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Fernando Vergara, Associated Press
Health worker Javier Lozano empties stagnant water from a tire during a campaign to destroy potential hatcheries of Aedes aegypti mosquitoes that transmits the Zika virus in Villavicencio, Colombia, Thursday, Feb. 4, 2016. With more than 20,000 cases confirmed in Colombia and fearing that the virus could affect more than half a million people, the government launched a nationwide prevention campaign.

BOGOTA, Colombia — Colombia's President Juan Manuel Santos says there's no evidence that Zika has caused any cases of the birth defect known as microcephaly in his country, though it has diagnosed 3,177 pregnant women with the virus.

Santos made the announcement Saturday while announcing that a U.S. medical-scientific team will arrive to help investigate the mosquito-borne virus.

Brazilian officials say they suspect Zika is behind a seemingly unusual number of microcephaly cases, in which children are born with unusually small heads. The link is not confirmed, but it's help prompt the World Health Organization to declare an emergency over the virus.

Santos says Zika apparently has affected more than 25,600 Colombians overall.

Colombian officials said Friday that three people had died of the paralyzing Guillain-Barre syndrome they attributed to cases of Zika.