Heartbreaking photos of babies with shrunken heads can make it easy to jump to the conclusion that the sweeping Zika outbreak is causing the rise in birth defects across Latin America.
But we still don't know for sure if Zika is the culprit behind what appears to be a dramatic increase in birth defects, most notably a condition known as microcephaly that can cause developmental delays, seizures, and problems with vision and hearing. Even if Zika is behind all this, we still don't know exactly how it might be happening.
Scientists are just beginning to publish the research that will help us figure it out.
In a new study published in Cell Stem Cell March 4, researchers infected different brain cells in petri dishes to see how the Zika virus would affect them.
They found that the virus preferentially infected human neural progenitor cells (hNPCs), a type of cell that develops into neurons and glias, two major components of the brain. The virus replicated in these cells and made them more likely to die and divide abnormally. In a developing fetus, these effects could lead to brain damage.
If mothers are infected with Zika, the authors propose this is the way the virus could cause microcephaly in their unborn children.
"By determining whether Zika virus infects cells in the brain and what happens to a cell that is infected, this paper begins to tackle questions surrounding how a virus that had previously been known to cause a mild illness could be linked to microcephaly," Amelia Pinto, an immunologist at Saint Louis University who wasn't involved in the research, said in a statement.
The researchers studied cells, though, so we still don't know if the same thing could be happening in humans.
And scientists aren't convinced this is the mechanism that would allow Zika to cause microcephaly. It is some of the strongest evidence yet, but it's not the only theory for what's going on.
"It is an interesting model but it does not provide an explanation if we look at the developmental stage," Dr. Gil Mor, the director of the Reproductive Sciences division at Yale University's School of Medicine, told Tech Insider. "My thoughts have been that the virus is not able to reach the brain at the early stage of development."
Mor proposed in a study that microcephaly instead arises from the virus infecting the placenta.
Whether this new study found the mechanism or not, it is a step in the right direction, offering some preliminary evidence that suggests how Zika could be linked to neurological problems in babies.
"What this paper does is what we all hope to achieve," Pinto said in the statement. "It allows us to ask more questions and perhaps with further study of these Zika infected hNPCs we will gain insight into this re-emerging pathogen."
Finding the answers to these questions becomes increasingly important as Zika takes hold of more and more countries across the Americas.
Now Colombia has reported its first cases of microcephaly linked to Zika, which started circulating there in September, Nature reports.
Hopefully scientists can figure out if and how Zika might be causing these birth defects, so they can then develop ways to stop it.
