Florida health officials have found evidence of local Zika virus transmission in Miami Beach, one of the world's most popular tourist destinations, opening a new front in the fight against the mosquito-borne virus, according to a source familiar with the investigation.A handful of Zika cases have been identified and health officials are deciding which area or areas to include in any updated travel guidance, the source said. An announcement is expected to be made as early as Friday.The virus, which has spread rapidly through the Americas since it was first detected in Brazil last year, can cause the rare birth defect microcephaly, marked by abnormally small heads and developmental problems.A spokeswoman for Florida's health department, Mara Gambineri, said the department believes active transmissions are still only occurring in a small area in the Wynwood area of Miami but acknowledged two new Zika cases outside that area."If investigations reveal additional areas of likely active transmission, the department will announce a defined area of concern," she said in a statement.Miami Beach Mayor Philip Levine told a press conference late on Thursday that state and federal health officials have yet to conclude the tourist hotspot is the latest area where Zika has been transmitted."We don't know the exact link, one could be a tourist, one could be someone who may have worked on Miami Beach," Levine told reporters. "If it was confirmed we'd be able to talk about that, but it's not."