Among the many immigrants who arrived in New York City in the summer of 1999, none made a name for itself more quickly than West Nile virus. Traced to a virus spread by mosquitoes, the disease had never been seen in this country, or even in the western hemisphere. It first struck birds, then people, killing seven and sickening dozens more. The city hoped to control it by killing the mosquitoes with malathion, a pesticide chemically related to nerve gas. Though many protested, Mayor Rudolph Giuliani insisted the spraying was perfectly safe.
