More than 30 U.S. troops have been infected with Zika, according to a Pentagon spokesman.

Maj. Ben Sakrisson said on Tuesday that 33 service members have been infected with the virus as of last week. One of them is reportedly pregnant.

He could not say where the infected service members are located.

The disease, which is primarily spread by mosquitoes but also sexually, causes a mild infection in most people. However, it can cause a birth defect called microcephaly, in which babies are born with unusually small heads and underdeveloped brains. It is rapidly spreading throughout South and Central America, with thousands of cases. It also is linked to a neurological disorder called Guillain-Barre Syndrome, which can lead to temporary paralysis.

Florida health officials have discovered 15 cases of mosquito-borne Zika in a neighborhood north of downtown Miami. More than 1,600 Americans have been infected, but almost all of them are people who traveled to one of the 50 countries where the virus is spreading.