Tracing the path of Chikungunya virus--evolution and adaptation.

Chikungunya fever has caught fresh attention as it raves around the globe. Since the first report of a major outbreak in Kenya in 2004, the disease has travelled across the Indian Ocean to the Indian subcontinent and subsequently to south-east Asia, resulting in millions of cases. Incidentally, the pandemic is panning out in a post-genomic era equipped with advanced molecular and bioinformatics tools that have facilitated the tracing, tracking and dissection of the Chikungunya virus (CHIKV). The rapidly accumulated data and information have offered us a glimpse of the evolution and adaptation of the virus as the pandemic unfolds. This paper reviews the history of the disease and current knowledge of the evolution of CHIKV. The virus is known to have emerged from the sylvatic cycle in Africa, resulting in three genotypes - Western African, Eastern/Central African and Asian. Evidence from Asia suggests that the virus has the potential to return to the forest. Integrating genetic signatures with spatial and temporal data, we present a network that shows the possible geographical routes of the recent spread of CHIKV. Though evolutionary constrains are imposed on arboviruses by their obligations to fulfil the biological criteria of two different hosts (vertebrates and mosquitoes) during the transmission cycle, CHIKV has accumulated biologically important mutations that facilitated the recently changed epidemiology. It is evident that the virus has adapted to Ae. albopictus, without compromising its fitness in Ae. aegypti and the human host. Besides the E1-A226V and E2-I211T mutations that have led to the virus' adaptation to Ae. albopictus, we discuss the possible initial adaptation to urban Ae. aegypti and the role of environmental factors. CHIKV may continue to scorch regions with competent vectors, especially Ae. albopictus and a susceptible human population. A preemptive approach is necessary to combat this disease with very high epidemic potential.