New York disease turns out to be West Nile virus

THE OUTBREAK of mosquito-borne disease in New York has taken another sinister turn. The disease was not, as scientists had believed, St Louis encephalitis: instead, it is a variant of West Nile virus, a disease hitherto found only in Africa, the Middle East and parts of West Asia.

United States health officials fear that the disease may now become prevalent in the Americas. Researchers for the Centers for Disease Control and Prevention (CDC) found the virus in birds that had died in the city.

The city of New York and its outskirts were sprayed with malathion, a pesticide, in an effort to destroy the mosquitoes that spread the disease. "It's a big surprise to us to see this virus in this part of the world," said Duane Gubler, director of the CDC's Division of Vector-Borne Infectious Diseases. The spread of infected birds as they migrate south for the winter could rapidly take the disease to central and South America, where it could be far harder to control.

Both viruses are spread by mosquitoes. But the new virus may be spread directly from humans to mosquitoes and back again, while St Louis encephalitis spreads from birds to mosquitoes, and thence to people.