Influenza virus

Three types A, B, C.

Enveloped RNA viruses with segmented genome and demonstrate significant antigenic diversity.

Belong to the orthomyxoviridae family.

A Infects a variety of mammals, birds, and animals unlike B and C viruses, and this characteristic makes it a potential source of pandemics.

Classified by code proteins A, B or C, the species of origin, geographic site of involvement, serial number and for influenza hemagglutinin (HA) and neuraminidase (NA) subtypes.

Influenza viruses have a gene segments that code for surface glycoproteins such as hemagglutinin (HA) an neuraminidase (NA).

15 HA and 9 NA subtypes exist.

Only type A exhibits subtype variation defined by hemagglutinin and neuraminidase surface proteins, ref2242ed to as H and N, respectively.

Surface glycoproteins encapsulate the viral RNA and play a role in attacking host cells.

HA proteins attach virus to host cells by binding sialic acid receptors and are determinant of infectivity.

Viruses have two mechanisms for defensive responses against the human immune system that includes antigenic drift and antigenic shift.

Antigenic drift and antigenic shift are the driving forces for evolving new viral variants.

Antigenic drift refers to a process where two viruses re-assort and exchange different glycoproteins leading to novel HA proteins for the immune systems Of infected organisms to deal with.

Novel glycoproteins produced pose a threat to human immunity and can lead to pandemics.

Viruses accumulate mutations during replication resulting in surface glycoproteins with selected defensive advandages against immune function.

Mutation can lead to the formation of a HA proteins not identified by human antibodies and will be more successful invadinf the host cells.

NA proteins determine the virulence of the viral strain and cleave the glycosidic linkages to sialic acid assisting in the release of virus after replication inside infected cells.

A type infection responsible for frequent, usually annual, outbreaks of epidemics and occasional pandemics.

B causes outbreaks every 2-4 years.

HA1-16 ad NA1-9 viral subtypes occur in natural reservoir of aquatic birds only H1, H2, H3 have caused widespread human respiratory infection, indicating a degree of host specificity.

Viruses are versatile, and adaptable which pose a challenge to infection control and treatment.

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