Emergence of Epidemic Zika Virus Transmission and Congenital Zika Syndrome: Are Recently Evolved Traits to Blame?

Abstract

The mechanisms responsible for the dramatic emergence of Zika virus (ZIKV), accompanied by congenital Zika syndrome and Guillain-Barré syndrome (GBS), remain unclear. However, two hypotheses are prominent: (i) evolution for enhanced urban transmission via adaptation to mosquito vectors, or for enhanced human infection to increase amplification, or (ii) the stochastic introduction of ZIKV into large, naive human populations in regions with abundant Aedes aegypti populations, leading to enough rare, severe infection outcomes for their first recognition. Advances in animal models for human infection combined with improvements in serodiagnostics, better surveillance, and reverse genetic approaches should provide more conclusive evidence of whether mosquito transmission or human pathogenesis changed coincidentally with emergence in the South Pacific and the Americas. Ultimately, understanding the mechanisms of epidemic ZIKV emergence, and its associated syndromes, is critical to predict future risks as well as to target surveillance and control measures in key locations.

FIG 1

Map of ZIKV evolution in sub-Saharan Africa, spread to Asia, and introductions into Yap Island, the South Pacific, and the Americas inferred from phylogenetic data. Adapted from reference with permission.