I happened to be watching a New York Knicks game on television the other night when the revolving billboard beneath the scorer's table unfurled an advertisement for Propecia, the Merck drug that prevents hair loss. In one of those Proustian leaps of association that often come to me while I'm in couch-potato mode, I found myself thinking about April showers, and mosquitoes, and medicine. The connection may seem circuitous, but hang on-we'll get there.

April showers will bring May mosquitoes in the New York City area, and with them renewed concerns about West Nile fever, the exotic mosquito-borne virus that caused an outbreak of encephalitis in the city last year. The question perplexing many public health officials is this: Will the virus survive the winter in infected mosquitoes, like other mosquito-borne viruses (or arboviruses) in this country? And will it reappear in the city this spring?