EvoLaps: a web interface to visualize continuous phylogeographic reconstructions

Spatio-temporal spread of Lassa virus and a new rodent host in the Mano River Union area, West Africa

The spread of Lassa virus (LASV) in Guinea, Liberia and Sierra Leone, which together are named the Mano River Union (MRU) area, was examined phylogeographically. To provide a reliable evolutionary scenario, new rodent-derived, whole LASV sequences were included. These were generated by metatranscriptomic next-generation sequencing from rodents sampled between 2003 and 2020 in 21 localities of Guinea and Sierra Leone. An analysis was performed using BEAST to perform continuous phylogeographic inference and EvoLaps v36 to visualize spatio-temporal spread. LASV was identified as expected in its primary host reservoir, the Natal multimammate mouse (Mastomys natalensis), and also in two Guinean multimammate mice (Mastomys erythroleucus) in northern Sierra Leone and two rusty-bellied brush-furred mice (Lophuromys sikapusi) in southern Sierra Leone. This finding is consistent with the latter two species being secondary host reservoirs. The strains in these three species were very closely related in LASV lineage IV. Phylogenetic analysis indicated that the most recent common ancestor of lineage IV existed 316-374 years ago and revealed distinct, well-supported clades from Sierra Leone (Bo, Kabala and Kenema), Guinea (Faranah, Kissidougou-Guekedou and Macenta) and Liberia (Phebe-Ganta). The phylogeographic scenario suggests southern Guinea as the point of origin of LASV in the MRU area, with subsequent spread to towards Mali, Liberia and Sierra Leone at a mean speed of 1.6 to 1.1 km/year.

EvoLaps 2: Advanced phylogeographic visualization

EvoLaps is a user-friendly web application designed to visualize the spatial and temporal spread of pathogens. It takes an annotated tree as entry, such as a maximum clade credibility tree obtained through continuous phylogeographic inference. By following a 'Top-Down' reading of a tree recursively, transitions (latitude/longitude changes from a node to its children) are represented on a cartographic background using graphical paths. The complete set of paths forms the phylogeographic scenario. EvoLaps offers several features to analyze complex scenarios: (1) enhanced path display using multiple graphical variables with time-dependent gradients, (2) cross-highlighting and selection capabilities between the phylogeographic scenario and the phylogenetic tree, (3) production of specific spatio-temporal scales and synthetic views through dynamic and iterative clustering of localities into spatial clusters, (4) animation of the phylogeographic scenario using tree brushing, which can be done manually or automatically, gradually over time or at specific time intervals, and for the entire tree or a specific clade, and (5) an evolving library of additional tools. EvoLaps is freely available for use at evolaps.org.