The researchers first compared a strain of the Zika virus from an outbreak in 2010 in Cambodia with three strains from the recent Latin American outbreak.
Next, the researchers created a Zika virus with several of the seven mutations that have appeared since 2013
and found that it caused greater mortality in newborn mice than the Cambodian strain.
But the virus with the S139N mutation — in which only one nucleotide differs from the Cambodian version — killed more mice and caused more brain damage.
The study, by scientists in China, found that strains of Zika with the S139N mutation caused substantially more death and microcephaly in mice than other strains.
About 17 percent of mice infected with the Cambodian strain died, compared to 100 percent of mice infected with the Latin American strains.
(There is a video explanation at the news site )
Infectious Disease - Zika mutation
Possibility of a single mutation made Zika more destructive
The South American variety seems to be related genetically to a Cambodian strain
Conjecture that it may have been brought into Brazil accidentally via Polynesian soccer players
(Video explanation at the news source)