Humans a hostile host to bird flu
Scientists have discovered why the H5N1 avian flu that is so lethal in birds has not spread easily among humans.
ELMAT: this is bad news for those guys cashing in on the bird flu scare!!
Unlike flu viruses that are passed easily between people, H5N1 has a hard time attaching to cells in the nose, throat and upper airways. However, it readily attaches to cells deep in the lungs.
This suggests that people need close and heavy exposure to the H5N1 virus for it to get into the lungs, where it can take hold. But once there, it causes extensive damage to the machinery of respiration - the cells and air spaces where oxygen is exchanged for carbon dioxide.
"For the viruses to be transmitted efficiently, they have to multiply in the upper portion of the respiratory system so that they can be transmitted by coughing and sneezing," said Yoshihiro Kawaoka, a virologist at the University of Wisconsin-Madison, who led the research team.
The H5N1 bird flu virus has killed 103 people and infected 184 since late 2003.
People infected with the virus, which has spread from Asia to Europe, the Middle East and Africa, have had close contact with diseased birds. Scientists fear the virus could mutate into a pandemic strain that could become highly infectious and capable of killing many millions of people.
"Our findings provide a rational explanation for why H5N1 viruses rarely infect and spread from human to human, although they can replicate efficiently in the lungs," Dr Kawaoka and his team said in a report in the journal Nature.
Dr Kawaoka and researchers in Japan infected human tissue with bird flu viruses. Their findings suggest that strains of H5N1 circulating in birds would have to undergo several key genetic changes to become easily transmissible in humans.
In another paper, published in Science, Thijs Kuiken and colleagues in the Netherlands found the bird virus attached predominantly to cells at the entrance to the air sacs and in them, as well as to immune-system cells that patrol the area.
The new understanding may help in the testing of vaccines and antiviral drugs against H5N1, Dr Kuiken said.
Reuters, The Washington Post |
