Cuba reported its first case of Zika on Wednesday, diagnosed in a 28-year-old Venezuelan doctor whose husband and brother-in-law previously contracted the virus in their home country.

The World Health Organization declared the Zika outbreak, suspected of causing thousands of birth defects in Brazil, an international health emergency on Feb. 1, although much about the virus remains unknown.

The patient arrived in Cuba on Feb. 21 to take a post-graduate course in medicine along with 37 others.

She reported a fever a day later and was diagnosed with Zika on Monday. She was recovering well in hospital, the Health Ministry said in a statement on Wednesday.

Her husband was diagnosed with Zika two months ago and her brother two weeks before she traveled, the statement said.

Zika is carried by mosquitoes, which transmit the virus to humans, though the U.S. Centers for Disease Control said on Feb. 23 it was investigating possible cases of sexual transmission.

The outbreak has spread to many parts of Latin America and the Caribbean and the WHO estimates Zika could eventually affect as many as four million people in the region.

The Zika virus - in pictures Show all 5 1 /5 The Zika virus - in pictures The Zika virus - in pictures A three-month-old, who has microcephaly, in Recife, Brazil. A rise in microcephaly cases is thought to have been caused by the spread of the Zika virus in affected countries Getty Images The Zika virus - in pictures A mother holds her baby who has microcephaly Getty Images The Zika virus - in pictures A five-month-old baby, who has microcephaly, in Recife, Brazil Getty Images The Zika virus - in pictures A pediatric infectologist examines a two-month-old baby, who has microcephaly, in Recife, Brazil Getty Images The Zika virus - in pictures A baby affected with microcephaly

The Cuban government, which has fumigated neighborhoods and homes for decades to contain dengue — also a mosquito-borne virus and a close cousin of Zika — put doctors on alert for the virus weeks ago and ramped up mosquito eradication efforts.

The WHO is investigating a “strongly suspected” relationship between Zika and microcephaly, a condition marked by abnormally small head size. There is no vaccine or treatment for the virus and some 80 percent of people infected show no symptoms.