Use your mosquito repellant this summer, wherever you live: West Nile virus causes an encephalitis for which there is no specific treatment and which seems to kill around 10% of those infected. Spread to humans by mosquitoes infected after biting birds which are a reservoir of the virus, the virus appeared in New York last year (either via an imported bird or, for you conspiracy buffs, released from an experimental protocol at Sloan Kettering) and a massive mosquito eradication effort has apparently not impacted on its persistence in New York area birds, where it was hoped that it would not survive a winter. Now researchers say that there are 77 species of migratory birds in North America capable of carrying the virus and that it has probably spread all over the continent by now. Experts project a Gulf Coast outbreak where migratory birds congregate. A finding of infected birds in a region could trigger targeted mosquito spraying to reduce risks of transmission to humans, but debates rage among public health officials about whether funding for extensive screening of wild birds would be “cost-effective”. For those who think the undisputed triumph of 20th century medicine was the control of microbial illness, if you haven’t been chastened over the last decade by AIDS, keep an eye on the ongoing outbreaks of often mysterious emerging infectious diseases.