Enzootic transmission of yellow fever virus, Venezuela

Abstract

Phylogenetic analysis of yellow fever virus (YFV) strains isolated from Venezuela strongly supports YFV maintenance in situ in Venezuela, with evidence of regionally independent evolution within the country. However, there is considerable YFV movement from Brazil to Venezuela and between Trinidad and Venezuela.

Figure 1

A) Bayesian maximum clade credibility (MCC) tree for YFV in the Americas based on 654 nt of the prM/E fragment. Taxon labels include year of isolation, GenBank accession number, strain designation, and country of isolation. Terminal branches of the tree are colored according to the sampled location of the taxon at the tip. Internal branches are colored according to the most probable (modal) location of their parental nodes. Nodes with posterior probabilities (clade credibilities) >0.95 are labeled accordingly in black. Scale bar indicates time in years. B) Magnified inset of the MCC phylogeny showing the tree topology for a subset of South American genotype I strains. C) Bayes factor (BF) test for significant non-zero rates indicating the statistical support for epidemiologically linked countries. Rates supported by a BF >5 are shown. The thickness of the arrows represents the relative strength by which the rates are supported. The Technical Appendix presents the details of the 124 sequences used in this study

Figure 2

Midpoint rooted Bayesian Markov chain Monte Carlo phylogeny based on yellow fever virus (YFV) complete open reading frame sequences. Numbers at nodes indicate posterior probabilities >0.9. Eastern and western Venezuelan sequences are indicated. Substitutions resulting from nonsynonymous, synapomorphic mutations that define sequences in a clade/lineage are highlighted at relevant nodes. Two substitutions (NS2b A98T and NS5 A200T) occurred in earlier isolates from Brazil. The capsid A79V and NS5 A200T substitutions include the Brazilian isolate BeH655417, which lies directly basal to the Venezuela isolates. This indicates that these substitutions were probably present in the YFV progenitor when it was introduced into Venezuela. Furthermore, substitutions NS2a V10I, NS2a S184T, and NS2b A98T all appear to have arisen after YFV was introduced to Venezuela, further supporting enzootic YFV maintenance there. Taxon/tip labels include year of isolation, strain name and country where the virus was isolated. Scale bar indicates percentage of nucleotide sequence divergence.