Where do influenza epidemics come from? Where do human viruses come from? What is the difference between a cold and the flu

Exactly a century ago, in December 1918, world medicine received a resounding slap in the face, from which it could not recover for many decades. The influenza pandemic, the so-called “Spanish flu,” claimed 100 million lives. This is 5 times more than the losses of all the warring countries in the First World War. The influenza virus is a ruthless killer. Is the modern global health system ready for a new attack?

The Spanish flu pandemic did not start in Spain, as you might think, but in China. It was there that the first symptoms appeared among residents of villages located along the Great Wall of China. The United States and England, both in need of cheap labor in those years, traditionally imported peasants from Southeast Asia. With them, the virus slipped into America and then came to Europe.

Despite the terrible consequences, data about the epidemic was kept silent on both sides of the ocean. The only country that retained a free press was Spain. When the number of cases amounted to 40% of the total population, and 100 people died a day, it was publications in the Spanish press that shook the whole world. The pandemic was called the "Spanish flu".

The pandemic that started in the spring of 2009 was called “swine flu.” The killer virus was born from the fusion of three pathogens: human, avian and swine. In general, Russia escaped with a slight fright: only 8.5% of the sick. Epidemiologists note that severe cases and deaths were observed among patients who were not vaccinated with seasonal vaccines.

Firstly, any acute respiratory infection after vaccination is much easier. Secondly, and this is the main thing, your immunity is prepared for a pandemic, and you will not add to the sad statistics. This is the WHO statement. The global influenza control system includes 152 national centers in 116 countries (of which 6 are located in Russia). Such centers operate 365 days a year.

In the USA alone, the use of a vaccine against 4 strains of viruses reduced the incidence of influenza by 1.3 million cases, there were 12,472 fewer hospitalizations, and 664 fewer deaths. So the vaccinated part of humanity is ready for the Spanish flu.

The free vaccination period has ended. If you don’t have time, folk remedies will help maintain your immunity: onions, garlic, hardening.

There are two known ways of variability of the influenza virus: antigenic drifts, that is, progressive changes in the structure of viruses circulating among the population, and antigenic shifts, the emergence of new or the return of old viruses.

Antigenic drift has been most fully traced in viruses of the so-called Hong Kong series. This virus (Hong Kong/68) first appeared in 1968 and has since continued to circulate among people for 15 years. During this time, it (mainly its hemagglutinin) has undergone such an intense drift and changed so much that the original virus and one of its latest variants, recently isolated in the Philippines, are strikingly different from each other in their properties.

Studies have shown that the vaccine against the Hong Kong/68 virus has virtually no effect on the Philippines/82 virus, which means that the immunity developed to the Hong Kong virus is absolutely incapable of protecting people from its Philippine descendant. Experts no longer argue about the mechanisms of drift; everyone recognizes that this path of variability is due to the gradual selection (selection) of new variants of the virus during its circulation among people.

Antigenic shifts - the sudden appearance of a new influenza virus with a dramatically changed hemagglutinin structure causes a wider, pandemic spread of the disease. Sometimes a virus that once circulated among people a long time ago becomes new and returns after many years of absence. This was the case, for example, when a variant of the influenza A virus returned in 1977, 20 years after the pandemic it caused.

There is still no exact answer to the question: where do old influenza viruses go and where do new ones come from? Scientists' opinions are divided. Some believe that disappeared influenza viruses continue to circulate latently (hidden) among people, not presenting any danger until their properties change. Some viruses settle in the body of animals, and this path is a dead end from which there is no return back to people. However, there is much that is unclear in this theory.

I am a supporter of another theory and believe that extinct influenza viruses circulate among animals before returning to humans. Having settled in their body, viruses do not end up in a dead end, but in a kind of cauldron, in which numerous recombinations (crossings) occur between viruses of humans, animals, and especially birds. As a result, new formidable enemies appear, which, returning to people, cause a flu pandemic.

Of course, this theory also needs additional confirmation.

V. M. Zhdanov, Academician of the Academy of Medical Sciences of the Russian Federation

Article "Where do old influenza viruses go and where do new ones come from" from the section

In the summer, the authorities of Belgian Wallonia asked municipalities to prepare graves in advance for those killed by “swine flu” (flu AH 1 N 1), because when frost comes, digging will be more difficult. In Russia, the chief sanitary doctor Onishchenko reported weekly all summer: 4 sick people were registered... 30 sick people... 55 sick people... Where swine flu came from, how dangerous it is and how you can protect yourself, the deputy told Neskuchny Sad. Director of the State Research Institute of Vaccines and Serums Institute named after. I. I. Mechnikova, virologist, doctor of biological sciences, professor Nadezhda YUMINOVA.

—Where did swine flu come from? Where do new viruses even come from?

— We know no more than 8% of the types of viruses existing on Earth. However, science is developing, scientists are discovering what they previously could not isolate and identify, so the number of viruses is “growing.” Actually, the influenza virus itself was first discovered only in 1931, although an influenza-like disease was described by Hippocrates.

The diversity of virus strains (variants) also arises due to mutations. When reproducing in a living organism, random changes occur due to errors in copying the virus in the victim’s cell - viruses exchange genetic material (genes) and thus mutate. Mutations that occur over time are called antigenic drift. But there is an antigenic shift - a sharp change. It leads to the formation of hybrids with completely new properties. Mutations occur constantly, increasing the survival rate of viruses and becoming fixed.

Not only people get sick with the flu, but also some birds and animals - horses, pigs, etc. Viruses are usually transmitted within their species, but under certain conditions they can be transmitted from birds, pigs, horses to humans, and vice versa. The peculiarity of the current strain is that its genetic code simultaneously contains fragments of pig, avian and human nucleotide sequences. This could happen under an unfavorable combination of circumstances - for example, three epidemics coincided at once: birds, pigs and humans. Pigs are sensitive to both human influenza viruses and avian influenza viruses, and it is possible that both viruses entered the pig's body at the same time, the final version multiplied and caused the epidemic that we are now seeing.

— What is the difference between an epidemic and a pandemic?

— An epidemic is a widespread disease within a region, with a high morbidity rate in the population (up to 40%), affecting all age groups. For many years, influenza A epidemics were thought to occur every 2–3 years, but since 1977 they have occurred annually. The duration of an influenza epidemic is usually 3–6 weeks.

A pandemic is an epidemic that has affected many countries around the world, with the process catching fire like straw from a match. Typically a pandemic lasts two years. The frequency of pandemics is 30–40 years. All influenza pandemics were caused by the A virus, the most famous being the Spanish flu, which was carried out in 1918–19. life approx. 40–50 million people. In the first months, the “Spanish flu” was not fatal, but during the stages of transmission from person to person, the pathogenic properties of the virus increased and most deaths were caused by the second wave of the virus, which had time to mutate. A large outbreak of H1N1 influenza, which spread to humans from pigs, was recorded in 1976 in Fort Dix, USA, among recruits. However, there was no subsequent swine flu epidemic. Apparently, a reverse mutation occurred, and the virus degenerated into an ordinary human one.

Two more major influenza pandemics of the last century, the Asian H2N2 influenza in 1957–58. and Hong Kong H3N2 influenza in 1968–69, killing 2 and 1 million people. With each pandemic, there are fewer victims thanks to the development of modern medicine.

When the next one will be is a matter of time. The influenza virus is so variable that it is impossible to make an accurate forecast.

— Is swine flu really that dangerous? After all, people also die from complications of the regular flu? And how can you avoid infection?

— The mortality rate for bird flu is 50–60%, and for swine flu it is at the level of regular flu. Danger of disease primarily in complications - hypertoxic syndrome, in which there is a high risk of bronchopneumonia and pulmonary edema; hemorrhagic lesions - runny nose with bleeding - a sign of toxicosis; shortness of breath caused by pneumonia, secondary bacterial infections and complications on the cardiovascular system.

The virus “more readily” affects people aged 25 to 40 years. Perhaps because the older generation has been ill and has a stronger immune system, and children are now regularly vaccinated against the flu.

Influenza is mainly transmitted through airborne droplets. But infection is also possible through direct contact: for example, when the virus gets on a wound, cut, or mucous membranes.

Many people are now afraid to eat pork. In fact, at a temperature of 76º C, the influenza virus, like most other viruses and bacteria, dies. But as long as we are talking about a new species, safety measures will not hurt. For meat - longer heat treatment.

How to protect yourself from infection? Observe normal sanitation and hygiene measures - avoid large crowds of people, close contact with infected people, wear a gauze bandage during contact, frequently wash your hands, especially after coughing, and clean your hands with alcohol-containing liquids.

At the state level, monitoring and prompt response to outbreaks and the coherence of the system of anti-epidemic measures will help. Of course, the level of modern medicine allows us to hope that the infection will not cause the same mortality as with the Spanish flu. But the danger is that the Russian pharmaceutical market contains only 30% of domestic drugs. And if, God forbid, a pandemic begins, states that have vaccines will first of all try to provide for their citizens. So the availability of vaccines in the country is a matter of national security.

— And if you do get sick, how to treat it? How do you know if it's swine flu or not?

— Incubation period for new influenza- as usual: from several hours to 3-4 days, maximum 7. Watch for symptoms: sudden onset, sudden increase in temperature, up to 40 degrees, headache, muscle pain, chills, weakness, inflammation of the upper respiratory tract, nasal cavities and mucous membranes of the eyes, lacrimation. Nausea, vomiting, and diarrhea may occur.

WHO recommends the use of neuraminidase inhibitors oseltamivir and zanamivir (Relenza and Tamiflu), and the same advice is given by the FDA, although there is no laboratory data on their effectiveness against the California strain. Under no circumstances should you reduce your fever with aspirin - this can cause hemorrhagic complications and bleeding.

To accurately establish the diagnosis, it is necessary to conduct a laboratory PCR test (nucleic acid polymerase chain reaction method). To do this, a respiratory sample is taken in the first 5 days of the disease. Swine flu can also be detected by the presence of specific antibodies in the blood and mucous membranes of a person. All these laboratory diagnostic methods are well established in the Russian Federation. True, this is expensive research.

Lyudmila Kovaleva

Worldwide, respiratory infections account for up to 95% of morbidity cases in the autumn-winter period. Moreover, most often ARVI is caused by the influenza virus. But what is this virus, where did it come from and why is it dangerous?

What is a virus?

Any virus is a microscopic particle consisting of proteins of different types, each of which performs a specific function. It includes:

• Chains of DNA or RNA that contain all the genetic information necessary for the reproduction of a new particle.
• A protein protective shell that preserves it under adverse conditions.
• Special protein molecules that are located on the shell and help recognize body cells and attach to their surface.

Viruses can infect any organism, including plants, insects, and even bacteria. Today, scientists know about six thousand different species of this pathogen, but in fact there are many more.

Basic properties

Unlike other sources of infectious diseases, such as bacteria, viruses have completely different properties:

• They cannot actively exist and reproduce outside the cell, since they do not have their own energy and protein-synthesizing systems. They borrow all this from the infected cell, literally forcing it to work for themselves.
• They have a durable shell that protects them from the negative influences of the external environment. Therefore, when outside the cell, pathogens are able to withstand heating or cooling to extreme temperatures.
• They are not able to grow, but reproduce only by reproducing a new particle from their own genetic material.

Due to its rather simple structure, the virus is able to penetrate any living cell, passing through all the body’s defense systems.

Bypassing the cell membrane, its nucleus, with the genetic information it contains, is introduced into the nucleus of the host cell and completely rebuilds its work. As a result, the cell itself begins to synthesize new particles of the pathogen, which, after its death, spread throughout the body and infect new cells.

Origin

Viruses have been known to mankind for thousands of years. The same flu was first described by Hippocrates back in 412 BC. True, it was not the ancient scientist who discovered the viral nature of this disease, but the American R. Shope in 1931.

As for its origin, the opinions of scientists are divided. Today there are three versions of this event:

• The theory of evolution, according to which all viruses, including influenza, occurred due to the fact that some single-celled organisms began to develop in the opposite direction.
• The theory of coevolution or joint evolution, according to which these pathogens evolved simultaneously with the first living cells on Earth, only their development followed a slightly different path.
• The theory of cell origin, which states that they were formed from remnants of genetic strands of DNA or RNA that were unnecessarily released from the genome of another organism.

Unfortunately, each of the existing theories of origin has its own weaknesses, and it has not yet been possible to determine exactly where the first viruses came from.

However, there is an answer to the question of where viruses dangerous to humans come from. They usually appear as a result of mutations of pathogens that previously affected only animals or birds. Thus, in 2003, the SARS virus appeared, which causes atypical pneumonia and which passed to humans from animals.

Many factors can lead to mutations and spread of viruses, but the main ones are:

• Constant growth of the planet's population.
• Increased opportunity to travel to other countries and even to other continents.
• Developing trade and industrial relationships that may allow pathogens to travel across oceans, for example in shipments of fruits, vegetables or meat.
• Development and creation of new antiviral agents, which can also cause changes in microparticles of the pathogen and lead to the emergence of other species.
• The development and development of regions with wild nature, each of which can harbor its own special microorganisms, not yet known to man and capable of causing infectious diseases.

Viruses are volatile and can reproduce themselves at amazing speeds. One infected human cell can produce up to 100 million viral particles. To date, the most effective method of combating this pathogen is vaccination.