? Introduction of Bluetongue Virus into American continent: a coalescent approach

DANILO LEGISA; GOLEMBA MARCELO; MARIA JOSE DUS SANTOS

Simposio; 12th International double stranded RNA virus symposium; 2015

Bluetongue virus (BTV) is the causative agent of Bluetongue disease (BT). The presence and detection of BT is associated with significant economic losses. BTV is the prototype member of the Orbivirus genus; the genome is composed by ten linear dsRNA segments. So far, 27 serotypes have been described and they are distributed worldwide between latitudes 35°S and 50°N. The information available is substantially different between regions and continents as a result of the dissimilar efforts and resources available, to cope the situation concerning BTV. In addition, climate change and animal trade are remodeling classical boundaries and virus spread. In this context, the information for the American continent is particularly limited and there are no historic-epidemiological data to understand the continental spread, besides guesswork from classic phylogeny. Genetic analysis provides us different layers of data to understand epidemiology of BTV: immunology features and geographic distribution defining serotypes and topotypes accurately. Materials and methods In this research, we have compiled and curated all sequences available, until 2014, from databases in order to conduct an exhaustive phylogenetic reconstruction, analyzing 696 sequences in five matrixes, the biggest analysis carried out so far. Coalescent algorithm for reconstruction were used to infer years of divergence for clades and strains, in other words, approach a reliable time of most recent ancestor between lineages (TMRCA). Phylogenetic analysis by Maximum-likelihood (RAxMLv8 -soft) was conducted for Seg2, Seg3, Seg7, Seg6 and Seg10 and Bayesian-Coalescent algorithms, to estimate divergence-times, were used to analyze Seg3, Seg7 and Seg10 (Beast v1.8-soft). Results and Discussion For phylogenetic analysis, American clades highly supported were recorded for all the segments analyzed. Times of divergence for Seg3, 7 and 10 analysis, recorded independent evolution with different TMRCA between clades, which supports previously, reported reassortment events. This data, allow us to approach the time when BTV spread out from Africa to Europe or Middle East, letting us infer dates of divergence for classical Eastern and Western lineages/topotypes. Moreover, into the American continent, we have approached the timeline for the most likely way of introduction and spreading of BTV in the continent, virus introductions in the Caribbean and Central America, spreading to North or South America. Conclusions In summary, we have covered the historic and current situation for the whole continent, integrating American data along with European and African BTV history.