Public Release: 

Zika arrived in Americas during mid-2013, following upsurge in air travelers

American Association for the Advancement of Science

By sequencing a small number of Zika virus genomes from Brazil, researchers have estimated that the virus had a single entry into the Americas, likely more than a year before the virus was reported in Brazil. This timing, they say, correlates with major events in the Brazilian cultural calendar associated with increased numbers of travelers to the country, particularly from areas where the Zika virus (ZIKV) circulates. Though the sample size used in this study is small (just seven ZIKV sequences), the work represents an important result given how little is known about this emerging virus to date. Brazil is in the midst of an unprecedented epidemic of Zika virus, which was first detected in the country in May 2015. Here, to better understand the evolution and molecular epidemiology of Zika in Brazil, Nuno Faria and colleagues sampled several ZIKV genomes linked to the recent Brazilian outbreak -one from a blood donor, one from a fatal adult case, and one from a newborn with congenital malformations and microcephaly, a rare disorder in which a baby's head is much smaller than expected (Faria et al. note that work remains ongoing to establish whether ZIKV is a causal factor in microcephaly). Using next-generation sequencing, the researchers generated seven Brazilian ZIKV genomes, finding little genetic variability among them. Following comparative analyses between these and existing ZIKV genomes, they conclude that there was a single introduction of ZIKV into the Americas, likely somewhere between May and December 2013 - more than 12 months prior to the virus's detection in Brazil. Airline data reveal that this timing coincides not only with an increase in air passengers to Brazil from ZIKV endemic areas, but also with reported ZIKV outbreaks in the Pacific Islands. Preliminary results from this study do not yet shed light on the link to microcephaly of babies, the authors note.

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