How Does the Flu Virus Spread?

The spread of the flu virus is a very important issue, because flu is a severe viral infection that attacks people regardless of gender and age. This disease is characterized by severe toxicosis, catarrhal symptoms, runny or stuffed nose, and cough.


The source of infection

Typically, the source of the virus is a sick person. However, recent studies have shown that influenza A virus can be transmitted from animals to humans.

A sick person is capable of transmitting the virus during eight days from the start of the disease. People sick with flu are mostly dangerous in the first two days of illness. Those who leave the house during these days are the greatest danger to other people. They visit public places, use public transport, thereby contributing to the rapid spread of the disease, especially in large cities. Continuing to lead an active lifestyle, they infect large numbers of people.

The spread of the virus

There are several ways to spread the virus.


Airborne is the most common way of transmitting the virus. Every day approximately 15,000 liters of air pass through the human respiratory tract. The microorganisms it contains are filtered and deposited on the surface of epithelial cells. The air inhaled is dangerous if it contains pathogenic bacteria and viruses.

When a sick person is talking, coughing, sneezing, or just breathing, the mucous membranes of his or her respiratory tract release particles of saliva, sputum, and mucus containing pathogenic microflora, such as influenza viruses, in the environment. Shortly, the patient is surrounded by the area of an increased infection risk, characterized by the highest concentration of aerosol particles. The mucosa of a healthy person is an entrance gate for the flu virus. Virus particles are transmitted through air from an infected person to a healthy one.

Virus particles emissions when sneezing

The flu virus concentration and its resistance are primarily dependent on the size of aerosol particles. Both figures are very high when you sneeze with your mouth open. If a patient sneezes with the mouth closed, the amount of air emitted decreases by 10-70 times, and, accordingly, the concentration of the flu virus in the air decreases.

Household contacts

The influenza virus can survive in the environment up to three weeks. Therefore, the risk of infection through infected household items is quite high. The virus can be transmitted through household items, linens, dishes, toys, toiletries. Remember that heating to 50-60°C inactivates the virus during several minutes, while disinfectants do it instantly.

How the virus attaches itself to the cell

The virus particles are retained on the respiratory tract epithelium. They are attached to epithelial cells by means of hemagglutinin. Neuraminidase enzyme destroys the cell mucous membrane and the virus penetrates the cell. The viral RNA enters the cell nucleus. As a result, the cell’s vital functions are violated, and it begins to produce viral proteins. Simultaneously viral RNA replicates and assembles viral particles. New viruses are released (simultaneously, the destruction of cells occurs), and they infect other cells.

Getting into the blood, the virus spreads throughout the body. The contagious period begins at the end of the incubation reaching its maximum in 1-2 days after the illness begins. On the 5th -7th day of illness, the virus concentration in the exhaled air is significantly reduced, and the patient is practically harmless to others.

Transmission peculiarities

  • The droplets spread through sneezing and coughing are quite small (from 0.5 to 5 microns in diameter). Each time you sneeze, you release up to 40,000 droplets. However, even a single droplet may be enough to catch the infection.
  • How long the influenza virus survives in the air depends on the humidity and ultraviolet radiation. Low humidity and lack of sunlight in winter contribute to its survival.
  • Since the flu virus can persist outside the body, it can also be transmitted through contaminated surfaces such as banknotes, doorknobs, light switches and other household items.

The virus persists:

  • Within a day or two on non-porous surfaces such as plastic or metal.
  • Within fifteen minutes on dry tissues and paper.
  • Only five minutes on the skin.
  • However, if the virus is present in the mucus, it can survive a longer period.
  • The bird flu virus can survive freezing.
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