Evidence is mounting that the Zika virus causes a debilitating birth defect, but the World Health Organization is not prepared to confirm such a link.
Zika has spread to more than 50 countries and territories, but so far officials have said that only one country has experienced a spike of the birth defect microcephaly linked to Zika. That country is Brazil, which was the first to be affected by the outbreak that started last spring.
The World Health Organization said Friday that it will be “some months” before a link can be proven between Zika and microcephaly, which causes babies to be born with abnormally small heads and brain damage.
“Microcephaly is a pregnancy outcome, probably associated most with first trimester exposure [to Zika] if indeed that relationship is causal,” Bruce Aylward, executive director for Outbreaks and Health Emergencies at the WHO, said during a Friday press conference.
A recent small study is the latest to find evidence of a link between Zika and microcephaly.
The New England Journal of Medicine published a study Friday that followed 88 women from September 2015 to February 2016, about 72 of whom tested positive for Zika. The women got infected between five-38 weeks of pregnancy.
Researchers performed an ultrasound on 42 Zika-positive women and in all Zika-negative women. The ultrasounds were taken at different parts of the pregnancy, including between 20-30 weeks and after 30 weeks.
Fetal abnormalities were found in 12 of the 42 Zika-positive women and none of the other women. Eight of the 42 women have delivered their babies, and the ultrasound findings were confirmed, the study said.
Abnormalities included not just microcephaly, but other defects such as far too much fluid in the brain and fetuses that were very small.
The researchers behind the study said women with suspected or confirmed Zika infection need to be monitored very closely and have frequent ultrasounds.
“The establishment of a scientifically credible link between [Zika] and abnormal congenital findings is of utmost importance for the effective and successful management of this epidemic in Brazil and worldwide,” the study said.
The study was released on the same day as another finding that scientists discovered a potential link in how Zika affects pregnancies.
But so far the WHO said that Zika-linked cases of microcephaly were found only in Brazil and French Polynesia, which experienced an outbreak back in 2013-14. The spike in that country was found after the outbreak subsided.
Brazil, where the outbreak is ongoing, is investigating 4,222 cases of microcephaly and has confirmed 641, the World Health Organization said.
For now, health officials are taking a guilty-until-proven-innocent approach to the link, with U.S. agencies warning pregnant women and women of childbearing age to delay travel to any country where Zika is spreading.
Aylward said that an answer on a confirmed link between Zika and the neurological disorder Guillain-Barre Syndrome could happen quicker, mainly because it is not a pregnancy-related outcome.
A recent study looked at Guillain-Barre cases that were documented in 2013 and 2014 during a Zika outbreak. The study found that 100 percent of people who had the syndrome had Zika in their system.
Aylward said that part of the reason for the delay in confirmation is so that scientists can rule out other potential causes for a spike of birth defects or Guillain-Barre cases.
For instance, microcephaly can have genetic causes or be caused by exposure to alcohol or drug use in pregnancy, Aylward said.
Zika has been around since 1947, but this is the first time officials have found a link between the birth defect and the virus.
