Science is Sexy: What is Swine (H1N1) Flu? How Does an Animal Disease Spread to a Human Host?

Have you been watching the news at all recently?  If so, you’ve probably heard the term “Swine Flu” or “H1N1 Flu” bouncing around a lot.  While most people come down with the normal human flu at some point, it’s not really a danger to anyone but the very young and the very old.  Why is this flu different and what does it have to do with pigs?

Many Influenza ParticlesEssentially, influenza (aka, “The Flu”) is a viral infection that attacks our population in a yearly cycle.  Fortunately, the human immune system is there to recognize and neutralize the effects of the virus.  Each year, the virus mutates just slightly and most of the population is once again susceptible to the disease.  This is why a new vaccine must be created regularly to reflect the most recent influenza mutants out in the environment.  Under normal circumstances, this is all you need to know about the flu (aside from how to avoid infection and take care of yourself if you do come down with it).

Recently, some changes in the status quo have raised alarm bells at the Centers for Disease Control (CDC) and the World Health Organization (WHO).  There have been reports of “swine flu” in Mexico and several other countries whose citizens regularly visit Mexico, including the United States.  Since this is a general information article and not a “minute by minute” report, refer to major news outlets for more accurate information regarding confirmed cases.  As of this moment, though, it looks like over 80 deaths in Mexico are the result of contact with swine flu and there have been confirmed cases of the new pathogen in New York, Ohio, Kansas, California, and possibly other states.

A Cross Section of an Influenza Virion, note the peplomeres around the outsidePutting the news figures aside for a moment, let me explain exactly what swine flu is.  The influenza virus has a number of components, but the most variable parts of the virus are the spines found around its exterior.  These are proteins called “peplomers” and there are two major kinds.  The HA (hemagglutinin) peplomer is responsible for binding the virus to host cells and the NA (neuraminidase) peplomer allows the virus to break its bonds to the host cell once it is ready to move on.  When you hear about the H1N1 virus or the H3N2 virus, the viruses are being referred to and classified by their external receptors.  This is a bit of a simplification, but knowing the chemical nature of the peplomers isn’t crucial to understanding their function.

The peplomers are a double edged sword.  They allow the viral particles access to the machinery of the cell (this is how viruses replicate themselves), but they also allow the immune system to recognize and target the virus.  When the human flu virus mutates its external proteins, the body’s defenses still recognize them and eventually mount a response (the period of sickness occurs while the body is developing that response).  If this failed to happen, you would eventually succumb to the virus and die.

The virus didn’t originate in humans, though.  Birds, pigs, and even horses have their own versions of influenza.  Remember the “bird flu” or “avian flu” scare a while ago?  Scientists feared the influenza common in birds had “jumped the species barrier” and begun infecting humans.  This is called a “zoonotic” disease – a disease that moves from animals to people.  Now, the same worries have arisen about swine flu.  Why does this matter?  Won’t our immune system just deal with the new influenza virus the same way it has always done with the seasonal one?

Unfortunately the answer is a weak “maybe.”  While your immune system might not immediately stop a new human influenza infection, it DOES recognize that new mutant and begin building a response.  Avian and swine peplomers, on the other hand, are not easily recognized by the human system because our evolution did not include pressure from those particular viruses.  As humans have come into close contact with the animals that carry these viruses, the animal influenza has been able to mutate enough to cross the species bridge and infect humans as well.  In the past this would not have been a global problem.  An infected village might just die out in isolation.  Things are different now: a traveler can become infected in one region and fly thousands of miles to another, long before they experience symptoms.

CDC LogoSo what’s the take away message from all of this?  Can we do anything about this?  Well as individuals it’s wise to go through the same sanitary practices as we might during flu season.  Also, traveling to places which have reported cases probably isn’t a great idea.  Governments and regulatory bodies like the CDC and the WHO are in an “all hands on deck” kind of status right now.  As the outbreaks continue (they are expected to grow for at least the time being), these groups will be tracking  any reported cases and trying to treat those infected.

As a young microbiologist, I’d say that for the moment we shouldn’t worry too much.  There are people who have spent their whole lives preparing for just these kinds of events and they’re currently working very hard to provide the public with the best information and advice.  Hopefully you now have a better understanding of the science behind influenza and zoonotic diseases.  I’ve put some links at the bottom of this posting for further reading.  Also, feel free to post a comment or @me on Twitter should you have any more questions.

Update: The World Health Organisation says that the Swine Influenza virus, or “Swine Flu” will now be named the Influenza A(H1N1) or just H1N1 flu.

Additional Resources:

By Jimmy Rogers
Contributing Writer, [GAS]

[First Image of Influenza Virus from El_Enigma on Flicker with CC | Second Image of Influenza Virus from AJC1 on Flicker with CC | CDC Logo from the FDA website, Geeks Are Sexy does not represent the CDC or any other government agency]