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Q. Why would an influenza virus such as Swine Flu or H1N1 take a year or so to reach us?

Dr Smith: Each and every year, the flu spreads around the planet. It starts China and then travels, often not noticed in the Northern hemisphere (where most of the world’s population live) until Autumn or Spring.

Q: When and where do swine flu outbreaks occur?

WHO: Outbreaks in pigs occur year round, usually in the autumn and winter in temperate zones. Since international health regulations were implemented in 2007, WHO has been notified of swine influenza cases from the United States and Spain.

Governments do not have to notify international animal health authorities about swine flu outbreaks, therefore its international distribution in animals is not well known. The disease is considered endemic in the United States. Outbreaks in pigs are also known to have occurred in North America, South America, Europe (including the UK, Sweden, and Italy), Africa (Kenya) and in parts of eastern Asia including China and Japan.

Q: This super-virus we’re looking at now is said to be a cross between a pig flu, a human flu and also the bird flu, which has been deadly too. Does this make it even more dangerous?

Dr Smith: Flu is broken down into a number of different types: there’s flu A, flu B and flu C. Flu A is the bird form and, of course, humans also have a flu A. Then we further categorise it according to the surface molecules, the H (for Haemagglutinin) and the N on the surface.

This new strain is a H1N1 virus, which we know circulates in humans, pigs and birds. It’s possible that the pig initially got some of its flu from a bird and then co-mixed that with the human form to produce this hybrid, which is why you can find elements of all three.

It is very much early days and the big focus now, through infection control organisations like the Centres for Disease and Prevention (CDP) and the WHO, will be to interrogate this virus at a molecular level.

In other words, look at the genetic make-up, sequence the virus, and once they’ve got the genetic sequence you can begin to unpick where it’s come from, what its origins are, and therefore begin to build the story as to what its likely outcome will be.

WHO: Swine flu viruses are most commonly of the H1N1 subtype but other subtypes g (H1N2, H3N1 and H3N) are also circulating. The H3N2 swine virus was thought to have been originally introduced into pigs by humans.

An influenza virus containing genes from a number of sources is called a “reassortant” virus. Swine flu viruses are normally species specific and only infect pigs, but sometimes they cross the species barrier to cause disease in humans.

This interview was with the World Health Organization and Dr. Christopher Smith, Virologist at Cambridge University and the author of The Naked Scientists Science Radio Show Podcast