A vian flu appears to be spreading with increasing rapidity. In recent weeks, there have been confirmed reports of the disease in Europe and Africa, demonstrating that the H5N1 strain is hardier than thought and truly a global danger. While health officials call for continuing surveillance and vigilance, they also warn against overreacting to the threat. At the same time, those experts worry that other diseases may also emerge. Bird flu makes headlines, but other pathogens pose equal or greater dangers.

It is estimated that at least 200 million birds have died or been killed as a result of bird flu. Millions more are infected with the virus. Fifteen countries have reported outbreaks in the last month; more than 30 countries have reported cases since 2003. There have been more than 170 human infections in seven nations; more than 90 lives have been lost.

The sharp spike in the number of countries reporting infections is worrisome. Most recently, the disease has surfaced in India, Malaysia, Egypt, Bosnia, Croatia, Nigeria, Hungary, France and the Netherlands. Increasing awarness of the threat is one explanation, but the virus is plainly capable of traveling long distances -- which suggests it is growing stronger -- and adapting to a wide range of host environments. Especially worrisome is evidence that some "virus reservoirs," such as wild ducks, can host the disease without getting sick themselves. That makes the disease harder to track, isolate and eliminate.