A molecular map of Zika has revealed important structural differences on a key protein of the virus that may explain why the pathogen attacks nerve cells while other viruses in the same family do not, U.S. researchers said on Thursday.

A transmission electron micrograph (TEM) of Zika virus, which is a member of the family Flaviviridae is seen in this undated image from the Centers for Disease Control (CDC).

Variations in proteins on the outer shell, or "envelope," of the virus may explain how Zika enters human cells and suggests new ways to fight the virus with drugs or a vaccines, said Dr. Anthony Fauci, director of the U.S. National Institute of Allergy and Infectious Diseases, which funded the study published in the journal Science.

Zika is very similar to other members of the flavivirus family such as dengue, Yellow fever and West Nile, Fauci said, with one key difference.

"There was one very discreet stretch of the protein on the envelope that is really different than the other flaviviruses," Fauci said. "That is like a big red flag."

Fauci said the important structural difference from similar viruses may explain the link between the mosquito-borne Zika virus and two disorders, the birth defect microcephaly and the paralyzing autoimmune ailment Guillain-Barre Syndrome.

To better understand why Zika behaves so differently from related viruses, Richard Kuhn, Michael Rossmann and colleagues at Purdue University created the picture of a mature Zika virus particle with a technique that provides a very high resolution image of the pathogen.

The difference in Zika's structure compared to similar viruses was seen in a region of the envelope protein that flaviviruses may use to attach to some human cells.

This protein is also a key target of the immune system's response to the virus, making it potentially useful in vaccine development.

"They haven't proven it yet, but it is a very important first clue," Fauci said.

Zika is spreading rapidly in South and Central America and the Caribbean, and has been linked in Brazil to thousands of cases of microcephaly, a disorder marked by small head size and underdeveloped brains in babies. The World Health Organization in February declared the Zika outbreak a global health emergency.

Scientists believe Zika is neurotropic, meaning it specifically attacks nerve cells. It is the only mosquito-borne virus ever linked to a birth defect.

Zika has not been proven to cause microcephaly, but there is mounting evidence suggesting it does. Brazil, hardest hit by the virus, has confirmed more than 900 cases of microcephaly, and it considers most cases to be related to Zika infections in the mothers. Brazil is investigating nearly 4,300 additional suspected cases of microcephaly.

Source: Reuters