Bourbon virus (BRBV) and the rise of lone star ticks

Bourbon virus (BRBV) is an RNA virus in the family Orthomyxoviridae, genus Thogotovirus. Unlike other thogotoviruses typically found in Eurasia and Africa, BRBV is the first human thogotovirus discovered in the Americas.

The infection is rare, with only five confirmed cases reported since its discovery in 2014.

The virus appears to spread through lone star ticks (Amblyomma americanum). Molecular surveillance has detected BRBV in field-collected ticks from Missouri, with studies confirming live virus in cell culture. This evidence supports that these aggressive, human-biting ticks transmit Bourbon virus to people.

No animal reservoirs or person-to-person transmission have been documented. Critically, no approved vaccines or antiviral therapies exist for the Bourbon virus. Public health experts are monitoring its spread across lone star tick habitats in the southeastern and south-central United States.

Bourbon virus causes a nonspecific, flu-like illness that can be severe.

Symptoms include

• High fever
• Profound fatigue or weakness
• Headache
• Muscle and joint aches

Gastrointestinal symptoms (often early)

• Nausea
• Vomiting
• Diarrhea

A skin rash that often appears on the trunk or arms after several days. The rash has both flat, discolored spots and raised bumps.

Laboratory findings

• Leukopenia (low white blood cell count)
• Thrombocytopenia (low platelet count)
• Elevated liver enzymes (suggesting liver injury)

Diagnostic challenge

• Signs overlap with other tick-borne infections (e.g., ehrlichiosis, Heartland virus)
• It can also resemble meningitis

Diagnosing Bourbon virus requires a high index of suspicion and specialized testing.

Clinicians should suspect BRBV in patients with:

• Tick exposure history
• Fever, rash, blood cell abnormalities
• No alternative diagnosis

BRBV is rare and not included in routine diagnostic panels. Physicians must coordinate with state or CDC labs.

Molecular testing

• Real-time RT-PCR can detect BRBV RNA in blood or tissue.
• Specific PCR assays for Bourbon virus genes have been developed for surveillance

Serologic testing

Plaque reduction neutralization tests (PRNT) can detect BRBV antibodies in serum.

There is currently no specific antiviral treatment for Bourbon virus disease.

Since tests to confirm BRBV are specialized, initial management begins without a confirmed diagnosis.

Care is entirely supportive; no targeted therapy for Bourbon virus (BRBV) is currently available.

Hospital management focuses on complications

• Intravenous fluids and blood products
• Blood pressure support
• Dialysis for kidney failure if needed
• Oxygen or mechanical ventilation for respiratory failure (reported in at least one case)

Antiviral therapy

• No human clinical trials have been conducted
• Animal studies:
  • Favipiravir prevented death in BRBV-infected mice
  • Molnupiravir showed activity against BRBV in cell culture and mice
• Neither drug is approved for human use against BRBV

Ticks are thriving in many parts of the world, and the diseases they spread are becoming a growing public health concern. These parasites transmit a wide range of pathogens, and evidence shows their impact is expanding.

An extensive 2022 analysis found that about 14.5% of people globally test positive for antibodies against Borrelia burgdorferi and related species, the bacteria that cause Lyme disease. This suggests exposure is more common than previously thought, but not everyone who tested positive develops symptoms.  Some studies also suggest a higher prevalence in recent years compared to earlier decades.

In Europe, tick-borne encephalitis (TBE) is also on the rise. Over 3,600 cases were reported across EU/EEA countries in 2022. Beyond Lyme and TBE, ticks carry dozens of pathogens, including viruses such as Crimean-Congo hemorrhagic fever (CCHF) in parts of Africa and Asia.

The hidden scale of the problem

The United States offers a clear snapshot. Between 2004 and 2016, reported tick-borne disease cases more than doubled. Lyme disease makes up the vast majority of these. Yet reported numbers tell only part of the story.

In 2023, about 89,000 cases were officially logged, while the CDC estimates roughly 476,000 Americans are diagnosed and treated for Lyme disease each year. That gap underscores just how many cases slip past formal surveillance.

New threats are also emerging. Recently identified tick-borne viruses, such as Heartland virus and Bourbon virus, have also caused severe illness in the U.S. Currently, there is no specific treatment available for them.

Factors driving the rise of infections

One significant factor driving the increase in tick-borne infections is climate change. Warmer weather extends the habitats of ticks and lengthens their active breeding seasons.

Other reasons include deforestation and suburban expansion into wooded areas, which brings ticks closer to humans.

Adding to the challenge, surveillance is inconsistent across countries. Many places lack robust systems for detecting and reporting tick-borne diseases, which means global case counts likely underestimate the actual burden of these infections.

Prevention of Bourbon virus depends on avoiding tick bites, since no vaccine or prophylactic drug is available.

Lone star ticks are found across a wide part of the U.S., from the Southeast into the Midwest and even parts of the Northeast, so anyone in areas where these ticks live should practice tick precautions.

Key measures include:

• Protective clothing: Wear long sleeves and pants outdoors. Tuck pants into socks and wear light-colored clothing to spot ticks
• Tick repellents: Use EPA-registered repellents containing DEET or picaridin on skin or permethrin on clothing
• Avoid tick habitat: Stay on trails and avoid walking through tall grass or brush, especially in spring and summer when ticks are most active
• Tick checks: Perform a full-body tick check after being outdoors. Remove any attached ticks promptly with fine-tipped tweezers
• Home measures: Keep yards clear of brush, woodpiles, and leaf litter to reduce ticks near living areas

Because lone star ticks actively seek hosts and are expanding their range, these precautions are important.

Bourbon virus is a newly discovered, tick-borne virus that can cause severe, life-threatening illness. Healthcare providers in the U.S. should be aware of it in cases of unexplained fever, rash, and cytopenia with a history of tick exposure, especially when routine tick-borne tests are negative.

Diagnosis relies on specialized lab tests (PCR or neutralizing antibody assays) at reference centers.

Management is supportive; no specific therapy or vaccine is available. Vigilance and tick bite prevention remain the primary defenses.

Ongoing research is defining the true extent of BRBV infections, their animal reservoirs, and potential treatments. Given that lone star ticks are common and spreading in many regions of the United States, there is a potential risk for more Bourbon virus cases. Clinicians and public health officials should include BRBV in the differential diagnosis of severe tick-associated illnesses.

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