domingo, 28 de agosto de 2011

EVALUATION OF THE GEOGRAPHIC STRUCTURE IN DENGUE VIRUS TYPE 1 FROM A PHYLOGENETIC AND BIOGEOGRAPHIC APPROACH


INTRODUCTION

Phylogenetic relationships amongst strains of dengue virus often can show a strong structure associated with geography and temporality (Gray et al. 2011; Carvalho et al. 2009), however geography seems to be the main component in modeling these phylogenetic reconstructions. Likewise, global comparisons of lineages and their geographic location have allowed further classifications of isolates from the same serotype into new genotypes known as topotypes (Samuel and Knowles, 2001). However, due to the poor georeferencing of the isolates in public databases, sometimes to make inferences about geographic patterns is hard and doubtful because the management of country´s political division can be biogeographically inadequate and little detailed. Based on the above, the aim in this work was to assess the congruence between geographic patterns found from phylogenetic and biogeographic approaches in dengue virus type I circulating in America.

METHODS

Phylogenetic analysis of 50 DENV-1 E gene sequences were assess from the Bayesian inference criterion using BEAST v1.6.2 program (Drummond & Rambaut, 2007), under a General Time Reversible model of nucleotide substitution (Rodriguez et al.,1990) with gamma-distributed rate variation and a proportion of invariable sites (GTR + G + I) were selected and two runs of 4 chains were run for ten millions of generations. Sequences were sampled in American counties, including islands in the Atlantic and Pacific Oceans

From the topology (maximum clade credibility tree) obtained, in the Phylogeographic analysis were identified possible genotypes according to five areas intuitively postulated on the basis of geographic information contained in each clade. The criteria used were monophyletic clades and posterior probabilities values above 0.80. Results were constrasted with the subclusters found by Carvalho et al.2010.

Finally, the geographic patterns were evaluated following the method of track compatibility by Craw (1988a, 1989a). The areas used were those postulated in this work and the biotic components of Latin America and the Caribbean compiled by Morrone (2004). under the level of large regions and provinces.

RESULTS AND DISCUSSION


The phylogenetic relationchips from American sequences seems to be structured by geographics patterns. According with this, five areas were proposed corresponding to Pacific, Caribbean, southern South America, central América and Northern south America. These components were determined following the geographic information available to each viral isolated. Intuitively, central and Northern south America were taken as independent unities.

Figure 1. Maximum clade credibility tree in Bayesian analysis of E

gene sequences representing Latin America strains. Posterior probabilities are shown for key nodes.






Phylogeographic analysis pointed the same pattern like phylogenetic analysis, also SAN and CA were closely related. The strong geography associated structure posibbly indicates the continous viral movement between different countries and in differents directions. On the other hand, the viral exchange seems to be limited and uneven among areas, even though they are geographycally close, as with the Caribbean and Central America.

Figure 2. Phylogeographic patterns between genotypes and postulated areas in Dengue virus type 1

Tracks compatibility analysis resulted in a clique (based in regions) representing a pattern that related Mexican transition area with Neotropical Region, which is congruent with the relationship between SAN and CA areas in phylogeographic analysis. This is probably due to the magnitud of the areas which includes a higher proportion of distributions and strains that are distribuited in intermediate areas. Areas delimited as Provinces by Morrone (2004) and phylogeographic areas delimited here, do not showed compatible traks.

Figure 3. Traks compatibility analysis. a) Areas proposed in this study. Biotic components of Latin America and the Caribbean b) Provinces c) Regions.

CONCLUSION

Phylogenetic and Biogeographic analysis in dengue virus can reflect a similar geographic pattern however is necessary to know the level in which both approaches can be congruent. In this study, Central America and northern South America form a large unit that corresponds to the clique found in the track compatibility analysis, which supports the close relationship between the Mexican transition area and the Neotropical region. Obviously, the use of geopolitical units in the assessment of geographical structure in shaping the phylogenetic relationships dengue is not the most accurate and dengue virus strains behave as a large dispersive population connecting large areas in America.

REFERENCES

Carvalho SE, Martin DP, Oliveira LM, Ribeiro BM, Nagata T (2010) Comparative analysis of American Dengue virus type 1 full-genome sequences. Virus Genes 40: 60–66.

CRAW, R. C. 1988. Continuing the synthesis between panbiogeography, p

hylogenetic systematics and geology as illustrated by empirical studies on the biogeography of New Zealand and the Cha tham Islands. Systematic Zoology 37: 291-310.

CRAW, R. C. 1989a. New Zealand biogeography: A panbiogeographic approach. New Zealand Journal of Zoology 16: 527-547

Drummond AJ & Rambaut A (2007) "BEAST: Bayesian evolutionary analysis by sampling trees." BMC Evolutionary Biology 7, 214

Gray, R. R., Pybus, O. G. and Salemi, M. (2011), Measuring the temporal structure in serially sampled phylogenies. Methods in Ecology and Evolution. doi: 10.1111/j.2041-210X.2011.00102.x

Morrone, Juan J. 2004. Panbiogeografía,componentes bióticos y zonas de transición. Fonte: Rev. bras. entomol;48(2):149-162

Samuel, A. R., Knowles, N. J. 2001. Foot-and-mouth disease type O viruses exhibit genetically and geographically distinct evolutionary lineages (topotypes). Journal of General Virology 74, 2281-2285.