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Something we talk about fairly often with influenza viruses is just how much genetic diversity there can be within a single subtype. While the legendary mutability of influenza viruses hovers on the extreme end of the scale, all viruses mutate over time.
The Zika virus is no exception, and we've previously learned that Zika had split into two distinct lineages in the past couple of decades; African and Asian.
Today we've a look at the most complete genetic comparison of Zika viruses collected in Latin America, and the authors present evidence on the continual evolution of the virus.
They confirm that the South American Zika virus has origins in the Asian lineage, and that it was probably introduced to the Americas in mid-2013.
Furthermore, they show that the Asian lineage has now split into two distinct sub-lineages, which they dub Oceanian and Latin American.
And then it gets very interesting, for the authors write:
Soon after being imported to Latin America, ZIKV became highly diversified between late 2013 and early 2014 (Figure 1B), which was supported by the co-existence of several minor clusters, although statistical support for some of these clusters was not very high (Figures 1A and 1B).
These results implied that the ZIKV responsible for the current outbreak in Latin America may have become phylogenetically diversified and increased in genetic diversity.
The Brazilian ZIKV genomes did not cluster together rather, they were interspersed among the trees clustering with genomes' sampled worldwide isolates, indicative of a high level of genetic diversity of ZIKV in Brazil, although whether this arose from multiple introductions to Brazil remains unknown, based on current data.11
In addition, in the Latin American lineage, ZIKV genomes collected from 2015 and 2016 did not group together and were distributed throughout the clusters with no evidence of substantial lineage replacement (Figures 1A and 1B). This suggests that no circulating ZIKV strain has gained significantly higher fitness over the others to become dominant.
The authors go on to say that the virus's diversity is likely even greater than the currently available data suggests. It's a fascinating paper, and you'll want to read it in its entirety.
Citation: Emerging Microbes & Infections (2016) 5, e68; doi:10.1038/emi.2016.68
Published online 6 July 2016
Weifeng Shi1, Zhenjie Zhang1, Cheng Ling2, Michael J Carr3,4, Yigang Tong5 and George F Gao6,7
I'll leave it to those more versed in virology than I to speculate over what all this could portend, but I do wonder if this genetic diversity might help explain some of the uneven impact we've seen reported from countries where the virus is circulating.