By Jennifer C. Miller, PhD, Vice President of Clinical & Scientific Operations, Galaxy Diagnostics
Summary: Babesia, Bartonella, and Borrelia are three of the most clinically important tick-borne pathogens in North America, while simultaneously being three of the most diagnostically elusive. Each has evolved distinct biological strategies to hide from the host immune system, suppress the antibody response, and persist in tissues where standard testing cannot reliably reach them. This post, drawn from a Galaxy Diagnostics clinical webinar, explains the specific tick-borne pathogen immune evasion mechanisms each pathogen uses, why those mechanisms cause conventional serology and PCR to underperform in chronic presentations, and what a biology-informed testing strategy looks like in practice. Clinicians who understand why these pathogens evade detection are better positioned to know when to test, what to test with, and how to interpret results that don’t fit the textbook picture.
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Every clinician working with complex, chronic patients has encountered this moment: the labs come back negative, but the patient in front of you is clearly not well. The fatigue persists. The neurological symptoms don’t resolve. The standard answers don’t fully explain the clinical picture.
When that happens with tick-borne infections, there’s a reason. And it isn’t that the pathogens aren’t there.
It’s that these organisms have spent millennia learning how not to be found.
Understanding how they do that isn’t just academic. It changes how you test, what you test for, and how you interpret the results you get back. This post walks through what we currently know about the immune evasion strategies of three of the most clinically important and diagnostically elusive tick-borne pathogens: Babesia, Bartonella, and Borrelia species, and what those mechanisms mean for detection and diagnosis in real patients.
The Biology Is Not What You Were Taught
Most clinicians were trained on the textbook picture: Babesia microti causes acute disease. You have fever, hemolysis, parasitemia, you run a PCR, you catch it, you treat it. Done.
The problem is that the picture is incomplete. We now know that chronic babesiosis is far more common than previously appreciated, and that both small and large Babesia species can cause persistent, low-yield infection. In chronic presentations, you may not see fever or high parasitemia. PCR may not catch it. Antibody testing at the species level can miss it entirely and, in some cases, lead to misidentification.
The same mismatch between training and clinical reality applies to Bartonella and Borrelia. These are not simple organisms following a predictable course. They adapt. They evade. And the biology of that evasion has direct implications for every diagnostic decision you make.
Babesia: How This Tick-Borne Parasite Hides in Red Blood Cells
Babesia parasites infect red blood cells and have evolved sophisticated strategies to avoid being swept through the bloodstream and cleared by the spleen.
One of the most important of these is cytoadherence, the ability of parasite-infected red blood cells to stick to the capillary endothelium. By anchoring infected cells to vessel walls, the parasite avoids the shear forces of blood flow and makes it harder for host antibodies to tag the cells for splenic clearance. Research published in Frontiers in Cellular and Infection Microbiology confirms that cytoadherence allows the pathogen to complete its life cycle within the red blood cell without ever traversing the spleen, making it one of the most effective immune evasion mechanisms in parasitic biology. Some Babesia species go even further, varying the antigens expressed on the red blood cell surface to continuously keep the immune system guessing.
In sequestering Babesia species, there is another mechanism at work: fibrin nest formation. Through a cascade involving outer surface protein fragments, inflammatory cytokines including IL-6, and an acute-phase response in the liver, infected red blood cells become coated in fibrin. These fibrin-encased cells then clump together in a process called rosetting, forming dense nests within capillaries that are physically difficult for antimicrobial therapies to penetrate. A review in PMC examining Babesia microti genomics and pathogenesis documents how this excessive erythrocyte adherence contributes to babesiosis complications and highlights why chronic presentations are so much harder to catch than acute ones.
This isn’t just a diagnostic problem. It’s also a formidable treatment challenge. For patients who have been on antiparasitic therapy without improvement, it’s worth asking whether their Babesia is sequestered in fibrin nests where the medication may not be reaching it.
When sequestering Babesia breaches the blood-brain barrier, which has been documented in mouse model studies and observed in published clinical cases, the neurological consequences are significant: headache, numbness, fatigue, confusion, and neuropsychiatric manifestations, including hallucinations.
What this means for testing: Indirect serology for Babesia can result in species misidentification, particularly as additional species are increasingly recognized in human infection. Chronic babesiosis is harder to catch with standard methods precisely because parasitemia is lower and the immune response is more muted. Direct detection via molecular methods at the genus level is a clinically important complement to serologic testing. Galaxy’s Suspected Tick-Borne Bundle includes genus-level digital PCR that provides detection coverage across Babesia species, not just the most commonly tested ones.
Bartonella: Why a Single Blood Draw Isn’t Enough
Bartonella is in a category of its own when it comes to immune evasion. It is an intracellular pathogen with an extensive arsenal of virulence determinants, and it uses all of them.
After gaining entry through a blood meal, contaminated flea feces, or a scratch/bite from an infected host, Bartonella engages in an immediate tug-of-war with dendritic cells and macrophages in the skin. Once inside those immune cells, it has commandeered a vehicle for systemic dissemination. It cycles into the blood, binds to red blood cells, replicates, and is released, and then retreats to the tissues to avoid immune-mediated killing. This cycle repeats approximately every five to seven days.
The implications of this cyclical bacteremia are profound, both for understanding why symptoms wax and wane and for understanding why a single blood draw often fails to detect Bartonella infection. Peer-reviewed research published in Microbiology Spectrum describes this stealth infection strategy in detail, documenting how the bacteria colonize a primary vascular niche before being seeded periodically into the bloodstream.
Within host cells, Bartonella deploys a series of strategies to avoid destruction. A 2024 review in Virulence catalogues the full spectrum of these mechanisms: it prevents phagocytosis by neutrophils, triggers biofilm formation, packages itself inside Bartonella-containing vacuoles that prevent fusion with the lysosome, and blocks infected cells from undergoing apoptosis. This prevents the host’s most basic cellular defense (the ability to sacrifice an infected cell to trap the bacteria) from working as intended.
Bartonella also engages in antigenic variation, cycling through different outer membrane proteins to continually present a moving target to the adaptive immune response. And critically, it manipulates cytokine signaling, suppressing pro-inflammatory cytokines and triggering anti-inflammatory ones, to mute the host’s danger alarm and create immune tolerance.
In some species, this immune manipulation goes further still. Bartonella can stimulate the production of vascular endothelial growth factor, driving endothelial cell proliferation and the formation of vascular tumors. It is also capable of breaching the blood-brain barrier through multiple mechanisms, including neurotoxin production, direct cellular damage, and the triggering of autoimmune responses, producing neurological and neuropsychiatric symptoms that are wide-ranging and frequently misattributed. For a deeper look at Bartonella’s neurological and systemic impact across real patient cases, see Galaxy’s companion post, Bartonella: The Blind Spot Pathogen.
What this means for testing: Because Bartonella cycles in and out of the blood on a roughly five-to-seven-day window, a single blood draw gives you one chance to catch it during that span. Galaxy’s triple draw protocol (three serial blood draws collected across that five-to-seven-day period) is designed to give clinicians three chances rather than one. When combined with sample enrichment to increase diagnostic yield and run in parallel with Bartonella serology to capture the antibody response during periods when the bacteria are in tissues, you are using the biology of the pathogen to your advantage rather than working against it. Learn more about the science behind Galaxy’s approach at the Bartonella Testing Bundle page.
Borrelia and Lyme Disease: Why Standard Testing Misses Chronic Infection
Lyme Borrelia takes a fundamentally different approach from the other two pathogens. Notably, they don’t produce toxins or rely on type III/IV secretion systems. Their virulence is almost entirely immune-mediated, and their persistence depends on their extraordinary ability to “change” who they appear to be.
Borrelia enter the skin and immediately face an immune response from dendritic cells and Langerhans cells in the dermis. Many die there. The ones that survive transiently enter the bloodstream for a very narrow window and must quickly adhere to capillary endothelium to avoid being swept away. They then extravasate into tissues, changing their protein expression at each step of the journey to adapt to the local environment.
In the blood, Borrelia inhibit key components of the complement system. In the tissues, they express proteins that bind collagen, fibronectin, integrins, laminin, and glycosaminoglycans(the structural scaffolding of the host) and use these bindings to persist and spread. They release antigens into the blood that sequester host antibodies before those antibodies can do their job. They trigger anti-inflammatory cytokine production to establish immune tolerance. And they change their surface proteins continuously, so the immune system is perpetually responding to a target that has already moved. A comprehensive review in Microorganisms titled “The Brilliance of Borrelia” details how B. burgdorferi disables the germinal center response, inhibits complement at multiple pathway steps, and employs antigenic variation to sustain persistent infection.
Borrelia also alter their physical form. In addition to their normal spiral (planktonic) morphology, they can distort their outer membranes into cyst forms or blebs (also called round bodies), configurations that allow them to avoid antibiotic detection and facilitate dissemination to distant tissue sites. They also swim faster than immune cells. And they can crawl between endothelial cells to cross the blood-brain barrier without disrupting it, resulting in a stealthy entry that produces cognitive and neuropsychiatric manifestations without the inflammatory footprint you might expect.
One of the most underappreciated aspects of Borrelia biology is its effect on the adaptive immune response itself. Lyme Borrelia are known to subvert class switching, the process by which the immune system transitions from producing short-lived, low-affinity IgM antibodies to producing long-lived, high-affinity IgG. Research published in Frontiers in Immunology demonstrates that B cell responses to B. burgdorferi are suboptimal, with germinal centers collapsing early and IgM production dominating in place of class-switched, tissue-penetrating IgG. In some patients, this means the antibody response never fully matures. They produce only IgM. Or they produce IgG but with incomplete affinity maturation, yielding weaker antibodies and thus a weaker test signal.
This is not a laboratory error. It is the pathogen doing what it was designed to do.
What this means for testing: Using IgG serology alone as the primary diagnostic tool for Lyme disease has a structural limitation. Long-lived antibodies can persist well after pathogen clearance, making it difficult to distinguish current infection from prior exposure. And in patients whose immune response has been subverted, serology may simply be absent even in the presence of active infection. Galaxy’s Lyme Borrelia Direct Detect urine antigen test detects proteins shed by Lyme Borrelia directly, including outer surface protein fragments that are released during bacterial growth and cleared through the kidneys, providing a measure of current pathogen presence that is independent of the antibody response.
The Clinical Takeaway: Use the Biology
These pathogens are not failing to evade your tests by accident. The immune evasion mechanisms described here (such as cytoadherence, fibrin nest sequestration, intracellular concealment, antigenic variation, and immune suppression) are the reasons standard tick-borne disease testing often underperforms in chronic presentations.
But understanding those mechanisms also provides leverage. The cyclical bacteremia of Bartonella tells us to serially collect blood samples within a given time period. The shedding of Lyme Borrelia antigens into host urine tells us to test there directly.
The patients who benefit most from this kind of thinking are often the ones who have already been through the standard workup. The ones where the usual labs have come back negative due to the tools these institutions are using not being as specific as what Galaxy Diagnostics’ uses, meaning the clinical picture has not been resolved. These are the patients who deserve a more complete answer.
At Galaxy Diagnostics, that is exactly who we are built to serve.
Want to go deeper? Watch the full webinar, “How Vector-Borne Pathogens Evade the Immune System,” presented by Dr. Jennifer Miller, in the Galaxy Diagnostics Clinical Learning Center. To learn more about Galaxy’s testing approach or to speak with a member of our clinical team, visit galaxydx.com.
Frequently Asked Questions
Why do standard tick-borne disease tests often come back negative in chronic patients?
Standard testing, particularly single-draw conventional PCR and IgG serology, was designed around the biology of acute infection, not chronic, low-yield presentations. In chronic tick-borne disease, pathogen abundance in the blood is much lower, the immune response may be suppressed or subverted by the pathogen itself, and microorganisms like Bartonella spend the majority of their time in tissues rather than the vascular compartment. Each of the three pathogens covered here has evolved specific mechanisms to evade detection: Babesia sequesters infected red blood cells in fibrin nests away from antibodies and drugs; Bartonella cycles in and out of the blood at roughly five-to-seven-day intervals; and Borrelia actively disrupts the class-switching process that produces the high-affinity IgG antibodies standard testing is designed to look for. A negative result from conventional testing doesn’t mean the pathogen isn’t there. It often means the test wasn’t designed to find it at the stage and level present.
What is fibrin nest formation, and why does it matter for Babesia treatment?
Fibrin nest formation is a sequestration strategy used by certain Babesia species. Through a cascade involving outer surface protein fragments and inflammatory signaling, parasite-infected red blood cells become coated in fibrin and clump together through a process called rosetting, forming dense masses within capillaries. These fibrin nests are physically resistant to antiparasitic drug penetration. For patients on antiparasitic therapy without clinical improvement, sequestration in fibrin nests may explain why treatment is failing to reach the parasites. The nests also shield the parasites from antibody tagging and splenic clearance, compounding both the diagnostic and the therapeutic challenge. Finally, while not discussed in great detail, these nests can also potentially harbor other pathogens (e.g. Bartonella), making co-infections a serious concern and complication.
Why does Bartonella require serial blood draws rather than a single test?
Bartonella induces a relapsing bacteremia, cycling into the bloodstream at roughly five-to-seven-day intervals before retreating to tissue niches to evade immune-mediated killing. A single blood draw captures only one moment in that cycle. If blood is collected during the tissue phase, no bacteria will be detectable in the sample, regardless of how sensitive the assay is. Galaxy’s triple draw protocol collects serial samples across that five-to-seven-day window, providing three independent chances to capture Bartonella during active bacteremia. When combined with enrichment culture and digital PCR, the probability of detection increases substantially compared to any single-draw approach.
Can Lyme disease be present even with a negative antibody test?
Yes. Lyme Borrelia are known to disrupt the germinal center response, the biological process through which the immune system refines antibody production and transitions from short-lived IgM to high-affinity, long-lived IgG. In some patients, this subversion is significant enough that the standard two-tier serologic test, which depends on detecting IgG antibodies, produces a negative result even during active infection. Seroconversion can also be delayed by weeks in early disease. Galaxy’s Lyme Borrelia Direct Detect urine antigen test was developed specifically to address this limitation, detecting outer surface protein fragments shed by Lyme Borrelia species directly in urine, independent of the antibody response.
What is the difference between direct and indirect tick-borne disease testing?
Indirect testing detects the host’s immune response to infection, primarily through antibody measurement in serology. It is most useful when the infection has been present long enough for a robust immune response to develop, and when that immune response hasn’t been suppressed by the pathogen or the patient’s underlying condition. Direct testing detects the antigens that the Lyme Borrelia sheds or its molecular components, either through PCR targeting pathogen DNA or through antigen tests detecting pathogen-derived proteins. Direct testing is more useful in early infection, in cases where the immune response has been disrupted, or when a clinician needs to assess current pathogen presence rather than historical exposure. Both approaches have clinical value, and the strongest diagnostic strategy for chronic tick-borne infections pairs both methods rather than relying on one alone.
Which tick-borne pathogens are most likely to co-occur in the same patient?
Babesia, Bartonella, and Borrelia share overlapping vectors, particularly the Ixodes scapularis tick or other arthropods, and frequently co-occur in patients with complex chronic presentations. Research has documented synergistic effects between these organisms, with co-infection compounding clinical severity and complicating the immune response in ways that single-pathogen infection does not. A patient whose neurological symptoms are not resolving on Lyme therapy may have an undetected Babesia or Bartonella co-infection driving the underlying persistence. Testing that is limited to a single microorganism misses this complexity. Galaxy’s Suspected Tick-Borne Bundle is designed to assess all three genera simultaneously, reflecting the biological reality of how these infections present in clinical practice.
How does understanding immune evasion change how clinicians should approach testing?
It changes the entire framing of a negative result. If a clinician knows that Bartonella cycles out of the blood every five to seven days, a negative single-draw PCR is not reassuring. It is expected. If a clinician knows that Borrelia can suppress IgG class switching, a negative IgG-based serology is not a rule-out. It is a limitation of the test applied to a pathogen that disrupts the very mechanism the test depends on. Immune evasion biology doesn’t just explain why patients remain sick. It explains which tests to order, how to collect samples, what combination of testing methods provides adequate coverage, and how to communicate to patients why a negative result doesn’t mean there is nothing to worry about. Testing strategy should be designed around pathogen biology, not around what is easiest to order.