Influenza: New You, New Flu

Alias: influenza, flu

It’s traditional to ring in the New Year by making resolutions, promising ourselves that this year we’ll change for the better. While, generally speaking, the flu isn’t a great role model (let’s hope making people sick isn’t a common resolution), it could teach us a thing or two about change. Influenza A (the type that causes seasonal flu) mutates at a breakneck pace: about 1 mutation per genome per replication, which is close to the maximum rate a viable organism (one that can survive and reproduce) can reach1.

Influenza mutates in two ways: slow and steady or all at once. Small mutations that commonly occur when the virus replicates are called antigenic drift. An antigenic shift is a very rare, sudden, and dramatic change that results in new surface proteins on the virus. These shifts and drifts have created a smorgasbord of human flus, including seasonal, avian (from birds), and swine and variant (both from pigs), with a wide range of severity and symptoms. The seasonal flu can cause everything from its typical mild illness to death. The elderly are particularly vulnerable; from 1976-2006, mortality has ranged from about 3,000 to 49,000 people per year, with 90% occurring in people over 65 years old2.

Antigenic shifts are the bigger, showier mutations, and they get most of the press, because they can produce new virus subtypes that humans are highly susceptible to, sometimes from a non-human source (i.e. bird flu). However, although it’s a bit less flashy, antigenic drift can also have big effects. This year, the form of influenza virus circulating in the US, H3N2, seems to have drifted just enough to reduce the efficiency of the flu vaccine, leaving more people than usual susceptible to the illness. This virus subtype caused greater than normal amounts of disease when it struck the US in 2012-2013, and it looks like 2014-2015 will be a repeat performance. So far, forty-three states have reported high levels of the disease, and in the last week of 2014, flu accounted for 5.9% of all clinic visits2. Change isn’t always good.

flu
High resolution.

Cause: The flu is caused by a suite of influenza viruses. Two main types (Type A and B) spread in humans. Type A is broken into subtypes based on which forms of two surface proteins it contains: there are 18 different hemagglutinin (H) and 11 neuraminidase subtypes (N), and subtypes are named accordingly. The virus is spread through droplets coughed, sneezed or spat by infected people and inhaled or ingested by the uninfected. The ill can spread the flu to people up to 6 feet away. Most adults are infectious from 1 day before they show symptoms to up to a week after they become sick2.

Consequence: Seasonal flu results in a familiar suite of symptoms, including fever, chills, cough, sore throat, nasal congestion, muscle ache, headache, and fatigue. More rarely, it can cause vomiting and diarrhea. Most people recover within two weeks, but some develop complications that can lead to more serious illnesses, such as bronchitis or pneumonia, which can result in death. Avian flu and variant flu may result in severe respiratory illness2.

Cure: Prevention is the most effective protection against influenza; the flu vaccine reduces incidence of flu-related doctor visits by 60%, and even if it is not effective against the virus and the virus is contracted, it may still prevent illness and more serious complications. Other preventative hygiene practices, like washing hands with soap and water, and disinfecting commonly touched surfaces, are also essential in combatting influenza. A small number of anti-virals, like Tamiflu, are currently the only treatment for the flu2. Hopefully, that too will change.

References

  1. Drake, JW. (1993). Rates of spontaneous mutation among RNA viruses. Proceedings of the National Academy of Science, 90:4171-4175.
  2. “Influenza (Flu)”. Centers for Disease Control and Prevention. 9 January 2015. Web. 11 January 2015.

Image source: Creative Commons, http://commons.wikimedia.org/wiki/File:Influenza_virus_particle_color.jpg

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Suzi Claflin

I am a postdoctoral fellow studying chronic disease epidemiology.

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