Concern is growing in the UK about the spread of bird flu from birds to humans and the possibility of the H5N1 virus mutating so it can pass easily from human to human.
The case of a cat in Germany dying of bird flu has also raised fears for pets.
The BBC news website asked two experts, a virologist and a veterinary expert, to answer your questions on the issues.
DR JIM ROBERTSON, PRINCIPAL SCIENTIST FOR THE NATIONAL INSTITUTE FOR BIOLOGICAL STANDARDS AND CONTROL
What is the likelihood of the virus getting to the stage where it is possible for humans to pass it on to each other and it becoming a pandemic?
Matthew Spawton, Newcastle Upon Tyne
The likelihood exists but is very, very low.
This current epidemic of avian flu in birds has been going strong now for two years and so far the virus has not mutated to pass from humans to humans, but it still might.
However, it really is impossible to predict when that might happen.
Vaccine development is making good progress. Many clinical trials are now underway to assess H5N1 vaccines and they are at different stages.
The main issues are determining how much vaccine has to go into each dose to provide protection, and finding ways to reduce this so that in the event of a pandemic, there will be plenty to go around.
In the event of a pandemic, vaccine will ultimately be available to everyone in the UK.
The last flu pandemic was in 1918. How did it stop?
Pandemics don't stop but peter out as more and more of the population become immune.
Remember, although many people might die, most will not, and they will have immunity, either from infection itself or from vaccine (although for the 1918/19 virus, there was no vaccine).
Thus the virus will run out of people to infect and this may take 1-2 years.
After this the virus is likely to remain in circulation and cause annual epidemics just like current human flu.
This is what happened after the 1918 pandemic.
If the bird flu mutates so it can be spread amongst humans, how quickly can a vaccine be produced and how will it be decided who in the general public gets the vaccine first?
C P, Gloucestershire
As soon as a pandemic has been declared by the World Health Organization, a vaccine strain will be made from the pandemic virus; this strain will then be used by vaccine manufacturers worldwide to make vaccine.
Estimates are about two months for the vaccine strain and about three to four months for vaccine to appear from the manufacturers; so about five to six months for the first lots of vaccine.
The Department of Health will decide on vaccine priority.
If or when bird flu comes to the UK will we all be vaccinated if it mutates into the deadly form?
If the bird flu virus mutates into a form that will pass readily from human to human (a pandemic), the aim of the UK Dept of Health is to vaccinate all within the UK.
My nine-year-old daughter has recently been diagnosed as asthmatic and I'm concerned this puts her at increased risk if she contracted bird flu. Should I ask for her to be given the flu vaccine and would this help to protect her against bird flu or just normal flu?
Mrs Beverly Montgomery, Benfleet, England
There is a general recommendation for those with chronic diseases such as asthma to be vaccinated against seasonal flu, you should consult your GP on this.
The seasonal/normal flu vaccine will only protect against seasonal flu and not bird flu.
Is the disease painful, how will we know if we have it? When is bird flu estimated to hit the UK?
Lauren Smith, Broadstairs, England
Normal influenza itself has associated aches and pains but this depends very much on the severity of the infection, and the same is likely to be true for bird flu.
If someone has a severe case of bird flu, it will be obvious from fever and respiratory illness that something is wrong.
However, we still do not know how many people may contract bird flu but show no symptoms, or have only a mild disease.
Currently, we are aware mainly only of the severe cases that are taken to hospitals.
It is very difficult to estimate when bird flu will enter the UK, but from recent events probably sooner rather than later.
DR BOB MCCRACKEN, IMMEDIATE PAST PRESIDENT, BRITISH VETERINARY ASSOCIATION
If avian flu can pass to humans, does anyone know if it could pass to domestic cats, then to humans, as an infected bird would be killed and eaten fairly quickly by most domestic pets?
Mrs Devlin, Wymondham
The avian influenza virus can infect cats. However, there are records of less than 10 cats having been infected with avian influenza virus.
Whilst cats can excrete (pass out) the virus there is no clear evidence of any human being having acquired avian influenza from an infected cat.
We must also keep in mind that whilst millions of people have had intimate contact with infected birds only 200 people are known to have become infected.
What should be done with regard to having budgies in an outside aviary and other pet birds in aviaries?
Sue Cornell, Witham, Essex, England
The risk of such birds becoming infected, even if the UK's wild bird population were infected, is very small.
The budgies or pet birds would need to make contact with infected, wild birds or their droppings.
Whilst this is possible, from infected birds flying over the aviaries, the risk is very small.
As a precaution and in the event of avian influenza reaching the UK such birds should be brought indoors or the aviary proofed against wild birds and their droppings.
As a pigeon fancier, I've read reports saying that pigeons are at low risk of avian flu. But breeding time has raised concerns over squabs (young pigeons) over 24 days old that need to go outside the loft to get their bearings. Should I be worried?
Jan Bailes, Loftus, Cleveland, England
In the past, the high pathogenic avian influenza virus has been associated with domestic poultry and has only rarely been isolated from wild birds.
Consequently, we still do not know a lot about how the H5N1 high pathogenic virus affects many species of wild birds.
However, deaths have been reported in pigeons and doves infected with avian influenza.
Whilst avian influenza remains undetected in the UK there is very little risk of the squabs acquiring infection.
Are steps being taken to compile a register of owners of small flocks of hens which are being kept in people's back yards?
Mrs J H Parlett, Cheltenham, UK
There is no legal requirement in either EU or UK law for flocks of less than 50 birds to be registered.
However, Dr Debbie Reynolds, the Chief Veterinary Officer, has requested all such owners to register at their local State Veterinary Service office.
The BVA would encourage all back yard poultry keepers to register.
Will the migration of birds back to England affect the risk of bird flu?
Clare Finn, Birmingham, Britain
We do know that some species of ducks can become infected, yet remain healthy and can pass the virus out in their droppings for at least 16 days.
Thus migrating ducks are recognised as a potential means of introduction of the H5N1 virus.
The autumn migration of ducks is a known high risk period as it is mostly from east to west - from infected countries to Europe including the UK.
It is thought that this is how infection arrived in Romania and Turkey.
We have a cat that loves the outdoors and she sometimes drinks from the bird bath. Is our cat at risk and, more to the point, are we?
A Smith, Kings Lynn, Norfolk, UK
Bird baths do become contaminated with droppings from birds.
If the birds were infected with avian influenza virus then the bird bath water would become contaminated with the virus.
The avian influenza virus can infect cats so, in theory, if a cat drank from a bird bath that was contaminated with virus then there is a possibility of the cat becoming infected.
Whilst infected cats can excrete (pass out) the virus there is no clear evidence of any human being having acquired avian influenza from an infected cat.
My cat frequently brings home dead birds. Could this pass on bird flu to my cat and humans?
Susan Acton, Melton Mowbray, Leicestershire
The avian influenza virus can infect cats. It is believed that cats become infected through eating the carcasses of infected birds.
Whilst avian influenza remains absent from the UK there is no chance of the virus affecting cats or human beings.
If avian influenza virus were to arrive in the UK there is a possibility that a cat could become infected through eating an infected dead bird.
However, bearing in mind that less than 10 cases have been described in cats the probability of your cat becoming infected must be extremely small.