the nature of the disease, the main mechanisms of transmission of the pathogen during an epidemic may be:

  • fecal-oral (implemented through the water, food or contact-household route);
  • airborne droplets (for example, with the flu);
  • transmissible (for malaria and typhus);
  • contact (for HIV infection, rabies).

Sometimes several mechanisms of transmission of the infectious agent play a role. The course of an infectious disease will depend on how it entered the human body.

For example, the pulmonary, intestinal, and skin-bubonic forms of plague or anthrax are very different. Infectious factors can also be risk factors for non-communicable diseases.

Largest epidemics

  • "Justinian's plague". It originated in the Eastern Roman Empire and encompassed the entire Middle East. About 100 million people died from this epidemic.
  • The Black Death is an epidemic of both bubonic and pneumonic plague that swept across medieval Europe in the 14th century. It claimed the lives of 100-200 million people.
  • "Spanish flu" ("Spanish flu") - as a resultepidemics after the First World War, more than 550 million people were infected, or 30% of the world's population. Died approximately 50-100 million people, or 2.7-5.3% of the world's population, which makes this epidemic one of the largest catastrophes in the history of mankind. Thus, the mortality rate among the infected was 10–20%.

Plague of Athens (c. 1652-1654, Michael Swerts), illustrating the devastating epidemic that struck Athens in 430 BC. e.

How fatal diseases have changed humanity?

  • Tuberculosis

Tuberculosis affects carriers the mostmutations P1104A in the TYK2 gene. It affects the activity of monocytes - special cells of the immune system - and makes the body more vulnerable to infection. Today, thanks to natural selection, this variation in the human population is very rare.

  • Plague

According to the work of researchers from the University of South Carolina (USA), people who survived the epidemic of the medieval plague, on average, were healthier than those who inhabited Europe before the spread of the Black Death.

Paleogenetics came to this conclusion by studyingthe remains of over a thousand people. Some of them died before the outbreak of the plague in the XIV century, the rest - during or after it. Experts paid attention not only to the causes of death, but to the condition of bones and teeth.

It turned out that survivors of the epidemic and their descendants often reached 70-80 years of age and generally had good health.

  • Cholera

As scientists from Harvard University found out(USA), least often the disease is diagnosed in the inhabitants of the Ganges delta - Indians and Bangladeshis. More than a thousand years of constant contact with the infectious agent provoked changes in their DNA, and they are virtually immune to cholera.

First of all, we are talking about genes encoding potassium channels that release chloride ions in the intestine. It is the disturbances in their work in the infected that lead to diarrhea.

  • HIV

HIV originated in Africa.It was among the inhabitants of these places that scientists discovered the first signs of an emerging natural defense. Researchers studied blood samples from HIV patients from Congo and found that almost 4% of them are elite controllers, that is, their viral load is extremely low, and the disease itself, although they do not take special antiretroviral therapy, does not manifest itself in any way.

For comparison: in the rest of the world, this figure does not exceed 1% of all HIV-infected.

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