Zika virus is a distant relative to yellow fever. It's native to Uganda and was mostly considered harmless. That is, until it came to Brazil, where it's being blamed for babies being born with unusually small brains. And now, paralysis.
On Tuesday, Texas county officials confirmed the first case of Zika virus transmitted person-to-person through sex. The mosquito-borne virus has spread quickly in the past two years through the Pacific Islands and South America.