Orthomyxoviridae (from Ancient Greek ὀρθός (orthós) 'straight' and μύξα (mýxa) 'mucus')[1] is a family of negative-sense RNA viruses.

The four genera of Influenza virus that infect vertebrates, which are identified by antigenic differences in their nucleoprotein and matrix protein, are as follows: The influenzavirus virion is pleomorphic; the viral envelope can occur in spherical and filamentous forms.

[6] The viral envelope composed of a lipid bilayer membrane in which the glycoprotein spikes are anchored encloses the nucleocapsids; nucleoproteins of different size classes with a loop at each end; the arrangement within the virion is uncertain.

[citation needed] Viruses of the family Orthomyxoviridae contain six to eight segments of linear negative-sense single stranded RNA.

[9] In contrast, neuraminidase is an enzyme involved in the release of progeny virus from infected cells, by cleaving sugars that bind the mature viral particles.

The hemagglutinin (H) and neuraminidase (N) proteins are key targets for antibodies and antiviral drugs,[10][11] and they are used to classify the different serotypes of influenza A viruses, hence the H and N in H5N1.

In the acidic pH environment of the endosome, part of the hemagglutinin protein fuses the viral envelope with the vacuole's membrane, releasing: the viral RNA (vRNA) molecules, accessory proteins and RNA-dependent RNA polymerase into the host cell’s cytoplasm (Stage 2).

Newly synthesised viral proteins are either secreted through the Golgi apparatus onto the host cell surface (in the case of neuraminidase and hemagglutinin, step 5b) or transported back into the host nucleus, where they bind vRNA and form new viral genome particles (step 5a).

[19] A virion assembles from negative-sense vRNAs (that form the genomes of newly created viruses), RNA-dependent RNA transcriptase and other viral proteins.

[26][27][28] Influenza A viruses are further classified, based on the viral surface proteins hemagglutinin (HA or H) and neuraminidase (NA or N).

It is thought that all influenza A viruses causing outbreaks or pandemics originate from wild aquatic birds.

[50] The influenza C virus infects humans and pigs, and can cause severe illness and local epidemics.

Mammalian influenza viruses tend to be labile, but they can survive several hours in a host’s mucus.

[57] Influenza viruses are susceptible to bleach, 70% ethanol, aldehydes, oxidizing agents and quaternary ammonium compounds.

Scientists pick an infectious strain that carries the desired HA and N receptors that the final product should prevent from infection.

They choose these strains by picking the surface HA and NA versions circulating the most in the public, and the ones thought most likely to be prevalent in the upcoming flu season.

Finally, of the newly created viruses, scientists pick six versions that multiplied the best in chicken eggs which also carry the necessary HA and NA genes.

Ultimately, millions of eggs are injected with those noninfectious strains—which carry the desired proteins—so that the genes can be harvested and used for the vaccine product.

[58] Another method of making the vaccine is by splicing genes from infectious strains and then creating copies in a lab, without the need for the tedious process of chicken egg culture.

[58] Drugs available for the treatment of influenza include Amantadine and Rimantadine, which inhibit the uncoating of virions by interfering with M2 proton channel, and Oseltamivir (marketed under the brand name Tamiflu), Zanamivir, and Peramivir, which inhibit the release of virions from infected cells by interfering with NA.