By Mark Kinver
Science and nature reporter, BBC News
The latest outbreak of bird flu could not have come at a worse time for British poultry farmers.
The lucrative Christmas period is fast approaching and the farmers have been hoping for a much needed financial boost from the festive market.
The discovery of the H5 strain of the virus on a Suffolk farm rounds off a bleak year that has seen farms hit by a series of outbreaks.
The industry over the past 10 months has had to deal with the impacts of foot-and-mouth and bluetongue diseases, as well as an earlier case of bird flu.
It seemed there was a light at the end of the tunnel last week when it was announced that EU export restrictions on meat products were to be relaxed for the first time since August's outbreak of foot-and-mouth.
National Farmers' Union (NFU) president Peter Kendall has described the latest outbreak as a huge blow for the beleaguered sector.
Bird flu has been discovered near Diss on the Norfolk/Suffolk border
He said the key thing now was to stop the virus spreading from the infected farm.
A 3km (1.9-mile) protection zone and 10km (6.2-mile) surveillance zone around the infected farm were set up immediately after the H5 strain was identified on Monday.
Scientists hope the early identification of bird flu and tight controls on the movement of poultry and their waste will stop the virus spreading.
Lessons learned from February's H5N1 outbreak at a turkey farm, also in Suffolk, highlights how important bio-security measures are.
Farmers within the 3km protection area have been told to bring their flocks indoors and check for any signs of the virus.
Symptoms include swelling of the head, a blue discolouration of the neck and throat, loss of appetite and breathing problems. Other signs include inactivity and a drop in egg production.
Senior vets have urged all poultry farmers, not just those in the surrounding area, to be extra vigilant.
Finding the source
A lot of people will be asking how did this outbreak happen? In short, it is too early to say with any certainty.
Over the coming days, analysis of the virus should be able to identify its origins and offer an insight into how the farm's bio-security measures were breached.
February's H5N1 outbreak was quickly linked to viruses that had originated in Hungary. A subsequent inquiry concluded that an infected bird was transported from Hungary to East Anglia.
Another possible source for the latest outbreak is the wild bird population, which is known to carry the virus.
The most common mode of transmission is faecal-to-oral transmission. Infected birds can carry the virus in their intestines and shed it in saliva, nasal secretions and faeces.
However, some scientists challenge the "wild bird" theory. They say it offers no explanation as to why certain countries on flight paths of birds from Asia remain flu-free, whilst their neighbours suffer repeated infections.
While the H5N1 strain is deadly for birds, scientists say the risk to the public is minuscule.
Defra officials say it is very rare for the disease to pass to humans, and it can only be contracted by someone coming into very close contact with an infected bird.
The Food Standards Agency advises that properly cooked meat and poultry products, including eggs, are safe to eat.
However, farmers are aware that these reassurances may not be enough to convince the public.
Market analysis following the February outbreak showed that turkey sales in the UK fell by a third.
For many farmers, it looks as if 2007 is likely to be remembered as an annus horribilis.