Mouse studies link Zika virus infection to microcephaly

Three new studies published May 11 further bolster the idea that Zika virus infection in utero causes birth defects.

One study shows that mice engineered to be susceptible to Zika can pass the virus to offspring via the placenta. In these pregnant mice, which have severely crippled immune systems, Zika infection can kill fetuses and developing brain cells, too, researchers at Washington University in St. Louis report in Cell. But the researchers can’t say for certain whether the virus itself snuffs out cells, or whether damage to the placenta starves cells of oxygen.

Answers might come from two other mouse studies. Injecting Zika virus straight into the brains of fetal mice halts cell growth and kills cells, scientists in China report in Cell Stem Cell. Just five days after infection, embryonic mice already have brains smaller than normal.

Even stronger evidence comes from a strain of mice called SJL that were infected with the Brazilian Zika virus — no tinkering with the mice’s immune systems required. Infected SJL mice transmitted the virus from placenta to pups, and newborn animals showed signs of microcephaly, an international team of researchers reports in Nature. But mice of a genetically different strain, called C57BL/6, resisted Zika’s brain-damaging handiwork.

The results suggest that genetic differences could help explain why Zika strikes the babies of some pregnant women but not others, the authors say.