A pregnant New York City woman was diagnosed with the Zika virus after visiting a country plagued by the mosquito-borne illness — the third confirmed case in the Big Apple, city health officials revealed Thursday.

None of the three adults has shown severe symptoms — but the pregnant woman could be at risk of her baby being born with microcephaly, a birth defect that results in a smaller than normal brain and head that health officials think may be linked to the virus.

New York City Health Commissioner Dr. Mary Bassett didn’t specify where and when any of the infected had traveled but said New Yorkers must now be extra cautious when planning a trip to areas now struggling to contain the virus — Latin America and the Caribbean.

“We can expect more cases because Zika is a widespread infection in many places that people commonly travel,” she said at an afternoon press conference in City Hall. “This might be a good winter to think about a vacation in the Catskills.”

Bassett urged those who do travel to the affected regions to avoid mosquitoes by using repellent containing DEET and wearing protective clothing.

“In particular, we want to advise that pregnant women — [and] women who are considering becoming pregnant — consider delaying travel to affected countries until we understand more about this virus infection,” Bassett said.

The theory that Zika causes microcephaly was first aired in October when doctors in Brazil noticed more babies born with the devastating condition during an outbreak of the virus in that country.

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