Diffusion in Italy of a new Aedes albopictus adapted variant of IOL Chikungunya Virus. Diffusion in Italy of a new Aedes albopictus adapted variant of IOL Chikungunya Virus

Chikungunya virus (CHIKV) is an emerging arbovirus, belonging to the Togaviridae family, Alphavirus genus, transmitted by Aedes spp. mosquitoes. In the summer of 2017, Italy experienced a Chikungunya virus outbreak that spread in Lazio from Anzio to Rome and caused a secondary outbreak in the Calabrian village Guardavalle, with a final case number of 436. The causative strain was recognized as an Indian Ocean lineage (IOL) virus lacking the E1 A226V mutation, a hallmark for efficient transmission by the Asian tiger mosquito (Aedes albopictus) vector. To understand the underlying genetic and molecular features of the outbreak virus, whole genome sequencing of isolates was performed. Viruses from mosquitoes and clinical samples were isolated in cell culture and used for NGS. We identified amino acid sequence mutations and constructed Maximum likelihood phylogenies based on the complete coding sequence of the viruses.Eight Chikungunya virus genomes were successfully assembled and used for sequence analysis. Amino acid sequence analyses revealed a unique substitution pattern in the Italian-2017 viruses (including mutations in nsP4, E1 and E2) that was partly shared with the Pakistani-2016 outbreak viruses. Evolutionary analyses indicate that these two recent outbreaks form a cluster of emerging viruses of the Indian origin IOL. This cluster also encompasses geographically widely distributed travel-associated isolates. While occasional importation of Chikungunya virus can be expected as result of growing global transport systems and the geographic dispersal of competent arthropod vectors, the Italian 2017 outbreak demonstrated that sustained Chikungunya virus transmission and secondary outbreaks are possible also in Southern Europe, calling for strengthened preparedness measures. The E1 226V mutation was not required for CHIKV dispersal in the environment dominated by Aedes albopictus. Emerging Indian-origin IOL viruses possess a demonstrated dispersion and transmission potential and consequently a significant public health impact.