At a Beijing press briefing today World Health Organization and UN Food and Agriculture Organization representatives said that the recent spike in human cases of bird flu in China did not mark the start of a flu pandemic. But they pointed to problems in China's agricultural sector, and said they had asked the government to agree to joint investigations into the causes of the infections.

Risk assessment unchanged

"Our risk assessment of the January outbreak is that nothing has really changed. There are a high number of cases, eight cases, but it follows the seasonal pattern that we see in the first quarter of every year," said Dr Hans Troedsson, representative of the World Health Organization (WHO) in China.

"There's no indication this is the beginning of a pandemic. The cases are geographically distributed and there are no links between them, and all of them had been exposed to sick or dead poultry or animal markets. There's no indication of human to human transmission."

Dr Troedsson said the H5N1 virus responsible for the bird flu cases fulfilled two out of three conditions for a pandemic in that most of the human population is susceptible and it causes severe illness, but it so far lacks the crucial third condition - ease of transmission between humans.

But he warned against complacency, pointing out that in recent years the size and intensity of outbreaks among animals had been growing, and that the range of species affected had broadened to include, for example, cats and tigers.

Dangers of backyard farming

Dr Edith Marshall and Dr Vincent Martin of the UN Food and Agriculture Program (FAO) said the danger was that virus would recombine with other viruses to produce a new strain with high infectivity between humans. They said the danger is heightened by the widespread existence in China, as in most Asian countries, of "backyard farming" in which several species of livestock are kept in close proximity with each other and with humans.

"Ducks and chickens should not be mixed because they have different susceptibilities to the virus and by mixing these species it gives more opportunities to the virus to evolve," said Dr Marshall.

She pointed out the wild bird population is the main reservoir of bird flu viruses. Flu viruses are endemic among wild birds and in most cases do not cause severe symptoms. Apparently healthy wild birds, however, can infect the more susceptible domestic poultry.

Request for joint investigations

Dr Troedsson said the causes of human outbreaks in China were not well understood and needed further investigation. "China is unique in one way. In most countries we can link human cases to poultry outbreaks. In China out of the 38 it's just two or three cases where you actually had a poultry outbreak precede the human cases."

"It's something both WHO and FAO are raising with the government and we have tried to get them to do joint investigations. That has been efficient in other countries and we suggest that they apply the same approach in China."

All three experts pointed out that the virus may be present in poultry and other livestock without causing any obvious symptoms. Vaccination programs that have been widely used in China may suppress symptoms and cut the overall viral load in the livestock population, without entirely eliminating the virus.

Move to industrial scale farming

Dr Troedsson called for a move away from backyard farming to large scale agriculture over the long term. "When you have industrial production of poultry it's so much easier to have surveillance and if there is an outbreak, confine it. Another factor is that backyard farming can't meet the needs of economic growth."

Need for continued vigilance

Dr Troedsson said that although the H5N1 virus may not mutate and cause a pandemic, whatever the eventual source, a flu pandemic is inevitable and overdue as one occurs on average every 25 to 30 years. "There is less interest among the media because this story has been going on for some time, but it is important that governments continue to do their preparedness planning."

(China.org.cn by John Sexton February 18, 2009)