Polio is resurfacing worldwide.
Polio, short for poliomyelitis, is a highly contagious virus spread in feces. It has no cure. The disease primarily strikes children.
Unlike influenza or other winter viruses, polio thrives in hot weather. Cases start rising in the summer and often explode when the monsoon rains break.
The World Health Organization declared a global health emergency on Monday for only the second time.
Pakistan, Syria and Cameroon have recently allowed the Polio virus to spread — to Afghanistan, Iraq and Equatorial Guinea, respectively.
The WHO declaration imposes travel restrictions on the three countries.
Health officials recommend immunization for people traveling to or from 10 countries affected by polio.