The first set of experiments which demonstrate how the Zika Virus manages to create microcephaly in infants have been published. Previously the link between the two was purely speculative and circumstantial, now it is beginning to be proven.

The Zika Virus originated in Africa and until recently cases in South America were sparse and mostly inconsequential. Doctors in Northern Brazil began to notice cases of the virus in 2014, it quickly began to spread across Brazil and into neighbouring countries, aided by the abundance of its host mosquito. With the virus’s spread the rates of microcephaly, a disorder which causes the brains of infants to not develop entirely, rose sharply.

Two teams of researchers working independently out of separate universities in the United States have finally managed to provide some evidence, beyond the statistical correlation, that the Virus causes microcephaly. The teams took adult cells and reprogrammed them into stem cells which they then grew into immature brain cells, like those found in an fetus.

The researchers then exposed the neural stem cells to the virus, the result was that 85% of the exposed cells becoming infected by the virus within 3 days. The infection did not kill the cells immediately but caused them to grow more slowly and interrupted natural cell division. The researchers replicated the process with fetal kidney tissue, embryonic stem cells, and unspecified reprogrammed stem cells and found that only 10% of the cells were infected after 3 days.

Scientists believe Zika causes microcephaly by depleting the amount of neural stem cells during development. However, scientists still aren’t sure how the virus manages to cross the placenta, a feat which viruses generally aren’t able to do.