Three people in New York have tested positive for the mosquito-borne Zika virus, an emerging pathogen that has caused millions of infections in predominantly tropical regions of the world, state health department officials said Friday.

The three, who were not identified by name or place of residence, had traveled to endemic parts of the world where they were bitten by Zika-carrying mosquitoes. One is said to have fully recovered and the others are recovering without complications.

“There is virtually no risk of acquiring Zika virus in New York State at this time as the virus cannot be spread by casual contact with an infected person and mosquitoes are not active in cold winter months,” state Health Commissioner Howard Zucker said in a statement.

The pathogen is spread only by mosquitoes when they bite to obtain a blood meal, experts at the Centers for Disease Control and Prevention said during a recent news briefing.

Dr. Robert Glatter, an emergency physician at Lenox Hill Hospital in Manhattan, noted the lack of a vaccine and said the best protection is heeding recent travel warnings issued last week by the CDC.

The agency is advising women of childbearing age to avoid traveling to endemic countries because the virus has been linked to severe birth defects.

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“Effective education to help the public understand the potential risks for pregnant women and those planning to become pregnant . . . should be sufficient to help reduce the possibility for ongoing infections,” Glatter said, referring to travelers who might return to New York with the virus.

Zika viral infection can result in the birth of babies with severe microcephaly, or small head size and a poorly developed brain. The virus is carried by the Aedes aegypti mosquito, a species that has long been widespread throughout New York and is a known disease-spreading menace worldwide.

In addition to Zika, Aedes aegypti is a carrier of the chikungunya fever virus, another emerging pathogen, which has been diagnosed in New York, including several cases on Long Island in recent years. All have involved people who recently returned home from affected countries. The mosquito also can transmit West Nile, dengue and yellow fever viruses.

The insect is present throughout a broad swath of countries and tropical islands that have been seriously affected by Zika viral infections in recent months. These areas range from Mexico and parts of the Caribbean to several South American countries, including Brazil where health authorities have mounted an all-out assault.

In major Brazilian cities armies of genetically engineered male mosquitoes, developed by British scientists, have been set aloft with an aim of mating with normal female mosquitoes. The male insects are lab-equipped with genes to fatally cripple their progeny. Offspring are endowed with suicide genes that kick in before the mosquitoes are old enough to reproduce.

Brazil has been hit by an estimated 1.5 million Zika virus infections, according to the Pan American Health Organization.

Across the Atlantic, countries stretching from West Africa to the Congo — already home to a multitude of mosquito-carried illnesses — have been hit by Zika virus as well. Beyond Africa, regions throughout Southeast Asia have been stricken, including vast portions of the Indonesian archipelago.

Public health experts with the World Health Organization say there is circumstantial evidence that the virus is being transmitted in India and may be infiltrating deeper into Africa.

Brazilian health authorities are urging women of childbearing age to postpone pregnancies for at least two years as public health officials escalate their combat against mosquitoes.

Zucker, echoing experts in infectious diseases at the CDC, said it is important that Americans, especially women of childbearing age, plan their travel carefully.

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“Since this is a time of year when people travel to warmer climates and countries where Zika virus is found, we are urging residents, especially pregnant women, to check all health advisories,” Zucker said.