Estudo in vitro da diversidade genética e dinâmica de adaptação do vírus da encefalite de Saint Louis (SLEV) durante ciclo de transmissão

Abstract

Introduction: The Saint Louis encephalitis virus (SLEV) is a single-stranded positive-sense RNA virus belonging to the Flaviviridae family, Orthoflavivirus genus. Alongside other well-known viruses such as dengue virus (DENV), West Nile virus (WNV), and Japanese encephalitis virus (JEV), itis part of the arboviruses, a group of viruses capable of being transmitted by arthropod vectors. Although not considered a global health problem like other arboviruses, SLEV has caused outbreaks in Brazil and has the potential to cause new outbreaks and epidemics in the future. Objectives: This study aimed to assess the genetic variability and adaptive dynamics of SLEV in cell culture during transmission cycles between the invertebrate and vertebrate hosts, as well as the intrahost adaptive dynamics for each of its hosts. Materials and Methods: Interhost and intrahost infection cycles were mimicked in cell culture using mosquito (Aag2) and primate (LLC-MK2) cell lines, where the genetic diversity of SLEV between passages of each cycle and at the end of the cycles was evaluated using next-generation sequencing. Results: Overall, many mutations became fixed in the population, with 82.45% being synonymous. In the interhost cycle, among all mutations, NS2A:T3727C and NS2B:C4576A became fixed with a modulation between 30% and 70% during passages. Infection in this cycle was prematurely interrupted after the second passage, as the virus collected at this point lost infectivity, possibly due to the emergence of numerous substitutions. For the intrahost cycle in vertebrate cell lines, there was a fixation of 99% for mutations NS1:R100K and NS4B:T7075C. Finally, in the invertebrate cycle, E:H285R emerged and reached a frequency of 61%. Phenotypically, in both interhost and intrahost vertebrate cycles, a smaller viral plaque phenotype occurred, directly impacting the increase in titer. Conclusion: These data suggest that intrahost passages, whether in mosquito or primate cell lines, exert distinct selective pressures that drive the rapid evolution of SLEV, with a direct impact on the viral plaque phenotype and replicative fitness. Comparatively, host alternation apparently poses a greater barrier to viral evolution. The evolutionary and adaptive dynamics of SLEV to different hosts are still a major question, but the findings described here provide insights into possibly understanding how this arbovirus behaves in its infection cycle and adapts to new potential hosts.