Scientists in Hong Kong have found that the H5N1 bird flu virus can infect cells in the upper airway of humans, and that they don’t have to penetrate deep into the lungs to cause an infection.
A study by scientists based in the United States in 2006 suggested that H5N1 could not infect people easily because it had to lodge itself deep inside the lungs, where it binds more easily to receptors called the Alpha 2-3.
In an article published in the January issue of Nature Medicine, scientists from the University Hong Kong found that the virus could infect the nasopharynx, the area behind the nose and above the soft palate, and throat.
“On the earlier hypothesis, the virus had to go deep into the lungs to infect anybody, but our research suggest that is not the case. The virus can settle itself in the upper respiratory tract. It does not have to go deep down into the lungs,” Microbiology Professor Malik Pieris reported on Friday.
By the testing of discarded tissues, Malik found that the virus could, indeed infect both the upper and the lower respiratory tracts.
“even in the upper respiratory tract where the Alpha 2-3 seem to be lacking, the H5N1 can still infect the cells…so it raises the question of whether there may be other receptors that the virus is using, which indicates that further study is much needed.” However, he said that there was no reason to panic.
“It is still not able, in most cases, to be transmitted from human to human (efficiently). It does not change that situation, as such,” said Pieris, who has studied th H5N1 virus since 1997 when it was first made known that it could jump to humans in Hong Kong, killing six people.
The virus made a comeback in 2003, and has become endemic in several places in Asia. Since then, it has infected 270 people around the world, killing 164 of them, according to the latest figures from the World Health Organization.
It has flared up again in recent months, spreading through poultry flocks in Japan, Vietnam, and Thailand, killing six people in Indonesia, and claiming it’s first human life in Nigeria.
Depending upon where Avian Influenza is active in the world, such patients may be recently returning travelers entering US health care facilities, or individuals who have had close contact with domestic poultry infected with Avian Influenza in the United States.
Although it remains a bird disease, experts still fear that the virus could kill millions once it learns how to efficiently pass through humans.
Currently, no vaccine is available to protect humans against the H5N1 virus that is being seen is Asia. However, vaccine development efforts are under way. Research studies to test a vaccine to protect humans against the H5N1 virus began in April, 2005. (Researchers are also working on a vaccine against H9N2, another bird flu virus subtype.)