The first case of brain damage linked to the Zika virus within the United States was reported on Friday in Hawaii.
The Hawaii State Department of Health said that a baby born in an Oahu hospital with microcephaly — an unusually small head and brain — had been infected with the Zika virus, which is believed to have caused the same damage in thousands of babies in Brazil in recent months. The presence of the virus was confirmed by the Centers for Disease Control and Prevention.
The child’s mother had lived in Brazil in May last year and probably was infected by a mosquito then, early in her pregnancy, the health department said. The virus presumably reached the embryo and damaged its developing brain.
“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. “This case further emphasizes the importance of the C.D.C. travel recommendations released today.”
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As of Saturday, those included 17 Latin American and Caribbean countries and territories: Brazil, Colombia, Ecuador, El Salvador, French Guiana, Guatemala, Guyana, Haiti, Honduras, Martinique, Mexico, Panama, Paraguay, Saint Martin, Suriname, Venezuela and the Commonwealth of Puerto Rico. The list of countries with transmission has been steadily growing; on Saturday, Barbados reported its first cases.
Women considering becoming pregnant were advised to consult doctors before going to Zika-infested areas, and all travelers headed to such areas were urged to take vigorous measures to avoid mosquito bites.
There have been no confirmed cases of Zika virus transmission within Hawaii, Dr. Park said. Six Hawaii residents are known to have had the virus since 2014, but all picked it up through travel elsewhere. Nevertheless, Hawaii is undergoing an outbreak of dengue fever, and the same mosquitoes that transmit it also can transmit Zika.
A C.D.C. epidemiologist recently predicted that Zika would follow the same pattern that dengue has, with local transmission during hot weather in tropical parts of the country, including Florida, the Gulf Coast and Hawaii.
In Washington, administration officials said the decision to issue a travel alert developed quickly at the end of the week and triggered a flurry of diplomatic contacts with the countries named in the alert, given the potential economic and tourism impact that the decision could have. Officials said that notification effort delayed the C.D.C. announcement for several hours on Friday.
Scientists do not yet know how the Zika virus damages fetal brains. It is related to the dengue, yellow fever and West Nile viruses, which normally do not cause such damage; it is not closely related to rubella or cytomegalovirus, which are known to cause microcephaly.
The virus was first discovered in monkeys in the Zika Forest in Uganda in 1947. It is widespread in Africa and Southeast Asia but had never been seen as a major threat because the disease it causes is usually mild. About 80 percent of people who get the virus show no symptoms; those who do usually get a fever, rash and red eyes, but they rarely require hospitalization.
In 2007, the Asian strain of the virus was detected moving across the South Pacific; it caused a large outbreak on Yap Island that year. By late 2014, it had reached Easter Island, off the coast of Chile.
The connection to microcephaly was not made until late last year in Brazil. The virus first appeared in the country in May, and epidemiologists estimate that more than 1.5 million Brazilians have been infected.
In October, doctors in Pernambuco State noticed a surge in cases of microcephaly. Normally, about 150 cases of the birth defect are reported in Brazil each year. Since October, more than 3,500 have been reported there.
It is also not known whether the virus alone causes microcephaly or if it happens only if the mother has a previous infection, such as with dengue virus.
Dengue is unusual in that a first infection is rarely life-threatening, but a subsequent infection with a different strain can trigger dengue hemorrhagic fever, which can be fatal.
Hawaii is conducting a “Fight the Bite” campaign intended to stop its dengue outbreak. Residents have been urged to get rid of all standing water on their properties, to apply mosquito repellents and to try to avoid being bitten.
The Zika and dengue viruses — like virtually all mosquito-borne diseases — do not occur in mosquito larvae. Adult female mosquitoes pick them up by biting one infected human, and then, some days later, after the virus has traveled from their gut to their salivary glands, they infect another human. Dr. Park said neither the mother nor the baby in Hawaii is still infectious.