What is bird flu?
As news breaks that the potentially deadly strain of bird flu - H5N1 - has been identified in a poultry farm in Suffolk, we publish an extract from Jo Revill's book, Everything You Need To Know About Bird Flu
Saturday February 3, 2007
Bird flu, or avian influenza, is a viral disease that causes illness in many species of birds. It's been around for more than 100 years, and there are 15 different types of it.
So what is H5N1?
This is the subtype of one strain which is currently causing worldwide concern. But even this subtype has its own variations, and it can be a lethal kind (higly pathogenic), or it can be mild (low pathogenic).
Why should we be so worried?
This subtype can jump into different species from birds which makes it quite unusual. So far the H5N1 strain has infected more than 250 people, mainly in south east Asia, and caused 164 deaths between January 2003 and September 2006. Most animal viruses never affect humans.
How is it spread?
There are thought to be millions of migratory ducks and wildfowl which carry the disease. Some of them will die of the symptoms, but others appear to be able to carry the virus without showing any symptoms at all - which makes it hard for the authorities to know where the danger lies.
How do humans get it?
The people who have caught it so far are those who have had daily contact with infected, live birds. The virus can live in the excretions of the birds, but they can also breathe it out. Also, when the dropping dry, people may breathe in the germs.
Can it pass between people?
The good news is that so far there has not been any proven human-to-human transmission. All the cases have been from birds to people.
When will it become a human disease?
This is the million-dollar question. There is simply no way of predicting when the virus will mutate in order to become an infection that can be easily transmitted between people. However, most experts do think this will happen at some point over the next two years.
When it mutates, will it be deadly?
Again, this is very difficult to answer. Often there is a trade-off in viruses, so that as they keep changing their coats in order to spread more easily within a species, they become less virulent. There would be no point in a virus killing all its victims within two days, as it would never be able to spread quickly enough. But if it is the H5N1 which becomes a human disease, that is bad for us because we have no natural immunity to any H5 strain.
What makes it mutate?
The spiky-coated flu virus mutates every time it replicates. What the experts are worried about is that it could mix with a normal human flu strain, and create a new virus. Or it might simply evolve into a form which was easier to spread.
What are the first symptoms?
In the cases we have seen in south-east Asia, the early symptoms have been very like common-or-garden flu - a high temperature, coughing and feeling aches. Within three days however, their breathing has become far worse and they are seriously ill.
When the disease becomes fully transmissible between people, it is likely that the disease will have its own 'profile' or set of recognisable symptoms - but these may still look quite like normal flu at first.
Can it be treated?
There are antiviral drugs known as neuraminidase inhibitors, of which the chief one is Tamiflu, and this has shown in trials to give a certain amount of protection against the disease. It does appear to be able to prevent some people from being infected, and it also helps people once they have the symptoms, but it may not work for everyone. Another class of drugs, which includes Relenza, may also be effective. These are the drugs which governments around the world have stockpiled in order to control a future pandemic. However, there are worries about people becoming resistant to them.
Why not a vaccine?
There are several possible vaccines which are being studied, and some of these are already in clinical trials. But the problem is that until the virus mutates to become a fully human strain, we don't know exactly what the target should be for the vaccine. The other problem is that there are not enough vaccine factories worldwide to make the quantity of doses we would need.
What is the flu vaccine which the government has been asking the elderly to have?
This is the vaccine shot against the normal, seasonal flu. It will not protect you from bird flu, but it means that if bird flu comes to Britain via our poultry flocks, there will be less genetic chance of the virus mixing with a normal flu strain.
This vaccine is for the elderly and people who are susceptible to respiratory infections. In America, it is also given to children, who often spread the flu within a family.
Understanding Avian Influenza