Q. So what is avian flu?
A. Avian or bird flu is a type of influenza A virus which generally only affects birds and sometimes pigs. Previous outbreaks resulted in the first known human case in 1997. The current outbreak of avian flu began in South-East Asia in 2003 causing the deaths of thousands of chickens. What makes this outbreak unusual is that it has spread widely because of the movement of migratory birds.

Q.What is the influenza virus?
A. There are thousands of different strains of influenza virus, which is why the human body has such difficulty developing resistance to the infection. While Type C usually only causes very mild illnesses, which are similar to the common cold, and Type B causes less severe illness although it can still result in widespread or local outbreaks, Type A viruses are the most virulent (powerful) and are responsible for most major epidemics or pandemics.

The reason why the flu virus is of such concern is that our immune systems can 'remember' our previous encounters with viruses and we mount rapid, vigorous 'memory-based' responses when we reencounter a virus of a type that we have previously repelled. However, even small changes in the make-up of the virus mean that the body does not recognise it and therefore has to start from scratch when it tries to fight off the infection.

Q. What is special about the H5N 1 strain of avian flu?
A. Influenza A viruses have many different so-called subtypes which are referred to by different H and N numbers to distinguish one from another. It has been found that the H5 and H7 subtypes cause a dangerous type of bird flu in that the disease passes to humans and has a high mortality rate in people who are infected.

Q. How is it caught?
A So far most cases have been as a result of a person being in direct contact with infected birds or their droppings. The virus is not easy for a human to catch since there have been only a small number of reported cases of the disease in humans compared to the large number of infected birds, many of which live in close contact with their human owners.

Q. Can avian flu be caught by eating chicken or eggs?
A. It is not thought that eating properly cooked chicken or eggs poses any risk because the illness is transmitted via contact with live birds that have the flu virus or the faeces of infected birds.

Q. What are the symptoms?
A. Similar to other forms of severe influenza: high fevers, sweats, muscle pains, cough, and a runny nose. It is impossible to distinguish avian flu from other forms of influenza without a specific blood test or by analysing a sample of infected tissue.

Q. Is there a treatment for avian flu?
A. There are two types of drugs available for prevention and treatment of flu. These types of drugs are called M2 inhibitors (amantadine and rimantadine) and neuraminidase inhibitors (oseltamivir commercially known as Tamiflu - and zanimivir). However, initial analysis of viruses isolated from the recently fatal cases in Vietnam indicates that the viruses are resistant to the M2 inhibitors although further testing is under way to determine the effectiveness of amantadine. It is thought the H5N1 virus may respond to treatment with the neuraminiclase inhibitors if given within 48 hours of the start of symptoms and as a result may improve the chances of survival.

Q. Is there a vaccine against avian flu?
A. At the time of writing, there is no effective vaccine, although one is under development. The usual flu vaccine given to certain groups of people in the UK, such as the elderly and those with lung and heart conditions, does not protect against avian flu. However, it is thought that preventing as many people as possible from developing the usual types of flu may reduce the chances of one person catching both human flu and bird flu simultaneously and therefore make the chances of the emergence of a human form of bird flu less likely.