Will it come back? That question has been haunting public health officials in New York City and state since a surprise outbreak of the West Nile virus sickened more than 60 people late last summer and killed seven. No more cases of this rare illness were detected after temperatures started dropping in September, rendering the climate inhospitable to the mosquito that transmits the disease, most likely a subspecies of Culex pipiens. But nobody knew whether the virus would be able to survive the winter, either in mosquitoes or their eggs, or in birds, the virus's animal reservoir.
Now evidence suggests that the New York region may indeed be at risk again this summer. Over the past few months, the Centers for Disease Control and Prevention (CDC) and city and state researchers have been monitoring mosquito populations in sewers, abandoned hangars, swimming pool utility rooms, and other likely winter shelters. Last week, they announced that a sensitive polymerase chain reaction test had picked up traces of viral genetic material in three Culex samples in Fort Totten, an historic site in the New York borough of Queens.
Although the find suggests that the insects still harbor the virus and may start spreading it anew when they go looking for bird and human blood, researchers cannot be sure, because they only detected RNA fragments; another test that looks for live viruses came up negative. One interpretation is that the number of viral particles was low enough to escape detection, CDC officials say. Another possibility is that the virus may have become inactivated in the mosquitoes or killed as the specimens were processed. Attempts to isolate the virus using a different technique are under way.
Despite the uncertainty, the results have experts worried--most notably some entomologists, who question the city's and state's ability to wage an effective war against mosquitoes this spring and summer. With viral epidemics such as AIDS taking a huge toll, insect-borne diseases have been "pretty far back on the burner" in New York, says John Edman, director of the Center for Vector-Borne Disease Research at the University of California, Davis. He points out that New York state is still in the process of hiring personnel for new surveillance and control programs, making it difficult to mount an aggressive larvae control campaign in early spring, as experts recommended during a workshop in January. "I'm really worried," adds Yale medical entomologist Durland Fish. "In all honesty, I don't think they'll be able to mount an effective response."
But state officials dismiss those worries. "We have been working very diligently," says a spokesperson for the state Department of Health in Albany. "We will be prepared."