Dr Paul Yeo, an expert on viruses, from Durham University's Centre for Bioactive Chemistry, answers questions on swine flu…

Swine influenza is a respiratory disease normally found in pigs but human cases can and do happen.

The current human cases were first reported in Southern California and Texas. Cases of swine influenza have now been confirmed in several countries including Mexico, US, Canada, Spain and the United Kingdom.

This strain of swine influenza contains a combination of genetic material typical to avian, swine and human flu viruses. Transmission of this new swine influenza virus is thought to occur in the same way as seasonal flu. Antiviral drugs are available which can effectively prevent and treat the infection, most reported cases of this infection outside of Mexico have recovered fully without the need for medical attention or antivirals.

1. What is the science behind how new flu strains arise - this one has pig, human and bird components (mainly pig)?

Viruses change and can undergo enormous change at a rapid pace; they are in that sense 'clever' and it can only takes a few changes for a pig virus to adapt to a human. The pig has been considered the mixing bowl of influenza viruses, both avian flu and pig flu viruses have spread via the pig to humans. The problem now with this virus is that it has now picked up a mixture of elements, now including human elements; it's a complex virus. Flu strains change and mutate, they are very adaptable.

2. Why is the testing taking so long? Are they re-testing samples?

Delays in testing could be perceived delays and these may simply be due to the fact that people are unrealistic about timescales. It takes time to check, test and validate tests. There may be only a few places in the world where you can do this form of testing. It takes time.

3. How long it will take to come up with a viable vaccine for this particular strain of flu, and how long after that it could be massed produced?

It is likely to take at least 6 months to build up enough stocks of the vaccine. You have to grow enough of the virus culture, and then develop and build up stocks of a vaccine. The culture is grown in special, pathogen-free chicken eggs that have to be kept in sterile conditions in specialised facilities, in constant temperature rooms. These eggs have to be inoculated with the virus and the culture developed. You need lots of eggs and room to store them, and enough people to check and test the eggs. Then there's the issue of processing the vaccine and checking that it's safe.

ANTI-VIRAL drugs will be a major weapon in the armoury of health organisations if the number of swine flu cases continues to accelerate.

The UK has stockpiles of two anti-viral drugs in particular - Tamiflu and Relenza - both of which have been effective in treating the H1N1 strain of swine flu in other countries.

Anti-virals are designed and used specifically for fighting viral infections.

They are typically used to treat influenza, reducing the length of symptoms and usually their severity.

If a flu pandemic was to start, anti-viral drugs would be the first line intervention.

If administered quickly to all patients with symptoms, they can reduce the duration of the disease and the risk of complications, the Department of Health said.

Anti-virals are also commonly used to treat HIV and the herpes virus.

4. How much potential does it have to alter as it spreads?

Swine flu can alter as it spreads - it's a virus and that's what a virus does, they mutate and change and, for example, that's why we need a new influenza vaccine every year.

5. Why has so far proven deadly in Mexico but far less so elsewhere, even if the infection rates are on the rise?

There's no clear answer to this - if we knew the answer, it would be like finding 'the answer', the holy grail of virology.

6. How much of a threat does swine flu pose?

We have to wait and see. It is very early days but it's not hype if people are dying in large numbers. The worrying feature here is that we have a virus that has jumped species; it has spread from animal to human. In avian flu, the outbreak was contained to a large extent. It didn't jump from human to human. Swine flu has jumped species and is now spreading from human to human; that's a significant change.

7. The two confirmed cases in Scotland have not shown any symptoms for more than 24 hours now, why are they still in isolation? What can be learned from their cases?

There is a need for safe period once someone is diagnosed with swine flu, even though they may seem to be getting better, the virus may still be in the patient and they could still transmit it.

8. I am hearing conflicting messages about transmission and symptoms.

Transmission refers to 'respiratory fluid transmission' and this is achieved mainly via sneezes, hands, and contact with handkerchiefs and tissues.