Zika virus, which has been linked to thousands of birth defects in Latin America, has spread rapidly and made its way to North America. Here are five things you need to know about the virus. VPC

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A new study from French Polynesia shows that the territory's rate of birth defects rose after a Zika virus outbreak there in 2013 and 2014, strengthening the link between the virus and medical problems in infants.

Doctors in French Polynesia didn't notice the small increase in birth defects during the island chain's Zika outbreak. But researchers in the French territory reviewed pregnant women's medical records after Brazil announced last fall that it had experienced a dramatic increase in cases of microcephaly, in which babies are born with abnormally small heads.

Researchers found that eight fetuses in French Polynesia were diagnosed with microcephaly following the Zika outbreak, according to the study, published online Tuesday in The Lancet. Five of the pregnancies ended in abortion. Researchers did not say whether any of the pregnancies ended in miscarriage or stillbirth.

Two-thirds of French Polynesia's population was infected during the 2013-2014 outbreak, according to the study, led by researchers in Tahiti, the largest island in French Polynesia, as well as Paris and Johns Hopkins University in Baltimore.

Judging by the rate of microcephaly seen in the study, nearly 1% of fetuses whose mothers were infected with Zika virus during the first trimester could be expected to be diagnosed with the condition, researchers concluded. That rate is almost 50 times higher than the usual rate of microcephaly for French Polynesia.

Yet this rate is lower than expected, according to an accompanying editorial by Laura Rodrigues of the London School of Hygiene & Tropical Medicine.

In the Brazilian state of Pernambuco, the hardest-hit area of that country, 2% of newborns born to all mothers  — not just those with Zika virus  — have suspected microcephaly, Rodrigues wrote.

Brazilian health officials are currently investigation more than 4,000 suspected cases of microcephaly.

A study published earlier this month in The New England Journal of Medicine also found high rates of abnormalities in mothers with Zika.

In that study, ultrasounds detected major abnormalities in 29% of fetuses of Brazilian mothers infected with Zika. Eight of the 88 women with Zika infections in the study have given birth; one of their babies had microcephaly. Researchers plan to follow the rest of the women through delivery and beyond, to evaluate the risk of birth defects.

The rate of Zika-related birth defects in French Polynesia is also much lower than the rate of illness seen among children infected with other viruses known to cause medical problems, according to the Lancet study authors.

Research shows that 13% of babies infected prenatally with cytomegalovirus, a type of herpes virus, are born with birth defects. The percentage of babies with birth defects caused by prenatal infection with rubella, or German measles, ranges from 38% to 100%, according to background information in the Lancet study.

It's possible that authors of the Lancet study, who relied on medical records, missed some Zika-related birth defects, said Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, who was not involved in the new study.

Study authors could have missed some women who were infected with Zika but never developed symptoms, Fauci said.

About 80% of people infected with Zika never become ill. The rest usually develop mild symptoms, such as a rash, fever, joint pain and pink eye, according to theCenters for Disease Control and Prevention. Deaths from Zika are rare.

Doctors in Brazil are performing research that could help to answer questions about Zika's relationship to microcephaly, such as whether the virus causes the condition.

Researchers in Brazil are following two groups of pregnant women —  those who are infected with Zika and those who are not — and will assess whether children born to Zika-positive mother have a higher rate of birth defects.

http://www.usatoday.com/story/news/2016/03/15/zika-linked-microcephaly-2013-2014-outbreak-french-polynesia/81783422/