A single tick carries its own microbial ecosystem — a community of bacteria, viruses, and parasites that it has accumulated across its multi-year life cycle. Most tick bites result in no infection. But when infection does occur, the question "what exactly did it transmit?" is rarely asked thoroughly enough. The organisms on this page are less commonly discussed in the Lyme community — but they are real, they cause real illness, and some of them are life-threatening without prompt treatment.
Rickettsia — the endothelial invader
Rickettsia bacteria invade the endothelial cells lining blood vessels — the same vascular tropism seen in Bartonella, but with a much more acute and dangerous presentation. Unlike Bartonella, which often causes insidious chronic illness, Rocky Mountain spotted fever (RMSF) and related rickettsial infections can kill within days if untreated. Without prompt treatment, mortality from RMSF reaches 20–30%.
Despite the name, RMSF is most common in the southeastern and south-central United States, not the Rocky Mountains. It is also found throughout Central and South America. Other Rickettsia species cause illness worldwide — Mediterranean spotted fever in Europe, African tick bite fever in sub-Saharan Africa, and others across Asia.
The classic triad: fever, headache, and rash — but the triad is often incomplete, especially in early illness. The characteristic rash usually appears 2–5 days after fever onset, starting on the wrists and ankles and spreading toward the trunk. Crucially, up to 10% of RMSF patients never develop a rash at all — meaning a normal-appearing skin does not rule out the diagnosis.
Several Rickettsia species (though not R. rickettsii itself) produce a dark, crusted ulcer at the tick bite site called an eschar. The presence of an eschar in a febrile patient after a tick bite strongly suggests rickettsial disease. If you notice a dark crusty area where a tick was attached, photograph it and seek medical attention promptly — this is a clinically meaningful sign.
Rickettsia does not grow in standard blood cultures. Diagnosis is by PCR (most sensitive in early illness) or serology (retrospective). Given the potential severity, treatment with doxycycline should begin empirically on clinical suspicion — before laboratory confirmation is available.
Tick-Borne Encephalitis (TBE) — Europe and Asia's neurological threat
Tick-borne encephalitis virus is transmitted by the same Ixodes ticks that carry Lyme disease in Europe and Asia. This means that in endemic regions — which include most of central and eastern Europe, Scandinavia, and large parts of Russia and Asia — a single tick bite can theoretically transmit both Lyme disease and TBE virus simultaneously. Approximately 10,000–12,000 clinical cases are reported annually in Europe, with the true number believed to be significantly higher.
What makes TBE particularly significant is its biphasic course — and the dangerous second phase that targets the central nervous system:
Most TBE infections are asymptomatic. Of those who develop symptoms, roughly one third progress to the neurological second phase. Of those, approximately one third will have persistent neurological symptoms — cognitive dysfunction, headache, depression, personality changes — lasting a year or more after apparent recovery.
TBE was historically absent from the UK — but the first domestically acquired cases were confirmed in 2019. The Netherlands detected the virus in ticks in 2016. Climate change is driving both Ixodes tick expansion and TBE virus spread into regions considered previously non-endemic. If you live in or travel to any temperate European or Asian forested region, TBE is relevant to you.
Unlike Lyme disease, for which no approved human vaccine currently exists in most countries, TBE has a highly effective vaccine available across Europe and some Asian countries. Vaccination is recommended for people living in or regularly visiting endemic areas. Unpasteurised milk from goats, sheep, or cows can also transmit TBE virus — a route that is occasionally relevant in rural endemic regions.
Powassan virus — North America's neurological tick virus
Powassan virus is the North American equivalent of TBE virus — closely related, transmitted by the same Ixodes ticks that carry Lyme disease, and capable of causing severe encephalitis. Cases are rare but have been increasing in recent years. What makes Powassan uniquely dangerous is its transmission speed: unlike Lyme disease, which typically requires 24–36 hours of tick attachment to transmit Borrelia, Powassan virus can be transmitted within minutes of the tick beginning to feed.
Symptoms begin 1–5 weeks after infection and can include fever, headache, vomiting, followed by encephalitis, seizures, and respiratory failure in severe cases. The case fatality rate is approximately 10–15%, and roughly half of survivors have permanent neurological damage — memory problems, recurrent headaches, muscle wasting, and cognitive impairment.
The standard advice to remove ticks within 24 hours to prevent Lyme transmission is sound advice for Borrelia — but it provides essentially no protection against Powassan virus. This is not a reason to panic, as Powassan cases remain relatively rare, but it is a reason to take tick prevention seriously before exposure — not just tick removal after attachment. No vaccine exists for Powassan.
Alpha-gal syndrome — the tick bite that changes how you eat
Alpha-gal syndrome is one of the most peculiar consequences of a tick bite — and one of the most underdiagnosed. It is not an infection at all. It is an acquired allergic sensitisation to a carbohydrate called galactose-α-1,3-galactose (alpha-gal), which is present in the tissues of all non-primate mammals — including beef, pork, lamb, venison, and dairy products. Humans and other primates do not produce alpha-gal naturally, which is why our immune systems can react to it when provoked.
When a Lone Star tick (or certain other species) bites, it injects alpha-gal from its saliva into the human bloodstream. The immune system treats this as a threat and produces IgE antibodies against it. Subsequently, every time the person eats red meat or dairy containing alpha-gal, these antibodies trigger a mast cell response — an allergic reaction, sometimes severe, that can include hives, gastrointestinal distress, or anaphylaxis.
As many as 450,000 people in the US may be affected. The condition was only first described in 2009, and commercially available testing became available in 2012. Many physicians are still unaware of it. Diagnosis is confirmed by a blood test showing elevated alpha-gal specific IgE antibodies.
Alpha-gal allergy can remit over time if the person avoids further tick bites. However, subsequent tick bites can restimulate the immune response and worsen the allergy. The condition affects not just red meat but can include dairy products, gelatin, and some medications derived from mammalian tissues — including certain cardiac stent coatings and some cancer drugs that use alpha-gal-containing materials. People with AGS who require such medications need to notify their medical team.
Mycoplasma — the chronic illness amplifier
Mycoplasma species are the smallest known bacteria capable of self-replication. Because they have no cell wall, they are invisible to antibiotics like penicillin and cephalosporins that target the cell wall — a major reason why they often persist despite standard antibiotic treatment. Mycoplasma fermentans and Mycoplasma pneumoniae are the species most commonly discussed in the context of Lyme co-infection.
The evidence for tick transmission of Mycoplasma is less established than for the other organisms on this page — but it has been detected in tick populations, and many chronic Lyme patients test positive for Mycoplasma at specialist laboratories. Whether this reflects tick transmission, prior independent infection, or immune dysfunction that allows normally controlled Mycoplasma to reactivate is not yet fully clear.
What is clinically relevant is that Mycoplasma infections, when persistent, can cause chronic fatigue, widespread muscle pain, neurological symptoms, and immune dysregulation that significantly overlaps with — and potentially amplifies — Lyme disease presentations. Doxycycline and azithromycin, both commonly used in Lyme treatment, also have activity against Mycoplasma — which may partly explain why some patients improve on these regimens even when Lyme itself is uncertain.
Mycoplasma's role as a tick co-infection remains an area of active investigation and genuine uncertainty. It is worth knowing about — particularly for patients with persistent fatigue and inflammatory symptoms who test negative for other co-infections. Specialist laboratories including IGeneX offer Mycoplasma PCR testing. The clinical picture matters more than any single test result.
The tick as a vector ecosystem
Ticks are not simple vehicles for single infections. A single Ixodes tick can simultaneously carry Borrelia, Babesia, Anaplasma, TBE virus, Rickettsia, and Bartonella — a full spectrum of pathogens from different kingdoms of life. In practice, co-infections of two or three organisms from a single bite are documented regularly. The more time someone spends in tick habitat over years, the more exposures they accumulate.
This is not a reason for paralysing fear of the outdoors. It is a reason for intellectual honesty in clinical assessment. When a patient's symptoms don't fit neatly into any single diagnosis — when Lyme treatment helps some things but not others, when fatigue is disproportionate, when neurological symptoms appear unexpectedly — the possibility of multiple simultaneous infections deserves serious consideration.
The Lyme diagnosis is often a starting point, not a complete picture. Each of the organisms covered in this module — Bartonella, Babesia, Ehrlichia, Anaplasma, Rickettsia, TBE, and others — can be present alongside Lyme, can change the clinical picture dramatically, and requires specific attention rather than being dismissed as "part of Lyme." The goal is not to create anxiety, but to build the knowledge needed to ask the right questions — and to find practitioners who will engage seriously with those questions.
Sources & further reading
- ECDC — Tick-borne encephalitis factsheet and epidemiology, ecdc.europa.eu
- WHO — Tick-borne encephalitis overview, who.int
- CDC — Spotted fever rickettsioses and RMSF, cdc.gov
- CDC — Alpha-gal syndrome overview, cdc.gov
- CDC — Tick-borne encephalitis clinical signs, cdc.gov
- StatPearls — Rocky Mountain Spotted Fever, NBK430881
- Cleveland Clinic Journal of Medicine — Alpha-gal syndrome: recognising and managing a tick-bite related meat allergy, 2025
- PMC8606763 — Mammalian meat allergy emerges after tick bite: the alpha-gal syndrome
- PMC10383662 — TBE: comprehensive review of transmission, pathogenesis and clinical manifestations
Last updated: April 2026