Chinese researchers have identified the single genetic change that turned the once harmless Zika virus into a fearsome plague affecting pregnant women and their babies in Brazil and across the Americas.
The change resulted in thousands of cases of microcephaly as also other grievous brain abnormalities that sometimes caused death.
In a study published in the US journal Science, a team led by Cheng-Feng Qin of the Beijing Institute of Microbiology and Epidemiology reported that one single genetic change, which likely happened in 2013, gave the mosquito-borne virus the ability to cause severe foetal microcephaly.
"Our findings offer a reasonable explanation for the unexpected causal link of Zika to microcephaly, and will help understand how Zika evolved from an innocuous mosquito-borne virus into a congenital pathogen with global impact," Qin said, IANS reported.
The virus was first identified in 1947 in Uganda, and until its recent emergence in the Americas, was known to sporadically cause mild infections, Xinhua reported.
The virus then swept rapidly across South and Central America in 2015, and due to its link to congenital brain abnormalities, especially microcephaly during pregnancy, the World Health Organisation declared in early 2016 the current epidemics a public health emergency of international concern.
According to the research, a change of a single amino acid molecule - likely occurring sometime in 2013 - created a new strain of Zika highly dangerous to developing brain cells. The virus was shortly after, seen to cause a dramatic increase in cases of microcephaly, in which babies' heads are abnormally small, and a range of other birth defects.
''This answers the question everybody has been wanting to know. Why is it only in the last few years that Zika became so explosive, not just in its virulence but in severity of symptoms,'' said Pei-Yong Shi, a virus and genetics expert at University of Texas Medical Branch who is a co-author of the new study, The Washington Post reported.