Influenza virus information

Influenza virus information

Influenza viruses cause influenza and are divided into three types, designated A, B, and C. Influenza A and B are responsible for epidemics of respiratory disease that occur nearly every winter and are often associated with increased hospitalization and mortality. Influenza C differs from types A and B in important ways. Type C infection usually causes very mild respiratory illness or no symptoms at all; it does not cause epidemics and does not have serious public health implications for influenza A and B. Efforts to control the effects of influenza are targeting influenza A and B.

Influenza viruses change over time, usually through mutations (changes in viral RNA). This constant change often allows the virus to evade the immune system of the host (humans, birds, and other animals), leaving the host vulnerable to changing influenza viruses throughout life. The process works as follows: a host infected with the influenza virus develops antibodies against the virus; as the virus changes, the "primary" antibody no longer recognizes the "newer" virus, and infection can occur because the host is not infected with the virus A new flu virus will not be identified as a problem before proceeding. In some cases, the first antibodies developed could provide partial protection against contracting the new flu virus. In 2009, almost everyone had no antibodies that immediately recognized the novel H1N1 virus.

Type A viruses are divided into subtypes or strains based on differences in two viral surface proteins called hemagglutinin (H) and neuraminidase (N). There are at least 16 known H subtypes and 9 known N subtypes. These surface proteins can occur in various combinations. When spread by droplets or direct contact, the virus replicates in the respiratory tract and destroys host cells if not killed by the host's immune system. In immunocompromised people (e.g. pregnant women, infants, cancer patients, asthma patients, lung disease patients, etc.), the virus can cause viral pneumonia or stress the individual's system, making them more susceptible to bacterial infections, especially Bacterial pneumonia. Both types of pneumonia, viral and bacterial, can cause severe illness and sometimes death.

Antigen transfer and drift

Influenza A viruses have undergone two major changes. One is a series of mutations that occur over time and cause the virus to gradually evolve. This is called antigenic "drift". Another change is a sudden change in the hemagglutinin and/or neuraminidase proteins. This is called an antigenic "shift". In this case, a new virus subtype suddenly appeared. Type A viruses undergo two changes; influenza B viruses only change through a more gradual process of antigenic drift and thus do not cause a pandemic.

The H1N1 virus that caused the pandemic in 2009 is a classic example of antigenic transfer. Research shows that the RNA genome of the novel H1N1 swine flu contains five RNA strands from various swine flu strains, two RNA strands from avian flu (also known as bird flu) strains, and only one from human flu strains RNA strands. According to the CDC, a major antigenic shift in about 20 years led to the development of the novel H1N1 influenza virus. The figure below illustrates antigenic shift and drift (see figure) and is characterized by A (H1N1) and avian influenza (H5N1), but nearly all influenza A strains can go through these processes to alter viral RNA.

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