HUGO GREENHALGH PIONEERING AIDS researcher Joseph Sonnabend, one of the first doctors to warn of the emergence of a new virus in the late 1970s, has died at the age of 88 in a London hospital. Sonnabend first noticed the rise in the number of similar illnesses among his gay male patients at a private sexual health clinic he had founded in Greenwich Village in downtown New York. But his warning in 1979 went unheeded. "I wrote to the city health department, asking, 'Are people reporting this? Am I the only one seeing this? Is there something going in the…