P-52 Effects of immunity on genetic divergence of measles and dengue viruses

Buller Hallway

Phylogenies capture biological change in lineages through time, and for pathogens, this change is shaped by interaction between the pathogen and its hosts. In this study, we explore both published and novel methods to quantitatively define the shape of phylogenetic trees from outbreaks of two human pathogens: measles virus and dengue virus. Although both viral infections are acute in the human host, they experience very different immune pressures. Virus sequences were obtained from GenBank and aligned in MUSCLE, and trees were constructed from genetically defined outbreaks using Bayesian methods. To compare tree shapes, we used published methods to approximate Sackin’s index as a measure of tree asymmetry and to detect the number of “cherries,” or tips in each tree that share common ancestors. In addition, we explored the use of a novel summary statistic to compare virus tree shapes. While in-host exposure to strong cross-immunity by measles virus versus partial immune enhancement of dengue virus results in qualitatively different tree shapes, we demonstrate how tree asymmetry due to immune pressure can be quantitatively defined by these methods.