The United States has its first case of an infant born with a serious birth defect possibly as a result of a Zika virus infection during its mother’s pregnancy.

Health officials in Hawaii have announced that a baby born recently on Oahu has microcephaly, a condition where the head is smaller than normal. Babies with microcephaly can also have underdeveloped brains, which may lead to lifelong developmental problems.

State officials said testing at the Centers for Disease Control and Prevention confirmed that the baby had previously been infected with Zika virus.

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The baby’s gender and name have not been released. Its mother was living in Brazil last May which — given that the baby was said to have been born recently — would have been early in her pregnancy. Brazil has been experiencing a huge Zika virus infection that began last May, and has seen a startling increase in infants born with microcephaly.

“We are saddened by the events that have affected this mother and her newborn,” Dr. Sarah Park, Hawaii’s state epidemiologist, said in a statement. Park said the case underscores the importance of the travel recommendations the CDC issued Friday for pregnant women and women who might become pregnant.

Late Friday, the agency urged pregnant women to avoid, if possible, travel to 14 countries and territories in the Americas which are currently experiencing Zika virus infections. The locations named are: Brazil, Colombia, El Salvador, French Guiana, Guatemala, Haiti, Honduras, Martinique, Mexico, Panama, Paraguay, Suriname, Venezuela, and the Commonwealth of Puerto Rico.

It’s impossible at this point to say how long the travel advice will remain in effect, Dr. Lyle Petersen, director of the CDC’s division of vector-borne diseases, said at a news conference announcing the guidance. The situation is too new and too little is known, he said.

It is a question, though, that will be asked with increasing frequency as the 2016 Summer Olympics in Rio de Janeiro approach. The Rio Games are slated to run from Aug. 5 to Aug. 21.

Zika virus, which can be transmitted by mosquitos, has exploded onto the world stage in recent weeks. Alex Hogan/STAT

While the link between Zika infection in pregnancy and babies born with microcephaly has not yet been proven, mounting evidence supports the theory that there is a connection.

Traces of Zika virus have been found in the amniotic fluid from two women in Brazil who were seen to be carrying fetuses with microcephaly during ultrasounds.

And this past week, the CDC confirmed it had found evidence of the virus in the brains of two Brazilian infants with the condition who died shortly after birth. CDC scientists also found traces of the virus in placenta samples from two Brazilian women who miscarried fetuses with microcephaly.

The CDC’s travel advice suggests that women who might become pregnant and are planning travel to Zika-affected areas should discuss the issue with their doctors. If a pregnant woman cannot postpone travel to an affected area, she should do the same, the CDC said. And in both cases, women should take stringent precautions to try to avoid being bitten by mosquitoes.

There have been 26 Zika infections diagnosed in the United States, dating back to 2007, CDC officials said Friday. But all were people who were infected during travel outside the country. However, in late December, it was reported that Puerto Rico had seen a case of locally acquired Zika infection. The infected person had not travelled.

The CDC has said the virus is likely to come to the United States. The mosquitoes that transmit it — from the Aedes family — are found in a number of states, especially in the south. Florida and southeast Texas have been identified as areas that are especially vulnerable.

“I think the bottom line is, yes, local transmission can occur, particularly in the areas of the southern United States where vector mosquitoes are present. But we don’t expect very large outbreaks,” Dr. Lyle Petersen, director of the CDC’s division of vector-borne diseases, told STAT this week.

Petersen said US experience to date with similar mosquito-borne diseases like dengue and chikungunya suggests that facets of the North American lifestyle — living in air-conditioned homes and dwellings with screens on windows and doors — should limit how much the virus would spread here.

The little-known virus transmits in a cycle involving mosquitoes and people. A mosquito becomes infected by taking a blood meal from an infected person, then passes the virus on when it bites additional people.

It can spread geographically when an infected person travels to a place where Aedes mosquitoes exist or when infected mosquitoes are relocated, for instance, in shipped goods.

Zika virus is related to the viruses that cause yellow fever and dengue fever, but triggers much milder illness. As a consequence, it has not been well studied; up until recently, it has not been a scientific priority.

But when Brazilian health officials started to realize they were seeing a surge in microcephaly cases, investigations began to point to Zika infection in pregnancy as a possible cause. A few other viral infections during pregnancy, including rubella and cytomegalovirus, are known to sometimes lead to infants born with microcephaly.

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