Is Southern China the perfect incubator for bird flu pandemic?

The little boy jumped on a crate of clucking chickens as his father called out to him to transfer more birds from a large enclosure into the crate.

In this dank, poultry wholesale market in Guangzhou in southern China, a woman in the next stall selling ducks chomped on an apple while five bare-chested men sat down to lunch.

All around the humans are cages of live chickens, ducks, geese, rabbits, goats, pigeons and pheasants - the perfect setting for the H5N1 bird flu virus to mix with other viruses or mutate into what experts predict would be the next pandemic strain.

Once the hybrid is easily transmissible among people - which experts say will ultimately happen as the virus changes - they predict more than 25 million hospital admissions and up to seven million deaths globally within a short period.

At least two of the three pandemics in the last century originated in southern China. And it seems more than a coincidence that the H5N1 made its first known jump to humans in 1997 in Hong Kong, which lies in southern China.

So why is this region such a hotbed for new deadly bugs? "A large proportion of the global population is in this region, and beyond that there is a diversity of animals that are thought to be important in the generation of these pandemic viruses," Malik Peiris, a microbiologist at the University of Hong Kong who has worked extensively on the H5N1 virus and SARS, said in an interview.

"These include waterfowl, particularly ducks which are reared in large numbers in this region, pigs and the fact that poultry, pigs and humans are present in very large numbers and in very close proximity to each other in this region. Not just China but southeast Asia," said Dr Peiris.

Spread across Guangdong province in southern China are tiny farms, where villagers raise small numbers of pigs in open sheds. Outside, chickens and ducks are free to roam.

"In places where you have pigs, birds and humans living close to each other, they create the ecology for the emergence of new strains. In southern China, you can easily see them keeping chickens, water birds very close to pigs and humans. This environment makes gene reassortment more likely," said Paul Chan, a microbiologist at the Chinese University.

Gene reassortment is the closest things viruses have to sex. They can swap genes with other viruses, often allowing them to acquire vastly new abilities overnight.

It is a faster way to change than simple mutation - which could also lead to a new H5N1 strain deadlier to people.

The H5N1 strain has haunted the world since it made its debut in humans in 1997. It is now endemic in parts of Asia, where it has killed more than 60 people since late 2003.

The crisis deepened this year when wild migratory birds began dying from it in central China and experts have since warned that species which survive could carry the virus all over Europe and Africa within the next two migrating seasons.

So far, the virus has been detected in regions north of China in Kazakhstan, Russia and Mongolia. It has also been found in China's southwestern regions of Xinjiang and Tibet, which hangs just over Nepal and the rest of the Indian subcontinent.

But such worries cannot be farther from the minds of farmers and poultry vendors in southern China, where such husbandry practices have been handed down for generations. "Sick? I have never been sick!" snapped the woman at the market as she carried on eating her apple.

But health experts continue to be alarmed and governments around the world have hammered out contingencies in the event of a pandemic, which is certain to put a stop to all air travel, trade and other aspects of ordinary life.

Dr Chan said the threat of a pandemic has become infinitely larger with the involvement of migratory birds.

"With land birds you can catch and kill them, but with migratory birds you can't. What we fear is that migratory birds will spread the virus to poultry (in other parts of the world). Poultry is closest to humans, that's the tipping point," he said.

Factbox

The H5N1 avian flu virus has killed 63 people in Asia since late 2003. It is one of 15 known subtypes of bird disease caused by type A strains of the influenza virus. Type-A avian influenzas were first identified in Italy more than 100 years ago.

Here are some facts about H5N1 avian flu.

¤ There are dozens of different known flu strains, named for two particular proteins that each virus carries. H5N1 refers to an avian flu strain that emerged in Hong Kong in 1997, killing or forcing the destruction of 1.5 million chickens, ducks and geese, infecting 18 people and killing six.

The World Health Organisation says the quick slaughter of all potentially infected birds may have averted a pandemic.

¤ H5N1 avian influenza re-emerged in Korea in 2003. It has now been found in birds in Cambodia, China, Indonesia, Japan, Kazakhstan, Korea, Laos, Malaysia, Mongolia, Philippines, Russia, Taiwan, Thailand and Vietnam.

¤ H5N1 is considered the biggest direct disease threat to humanity because it mutates rapidly and also can acquire genes from other viruses, making it a potential human pathogen.

¤ Experts predict that if it acquires the ability to infect people easily and to spread from person to person efficiently, it would make more than 25 million people seriously ill and would kill as many as seven million.

¤ These numbers could go even higher, according to other models, which show the virus would make 50 per cent of people where it is circulating ill, and five per cent could die.

¤ All influenza viruses change quickly, which is why the standard flu vaccine must be changed every year. But H5N1 is particularly good at changing. The fear is it would acquire a key gene from a flu virus that already easily infects humans and become a highly contagious and deadly strain.

¤ Birds that survive infection with H5N1 excrete virus for at least 10 days, orally and in faeces, making it highly likely to spread.

Migratory birds, usually wild ducks, are the natural "reservoir" of avian influenza viruses and usually do not become sick when infected. Domestic poultry, including chickens and turkeys, die quickly when infected.

¤ Several companies are working on an H5N1 vaccine. The furthest along in development is France's Sanofi-Aventis. Chiron Corp. aims to test its H5N1 vaccine later this year and GlaxoSmithKline plans large-scale clinical trials in 2006. The ordinary flu vaccine does not protect against avian flu.

¤ Two antiviral drugs can help against the infection and may even prevent it if taken at precisely the right time.

These are Roche's Tamiflu, known generically as oseltamivir, and GlaxoSmithKline's Relenza, or zanamivir.