The current Zika virus (ZIKV) epidemic in the Americas and the potential link to an increase in the number of cases of birth defects in regions where the virus is circulating has caused worldwide concern. ZIKV belongs to the Flaviviridae family of positive-strand RNA viruses; however, its structure, tropism and pathogenesis were largely unknown. Now, Sirohi et al. havesolved the cryo-electron microscopy structure of mature ZIKV isolated from a patient that was infected during the French Polynesia epidemic in 2013–2014 at 3.8 Å resolution. They found that the structure was similar to those of the flaviviruses dengue virus (DENV) and West Nile virus (WNV); however, the authors noted structural differences in the region surrounding the Asn154 glycosylation site in the viral envelope glycoproteins, a region that might be important for attachment to host receptors and may govern cellular tropism and disease outcome.

In another study, Faria et al. used phylogenetic, epidemiological and travel data to investigate the evolution of ZIKV and its introduction to the Americas. Using next-generation sequencing they generated seven complete ZIKV coding sequences from samples that were collected during the outbreak in Brazil, including four self-limited cases, one blood donor, one fatal adult case, and one newborn with microcephaly and congenital malformations. A comparison of these genomes with other available Brazilian strains showed that the isolates differ at several nucleotide sites in the coding region. Furthermore, the authors found that all of the viruses that were sampled in the Americas share a common ancestor with the ZIKV strain that circulated in French Polynesia in 2013 and, using molecular clock analysis, they estimated that a single introduction of ZIKV into the Americas had occurred between May 2013 and December 2013, a time period that coincided with an increase in air travel from ZIKV endemic regions and with reported outbreaks in the Pacific Islands. Finally, they found that viral genomes from Brazil are phylogenetically interspersed with those from other countries in South America and the Caribbean.