The influenza virus is a respiratory pathogen that is a member of the Orthomyxoviridae family.

First isolated in 1933, when scientists realised influenza was different to bacterial pneumonia, these pathogenic particles can be subdivided into types A, B and C. The latter two infect humans only, but type A is known to infect a range of other warm-blooded animals, including pigs, cattle, seals and birds.

An influenza virus is made up of single-stranded, negative sense RNA in eight segments. This means that the virus needs to use a host to convert its genetic information into positive sense (“forward”) material to be able to start transcription. The virus creates a membrane using host lipids, and the outside of the membrane is coated in glycoproteins. Influenza A has two proteins called hemagglutinin and neuramidase; these can both be seen in this influenza print.