Lesser Known Arboviruses Symposium II
Lesser Known Arboviruses Symposium II
Heartland virus (HRTV, Phenuviridae: Bandavirus) and Bourbon virus (BRBV, Orthomyxoviridae: Thogotovirus) are emerging tickborne viruses in the United States. HRTV and BRBV were both identified from human cases in the Midwestern US in 2009 and 2014, respectively. Since the initial discovery of HRTV, more than 60 cases have been recorded in 14 states and at least 4 cases of BRBV in 3 states. Vector surveillance conducted during the epidemiological investigations for HRTV and BRBV and results of experimental infection studies have implicated Amblyomma americanum, the lone star tick, as the vector for both viruses. While A. americanum are typically found in midwestern and southern regions of the US, this species has experienced a recolonization of former territory and an expanded geographic range in the Northeast. Passive surveillance first identified HRTV and BRBV in New York State (NYS) in 2018 and 2019, respectively. Enhanced surveillance efforts conducted in Suffolk County since have consistently detected positivity in A. americanum with high seropositivity rates in white-tailed deer. To further our understanding of the emergence and spread of these viruses, we conducted full genome sequencing and phenotypic characterization of isolates from 2018-2022. Preliminary sequencing revealed distinct clades for both HRTV and BRBV when compared to the original midwestern isolates. Characterization in mammalian cell culture and experimentally infected A. americanum nymphs revealed little phenotypic distinction among and between the midwestern and NYS HRTV isolates. NYS BRBV isolates, however, display high levels of both genetic and phenotypic variability compared to each other and representative midwestern BRBV isolates. Additionally, we found BRBV but not HRTV NY isolates efficiently infect and replicate in Ix. scapularis following virus immersion. Genotypic divergence of both HRTV and BRBV suggest multiple, separate introductions of each virus into NYS with emergence of varying phenotypes potentially due to adaptation to geographically distinct transmission cycles.