(Adds WHO comment, updates figures)By Tan Ee LynHONG KONG, March 11 (Reuters) - A Chinese expert on respiratory diseases says the H5N1 bird flu virus has shown signs of mutation and urged vigilance at a time when seasonal human influenza is at a peak, newspapers reported on Tuesday."When avian flu is around and human flu appears, this will raise the chances of avian flu turning into a human flu. We have to be very alert and careful in March," Zhong Nanshan was quoted by the Ming Pao newspaper as saying."People who were killed by bird flu last year and this year were too poor to seek treatment. If you happen to have high fever and pneumonia, you must seek treatment fast," said Zhong, director of the Guangzhou Institute of Respiratory Diseases in China's southern Guangdong province.Experts are worried about seasonal flu, because it could get mixed up with a deadly novel strain, such as the H5N1 bird flu virus. Such a hybrid would not only become easily transmissible between people, but packed with great killing power."The bird flu virus has shown signs of mutation. If infected people don't get treatment in a timely manner, they can die easily," Zhong was quoted as telling reporters on the sidelines of the Chinese parliament's annual meeting.But World Health Organisation (WHO) spokesman Gregory Hartl played down Zhong's concerns."Mutations occur in influenza viruses. Separately from that, the (bird flu) virus continues to be deadly. But there is no new jump in deadliness," Hartl said in Geneva.Three Chinese have died this year of H5N1 bird flu and they were infected probably through contact with sick poultry. The World Health Organisation said there was no evidence of transmission between humans in all three cases.HONG KONG SHUTS SCHOOLIn Hong Kong, the government shut a primary school early ahead of the Easter holidays after one of its students, a 7-year-old boy, died at noon on Tuesday. The boy was admitted to hospital last week with flu-like symptoms and authorities are still trying to determine the cause of his illness.Thomas Tsang, controller of the Centre for Health Protection, said five other pupils at the school have been admitted to hospital for respiratory infection and their conditions were stable. Three samples have tested positive for influenza A, Tsang said, without specifying the strain."The school will close early for Easter from tomorrow ... to facilitate disinfection," Tsang told a news conference. But he said there was no reason to close all schools in Hong Kong, although they would monitor the situation closely.Hong Kong, which lies at the south of China, is in the grip of a seasonal flu peak, with outbreaks reported in a growing number of schools.A 3-year-old girl died last week of human H3N2 flu and authorities have ordered schools to conduct fever checks and advise those who are unwell to stay home.Although the H5N1 virus has infected only 372 people around the world since 2003, its mortality rate has been high, killing 235 of them. (Additional reporting by Donny Kwok in Hong Kong and Stephanie Nebehay in Geneva; Editing by Jeremy Laurence)
Researchers involved in a study at the University of Wisconsin have discovered that the H5N1 Avian Flu virus has mutated into a strain that may make humans more vulnerable to the disease.

Prior to the study, it was known that the virus could only thrive or live in a body which have temperatures of 106°F (41°C). A human's normal body temperature is 98.6°F (37°C). This difference in the temperatures of bodies makes the virus less likely to infect a human, but the recent study suggests the virus has adapted to survive in bodies with temperatures lower than 106°F.

"We have identified a specific change that could make bird flu grow in the upper respiratory tract of humans," said Yoshihiro Kawaoka, the researcher in charge of the study.

Kawaoka also stated that the "viruses that are circulating in Africa and Europe are the ones closest to becoming a human virus," but also stated that the H5N1 virus must undergo several mutations before it can infect a human, who can then spread the virus to other humans.

"Clearly there are more mutations that are needed. We don't know how many mutations are needed for them to become pandemic strains," added Kawaoka.

The World Health Organization (WHO) has stated that despite the study, influenza viruses are constantly mutating from season to season, but that the H5N1 virus is not anymore deadly to humans than before the study.

"Mutations occur in influenza viruses. Separately from that, the (bird flu) virus continues to be deadly. But there is no new jump in deadliness," said Gregory Hartl, a spokesman for the WHO.