By Karen Pallarito HealthDay Reporter THURSDAY, Jan. 21, 2016 -- As cases of the mosquito-borne Zika virus are spreading across central and South America and the Caribbean, experts say it's only a matter of time before the disease, which has been linked to an alarming increase in birth defects in Brazil, is transmitted within the United States. "It's not if, it's when," said Mustapha Debboun, director of the mosquito control division at Harris County Public Health and Environmental Services in Houston.