This is a close-up picture of a Zika virus. Scientists took it using a method called cryo-electron microsopy. This involves shock-freezing the virus, preserving its molecular structures. Scientists can then analyze the shell of the virus down to the molecular level.

The result: Zika looks very similar to the Dengue virus.

There are, however, small but relevant differences, particularly when it comes to a protein located on the surface of the virus and that's rich in sugars (a glycoprotein)

The tiny difference in the structure of this protein could be the key as to why the Zika virus is able to penetrate into the fetuses of pregnant women and cause microcephaly in newborn babies. Microcephaly is a severe birth disease involving a deformed and smaller-than-average skull - and also brain damage.

Devika Sirohi and Richard Kuhn, virologists from Purdue University in West Lafayette, Indiana, published their study on the Zika's structure in the journal "Science" on March 31st 2016.

Passing the blood-brain barrier and the placenta

Most viruses are not able to infect the nerve system or the developing fetus because of the blood-brain barrier - a natural protection system. The placenta also has a similar protective function for the fetus. But the Zika virus seems to be able to penetrate those barriers.

What is not known yet is how the actual infection takes place.

But it is already known that that some flaviviruses - which include the Japanese encephalitis virus, the tick-borne encephalitis as well as the Zika virus - are indeed able to penetrate into the brain.

Hope for better diagnostics and vaccinations

Thus far, Zika infections have occurred in more than 30 countries.

Brazil and French Polynesia have been severely hit, where there a large number of children have been born with microcephaly.

Co-author Kuhn said that the new discovery of the virus' structure could help in developing new forms of diagnostics and push forward the development of vaccines.

The flavivirus expert, together with his colleagues, also discovered the molecular structures of the Dengue and West Nile viruses in 2002 and 2003.

fs/cd (dpa/)