Abstract
Host species-specific fitness landscapes largely determine the outcome of host switching during pathogen emergence. Using chikungunya virus (CHIKV) to study adaptation to a mosquito vector, we evaluated mutations associated with recently evolved sub-lineages. Multiple Aedes albopictus-adaptive fitness peaks became available after CHIKV acquired an initial adaptive (E1-A226V) substitution, permitting rapid lineage diversification observed in nature. All second-step mutations involved replacements by glutamine or glutamic acid of E2 glycoprotein amino acids in the acid-sensitive region, providing a framework to anticipate additional A. albopictus-adaptive mutations. The combination of second-step adaptive mutations into a single, ‘super-adaptive’ fitness peak also predicted the future emergence of CHIKV strains with even greater transmission efficiency in some current regions of endemic circulation, followed by their likely global spread.Supplementary informationThe online version of this article (doi:10.1038/ncomms5084) contains supplementary material, which is available to authorized users.
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