HAVANA -- Cuban state media on Thursday reported a surge of Zika cases on the island, though the overall number of cases was still far fewer than elsewhere in the Caribbean.

State media said there have been nearly 1,850 cases of the mosquito-borne illness for all of 2016 and the first months of 2017. A senior civil defence official said the provinces with the most cases include Havana, Guantanamo and Cienfuegos.

Zika causes relatively mild symptoms in most adults but can be passed from a pregnant woman to her fetus and cause birth defects. There is no vaccine and prevention efforts have focused on control of the mosquito species that spreads Zika.

A nationwide spraying campaign had seemed to be working, with only three locally spread cases reported last year before Cuba stopped publicly reporting cases. Health officials were silent for months as hundreds of cases were apparently detected, then announced them in mass Thursday.

Puerto Rico has reported about 40,000 cases.