In a new study, scientists from the Florida campus of The Scripps Research Institute (TSRI) have identified a specific trait in the Zika virus that allows it to cross the placental barrier and infect a fetus.

The Zika virus has been associated with multiple neurological disorders in children exposed in utero, including microcephaly, a condition that causes babies to be born with abnormally small heads and cognitive issues. Zika in pregnant mothers has also been linked to eye and joint problems and brain damage in unborn children.

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According to a press release from TSRI, Zika is in the flavivirus family, which also includes dengue fever and West Nile. These viruses don't cause the same problems in unborn children, so how is Zika different? 

Researchers examined umbilical endothelial cells donated from four people and found that they were much more susceptible to Zika infection than from other similar viruses. The team discovered that the virus learned to exploit a type of “secret passage,” which is a cell surface molecule known as AXL.

“Zika uses AXL to efficiently slip past one of the major barrier cell types in the placenta: fetal endothelial cells, which are the gateway to access fetal circulation,” said lead researcher Hyeryun Choe, according to the release.

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The study supports the idea that Zika — unlike West Nile or dengue — can efficiently access and infect the fetal bloodstream. But scientists are still trying to understand exactly why Zika is more infectious in cells than other flaviviruses.

“We don’t yet understand why Zika virus uses AXL and the others don’t,” Choe added. “The common belief is that all flaviviruses have similar structures, but our findings suggest that Zika virus may have a different average population structure than others. This has significant scientific and clinical implications.”

Source: Richard AS, Shim BS, Kwon YC, Zhang R, Otsuka Y, Schmitt K, Berri F, et al. AXL-dependent infection of human fetal endothelial cells distinguishes Zika virus from other pathogenic flaviviruses. Proceedings of the National Academy of Sciences. 2017.

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