320: Flu New
The H5N1 bird flu virus might be acquiring a greater ability to spread from human to human, recent cases in Vietnam suggest. But as two elderly relatives of patients killed by the bird flu test positive for the virus and yet have no symptoms, there are also indications that it may not be as lethal as currently thought.As Bigwig explains, as did Rachel some time back, viruses become less virulent because of evolution. The more deadly a virus, the less likely it is that the host will live long enough to pass it on. A non-virulent virus in a closed population will be more evolutionarily fit than a virulent virus. The opposite is true of viruses in transient populations. Then it's better for the virus to reproduce fast, kill its host, and spread to new hosts who will carry the virus to new populations.
The 2004 outbreak of H5N1 in Vietnam stopped in spring after the country killed millions of infected and exposed poultry. But outbreaks resumed in December, probably because the virus persisted in ducks showing no symptoms, say flu experts. Since December, 22 people have tested positive for H5N1 in Vietnam, of whom 14 have died, including one woman from Cambodia.
Evolutionary hypothesis tested.