Do not ignore strains of less toxic bird flu viruses

Experts have called for a more thorough study of the less lethal strains of the H5N1 bird flu virus because they could be the triggers of a pandemic flu outbreak.

Scientists have classified at least four major variants, or "genotypes," of the H5N1 virus since it spread to humans in 1997 in Hong Kong.

At the top of this list is genotype Z, which has been discovered in northern China, Indonesia, some parts of Africa, Europe, and the Middle East, and has caused more than half of the victims to be infected with the virus. must die

The less known Genotype V appeared in South Korea and Japan in late 2003. At least 9 Koreans were infected with mutated forms of this virus when participating in the destruction of poultry to stop the outbreak. translated in this country in late 2003 and early 2004. None of them had any severe symptoms and they all recovered.

H5N1 virus

There was one more worker exposed to this infected virus after the disease struck poultry farms in South Korea in November but he was also not seriously ill.

Scientists have warned against ignoring these less toxic strains of H5N1 because they are very similar to viruses that have killed millions of people before.

Julian Tang, an assistant professor of microbiology at the University of Hong Kong in China, said: " What makes the previous pandemics scary is not the high death rate but the ability to spread on people." of these strains . If there are many people infected, even low mortality will cause the death toll to the extreme.

Ms. Tang said: 'All flu pandemics have relatively low mortality (less than 3%, including pandemics in 1918-1919). The total number of deaths is high because many people are infected, but the vast majority, over 97%, still survive. '

The flu epidemic in Spain in 1918-1919 killed about 50 million people worldwide, but people will never know what the actual number of deaths is.

Ms. Tang said: 'There is evidence that even this virus is somewhat adaptable to humans before causing a pandemic. This is probably what we are seeing in milder and asymptomatic people with H5N1 in Korea. '

"If a virus kills so much that it kills 50% of the people carrying it, the virus will not spread to many people and will become extinct relatively quickly," said Tang . So it is unlikely that it will cause a global pandemic. '

The H5N1 virus has erupted in recent weeks, spreading among poultry flocks in Japan, Vietnam and Thailand, killing six people in Indonesia, and killing one person in Nigeria for the first time.

Although this is still a disease in poultry, it is known that the virus has infected 270 people since the end of 2003 and killed 164 of them. Experts fear that the virus can kill millions of people once it knows how to spread between people and people effectively.

Lo Wing-lok, an infection expert in Hong Kong, called for a more thorough study of all variants of the H5N1 virus. Mr. Lo said: 'How can genotypes V and Z cause serious infection in humans? I believe we should have some idea of ​​how toxic these two subtypes are. '

Tang believes that the virus strain is less toxic, rather than genotype Z, which causes serious illness, most likely a pandemic agent.

She said: 'If H5N1 is the flu virus that causes the next pandemic, it needs to adapt more to people to be able to spread among people effectively, not cause them to die. too fast, so infected people can spread the virus to others. '

Hong Linh