Influenza A is a type of flu virus which invades humans, other mammals and birds. It is often described as flu type H1N1. The form of this virus coming out of Mexico is called a chimeric virus because it is made up of the genetic material of all three; the human, bird and swine viruses. How is this possible? Well, the flu virus is an RNA virus. It is made up of 8 single strands of RNA encapsulated in a protein bundle. As RNA strands mix and rearrange, there is a risk of what is called an antigenic shift. In this particular outbreak, probably a pig was infected simultaneously with human and avian flu. This added chicken and human flu RNA strands to the swine flu genetic material. This allowed for a phenotypic change - surface proteins not previously “seen” by the human immune system. Thus we are now seeing a virulent flu type which can now spread easily from person to person. The surface proteins include one which allows the virus to bind to cells sites and one that is an enzyme which releases the virus. These two are the most important from a medical perspective as they are the targets for antibodies and antiviral drugs

The possibility of this type of genetic change occurring in the flu virus is very well known and governments through the UN and WHO have been preparing for this eventuality for a long time. Preparations have gone back at least to 1997 when there were outbreaks of bird flu spreading to humans. Bird flu spreads easily from bird to bird. Infected chicken products even manure bits can carry the virus across borders. Bird flu culls have been taking place in Canada regularly, the most recent in January 2009 when 60000 turkeys were euthanized. At the present time, there is no evidence that swine flu is transported by pork products.

We of course must take the same precautions we would whenever it is flu season. At least so far it has mostly been mild flu cases seen in Canada and in rest of world, except for Mexico. Scientists are working overtime to understand why this is so. I heard on the radio this morning that all of the human race is at risk with this flu outbreak. I am not that pessimistic. I personally have confidence that most of us will have some immunity and that scientists will be able to develop vaccines to halt the progress of the disease.

Worried about the flu? Check out these sites:

Advice to protect yourself

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