US researchers confirm Zika causes birth defects

The mosquito-borne Zika virus causes birth defects, including a syndrome in which babies are born with unusually small heads, US health authorities attributing scientists confirmed on Wednesday after months of debate and uncertainty.


"Scientists at the Centers for Disease Control and Prevention have concluded, after careful review of existing evidence, that Zika virus is a cause of microcephaly and other severe fetal brain defects," said a statement from the federal agency.


The decision was based in part on a series of studies in Brazil, where thousands of babies were born last year with birth defects, coinciding with a spike in Zika virus infections among the general public.


"This study marks a turning point in the Zika outbreak," said CDC chief Tom Frieden.


"It is now clear that the virus causes microcephaly."


There was no "smoking gun," or single piece of evidence that offered conclusive proof, said the full report, published in New England Journal of Medicine.


Rather, the decision was made based on "increasing evidence from a number of recently published studies and a careful evaluation using established scientific criteria," said the CDC.


Further studies are being launched to "determine whether children who have microcephaly born to mothers infected by the Zika virus is the tip of the iceberg of what we could see in damaging effects on the brain and other developmental problems," Frieden added.


Zika virus was first identified in 1947 in Uganda, but the virus was poorly understood and symptoms have typically been mild, including rash, joint pain and fever. Most of those infected report no symptoms at all.

Zika was first identified in Brazil in early 2015, and a surge in infants born with microcephaly began nine months later, in September.


Brazil has confirmed 907 cases of microcephaly and 198 babies with the birth defect who have died since the Zika virus outbreak started, officials there said last month.


The Brazilian health ministry said it is still investigating 4,293 suspicious cases.


"The severe microcephaly and other brain anomalies that have been observed in many infants are consistent with an infection occurring in the first or early second trimester of pregnancy," said the report in the New England Journal of Medicine.


Until now, no mosquito-borne virus has been known to cause birth defects, and the last infectious pathogen known to cause an epidemic of birth defects was the rubella virus more than 50 years ago.


Experts reviewing the evidence of microcephaly in Brazil found a similar increase in the birth defects in French Polynesia, which was hit by an outbreak of Zika in 2013 and 2014, though the number of microcephaly cases was small, totaling just eight.


Microcephaly is a rare defect that occurs in six out of every 10,000 births in the United States.


The lack of clarity on whether or not Zika could be established firmly as a cause of birth defects may have contributed to poor public understanding of the virus and its risks, the report said.


A recent poll of Americans found that one in four were unaware of any association between Zika and birth defects, and one in five believed, wrongly, that there was a vaccine to prevent it.


Women who are pregnant or considering becoming pregnant are advised to avoid the more than 30 places in Latin America and the Caribbean where Zika is circulating, and to wear mosquito repellant if they live in those areas.


While is now known to Zika cause microcephaly and other severe fetal brain defects, the actual risk of such birth defects remains unknown.


Indeed, some women who were infected with Zika while pregnant gave birth to apparently healthy children.

The CDC said it would not change it recommendations for women who are or want to get pregnant. They should continue to avoid traveling to Zika infected areas. Their partners should either use condoms or abstain from sexual contact while the woman is pregnant.


"Establishing this causal relationship between Zika and fetal brain defects is an important step in driving additional prevention efforts, focusing research activities, and reinforcing the need for direct communication about the risks of Zika," said the CDC.


"While one important question about causality has been answered, many questions remain."

Zika virus: Study supports link to microcephaly

In what experts describe as another piece of evidence linking Zika with the risk of birth defects, researchers on Wednesday reported finding the virus in the amniotic fluid of two pregnant women whose foetuses were diagnosed with microcephaly.

 

In a study in the Lancet Infectious Diseases journal, the scientists said their finding suggests Zika virus can cross the placental barrier, but does not prove it causes microcephaly, a condition in which babies are born with abnormally small heads.

 

More research is needed to understand the link, they said.

 

"This study cannot determine whether the Zika virus identified in these two cases was the cause of microcephaly in the babies," said Ana de Filippis, the doctor who led the study at the Oswaldo Cruz Institute in Rio de Janeiro, Brazil.

 

"Until we understand the biological mechanism linking Zika virus to microcephaly, we cannot be certain that one causes the other."

 

Many scientists believe Zika, a mosquito-borne disease that is currently sweeping through the Americas, may be a risk factor for microcephaly in newborns, as well as for a serious neurological disorder in adults called Guillain-Barre syndrome.

 

The World Health Organization has declared the Zika epidemic spreading from Brazil a global public health emergency and called for urgent studies to establish with its association with rising number of cases of suspected birth defects can be proven.

 

De Filippis' study noted that the number of suspected cases of babies with microcephaly in Brazil in 2015 has increased twenty-fold compared with previous years. At the same time, Brazil is reporting high numbers of Zika virus infections.

Babies born with microcephaly are at risk of incomplete brain development.

 

The condition has previously been linked to a range of factors including genetic disorders, drug or chemical intoxication, maternal malnutrition and infections with viruses or bacteria that can cross the placental barrier such as herpes, HIV, or other mosquito-borne viruses such as chikungunya.

 

For this study, de Filippis' team investigated the cases of two women, aged 27 and 35, from Paraiba in northeastern Brazil.

The women had symptoms of Zika infection - including fever, muscle pain and a rash - during their first trimester of pregnancy. Ultrasounds taken at approximately 22 weeks of pregnancy confirmed the foetuses had microcephaly.

 

The researchers took and analysed samples of amniotic fluid at 28 weeks of pregnancy. While the women's blood and urine samples tested negative for Zika, their amniotic fluid tested positive for the virus genome and for Zika antibodies.

"Details of the Zika virus being identified directly in the amniotic fluid of a woman during her pregnancy suggest ... the virus could cross the placental barrier and potentially infect the foetus," de Filippis wrote.

Jimmy Whitworth, a Zika expert and professor of international public health at the London School of Hygiene & Tropical Medicine, said the findings "strengthen the body of evidence" pointing to Zika as a cause of microcephaly in Brazil.

 

But he noted that while studies of this sort can show associations, they can't show direct causation.