The spread of bird flu - also known as avian flu - which has led to human deaths in South East Asia, is causing concern.
The virus is contracted through close contact to poultry
But what is the disease and what are the possible risks to humans?
Q: What is bird flu?
Like humans and other species, birds are susceptible to flu.
There are 15 types of bird, or avian, flu.
The most contagious strains, which are usually fatal in birds, are H5 and H7.
The type currently causing concern is the deadly strain H5N1.
Even within the H5N1 type, variations are seen, and slightly different forms are being seen in the different countries affected in this outbreak.
Migratory wildfowl, notably wild ducks, are natural carriers of the viruses, but are unlikely to actually develop an infection.
Domestic birds are particularly susceptible in epidemics.
This is why the confirmation of H5N1 in birds in Turkey and Romania is causing concern.
Pakistan has seen cases of the H7 and H9 strains of bird flu in poultry, but no cases of these strains have been passed to humans
Q: Is it possible to stop bird flu coming into a country?
The fear, after the Turkish and Romanian findings, is that H5N1 will spread across Europe.
Because it is carried by birds, there is no way of preventing its spread.
But that does not mean it will be passed to domestic flocks. Experts say proper poultry controls - such as preventing wild birds getting in to poultry houses - which are present in the UK, should prevent that happening.
In addition, they say monitoring of the migratory patterns of wild birds should provide early alerts of the arrival of infected flocks - meaning they could be targeted on arrival.
Q: How do humans catch bird flu?
Bird flu was thought only to infect birds until the first human cases were seen in Hong Kong in 1997.
Humans catch the disease through close contact with live infected birds.
Birds excrete the virus in their faeces, which dry and become pulverised, and are then inhaled.
Symptoms are similar to other types of flu - fever, malaise, sore throats and coughs. People can also develop conjunctivitis.
Researchers are now concerned because scientists studying a case in Vietnam found the virus can affect all parts of the body, not just the lungs.
This could mean that many illnesses, and even deaths, thought to have been caused by something else, may have been due to the bird flu virus.
Q: How many people have been affected?
As of 20 October, 2005, there had been 118 confirmed cases of avian flu in humans in Indonesia, Vietnam, Thailand and Cambodia, leading to 61 deaths.
In comparison, Sars has killed around 800 people worldwide and infected at least 8,400 since it first emerged in November 2002.
Q: Can avian flu be passed from person to person?
There are indications that it can, although so far not in the form which could fuel a pandemic.
A case in Thailand indicated the probable transmission of the virus from a girl who had the disease to her mother, who also died.
The girl's aunt, who was also infected, survived the virus.
UK virology expert Professor John Oxford said these cases indicated the basic virus could be passed between humans, and predicted similar small clusters of cases would be seen again.
It is not the only instance where it has been thought bird flu has been passed between humans.
In 2004, two sisters died in Vietnam after possibly contracting bird flu from their brother who had died from an unidentified respiratory illness.
In a similar case in Hong Kong in 1997, a doctor possibly caught the disease from a patient with the H5N1 virus - but it was never conclusively proved.
Q: Does this mean there is likely to be a large outbreak of bird flu?
Experts are concerned that this could happen. But in the Thai case, the virus was only passed to close relatives and spread no further.
In addition, it had not combined with a form of human flu.
This is the real fear. Experts believe the virus could exchange genes with a human flu virus if a person was simultaneously infected with both.
The more this double infection happens, the higher the chance a new virus could be created and be passed from person to person, they say.
Concern has also been raised by research which showed that the virus which caused the 1918 pandemic was an avian flu virus.
Q: What would be the consequence if this did happen?
Once the virus gained the ability to pass easily between humans the results could be catastrophic.
Worldwide, experts predict anything between two million and 50 million deaths.
Q: Is there a vaccine?
There is not yet a definitive vaccine, but prototypes which offer protection against the H5N1 strain are being produced.
But antiviral drugs, such as Tamiflu which are already available and being stockpiled by countries such as the UK, may help limit symptoms and reduce the chances the disease will spread.
Concerns have been prompted by news a Vietnamese patient has become partially resistant to the Tamiflu, drug experts plan to use to tackle a human bird flu outbreak.
Scientists say it may be helpful to have stocks of other drugs from the same family such as Relenza (zanamivir).
Q: Can I continue to eat chicken?
Yes. Experts say avian flu is not a food-borne virus, so eating chicken is safe.
The only people thought to be at risk are those involved in the slaughter and preparation of meat that may be infected.
However, the World Health Organisation recommends, to be absolutely safe all meat should be cooked to a temperature of at least 70C. Eggs should also be thoroughly cooked.
Professor Hugh Pennington of Aberdeen University underlined the negligible risk to consumers: "The virus is carried in the chicken's gut.
"A person would have to dry out the chicken meat and would have to sniff the carcass to be at any risk. But even then, it would be very hard to become infected."
Q: What is being done to contain the virus in the countries affected?
Millions of birds have been culled in an attempt to stop the spread of the disease among birds, which would in turn stop it being passed on to humans.