After 37 years treating Lyme disease, I’ve learned that the ticks carrying Borrelia burgdorferi transmit far more than just Lyme disease and the common coinfections like Babesia and Bartonella. A growing list of emerging and rare tick-borne infections—Borrelia miyamotoi, Rocky Mountain Spotted Fever, Bourbon Virus, Heartland Virus, Borrelia mayonii, and STARI—adds complexity to diagnosis and treatment.
These infections are less common than the major coinfections, but when they occur, they’re frequently missed. Testing is limited or unavailable. Symptoms overlap with Lyme disease and other tick-borne illnesses. By the time these infections are recognized, diagnosis and treatment may have been delayed for months or years.
Understanding these emerging and rare tick-borne diseases matters for patients who remain undiagnosed despite tick exposure, for clinicians evaluating complex cases that don’t fit typical Lyme patterns, and for anyone in endemic areas where multiple tick-borne pathogens circulate simultaneously.
Borrelia miyamotoi
Borrelia miyamotoi is a relapsing fever spirochete transmitted by the same Ixodes scapularis ticks that carry Lyme disease. Unlike Lyme disease, which causes the characteristic erythema migrans rash, Borrelia miyamotoi typically presents with fever, headache, fatigue, and muscle aches without rash.
Standard Lyme disease testing doesn’t detect Borrelia miyamotoi. Patients with this infection test negative for Lyme disease despite tick exposure and compatible symptoms. Specific testing for Borrelia miyamotoi requires PCR or specialized serology not routinely performed in most clinical settings.
The infection responds to the same antibiotics used for Lyme disease—doxycycline remains first-line treatment. However, without recognition that Borrelia miyamotoi is the culprit rather than Borrelia burgdorferi, diagnosis and appropriate treatment may be delayed.
Rocky Mountain Spotted Fever (RMSF)
Rocky Mountain Spotted Fever is a severe bacterial infection caused by Rickettsia rickettsii, transmitted primarily by the American dog tick and Rocky Mountain wood tick. Despite its name, RMSF occurs throughout the United States, with highest incidence in southeastern states.
RMSF presents with sudden onset of high fever, severe headache, muscle aches, and characteristic spotted rash that typically begins on wrists and ankles before spreading centrally. However, the rash may not appear until several days into illness, and some patients never develop a rash—leading to diagnostic delays.
RMSF is potentially fatal without prompt treatment. Doxycycline must be started based on clinical suspicion without waiting for confirmatory testing, as delays increase risk of severe complications including organ failure and death. Early treatment with doxycycline dramatically improves outcomes.
Bourbon Virus
Bourbon Virus is a newly discovered tick-borne virus first identified in Bourbon County, Kansas in 2014. The virus belongs to the Thogotovirus genus and has been associated with severe illness including fever, fatigue, rash, headache, body aches, nausea, and vomiting.
Only a handful of cases have been identified, making the full clinical spectrum of Bourbon Virus infection unclear. Several cases have resulted in death, suggesting potential for severe disease, though whether all infections cause severe illness or many remain mild and unrecognized is unknown.
There is no specific treatment for Bourbon Virus. Care is supportive. Testing is available only through specialized laboratories, and many clinicians remain unaware of this emerging pathogen.
Heartland Virus
Heartland Virus is another emerging tick-borne virus, discovered in Missouri in 2009. The virus is transmitted by lone star ticks and causes fever, fatigue, decreased appetite, headache, nausea, muscle aches, and decreased white blood cell and platelet counts.
Like Bourbon Virus, Heartland Virus has no specific treatment. Care is supportive, focusing on managing symptoms and monitoring for complications. Severe cases may require hospitalization.
The geographic range of Heartland Virus appears to overlap with lone star tick distribution, primarily southeastern and south-central United States. Testing is limited to specialized laboratories, and the true incidence of Heartland Virus infection remains unknown.
Borrelia mayonii
Borrelia mayonii is a recently identified Lyme disease-causing spirochete discovered in the upper Midwest. Like Borrelia burgdorferi, it’s transmitted by Ixodes scapularis ticks and causes Lyme disease with erythema migrans rash, fever, headache, and muscle aches.
What distinguishes Borrelia mayonii from typical Lyme disease is higher levels of bacteria in the blood, allowing detection by blood smear in some cases—unusual for Lyme disease. Some patients also experience nausea, vomiting, and diffuse rash rather than the single expanding erythema migrans typical of Borrelia burgdorferi.
Treatment is the same as standard Lyme disease—doxycycline or amoxicillin. However, standard Lyme disease testing may not detect Borrelia mayonii reliably, potentially leading to missed diagnoses in areas where this species circulates.
STARI (Southern Tick-Associated Rash Illness)
STARI is a rash illness associated with lone star tick bites, presenting with an expanding erythema migrans-like rash that’s clinically indistinguishable from Lyme disease rash. However, STARI occurs in regions where Lyme disease is rare or absent, and patients test negative for Lyme disease.
The causative agent of STARI remains unknown. Initial studies suggested Borrelia lonestari, but subsequent research failed to confirm this. Whether STARI represents infection with an unidentified pathogen or a local inflammatory reaction to tick saliva remains unclear.
STARI is generally milder than Lyme disease, with rash and fatigue typically resolving without treatment or with a short course of doxycycline. Unlike Lyme disease, STARI does not appear to cause chronic symptoms or disseminated disease affecting joints, heart, or nervous system.
Why These Infections Are Missed
Rare and emerging tick-borne infections are frequently overlooked because testing is limited or unavailable, symptoms overlap with more common tick-borne diseases, clinician awareness is low, and geographic assumptions lead to diagnostic anchoring on Lyme disease or common coinfections.
A patient presenting with fever and rash after tick exposure in the southeastern United States may be evaluated for Lyme disease despite living in an area where lone star ticks predominate and RMSF or STARI are more likely. Testing focuses on Lyme disease, results are negative, and alternative diagnoses aren’t pursued.
This pattern—testing for the wrong pathogen based on geographic assumptions or limited awareness—delays diagnosis and appropriate treatment for patients with rare tick-borne infections.
Clinical Takeaways
Emerging and rare tick-borne infections including Borrelia miyamotoi, RMSF, Bourbon Virus, Heartland Virus, Borrelia mayonii, and STARI add diagnostic complexity beyond the common Lyme disease and major coinfections. Testing for these infections is often limited or unavailable, requiring clinical diagnosis based on symptom patterns, geographic location, and tick exposure history. Standard Lyme disease testing does not detect most of these pathogens, leading to missed diagnoses when alternative tick-borne infections aren’t considered. Treatment varies by pathogen—some respond to doxycycline while viral infections like Bourbon and Heartland have no specific treatment, making accurate diagnosis essential for appropriate management.
Frequently Asked Questions
What are the most common rare tick-borne infections?
Borrelia miyamotoi and RMSF are most common among rare tick-borne infections. Bourbon Virus and Heartland Virus are extremely rare with only limited cases reported.
Can you have these infections with Lyme disease?
Yes. Multiple tick-borne pathogens can be transmitted in a single tick bite. Patients may have Lyme disease plus Borrelia miyamotoi, RMSF, or other coinfections simultaneously.
How are these infections diagnosed?
Testing is limited. Borrelia miyamotoi requires specific PCR or serology. RMSF is diagnosed clinically with confirmatory serology. Bourbon and Heartland Virus testing is available only through specialized labs. STARI is diagnosed by clinical presentation and negative Lyme testing.
Do these infections respond to Lyme disease antibiotics?
Some do. Borrelia miyamotoi, Borrelia mayonii, and RMSF respond to doxycycline. Bourbon and Heartland Virus have no specific treatment. STARI typically resolves with or without doxycycline.
Why haven’t I heard of these infections before?
Many are newly discovered (Bourbon Virus in 2014, Heartland Virus in 2009, Borrelia mayonii in 2016). Others like RMSF and STARI are regional. Clinician awareness remains low, and testing is limited.
References
- Krause PJ, et al. Borrelia miyamotoi sensu lato seroreactivity and seroprevalence in the northeastern United States. Emerg Infect Dis. 2014;20(7):1183-1190.
- Biggs HM, et al. Diagnosis and Management of Tickborne Rickettsial Diseases: Rocky Mountain Spotted Fever and Other Spotted Fever Group Rickettsioses, Ehrlichioses, and Anaplasmosis. MMWR Recomm Rep. 2016;65(2):1-44.
- Pritt BS, et al. Identification of a novel pathogenic Borrelia species causing Lyme borreliosis with unusually high spirochaetaemia: a descriptive study. Lancet Infect Dis. 2016;16(5):556-564.
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