About H1N1 Flu

What is H1N1 Influenza?
H1N1 Influenza (swine flu) is a respiratory disease of pigs caused by type A influenza virus that regularly causes outbreaks of influenza in pigs. H1N1 viruses cause high levels of illness and low death rates in pigs. H1N1 influenza viruses may circulate among swine throughout the year, but most outbreaks occur during the late fall and winter months similar to outbreaks in humans. The classical H1N1 virus (an influenza type A H1N1 virus) was first isolated from a pig in 1930.

Why is it called the swine flu?
The H1N1 virus is being called "swine flu" because of the 1918 outbreak in Spain. That virus probably had a wild bird origin but nonetheless became known as the swine influenza virus because it caused significant mortality in both swine and human populations.

How many H1N1
viruses are there?
Like all influenza viruses, H1N1 flu viruses change constantly. Pigs can be infected by avian influenza and human influenza viruses as well as H1N1 influenza viruses. When influenza viruses from different species infect pigs, the viruses can reassort (i.e. swap genes) and new viruses that are a mix of swine, human and/or avian influenza viruses can emerge. Over the years, different variations of H1N1 have emerged. At this time, there are four main influenza type A virus subtypes that have been isolated in pigs: H1N1, H1N2, H3N2, and H3N1. However, most of the recently isolated influenza viruses from pigs have been H1N1 viruses.

Sources: Centers for Disease Control & Prevention, USDA, World Health Organization, National Pork Board