WELLINGTON (Reuters) - New Zealand authorities are investigating whether the Zika virus was transmitted through sex from a man to his partner, the country's health ministry said on Thursday.

The New Zealand man had tested positive for Zika after he visited a country, which was not identified to protect the man's privacy, Ministry of Health spokesman Don Mackie said in a statement.

The man's female partner, who had not recently traveled to the Zika-affected country, tested positive for Zika after he returned. Both had since recovered and experienced only mild symptoms.

Zika has been linked to thousands of suspected cases of microcephaly, a rare birth defect, in Brazil.

The Health Ministry said that authorities were investigating whether the virus had been transmitted to the woman through unprotected sex or whether a mosquito could have entered New Zealand in the man's luggage and bitten the woman.

New Zealand has so far this year reported 71 confirmed cases of people infected by Zika, most of whom had been infected in Tonga or Samoa, according to Ministry of Health data.

U.S. health officials said last week they were investigating 14 reports of the Zika virus that may have been transmitted through sex, including to several pregnant women.

Much remains unknown about Zika, including whether the virus actually causes microcephaly in babies, a condition defined by unusually small heads that can result in developmental problems.

Brazil said it has confirmed more than 580 cases of microcephaly, and considers most of them to be related to Zika infections in the mothers. Brazil is investigating an additional 4,100 suspected cases of microcephaly

(Reporting by Charlotte Greenfield; Editing by Richard Pullin)