Influenza is an acute respiratory tract infection caused by a virus. Influenza virus is widely distributed in nature. Disease prone animals and people. Flu symptoms resemble those with a cold. Complications of influenza are serious and in some cases end in death. The disease is especially dangerous for young children, patients with severe chronic diseases and the elderly.
The virus multiplies rapidly and easily evolves. The flu incubation period is short and often takes several hours. Among all respiratory diseases, only with the flu are pronounced symptoms of intoxication, which begins to develop from the first hours of the disease. Redness of the soft palate and pharynx, high body temperature – the main signs of the flu.
Fig. 1. The photo shows the schematic structure of the influenza virus.
The flu has taken many human lives on the planet. His epidemics are recorded annually. In the 19th century alone, 45 epidemics were recorded.
The notorious flu epidemic “Spanish flu” in 1918 killed 20 million people. She went around the entire planet in a year and a half. In 1957, the Asian flu has bypassed the entire planet in just 7 months. The pandemic claimed the lives of more than 1 million people. In 1968, the “Hong Kong flu” raged on the planet. He claimed the lives of 2.5 million people. In 1931, “swine flu” was opened, the latest epidemic of which was registered in Russia in 2016.
Every year, 300-500 thousand people die from the complications of the flu.
The causative agent of influenza is evolving with amazing speed. Scientists do not have time to create new vaccines. Epidemics with a large number of deaths occur at intervals of 12 years. Epidemics with a smaller number of victims are recorded annually.
In Russia, more than 30 million people have the flu every year.
Among all respiratory infections, influenza accounts for up to 12%. The remaining 88% are:
- parainfluenza viruses – up to 50%,
- adenovirus infections – up to 5%,
- respiratory syncytial virus – up to 4%,
- Mycoplasma – up to 2.7%,
- enteroviruses – up to 1.2%.
Up to 23% of cases are mixed infections. Of all the above infections, only the influenza virus causes a devastating pandemic with high morbidity and mortality.
In the autumn, parainfluenza viruses are most commonly infected in the autumn, respiratory syncytial and influenza viruses in the winter, and enteroviruses in the late summer and early autumn, and adenoviruses infect humans throughout the year.
Influenza virus was first discovered in 1933. It is an RNA-containing virus of the orthomyxovirus family, having three independent antigen serotypes – A, B, C.
Fig. 2. The photo shows the structure of the influenza virus (3D model on the left and the diagram on the right). The virus has an elongated shape. Its oblong shape is due to the matrix – the structural protein M2, which contains 8 RNA molecules twisted into a helix. They make up the genome of the virus. The size of viral particles is thousands of times thinner than a human hair.
Fig. 3. The photo shows flu viruses in the light of an electron microscope.
Fig. 4. In the photo, the influenza virus (3D-model). Its outer side is represented by a membrane, the structure of which contains surface proteins (hemagglutinin and neuraminidase). The membrane is permeated with ion channels.
Hemagglutinin allows the virus to contact host cells and penetrate deep into it. Neuramidase promotes the separation of newly formed virus particles from the cell for subsequent penetration into new host cells.
Hemagglutinin and neuraminidase determine the narrow specificity of viruses – toxigenicity, variability and immunogenicity.
Fig. 5. In the photo, the influenza virus (3D-model). The M2 protein of the virus contributes to the formation of channels through which hydrogen ions penetrate inside it, triggering mechanisms for the proper unpacking of the genome and the production of copies of RNA.
Fig. 6. In the photo, the influenza virus (3D-model). The polymerase complex is involved in making copies of the virus RNA and the synthesis of structural proteins for new viruses.
The nuclear export protein delivers copies of RNA to the place where new viral particles are collected and packs them into a matrix. Next, the membrane of the virus is formed from the elements of the membrane of the affected cell.
Strains of influenza viruses
Influenza virus was first discovered in 1933. This is an RNA-containing virus of the orthomyxovirus family. They have three antigenically distinct serotypes – A, B, C.
Hemagglutinin promotes the formation by the human body of virus neutralizing antibodies. This protein consists of hundreds of amino acids, has a high variability. It is because of this that new strains of the influenza virus appear annually, and scientists have to constantly change the strains for the vaccine.
Neuraminidase, promotes the penetration of the virion into the host cell, also has antigenic properties.
Every 20 to 30 years, a new serotype of the influenza virus is formed. A change in serotype and causes a pandemic disease.
Influenza A virus is the culprit of the most severe forms of the disease. It is isolated from pigs, horses and birds. Serotype B and C viruses are dangerous only to humans.
Influenza B viruses less volatile. The disease is local in nature and is more common in large groups.
Influenza C viruses cause only sudden (sporadic) cases of disease, often in children of the first year of life. Its antigenic structure is constant and, as a rule, all children from the age of 10 have antibodies to this virus.
Swine flu was discovered in the USA in 1931 by the scientist Richard Shope. Strains associated with outbreaks of swine flu were found among influenza viruses of serotype C and serotype A subtypes (influenza H1N1, H1N2, H3N1, H3N2 and H2N3). The causative agent of avian influenza is an RNA-containing virus Influenza virus A. It belongs to the Orthomyxoviridae family. Complement-binding antigen (RNP) is related to influenza A virus.
Epidemiology and pathogenesis of the disease
The source of the flu virus is a sick person. It remains highly contagious from the first hours of the disease to 3–5 days. Contribute to the mass spread of the disease patients with erased forms of the disease. When coughing and sneezing, viruses spread to the surrounding environment with the slightest drop of moisture. With particles of moisture from the patient, with dust from the floor and household items of the patient, they enter the body of a healthy person.
Warming up to 50 ° C and the impact of disinfectants on viruses manifests itself instantly.
Virus multiplication occurs in the cytoplasm of the epithelial cells of the respiratory tract. Particularly sensitive is the cylindrical epithelium of the lower nasal conchae and the trachea, which is damaged, necrotized and exfoliated. Further, viruses penetrate into the bloodstream and act on the vascular endothelium, increasing their permeability. The blood vessels dilate and overflow with blood. Hemorrhages occur, blood clots form, and DIC develops.
The flu primarily affects the blood vessels and the nervous system (central and vegetative).
- Protect the body from ds-RNA-dependent viruses protein kinase and induction of type 1 interferon, activation of which is associated with the reproduction of viruses. As a result of their exposure, viruses begin to die within 20 to 40 hours after division (replication).
- Special subpopulations of blood cells protect the body from viruses. lymphocytes.
Suppression of immunity leads to the development of secondary flora, which contributes to the development of bacterial complications.
Signs and Symptoms of Flu
The incubation period for influenza lasts from several hours to 3 – 5 days. Next begins the period of the disease. The severity of the disease is influenced by the age of the patient and the type of virus.
Among all respiratory diseases of the upper respiratory tract, only with the flu, intoxication syndrome is pronounced, which begins to develop from the first hours of the disease:
- Body temperature in a short time it rises to maximum rates and lasts a short time (up to 3–5 days with influenza A and up to 7 days with influenza B). Another temperature pattern is indicative of a bacterial complication. Chills and chills accompany the fever.
- Headache localized in the frontal part and in the eyeballs. The movement of the eyeballs and the pressure on them causes increased pain.
- Weakness and severe muscle and joint pain.
There are mild and erased forms of influenza. It is this category of patients that spreads the infection during epidemics and pandemics.
Symptoms and symptoms of influenza in the upper respiratory tract
Influenza viruses possess tropism to the epithelium of the upper respiratory tract. On examination, patients noted redness of the soft palate and pharynx. In severe disease, nosebleeds and punctate hemorrhages in the soft palate are noted.
Fig. 7. In the photo acute catarrhal angina. The hyperemia of area of lateral rollers, a throat and a throat is noted.
Symptoms and signs of flu in severe disease
A severe course of the disease is indicated by an increase in the patient’s body temperature to 40 ° C. The brain suffers, which is manifested by excitement, hallucinations and convulsive seizures. Meningeal symptoms appear – signs of inflammation of the pia mater. Vomiting and nasal bleeding develop. There is a danger of death.
For rapid diagnosis of influenza in the reaction of immunofluorescence (RIF) use a smear from the nasopharynx. The method of paired sera is used for retrospective diagnosis of the disease.
Complications of influenza during influenza epidemics are 25-30%.
- One of the worst complications is infectious toxic shock, which develops acute cardiovascular failure, pulmonary and brain edema, DIC. In the case of fulminant form of the flu, an infectious toxic shock develops on the first day of the disease.
- Pneumonia (viral, bacterial or mixed) develops in 15 – 30% of cases. Especially hard viral pneumonia. The disease has a large percentage of mortality. Influenza viruses multiply in the epithelium of the upper respiratory tract and immediately begin to infect the tracheal epithelium, then the bronchi and alveoli. On the way to the lung tissue, the viruses mutate and the antiviral drugs that the patient takes are powerless. Without proper medical care, death occurs on the 3rd day. Proper treatment of influenza pneumonia is only in a well-equipped hospital. The causes of high mortality in influenza pneumonia are: untimely seeking medical help, self-treatment and the lack of vaccination.
- Aseptic meningitis and meningoencephalitis.
- Infectious-allergic myocarditis and pericarditis.
- Rhabdomyolysis syndrome develops, which is characterized by the destruction of muscle cells and the subsequent development of acute renal failure.
After flu, in 65% of patients, asthenic syndrome persists for several weeks, characterized by weakness, fatigue, headache, insomnia, and emotional disorders.
Recommendations for the prevention and treatment of influenza
Vaccine prophylaxis is the basis for the prevention of influenza. Tamiflu, Ingavirin, Kagocel and Arbidol – drugs recommended for the treatment and prevention of influenza by the Ministry of Health of the Russian Federation. They are highly effective for the first 3 days of the disease. On the 4th day, their effectiveness decreases to 50%. Before taking these drugs, you must carefully read the instructions.
Reduce the risk of spreading the flu and avoid disease can be, if you follow simple sanitary and hygienic rules, what is necessary for:
- Minimize contact with patients with the flu, do not come closer to them than a meter.
- Do not attend mass events during the flu period.
- Wash hands frequently and wipe with alcohol-based solutions.
- Wear a mask.
- Do not touch your face, eyes and nose with dirty hands.
Fig. 8. Capsules and powder for the preparation of Tamiflu suspensions for the treatment and prevention of influenza in children from the 1st year of life and adults. It has antiviral activity.
Fig. 9. Immunity stimulator Kagocel for the treatment and prevention of influenza in children from 3 years and adults and the antiviral drug Ingavirin.
Fig. 10. Antiviral agent Arbidol tablets and Arbidol maximum capsules. It is used for the treatment and prevention of influenza in children from 3 years and adults.
Thousands of people get the flu every year. The economic damage from it is enormous. Preventive measures will help a person to avoid the disease or reduce its manifestations. Adequate treatment will help avoid complications of the flu.
Read more about the treatment of flu and its prevention in the article.