Influenzavirus

Influenzavirus is a genus of the Orthomyxoviridae family of viruses. The genus includes the viruses that cause influenza in vertebrates, including birds (see Avian influenza), pigs (see Swine influenza), and humans. The genus is divided into seven species, each containing one or more serotypes or strains of virus.

Classification

The genus Influenzavirus is classified into seven species:

• Influenzavirus A
• Influenzavirus B
• Influenzavirus C
• Influenzavirus D
• Influenzavirus E
• Influenzavirus F
• Influenzavirus G

Each species is distinguished by variations in its nucleoprotein and matrix protein.

Structure and replication

Influenzaviruses are enveloped, with a spherical or filamentous shape. The virus particle is 80–120 nanometers in diameter and contains a segmented, single-stranded RNA genome.

The replication of influenzaviruses occurs in the nucleus of the host cell, a rare occurrence among RNA viruses. The virus enters the host cell by endocytosis and releases its RNA genome into the nucleus, where it is replicated and transcribed by the viral RNA polymerase. The newly synthesized viral proteins and RNA are then assembled into new virus particles, which bud from the cell membrane.

Pathogenesis and immunity

Influenzaviruses cause respiratory infections that can be mild or severe, depending on the strain of the virus and the immune status of the host. The virus is transmitted from person to person through the air by droplets produced when an infected person coughs or sneezes.

The immune response to infection with an influenzavirus involves both the innate immune system and the adaptive immune system. The innate immune response is the first line of defense and includes the production of interferon and other antiviral substances. The adaptive immune response involves the production of antibodies and T cells that specifically recognize and destroy the virus.

Prevention and treatment

Prevention of influenza is primarily through vaccination with an influenza vaccine. The vaccine is updated annually to include the strains of virus that are predicted to be most prevalent in the upcoming flu season.

Treatment of influenza includes rest, hydration, and the use of antiviral drugs such as oseltamivir and zanamivir. These drugs inhibit the viral neuraminidase enzyme, preventing the release of new virus particles from infected cells.