'Clear' evidence Zika virus causes microcephaly: CDC

In this Jan. 30, 2016 photo, Elielson tries to calm down his baby brother Jose Wesley, in Bonito, Pernambuco state, Brazil. (AP / Felipe Dana)

In the face of "mounting evidence," the U.S. Centers for Disease Control and Prevention has concluded that it is "clear" that the Zika virus causes microcephaly – a birth defect resulting in abnormally small heads and incomplete brain development.

In a statement released on Wednesday, the agency said it had come to the conclusion after a review of existing evidence. A report on its findings has been published in the New England Journal of Medicine.

"This study marks a turning point in the Zika outbreak. It is now clear that the virus causes microcephaly," Tom Frieden, director of the CDC, said in the statement.

"We've now confirmed what mounting evidence has suggested, affirming our early guidance to pregnant women and their partners to take steps to avoid Zika infection and to health care professionals who are talking to patients every day. We are working to do everything possible to protect the American public," he added.

The CDC said it came to its conclusion following a careful evaluation of a "number of recently published studies."

Health authorities around the world have been ramping up precautions against the spread of the mosquito-borne virus after it was linked to a surge in birth defects in pregnant women in parts of Latin America.

The virus has been native to regions in Africa and Asia for years, but was found in Brazil last year. The South American nation has been hardest hit by microcephaly, with health authorities saying they've had more than 700 confirmed cases and roughly another 4,000 that are still being investigated.

A Brazilian investigation in November 2015 also found an average 20-fold increase in the incidence of microcephaly among newborns in the areas where the virus was known to be prevalent.

The Zika virus had been previously considered a mild illness, associated with symptoms such as a fever, rash, red eyes and joint pain for several days to a week.

The CDC's findings indicate that women who are infected with the Zika virus during pregnancy have an "increased risk" of delivering babies with microcephaly and other severe fetal brain defects.

But it cautions that not "all women" will give birth to babies with these conditions.

"As has been seen during the current Zika outbreak, some infected women have delivered babies that appear to be healthy," said the statement.

The U.S. health authority says it is also planning to launch further studies to determine whether microcephaly is just the "tip of the iceberg" in terms of damaging effects and developmental problems in the brains of children born to mothers with the Zika virus.

The CDC said it is not changing its current guidelines related to the Zika virus, which are as follows:

Late last month, the agency also said women diagnosed with the Zika virus should wait at least eight weeks before attempting to get pregnant. It also advised men to wait at least six months after the first appearance of symptoms before having unprotected sex.