Scientists find clue to why Zika, but not its close relatives, causes birth defects

The most frightening aspect of Zika virus has been its ability to produce severe fetal birth defects during pregnancy, especially microcephaly--a small head. Now, scientists have uncovered the details behind the virus's unique ability to cross the placental barrier and expose the fetus to a range of birth defects that often go beyond microcephaly to include eye and joint injury, and even other types of brain damage.