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H1N1 and Pork Production

Most folks know that people don’t get the H1N1 flu by eating pork.  But what is the connection between this new flu and pigs?  Did it come from pigs?  Are large, concentrated pork farms responsible for H1N1?  We’ll try to answer some of those questions below.

Influenza Basics

The flu is caused by the influenza virus.  The many influenza viruses are grouped as Influenza A, Influenza B or Influenza C.  Pigs, like humans, are susceptible to various influenza viruses.  Most influenza viruses of swine are Influenza A—just like humans.  Symptoms of influenza in pigs mirrors those seen in humans.  It is largely a respiratory disease and, while contagious, influenza in pigs is not generally associated with high mortality rates, and pigs usually recover after 5-7 days.  Some of the influenza viruses that circulate in pigs can infect humans, but such infections are very rare.   

Why was it called “swine” flu?

Influenza viruses are broadly grouped Influenza A, B, and C.  Viruses within a group are often distinguished from one another based on two proteins on the outside of the actual virus: hemagluttinin and neuraminidase.  This is where the H and N come from.  There are many different H and N proteins and each has a number.  The virus is then named based on which H and N proteins it has., e.g., H1N1 or H5N1, etc. 

These H and N proteins can then be further distinguished from one another based on their sequences.  There are H1 proteins that are normally found in influenza viruses normally associated with pigs and H1 proteins found in influenza viruses normally associated with humans.  When  the new H1N1 virus was first characterized, it was determined that its H and N proteins were normally found in swine influenza viruses.  Thus, it was first referred to informally by researchers as a “swine flu” and the name caught on.

It’s a little more complicated than that.  Influenza viruses often mix and match genes with other influenza viruses.  The H protein in the new H1N1 is from an influenza virus sometimes found in North American pigs while the N protein is from influenza viruses sometimes found in European and Asian pigs. The seven other genes are from human influenza viruses, avian influenza viruses and different swine influenza viruses.   

So the new H1N1 is really a new virus.  While some of its ancestors (some distant, some recent) obviously can be found in pigs, the new H1N1 It is not among the influenza viruses that are normally associated with swine.

Is H1N1 found in pigs?

Yes.  H1N1 has been isolated from pigs in various countries including the United States.   

Are large, concentrated pork farms responsible for H1N1?

Researchers have been busy trying to determine a timeline of how this virus developed.  So far they have been successful in determining where different parts of the virus came from, but are still unclear as to how or where they came together to form the new H1N1.  One of the earliest cases of H1N1 infection was in a child who lived near a large pork farm in Mexico. These two facts are now known to not be connected. The virus was never detected in pigs at that farm and new studies have shown that the virus circulated undetected in humans for several months prior to any clinical cases. At this point, attributing the evolution of the virus to a certain type of pork production is speculation.

Have any questions?  Submit them to us here.

Paul Ebner, PhD
Assistant Professor
Dept. of Animal Sciences


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