H1N1 is a subtype of the influenza A virus. The "H" refers to the Hemagglutinin protein, and the "N" refers to the Neuraminidase protein.

H1N1 has mutated into various strains including the Spanish Flu strain (now extinct in the wild), mild human flu strains, endemic pig strains, and various strains found in birds. A variant of H1N1 was responsible for the Spanish flu pandemic that killed some 50 million to 100 million people worldwide from 1918 to 1919.

Low pathogenic H1N1 strains still exist in the wild today, causing roughly half of all flu infections in 2006. When the 1918 virus was compared with human flu viruses in 2005, it was noticed that it had alterations in just 25 to 30 of the virus's 4,400 amino acids. These changes had been enough to turn a bird virus into a version that was human-transmissible.

2009 H1N1 outbreak

In April 2009, an outbreak of a new strain of H1N1 was initially believed to have killed over 150 people in Mexico and to have infected more than 1500 individuals worldwide as of April 26. This strain of H1N1 appears to have genetic material from two strains of swine flu, a strain of human flu, and a strain of avian flu [2].

The 2009 Flu outbreak is a new strain of influenza, which the authorities have recently decided should not be called "swine flu". The CDC has confirmed that U.S. cases were found to be made up of genetic elements from four different flu viruses – North American swine influenza, North American avian influenza, human influenza, and swine influenza virus typically found in Asia and Europe. The name this wiki is moving to is "H1N1".

In April both the WHO and CDC expressed serious concerns about this new strain, because once it made the jump from pigs to people, it seemed to transmit from human to human, it had had a relatively high incidence in Mexico, and it had the potential to become a flu pandemic. Because we have learned a great deal about epidemiology and public health since the last great epidemic (the "Spanish flu" of 1918), international health bodies are better prepared for such a pandemic and may be able to prevent it from becoming widespread if it turns out to be a strain as dangerous as the 1918 virus. It may not -- a 1976 swine flu outbreak in humans prompted widespread vaccinations but only took one life.[3]

As can be seen from the accompanying table, dozens of people in Mexico and the United States have become infected with this new strain, with a few confirmed cases in Canada and Costa Rica, and places further away such as New Zealand, Spain, and Germany. It has caused at least 20 confirmed or suspected deaths in Mexico[18]. No definite conclusion can be reached, but the CDC reported recently that swine flu viruses in the US and Mexico match[19].


Adapted from: the CDC

The symptoms of H1N1 flu in people are expected to be similar to the symptoms of regular human seasonal influenza and include fever, lethargy, lack of appetite, and coughing. Some people with flu also have reported runny nose, sore throat, nausea, vomiting and diarrhea.

Transmission of swine flu

Swine Flu viruses can be directly transmitted from pigs to people, and from people to pigs. Human infection is most likely to occur when people are in close proximity to infected pigs. Human-to-human transmission of swine flu can also occur, thought to be in the same way as seasonal flu occurs in humans. This would be mainly through the coughs or sneezes of infected people. People may become infected by touching something with flu viruses on it, and then touching their mouth or nose.

You can not get swine flu from eating pork. Cooking destroys the influenza virus.

The exchange of proteins among flu viruses from humans, birds, and pigs is very common, and happens every year (and has nothing to do with genetic engineering). However, these combinations are usually only transmitted across the species barrier, so normally the number of people at risk is limited to those who work directly with pigs or poultry. Only occasionally do the combination strains mutate in a way that allows them to be transmitted from human to human.


Washing your hands regularly, preferably with an alcohol-based hand disinfectant, will significantly reduce the risk of contamination. If you are in a high-risk area, you should avoid directly touching well-touched surfaces (such as door handles). Surgical masks can also reduce the risk of contaminants reaching the mouth or nose, but these need to be well-fitting to the skin to give maximum protection, stopping any contaminants floating around the edges.



If you are concerned that you (or someone you) know may have flu, you should seek the advice of a medical professional. This gives the best chance of accurate diagnosis and early treatment.

To diagnose influenza A infection, a respiratory specimen (mucus/saliva) would generally need to be collected within the first 4 to 5 days of illness. This is when an infected person is most likely to be infectious. However, some persons, especially children, may shed virus for 10 days or longer. Identification as an influenza A virus requires sending the specimen for laboratory testing, such as to CDC.


The influenza virus can be carried by migratory birds, who are not usually affected. The bird droppings can infect pigs, where the virus may mutate. New strains may be able to infect humans.


See also

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