Tiny battlefields

"Poliomyelitis, better known as polio, is a crippling virus that can lead to paralysis or even death. A childhood vaccination program had diminished the incidence of polio worldwide to the point that scientists thought they had beaten it. They were wrong. Polio appears to be on the rise again. Disturbingly, some of the newly infected can spread the disease while not exhibiting the usual symptoms. How the virus spreads, the effect of vaccinations,...