Behind the print: Influenza virus

Behind the print: Influenza virus

What’s tiny, round, not quite alive, and killed over 50 million people in 1918?

The flu.

More specifically the influenza virus, 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. Birds in particular act as host reservoirs, basically storing the virus between human infections.

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.

Hemagglutinin and neuramidase are the most common proteins on viruses, and they are used to distinguish between virus types. Because this nomenclature system was created before the advent of genomic sequencing, the antigens are simply numbered in order of discovery. H1N1 was the first studied influenza A virus strain, and when scientists came across an antigen they did not recognise, it was named 2, and so on. This means that there is no phylogenetic basis to the names, and numbers that are close together are not necessarily more related – they just happened to be discovered by humans in that order! The proteins only give the virus its everyday name though; full names include type of virus, geographical region it was isolated in, host (if not first found in a human), lineage number, year and then lastly the antigen code numbers. An example of a full virus name is A/Black-headedGull/Sweden/2/1999(H16N3) – imagine your mum calling that down the road to get you home for dinner!

These proteins on the outside of the virus are also what trigger an immune response in humans that get infected. With many diseases, previous encounters lead to immunity, where the immune system is prepared and has the resources stored to immediately fight the infection. Influenza, however, repeatedly infects global populations every winter, and this is because of something called antigenic drift – the viral RNA does not have a proofreading mechanism, meaning that mutations occur rapidly, changing the virus every year. The immune system doesn’t recognise this “new” virus, and so the body is susceptible again.

The yearly winter flu brings symptoms like coughing, headache, high temperature and fatigue. It is more pathogenic than a common cold, with annual deaths of about 50 000 people (mainly elderly with primary illnesses, or young children). These vulnerable people are recommended to get vaccinated against that year’s strain, giving their immune systems a chance to build an army against the viral antigens before they get infected.

The annual flu is known as an endemic, but every 30 to 40 years, we see global influenza pandemics break out – like the Spanish flu in 1918 that killed 50 million people in a year, or more recently the H5N1 strain of avian influenza, better known as the bird flu. Pandemics are due to antigenic shift as opposed to drift: a strain that is animal adapted is transferred to humans. Because of outbreaks like these, scientists worldwide are constantly monitoring and researching the influenza virus in an effort to control it and stay one step ahead.

Despite being so intimidating, the influenza virus itself looks beautiful and intriguing. We think it makes a good print because it’s pretty cool that something so small can have such a big impact, taking over a human body and using its cells to replicate itself!

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