A single genetic mutation might explain why West Nile virus has, within a decade, switched from causing relatively mild infections in humans to outbreaks of deadly encephalitis.
The virus, which can pass to humans via mosquitoes that feed on infected birds, didn’t pose a serious threat until the mid-1990s, when outbreaks of deadly infection sprang up in Israel, Romania, Russia and eventually North America. Aaron Brault and colleagues at the University of California, Davis, discovered that these new strains have in common a mutation in the gene for helicase – a protein involved in viral replication. The mutation arose independently…
