By Ian Ransom
BEIJING (Reuters) - A 16-year-old boy died of bird flu in central China Tuesday, state media reported, the third death this year, as experts warned that surveillance gaps could mask the true extent of the disease in Chinese poultry.
A health official Tuesday also confirmed the mother of a toddler infected with the avian virus from the same province had died of pneumonia weeks before.
After not recording a case in almost a year, four human infections have been reported in China in the last two weeks, as millions of people flock to poultry markets to buy food ahead of the Lunar New Year holiday.
Three have died, and one remained in hospital.
The latest victim, a student, died in hospital in Huaihua, in central Hunan province, after falling ill in neighbouring Guizhou, Xinhua news agency said.
"Epidemiological investigation found the patient had come in contact with birds that had died from sickness before he fell ill," the agency quoted a notice from the Hunan Health Bureau as saying.
Chinese health authorities now say the patients in three of the four cases had had close contact with poultry prior to being infected. It was unclear whether the fourth case, a 27-year-old woman who died in eastern Shandong province on Saturday, had also come in contact with poultry.
With all the victims having fallen ill in different provinces without any prior reports of outbreaks among local bird populations, experts are concerned that surveillance gaps may be masking the true extent of the disease.
"Quite a few provinces now have human cases, so where is the source of the infection?" said Leo Poon, a virologist at the University of Hong Kong.
"The recent cases indicate that (the victims were directly infected by poultry) and that the outbreak of the disease in poultry may be very widespread. That increases the likelihood of people getting infected," Poon said.
The H5N1 flu remains largely a virus among birds, but experts fear it could change into a form that is easily transmitted among humans and spark a pandemic that could kill millions of people worldwide.
The disease is more active in the cooler months between October and March, experts say. There were only three recorded cases in China in 2008, all of which were fatal.
MORE CASES FEARED
A batch of smuggled Chinese chickens infected with bird flu made its way to neighbouring Vietnam, officials there said last week. An 8-year-old girl was hospitalised after being confirmed infected with bird flu earlier this month.
At least 34 people have been infected in China and 23 have died. China's Agriculture Ministry Monday warned of more bird flu cases as poultry is shipped from region to region ahead of the Chinese New Year holiday next week.
With the world's biggest poultry population and hundreds of millions of backyard birds, China is seen as critical in the fight to contain bird flu.
A 2-year-old girl confirmed infected with bird flu over the weekend remains in critical condition in a hospital in northern Shanxi province after falling ill in Hunan.
Peng Zaizhi, director of the emergency office of the Hunan Health Bureau, confirmed reports that her mother had died of pneumonia earlier this month after coming in close contact with poultry.
China's State Administration of Industry and Commerce instructed officials to "severely punish" illegal sellers of live poultry and bird flu vaccines, the Farmers' Daily, a state-run newspaper, said in a report posted on its website (www.farmer.com.cn).
In northern Shanxi province, officials were ordered to man provincial border control posts around the clock to "prevent the infiltration of disease," the official Shanxi Daily said.
Since the H5N1 virus resurfaced in Asia in 2003, it has infected 391 people, killing 247 of them, according to WHO figures released in mid-December.
(Additional reporting by Ben Blanchard and Yu Le in Beijing and Tan Ee Lyn; Editing by Alex Richardson)
