Early Release – Heartland Virus in Lone Star Ticks, South Carolina, USA, 2021–2024 – Volume 32, Number 12—December 2026 – Emerging Infectious Diseases journal

Heartland virus (HRTV; family Phenuiviridae, genus Bandavirus) and Bourbon virus (BRBV; family Orthomyxoviridae, genus Thogotovirus) are emerging tickborne pathogens. Both viruses were detected in the contiguous United States within the past 15 years (1,2). Symptoms of identified infections included acute febrile illness characterized by thrombocytopenia and leukopenia, with progression to multiorgan failure and death in severe cases (3). Wildlife serosurveillance suggests both pathogens are more widely spread than reported cases indicate (Appendix).

The lone star tick (Amblyomma americanum) is the primary vector for both Heartland and Bourbon viruses (4,5). Lone star tick range is well established across the eastern United States and continues to expand northward and westward, driven by host movement, land use changes, and climate change (6). White-tailed deer (Odocoileus virginianus) are a keystone host for lone star ticks; a retrospective wildlife serosurvey conducted in South Carolina reported HRTV antibodies in 20% (1/5) of white-tailed deer samples collected in 2001 and in 40% (2/5) of samples collected in 2008 (7). Similar studies have reported evidence of BRBV in neighboring states (3). Although South Carolina lies within the established range of lone star ticks, has a history of tickborne bacterial disease transmission (8), and has documented HRTV circulation in wildlife (3), testing of ticks collected in the state has not included HRTV or BRBV.

For our study, we used data from a multiyear surveillance program in South Carolina to test field-collected lone star ticks for HRTV and BRBV and assess potential risk. Statewide tick collection occurred April 2021–August 2024 with the use of standard drag/flag and CO₂-baited trapping methods (8). To maximize the likelihood of detecting viral infection, we limited testing to nymphal lone star ticks because of the epidemiologic importance and abundance of this life stage in human exposure. We identified specimens morphologically by using established dichotomous keys and maintained specimens under cold-chain conditions. We bisected ticks longitudinally, processing one half for RNA nucleic acid extraction and the other for DNA extraction. For viral detection, we extracted RNA by using the QIAamp Viral RNA Kit (QIAGEN, https://www.qiagen.com) according to the manufacturer’s protocol. We pooled >5 nymphs by collection site, date, and method before multiplex testing. Over a 4-year period, we collected a total of 1,665 nymphs, which we separated into 368 pools. Pools were distributed by year as follows: 2021, n = 223; 2022, n = 106; 2023, n = 21; and 2024, n = 18.

After assay optimization, we performed real-time reverse transcription PCR by using previously published primers targeting the HRTV small (S) segment and the BRBV nucleoprotein gene (9). We optimized the assay by performing gradient real-time reverse transcription PCR (54°C–64°C) and testing 10-fold serial of the positive control to generate standard curves and determine the optimal annealing temperature (62°C). We confirmed amplicon size and quality by electrophoresis. We classified pools as positive if they demonstrated exponential amplification with a cycle threshold (Ct) 35, equivocal at Ct 36–37, and negative at Ct >38 or no amplification. Each run included negative controls (nuclease-free water) and positive controls; we sourced HRTV and BRBV from the Centers for Disease Control and Prevention’s Arbovirus Reference Collection (https://www.cdc.gov/vector-borne-diseases/php/arbovirus-reference-collection/index.html).

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Figure. Geographic distribution of lone star ticks (Amblyomma americanum) and HRTV surveillance, South Carolina, USA, 2021–2024. Established counties were defined as those in which >6 lone star…

We tested 1,665 lone star ticks in pools of 5 nymphs: 6 of 368 pools were positive for HRTV and none were positive for BRBV. All HRTV-positive pools came from the same location in Colleton County, South Carolina (Figure). Positive pools comprised lone star tick nymphs collected in 2021 (5/6) and 2022 (1/6) (Table). Collection methods for HRTV-positive pools were distance dragging (2/6), carbon dioxide trapping (3/6), and removal from a collector’s body (1/6). HRTV-positive pools were collected in the months of April, July, and August.

Our study reports HRTV detection in questing South Carolina lone star tick nymphs, a widespread species associated with an increasing number of health threats in the United States (9). Collection of positive pools occurred during spring through late summer across 2 different years, consistent with expected nymphal host-seeking activity and demonstrating viral persistence across time. Lone star ticks use multiple strategies to find a host, as demonstrated in the HRTV-positive pools collected by dragging (ambush behavior) and by CO₂ trapping (active host-seeking). Our study results compliment previous data indicating seropositive animals and 1 human case, although the human case did not include follow-up and it remains unclear where the exposure occurred (7,10).

Healthcare providers should consider tickborne viral infections in patients who do not respond to antimicrobial therapy, because the overlapping prevalence of multiple lone star tick-associated pathogens can confound diagnosis. Supportive care is the primary management of patients with tickborne viral infections because no specific antiviral therapies are available. Continued and expanded testing can help better define the geographic range, epidemiology, and public health significance of emerging tickborne viruses in the United States. Tick bite prevention, early clinical recognition, and strengthened surveillance remain essential for treatment and control of tickborne viruses.

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