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Health
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2006-11-15 21:18:00-05
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Mutations that help bird flu virus turn virulent for humans found
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Washington, Nov 16 Researchers at the University of Wisconsin-Madison have identified two genetic mutations that appear to be involved in turning a deadly bird flu virus into a contiguous human one. The H5N1 strain has surface proteins that allow it to easily infect birds, but not humans. However, experts have been afraid it will gain the ability to spread easily among humans, leading to millions of deaths world-wide. "We identified two changes that are important. Both changes are needed for the H5N1 virus to recognise human receptors," says Yoshihiro Kawaoka, the senior author of the Nature paper and a virologist at the University of Wisconsin-Madison School of Veterinary Medicine. The scientists have identified the molecular blueprint for the genetic changes required to transform a virus that only infects birds to a virus capable of easily recognising human receptors. By knowing what genetic changes are required for the virus to easily infect human cells, it may be possible to detect the emergence of pandemic strains earlier, providing public health officials and vaccine manufacturers with precious time to prepare for a global outbreak of highly pathogenic influenza, the authors say. A virus must be able to recognise and attach to a host cell in order to infect the living being, but human and avian influenza viruses recognise different cell receptors. Avian flu viruses have demonstrated an ability to evolve to easily infect humans by exchanging genes with human viruses that subsequently permit them to recognise human receptor molecules and gain easy access to cells, typically in the human respiratory system. The change is thought to occur when human patients are exposed at the same time to a human flu virus and an avian flu virus. Most viruses, including influenza, readily swap genes with one another. "There are big differences between the virus first found in 1997 and the virus we see now. We are watching this virus turn itself into a human pathogen," Kawaoka explains. The international team of researchers claim that more mutations will be required for the virus to fully adapt to humans, but it is not known how many mutations are needed for such a change. However, if scientists are able to continue to monitor and secure viral isolates from humans infected with bird flu, they may be able to map a mutation trajectory that will help predict when the avian virus will cross the threshold to become a human pathogen.
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