Imagine a virus so serious the government recommends that women stop getting pregnant.
It exists, and it is now in Brazil, which is a big concern as the Olympics approaches. The Zika virus, native to parts of Africa and Asia, has been spreading locally among people who have not traveled abroad. There is no vaccine against the virus or antiviral treatment.
Zika is generally a mild illness, spread by a day-biting mosquito. However, there is a worrisome, but as of yet unproven, association of infected mothers in Brazil giving birth to babies with small heads and underdeveloped brains, Dr. Khan said. There has been a 20-fold increase in the number of babies born with this condition, known as microcephaly, since Zika first appeared in Brazil in May 2015.