By Rupert Wingfield-Hayes
BBC News, Beijing
The Chinese government says there is no need to be alarmed. So far, the only deaths reported from the latest bird flu outbreak are 178 wild geese found on the shores of Lake Qinghai earlier this month.
Medical workers sanitise a truck in north-western China
There are no reported cases of the disease among China's domestic poultry, let alone any cases of human infection.
But if there is no reason to be alarmed, why has China rushed to shut down all its national parks, sealed off Lake Qinghai, and ordered the vaccination of millions of poultry across vast areas of western China?
The reason is the potential this virus has to cause mayhem. The virus in question is known by the code name H5N1, and it is extremely deadly, not just to birds, but to humans.
On Monday, Vietnam confirmed a further death from the virus, bringing the total in South-East Asia to 54. Up to now outbreaks of the virus have been largely confined to southern China and South East Asia.
The first outbreak was in Hong Kong in 1997. Every single chicken in the territory was slaughtered to bring the outbreak under control.
Tens of millions more have been slaughtered in Thailand, Vietnam and Cambodia. But H5N1 has not been contained.
It continues to pop up all over South East Asia, and has now been discovered among migratory birds 2,000 kilometres away on the edge of the Tibetan plateau.
Every spring, millions of migratory birds leave South East Asia and head north across China to their summer nesting grounds. The fear now is that many more than the 178 geese which died may be carrying H5N1.
H5N1 BIRD FLU VIRUS
Principally an avian disease, first seen in humans in Hong Kong, 1997
Almost all human cases thought to be contracted from birds
Isolated cases of human-to-human transmission in Hong Kong and Vietnam, but none confirmed
Fifty-four human deaths don't sound many. In fact, bird flu has so far proved very poor at spreading to humans. Almost all of those who died had been in close daily contact with infected chickens and ducks.
But that may change. Viruses constantly mutate. Already H5N1 has mutated into a form that can pass from bird to human. Next it may combine with the human flu virus and produce a new subtype, which few if any humans would have natural immunity to.
If it does, the scenario is terrifying. A new and deadly flu epidemic would break out. It would spread around the world in a matter of weeks.
Tens, perhaps hundreds of millions would be hospitalised. Anywhere between two and fifty million people could die.
The world is overdue for a new "flu pandemic". Many scientists now say it is not a matter of if, but when. No one has died in China from this latest outbreak. But that is no reason to feel reassured.