SAN JUAN, Puerto Rico -- Puerto Rico is reporting its first case of Zika virus, an illness transmitted by mosquitoes that has recently been linked to a number of birth defects in Brazil.
Puerto Rico's Health Secretary Ana Rius said Thursday that the unidentified patient had not traveled recently and lives in the island's eastern region.
More worrying than the symptoms in adults, scientists in Brazil have linked Zika infections to a recent surge in cases of babies being born with abnormally small heads, a condition called microcephaly, which often results in mental retardation.
More than 2,700 babies in Brazil were born with microcephaly in 2015, up from fewer than 150 in 2014. Brazil's health officials say they're convinced the jump is connected to a sudden outbreak of the Zika virus, though international experts caution it's far too early to be sure and note the condition can have many other causes.
Since the first local case of Zika virus was detected in Brazil last May, health officials estimate between 440,000 and 1.3 million people there have caught it. The mosquito-borne illness was first identified in the Americas less than two years ago and has spread rapidly across South and Central America.
"We are looking at the beginning of an epidemic in a country that has in between 200,000 and 300,000 births per year, which shows how worried we are. It's a virus we don't know that much about," said Rodrigo Stabeli, vice president of the Rio de Janeiro-based Fiocruz research institute. "We are preparing for the unknown."
Brazilians are so concerned that some obstetricians, such as Helga Monaco at Sao Paulo's Samaritano Hospital, recommend women avoid becoming pregnant during the rainy season when mosquitoes are most prevalent.
"All the women I see at the hospital or in my office who are pregnant or wanting to get pregnant are very alarmed, almost panicky," she said.
The Zika virus was first detected in humans about 40 years ago in Uganda. It is spread by the same Aedes mosquito as dengue and chikunguya. Until a few months ago, investigators had no reported evidence it might be related to microcephaly.
Suspicion arose after officials recorded 17 cases of central nervous system malformations among fetuses and newborns after a Zika outbreak began last year in French Polynesia, according to the European Center for Disease Prevention and Control.
And in November, Brazilian researchers reported the Zika virus genome had been found in amniotic fluid samples from two women whose fetuses were been diagnosed with microcephaly by ultrasound exams. Brazil announced on Nov. 28 that researchers had found the Zika virus present in brain tissue of a newborn with microcephaly who died.
As more evidence arose from further Brazilian tests, PAHO and the World Health Organization recently urged officials in the Americas to watch for possible neurological problems or congenital malformations elsewhere related to cases of Zika.
While there's never before been a detected link between the virus and microcephaly, "there has never been an epidemic of Zika in the proportions that we are looking at now in Brazil," said Pedro Fernando Vasconcelos, a researcher at Evandro Chagas Institute who found the virus in the newborn child.
Some experts suggest that the apparent surge in cases may be due to a particular strain of the virus, or perhaps a more complex combination of factors.
"We don't know if it's only Zika or if it's a combination of Zika, dengue and chikungunya," Dr. Marco Collovati, the founder of OrangeLife, a Brazilian company that is working on a rapid test for the virus, told The New York Times. "Maybe a woman was infected by dengue a year before, and now is pregnant and gets Zika."
A recent message from the U.S. Centers for Disease Control and Prevention said "the association of Zika virus infection and microcephaly and is still under investigation" and added, "It will take time to determine the cause of the microcephaly for the cases being reported in Brazil." It noted there are numerous causes of microcephaly, including genetic abnormalities, infections or exposure to toxic substances during pregnancy.
"One shouldn't just jump to the conclusion that just because it's associated, it is causing it," said Sanjaya Senanayake, an associate professor of infectious diseases at the Australian National University who has studied the virus for decades.
"At the end of the day, it certainly could cause it," he said. "But they need to run more epidemiology studies looking at various groups of pregnant women."
Brazilian officials aren't waiting. Claudio Maierovitch, the director of Brazil's equivalent of the CDC, told a news conference on Tuesday "there is no doubt that the majority of the microcephaly cases (in Brazil) are related to the Zika virus." The Health Ministry announced it would send an army of 266,000 people to inspect every house, farm and business in the country and warn about the risks of Zika.
There are no known cases of infection by the Zika virus in the United States, though it has been seen in returning travelers.
In addition to Brazil and now Puerto Rico, other countries in the Americas reporting cases of Zika include Chile, Colombia, Panama, El Salvador, Guatemala, Mexico, Paraguay, Suriname and Venezuela. None except Brazil have found any indication of corresponding birth defects, according to the Pan American Health Organization.