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SAR experts shed new light on larger H5N1 attack scope
http://www.thestandard.com.hk/news_detail.asp?we_cat=4&art_id=38271&sid=12207681&con_type=1&d_str=20070214
Carol Chung
Wednesday, February 14, 2007
http://www.thestandard.com.hk/news_detail.asp?we_cat=4&art_id=38271&sid=12207681&con_type=1&d_str=20070214
Carol Chung
Wednesday, February 14, 2007
A groundbreaking study by Hong Kong scientists has shown the deadly H5N1 virus does not only attack the lungs as previously thought, but also the nose and throat, shedding new light on how the virus can attack other parts of the body.
But this does not suggest it is easier to contract the virus, the scientists said.
The study, started last June by the Hong Kong University Li Ka Shing Faculty of Medicine, aims to look at how the avian virus, believed to be transmittable only through poultry, attacks the human body.
According to pathologist Dr John Nicholls, previous US and Japanese studies showed H5N1 infects the lower respiratory tract because the virus preferentially binds to receptors called alpha 2-3 that populate the whole respiratory tract in poultry, but only the lower respiratory tract in humans.
But the new findings, which show infection can also occur in the upper respiratory tract despite a lack of alpha 2-3 receptors, overturned a previous theory that the widely believed receptors were what the virus uses to cause an infection in humans.
The search for the right receptor, out of four or five possibilities, that is responsible for the infection is expected to finish in six months, Nicholls said.
According to microbiologist Professor Malik Peiris, the result will also give new insight into how the virus can attack other parts of the body, where the responsible receptor exists.
The current belief is that H5N1 is limited to the respiratory tract, but there is clinical evidence where patients display some degree of diarrhea and problem in the central nervous system.
The gastrointestinal tract and the brain are other possible areas of infection, said Peiris, adding that the clinical evidence is so far not backed by studies.
Moreover, spotting the responsible receptors and locations of infection will also have implications for manufacturing drugs that can block virus entry.
The new findings do not affect how it is diagnosed, Peiris said. "It's quite difficult for people to differentiate in the early stage, but just because you have an upper-tract infection doesn't mean it's H5N1. There are other common flu viruses with symptoms in the upper respiratory tract," he said.
According to the World Health Organization, when assessing possible cases the level of clinical suspicion should be heightened for people showing flu-like illness, especially with fever and symptoms in the lower respiratory tract, and who have a history of close contact with infected birds.
Although the virus has been shown to cause infection in the upper tract, without going deep into the lower tract, it does not suggest it is easier to contract the virus or is moving closer to human- to-human transmission, Peiris said.
But the new findings do not suggest people should be more worried, he added.
The virus still has not mutated to cause efficient avian-human transmission, or human-to-human transmission at all. It is still difficult to infect humans, Peiris emphasized.
People need not worry too much because there are strict hygiene control measures on imported poultry, and a few dead wild birds in Hong Kong is not important, he said.
Those at risk are in close contact with poultry, as shown in past infection cases. The main worry remains the potential mutation of the virus which would make human-to-human transmission possible.
According to the WHO, of the hundreds of strains of avian influenza, the H5N1 virus is of the greatest concern at present because it has caused, by far, the greatest number of human cases of a very severe disease and the greatest number of deaths (165 worldwide so far). It has crossed the species barrier to infect humans on at least three occasions in recent years - 18 cases with six deaths (first documented case of human infection) in Hong Kong in 1997, two cases with one death in Hong Kong in 2003 and in the current outbreaks that began in December 2003.
The persistence of the outbreak of avian flu in Asia, which has spread to Russia, the Middle East, Europe and Africa, has been blamed in part on migrating birds.
Most of the past human cases have been linked to contact with infected birds.
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