Influenza virus – types, routes of infection, risk groups, diagnostics

Proven content

Influenza is an infectious viral disease that affects the upper and lower respiratory tract. Flu symptoms include: runny nose, high fever, cough, sore throat. It is caused by a wide range of flu viruses. Some of these viruses can infect humans and some are specific to different animal species. The WHO estimates that seasonal flu can result in 290 to 000 deaths each year from respiratory disease alone.

Influenza virus – types and characteristics

There are four types of influenza viruses: A, B, C and D. Influenza viruses have receptors responsible for their species specificity. Influenza A and B viruses infect humans every year during the epidemic season. There are many different strains and they can change every year.

Influenza A virus

1. It has several subtypes depending on the combination of the hemagglutinin (H) and neuraminidase (N) proteins, which are expressed on the surface of viruses.
2. A hemagglutinin protein (such as an antibody or viral capsid protein) that causes haemagglutination, which is the agglutination of red blood cells.
3. There are 18 different hemagglutinin subtypes and 11 different neuraminidase subtypes (H1-18 and N1-11).
4. Influenza A viruses can be characterized by types H and N, such as H1N1 and H3N2.

Influenza B virus

1. Not classified into sub-types, but can be categorized by origin.
2. Currently, the circulating influenza B viruses are of the B / Yamagata or B / Victoria lineage.

Influenza C virus it is detected less frequently and tends to cause mild infections and is therefore not relevant to public health.

Influenza D viruses they primarily attack cattle and are not known to infect or cause disease in humans.

See also: One of the flu viruses has disappeared. What could this mean? Two scenarios and a question mark

Flu virus – who is most at risk?

All age groups can be affected by the flu virus, but there are groups that are more at risk than others.

People at greater risk of developing serious illness or complications from infection include:

1. pregnant women;
2. children under 59 months of age;
3. elder people;
4. people with chronic conditions (such as chronic heart, lung, kidney, metabolic, neurodevelopmental, liver or hematological diseases);
5. people with immunosuppressive diseases (such as HIV / AIDS, taking chemotherapy or steroids, or suffering from cancer).

Healthcare workers are at high risk of infection with the influenza virus (due to increased contact with patients) and the risk of further spreading the virus, especially among vulnerable people.

Seasonal flu spreads easily, with rapid transmission in crowded places such as schools and nursing homes.

In temperate climates, seasonal epidemics mainly occur in winter, while in tropical regions flu can occur all year round, causing more irregular outbreaks.

The time from infection to disease, called the incubation period, is about 2 days, but varies from one to four days.

Influenza virus – pathophysiology

Influenza is an acute disease that affects the upper respiratory tract, causing inflammation of the upper respiratory tract and trachea.

Acute symptoms persist for seven to ten days, and the disease resolves on its own in most healthy people.

The immune response to viral infection and the interferon response are responsible for the viral syndrome, which includes high fever, runny nose and body aches.

High-risk groups (e.g., chronic lung disease, heart disease, and pregnancy) are more prone to serious complications such as primary viral pneumonia, secondary bacterial pneumonia, hemorrhagic bronchitis, and death. These serious complications may develop as early as 48 hours after the onset of symptoms.

The virus replicates in the upper and lower respiratory tract from the moment of inoculation and peaks after an average of 48 hours.

See also: The first symptoms of a respiratory infection that must not be ignored

Influenza virus – pathways of infection

Influenza virus and droplet infection

The sneezing and coughing of an infected person scatter droplets containing the flu virus. The droplets are relatively large and do not travel very far, but the virus can enter directly into the respiratory tract of people one to two meters from an infected person, causing infection as well. The virus can also enter the body directly through the mucous membranes of the eyes.

Influenza virus and contact infection

The flu virus enters the body through the mucous membranes when people unknowingly bring their hands containing the virus particles to the eyes, nose or mouth. Because the flu virus can survive for long periods in a dry environment, it spreads when it gets on items such as telephones, door handles, dishes, and railings on trains and buses, causing infections when other people touch them later.

Prevention of infections

Annual vaccination is the mainstay of flu prevention.

Remember to wash your hands regularly and gargle each day. If we feel even a bit sick, don’t forget to put on the mask. Other preventive measures include adequate sleep and proper nutrition, and generally paying more attention to daily health during the flu season.

See also: What are the types of face masks? [WE EXPLAIN]

Flu virus – symptoms and signs

Seasonal flu is characterized by:

1. sudden onset of fever, cough (usually dry), headache, muscle and joint pain, feeling unwell, sore throat and runny nose.
2. cough, which may be severe and last for 2 weeks or more.

Most people recover from fever and other symptoms within a week without needing medical attention. However, the flu can cause serious illness or death, especially in high-risk people.

Diseases range from mild to severe and even fatal, with hospitalization and death mainly occurring in high-risk groups. Globally, these annual epidemics are estimated to cause approximately 3 to 5 million cases of serious disease and approximately 290 to 000 respiratory deaths. In industrialized countries, the majority of flu-related deaths occur among people 650 years of age or older.

Outbreaks can result in high rates of employee / school absenteeism and loss of productivity. Clinics and hospitals can be overloaded during periods of peak disease.

The effects of a seasonal flu epidemic in developing countries are not fully known, but studies estimate that 99% of deaths of children under 5 from influenza-related lower respiratory tract infections occur in developing countries.

Influenza virus – diagnosis

Most cases of influenza virus are clinically diagnosed. However, during periods of low flu activity and outside epidemic situations, infection with other respiratory viruses such as rhinovirus, respiratory syncytial virus (RSV), parainfluenza virus and adenovirus may also present as a flu-like illness, making it difficult to clinically distinguish influenza from other influenza viruses. pathogens.

The final diagnosis requires the collection of appropriate respiratory samples and the use of a laboratory diagnostic test. Proper collection, storage, and transportation of respiratory specimens is the essential first step in the laboratory detection of influenza virus infection.

Laboratory confirmation of influenza virus from pharyngeal, nasal and nasopharyngeal secretions or tracheal or lavage aspirate is commonly performed using direct antigen detection, virus isolation, or influenza-specific RNA detection using reverse transcriptase polymerase chain reaction (RT-PCR). Various guidelines for laboratory techniques are published and updated by WHO.

Rapid influenza diagnostic tests (RIDTs) are used in a clinical setting, but have lower sensitivity compared to RT-PCR methods, and their reliability largely depends on the conditions under which they are used.

See also: Viruses that threaten you all year round. Is it possible to protect against them?

Flu virus – treatment

Mild flu goes away on its own without any treatment. Ways to relieve symptoms include:

1. rest;
2. drinking fluids, especially water;
3. taking paracetamol to reduce pain and fever;
4. the use of vasoconstrictors.

Patients who are not at high risk should receive symptomatic treatment and should stay home when symptoms develop to minimize the risk of infection to other members of the community. Treatment focuses on relieving flu symptoms such as fever. Patients should be monitored to see if their condition is worsening and seek medical attention. Patients known to be at high risk of developing severe or complicated disease should be treated with antiviral therapy in addition to symptomatic treatment whenever possible.

Patients with severe or progressive clinical disease related to suspected or confirmed influenza virus infection (i.e. clinical signs of pneumonia, sepsis, or exacerbation of chronic disease) should be treated with an antiviral agent as soon as possible.

Neuraminidase inhibitors (i.e. oseltamivir) should be prescribed as soon as possible (preferably within 48 hours of onset of symptoms) to maximize therapeutic benefit. Administration of the drug should also be considered in patients with later symptoms of the disease. A minimum treatment of 5 days is recommended, but may be extended until a satisfactory clinical improvement is achieved.

Corticosteroids should not be used routinely unless indicated by other reasons (e.g., asthma and other specific medical conditions); as it is associated with prolonged clearance of the virus, immunosuppression leading to bacterial or fungal superinfection.

All currently circulating influenza viruses are resistant to adamantane antivirals (such as amantadine and rimantadine) and therefore monotherapy is not recommended.

WHO GISRS monitors antiviral resistance among circulating influenza viruses to provide up-to-date guidance on the use of antivirals in clinical management and potential chemoprophylaxis.

Antibiotics should not be used to treat colds or flu, which are viral, not bacterial, infections.

See also: Sales of amantadine are growing rapidly. Even a veterinarian can give you a prescription

Flu virus – complications

The flu virus has a huge incidence. Many people have to take time off from work and school. In children and seniors, the infection can lead to death. Mortality is higher in people with pre-existing lung disease and diabetes. Overall, the condition caused by the flu virus can severely reduce quality of life for 1-2 weeks each season.

Complications include:

1. secondary bacterial pneumonia;
2. acute respiratory distress syndrome (ARDS);
3. muscle inflammation;
4. myocarditis;
5. multi-organ failure.

Influenza virus – prevention

Vaccination is the most effective way to prevent the flu virus. Safe and effective vaccines have been available and have been in use for over 60 years. As immunity to vaccination weakens over time, annual vaccination is recommended to protect against flu. Injectable inactivated influenza vaccines are the most widely used worldwide.

In healthy adults, the flu vaccine provides protection, even when the circulating viruses do not match the vaccine viruses exactly. However, among the elderly, influenza vaccination may be less effective in preventing disease, but it reduces the severity of the disease and the incidence of complications and deaths. Vaccination is especially important for people who are at high risk for influenza complications and for people who live with or care for high-risk people.

WHO recommends annual vaccinations for:

1. pregnant women at any stage of pregnancy;
2. children from 6 months to 5 years of age;
3. the elderly (over 65);
4. people with chronic diseases;
5. health professionals.

The flu vaccine is most effective when the circulating viruses are well matched with the viruses in the vaccines. Due to the constantly evolving nature of influenza viruses, the WHO’s Global Influenza Surveillance and Response System (GISRS) – the system of National Influenza and WHO Collaboration Centers around the world – continuously monitors influenza viruses circulating in humans and updates the composition of the vaccine flu twice in year.

For many years, WHO has been updating its recommendations on the composition of a (trivalent) vaccine that targets the three most representative types of virus in circulation (two subtypes of influenza A viruses and one influenza B virus). As of the 3–2013 Northern Hemisphere flu season, a fourth component is recommended to support the development of a tetravalent vaccine.

Quadrivalent vaccines contain a second influenza B virus in addition to the viruses in the trivalent vaccines and are expected to provide wider protection against influenza B infections. Many inactivated influenza vaccines and recombinant influenza vaccines are available as injectables. The live attenuated flu vaccine is available as a nasal spray.

Prevention before or after exposure to antiviral drugs is possible, but depends on several factors, including individual factors, type of exposure and exposure risk.

In addition to vaccination and antiviral treatment, public health management includes personal protective equipment, such as:

1. washing hands regularly with proper hand drying;
2. good hygiene of the respiratory tract – covering the mouth and nose when coughing or sneezing, using tissues and disposing of them properly;
3. early self-isolation of people who feel unwell, have fever and other flu symptoms;
4. avoiding close contact with sick people;
5. avoiding touching your eyes, nose or mouth.

See also: Vaccination myths

Influenza virus, bird flu and other zoonoses

People can be infected with avian, swine flu and other zoonotic viruses, e.g. avian influenza virus subtypes A (H5N1), A (H7N9) and A (H9N2), and swine influenza virus subtypes A (H1N1), A (H1N2) and A (H3N2). Influenza (H1N1) in particular led to the pandemic in 2009. It has been commonly referred to as “swine flu” due to the origin of the virus. The CDC (Centers for Disease Control and Prevention) estimates that between 1 and 1 people died around the world in the first year of the spread of the virus (H151N700). About 575% of these deaths are thought to be in people under the age of 400, which is remarkable. During typical seasonal flu epidemics, 80 to 65% of deaths occur in people over the age of 70.

Human infections are mainly acquired through direct contact with infected animals or a contaminated environment, these viruses have not acquired the ability to be permanently transmitted among humans.

Avian, swine, and other zoonotic influenza viruses in humans can cause a variety of diseasesranging from a mild upper respiratory tract infection (fever and cough), early sputum production and rapid progression to severe pneumonia, shock sepsis, acute respiratory distress syndrome, and even death.

See also: What is the symptom of phlegm in blood?

Flu virus – frequently asked questions

How is the flu different from the common cold?

The flu is different from the common cold in that it is more contagious and has more severe symptoms. In addition, the symptoms of a cold are dominated by a sore throat, runny nose, sneezing and coughing with a fever of about 37 ℃ to 38 ℃; it is not associated with severe systemic symptoms.

When should I get a flu test?

Given the relationship to treatment, it is strongly recommended that you do the test within 48 hours of onset of symptoms as this is when the flu virus is multiplying. The viral load peaks between 24 and 48 hours after the onset of symptoms.

What can be done to cope with dehydration during the flu?

Staying hydrated is very important for someone with the flu virus as high fever, diarrhea and vomiting can cause dehydration which can be life threatening. Rather than drinking only water, an effective way to prevent dehydration is to consume commercially available products with a good balance of sugars to aid absorption, such as sodium and potassium rehydration solutions (essential for maintaining the body’s water balance).