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Three Colombian newborns could be the country’s first group of children with Zika virus-linked brain abnormalities -- a sign of what's to come as pregnant Colombian women infected with the virus begin to give birth.

The babies were born with either microcephaly, which is a birth defect characterized by an abnormally small head, or congenital brain abnormalities, according to a news site run by the international science journal Nature. All three children also tested positive for Zika virus, a mosquito-borne disease that usually produces mild symptoms in adults but is believed to adversely affect fetuses and cause neurological issues in some adults. Zika virus has been spreading through the Americas since 2015.

The Colombian Collaborative Network on Zika, the group of researchers that diagnosed the children, is also investigating several more possible cases of microcephaly with a suspected link to Zika, Nature reported.

Experts predict that by June, Colombia will see a large increase in babies born with microcephaly. As part of the effort to determine if Zika virus causes microcephaly, Colombian officials are watching 2,000 of the country's pregnant women to see how their pregnancies and births proceed.

The outcomes for the three babies detailed in Nature puts a major dent in a central argument made by conspiracy theorists and doctors who are skeptical about the causal link between Zika and microcephaly. These skeptics have pointed to Colombia -- a country that has tens of thousands of people infected with Zika virus but had no previously confirmed related cases of microcephaly -- as evidence that Zika may not be behind the uptick in severe brain defects in babies reported in Brazil, where authorities have confirmed microcephaly in 641 children and are still investigating 4,222 cases. One fact the conspiracy theorists had not accounted for is that microcephaly can't be detected in ultrasounds until very late in the pregnancy, which may be one reason why Colombia had not seen any cases until now.

While scientists can't yet definitively say that Zika virus causes microcephaly, research to date on the link between the disease and the birth defects is highly suggestive. Lab studies have located Zika virus in the brain tissues and amniotic fluid of microcephalic fetuses and newborns, while population studies find microcephalic children in areas of Brazil that have recorded the highest Zika virus cases.

New in vitro studies that observed how the original Zika virus strain interacts with different kinds of stem cells found that the virus is especially adept at infecting brain stem cells, reports the Atlantic. These stem cells then reproduced Zika virus at their own expense, which lead to more virus and less brain cells.

The case studies of the three newborns come a few weeks after Colombia reported a “probable” case of microcephaly in an aborted fetus. Because its remains were improperly discarded, health officials could not confirm the initial microcephaly diagnosis, nor could they test tissues for presence of the Zika virus. However, traces of the virus were found in the amniotic fluid.