Scientists answer why avian flu virus isn’t easily spread
MIT study on cell receptors could help researchers spot greater potential pandemic threats to humans
American scientists may have figured out why avian influenza viruses such as H5N1 don’t readily infect people — a finding that could be used in future to watch for bird viruses in the process of becoming a greater pandemic threat. Influenza experts say the work may also provide clues to a couple of mysteries about the pattern of human H5N1 infections to date, namely whether some people are more genetically susceptible to the virus than others and why children seem to make up a disproportionate percentage of human cases.
The researchers, from the Massachusetts Institute of Technology, identified the shape of cell receptors to which invading avian viruses can attach and where those receptors are found in the upper airways and lungs of humans. The work was published yesterday in Nature Biotechnology.
The senior author of the study said it gives scientists a way to spot avian flu viruses that are becoming more transmissible to people.
“We now really know what to look for,” said Ram Sasisekharan, a professor of biological engineering at MIT, in Cambridge, Mass.
Previously, it was thought that the issue of which cells avian and human flu viruses could attach to broke down on simple lines. Avian viruses were thought to latch onto cells with a type of receptor called alpha 2-3 — found in birds and in the lungs of people. Human flu viruses docked to cells with alpha 2-6 receptors, found in the human upper respiratory tract. But that answer was too simplistic.
Sasisekharan and his colleagues set out to look at the strings of sugar molecules that make up these receptors. They found that alpha 2-6 receptors actually come in two shapes — a conelike shape similar to the alpha 2-3 receptor and a long, umbrella-like shape.
The research showed that human flu viruses of the H1N1 and H3N2 subtypes bind to these umbrellalike alpha 2-6 receptors, which predominate in the upper airways.
H5N1 viruses currently latch on to cone-like receptors and would have to mutate to be able to dock to the umbrella-like receptors if they are to more easily infect people, Sasisekharan said, likening the process to a lock-and-key scenario. “It seems like the shape of the key really matters,” he said. Scientists should be checking H5N1 and other non-human flu viruses for that type of alteration, said paper co-author Terrence Tumpey, an expert with the U.S. Centers for Disease Control. Sasisekharan agreed questions about why H5N1 can infect some people and why clusters of cases occur among blood relatives may be answered through study of the concentration of cone-like alpha 2-6 receptors in infected people.