Introduction and Dispersal of Sindbis Virus from Central Africa to Europe.

Bird-hosted viruses have the potential to be transported over large areas of the world and to be transmitted in distant geographical regions. Sindbis virus (SINV) is a mosquito-borne alphavirus that is locally amplified in a bird-mosquito enzootic cycle and distributed all over the Old World and Australia/Oceania. Sindbis virus genotype I (SINV-I) is the cause of disease outbreaks in humans in South Africa as well as in northern Europe. To trace the evolutionary history and potential strain-disease association of SINV-I, we sequenced 36 complete genomes isolated from field material in Europe, as well as in Africa and the Middle East, collected over 58 years. These were analyzed together with 30 additional published whole SINV-I genomes using Bayesian analysis. Our results suggested that SINV-I was introduced only once to northern Europe from central Africa, in the 1920s. After its first introduction to Sweden, it spread east and southward on two separate occasions in the 1960s and 1970s. Another introduction from central Africa to southern/central Europe seems to have occurred, and where these two introductions meet, one recombination event was detected in central Europe. In addition, another recombinant strain was found in central Africa, where the most divergent SINV-I strains also originated.IMPORTANCE This study shows that only a single introduction of SINV into a new geographical area is required for spread and establishment, provided that the requisite vector(s) and reservoir(s) of epizootological and epidemiological importance are present. Furthermore, we present the first report of recombination between two strains of SINV in nature. Our study increases the knowledge on new introductions and dispersal of arboviruses in general and of SINV in particular.

Phylogeographic structure and evolutionary history of Sindbis virus.

Sindbis (SIN) virus, Alphavirus, is a mosquito-borne and bird-associated virus with large geographic distribution in the Old World. We investigated the genetic diversity of 59 SIN strains after limited sequencing of their E2 glycoprotein genes. The SIN strains showed maximal diversity of 22.2% at the amino acid (aa) level, and formed five tentative genotypes. The SIN-I genotype included strains from Europe and Africa. Strains from Australia and East Asia formed SIN-II and SIN-III with about 12% and 15% aa divergence from SIN-I. The only isolate from New Zealand was distinct, and constitutes the SIN-V genotype. Isolates from Azerbaijan and China formed genotype SIN-IV with 15.6%-19.1% aa divergence from SIN-I to III and SIN-V. Phylogenetic analyses indicated that Aura virus was present before the recombinant alphavirus lineage arose. This is consistent with a South American origin of the SIN complex, and argue for a spread in North America before reaching Asia and Australia, followed by westward radiation into Africa and Europe. High levels of sequence identities were observed for geographic regions belonging to the same north-south axis, whereas the east-west genetic exchange appears to be limited. The observed phylogeographic structure was confirmed by distinct aa patterns within two-thirds of the structural protein-coding region of SIN virus strains from Saudi Arabia, Asia, and Australia. The present geography of the five SIN genotypes and subclusters within SIN-I correlate with major bird migration patterns.