The Zika virus that has doctors worried about birth defects is likely to spread to most countries in the Americas, the World Health Organization said Monday. But that doesn't necessarily mean all or even very much of the United States, NBC News reported.
Zika's already taken hold in 21 countries and territories of the Americas and the mosquito-borne virus will almost certainly spread further, WHO's western hemisphere branch, the Pan American Health Organization, said in an update.
Zika's spread wouldn't be of much concern if it weren't for fears that it causes a severe birth defect called microcephaly — an abnormally small head and brain. Babies with microcephaly die at birth, they miscarry or they suffer lifelong disability.
Health experts still are not sure how or even whether Zika is causing microcephaly in Brazil — the only country that's reported an increase in cases so far.
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But, as with any mosquito-borne disease, once Zika is in place, it will spread quickly. That's because so many people have never been infected before and because mosquitoes are so common.