Focal persistence and phylodynamics of Heartland virus in Georgia

Abstract

Heartland virus (HRTV) is an emerging tick-bone virus associated with severe illness in the U.S. There are large gaps in knowledge of HRTV diversity, evolution, and transmission due to a paucity of HRTV-positive samples and genome sequences. We identified a focal site of HRTV- positive Amblyomma americanum ticks in central Georgia and developed a novel multiplex- amplicon sequencing assay to generate full HRTV genome sequences. By screening over 21,000 field-collected ticks from 2021-2023, we identified six positive pools. Five were collected from the site in central Georgia where our group first detected HRTV-positive ticks in 2019, and one from a site in western Georgia approximately 175 km away. The HRTV genome sequences from Georgia were highly related, even across this distance and over five years. Reference HRTV genome sequences from across the U.S. were also geographically clustered. Time-scaled phylogenetic analysis suggested recent spread of HRTV in the U.S., with all available sequences sharing a common ancestor within the last 300 years, and sequences from Georgia sharing a common ancestor within the last 40 years. Our observed spatial clustering of HRTV and the high degree of genetic conservation in our persistent focus suggest the importance of small spatial dynamics in HRTV transmission ecology. Author SummaryHeartland virus (HRTV) was first discovered in humans in 2009 and has since caused over 60 cases of severe and fatal disease in the United States. HRTV is transmitted by the lone star tick, Amblyomma americanum, across the Southeast, East coast, and Midwest. Little information is known about how this virus circulates and changes across time and space due to a lack of genetic data. Here, we created a new procedure to generate more genetic sequence data for HRTV and collected over 21,000 ticks to screen for HRTV across three years in Georgia. We generated 6 new HRTV sequences and compared them to existing sequences from our group in Georgia, and across the country, finding evidence of regional clustering of HRTV and highly related HRTV across time in Georgia. Our analyses additionally found that this virus was likely introduced to the U.S. in the last 300 years. Our study provides new context and information in understanding the landscape and transmission of HRTV in the U.S.