Two additional cases of Zika virus infections have been identified in Suffolk County residents who had traveled to regions of the world where the mosquito-borne disease is flourishing, state health officials confirmed Tuesday.

All told, three cases have been counted among returning travelers who reside in Suffolk, according to a state tally of infections confirmed by experts at Wadsworth Center, the state laboratory in Albany. A total of 12 cases statewide have been confirmed to date, including one case in Nassau County, according to state health officials. All involved people who had returned home to New York after visiting countries where the infection is endemic.

“The mosquito that carries the Zika virus is not known to exist in New York, so the chance is very small that it can be transmitted here,” said Dr. James Tamarken, Suffolk’s health commissioner.

At Northwell Health in Manhasset, Dr. Bruce Hirsch, a specialist in infectious diseases, said his colleagues were evaluating a patient who may be infected with the pathogen. He provided no details about the case or whether the patient is male or female.

“What’s so striking about Zika virus is that the primary infection is so mild,” Hirsch said Tuesday, referring to the conjunctivitis — reddened eyes — flulike symptoms and general malaise reported by some patients with the infection.

Still others who have laboratory-confirmed infections have experienced no symptoms at all. And therein lies just one of many conundrums that has yet to be fully explained, Hirsch said. He predicts the virus is one of many emerging infections that will sweep across broad swaths of the planet in the not-too-distant future.

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Travel-associated cases of Zika virus have been cropping up around the country, federal health officials say, noting the popularity of Caribbean, Central and South American destinations for U.S. tourists.

The virus generally is transmitted by the bite of the Ades aegypti mosquito, although Texas public health officials and the Centers for Disease Control and Prevention last week confirmed an instance of sexual transmission. And though the infection has been associated with relatively mild symptoms, cases have been associated with microcephaly, a congenital birth defect marked by small head size, poor brain development and mental retardation. Doctors in Brazil and elsewhere in Latin America have yet to confirm the link, but the evidence is compellingly strong, global health officials said.

“We have to be aware of the potential for sexual transmission, especially male to female,” Tomarken said.

Men who have been to endemic regions and bitten by mosquitoes should either abstain from sex or use condoms for at least 21 days upon return, Tamarken said, emphasizing that curtailing travel to Zika virus hot zones can help limit the number of infections.

Hirsch defined the Zika virus as a cousin to West Nile, dengue, chikungunya and yellow fever viruses. All belong to the broad pathogenic family known as flaviviruses, and all are transmitted by mosquitoes. The Zika virus is named after the Zika Forest in Uganda where it was first identified in 1947, he said.

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West Nile emerged in Queens in 1999 and now is endemic across the country. Dengue has been documented in Texas and Florida. Chikungunya is being seen in an increasing number of travel cases, including among people in recent years who have returned home to Nassau and Suffolk counties from the Caribbean and Central America.

“This cascade of otherwise unfamiliar infectious diseases is giving us information that our world is changing,” Hirsch said. “Insect vectors that are close to us,” he said of mosquitoes and other carriers capable of spreading infectious diseases, “are becoming wildly successful.”