Excerpts: (...) picture is beginning to emerge of how a virus carves a new ecological niche (...).

If alert veterinarians and practicing physicians had not sought to identify the cause of the deaths of crows and of human encephalitis in New York City in 1999, health officials would probably have included the human cases in the large "cause undetermined" category of encephalitis. If West Nile had not been recognized until this year, scientists might have missed the evolving pattern and even concluded that the virus had been here a long time.

• Health: West Nile and Its Lessons for Doctors, Lawrence K. Altman, NYTimes, 02/08/13