Bartonella is a bacterial infection that often appears alongside Lyme. In the US there is no current evidence that ticks transmit it, and the question is still under investigation. The proven routes are cat scratches and bites, cat-flea feces, and body lice. It is hard to detect, which is why a thorough Lyme workup checks for it properly.
Bartonella is a bacterial infection that shows up alongside Lyme in many complex cases, though in the US there is no current evidence that ticks transmit it. The bacteria live inside red blood cells and the cells that line blood vessels. That is part of why the infection can persist quietly for a long time. More than a dozen Bartonella species can infect humans. The one most people have heard of is cat scratch disease, caused by Bartonella henselae.
It earns the co-infection label because it keeps appearing in the same patients who have Lyme, not because the same tick carries both. That distinction matters for how you get tested and treated, and it is where most of the online story gets Bartonella wrong.
The established routes of human infection are cat scratches and bites, cat-flea feces, and body lice, not tick bites. Bartonella henselae spreads through a scratch or bite from a cat carrying flea dirt. Bartonella quintana, the cause of trench fever, spreads through body lice. A third species travels by sandfly in parts of South America.
The tick question is where the confusion starts. Some studies have found Bartonella DNA in ticks, and that fact gets read as proof. Carrying a fragment of DNA is not the same as passing a live infection during a bite. In 2024, CDC researchers tested 1,641 blacklegged ticks across 23 states and found none. Transmission has been shown only in a European tick species under laboratory conditions, never for the US tick or for natural spread to people. A CDC review reached the same bottom line years earlier, that tick transmission of Bartonella has not been established. The research is inconclusive, no US tick transmission has been proven, and the question remains an ongoing subject of investigation.
| Claim | Evidence status | What the evidence shows |
|---|---|---|
| Cat scratches and bites, cat-flea feces, and body lice transmit it | Established | These are the recognized human routes. Cat scratch disease is the most common form. |
| Ticks transmit it to people in the US | Not proven, under study | A 2024 CDC survey found no Bartonella in 1,641 blacklegged ticks across 23 states. Carrying DNA is not proof of transmission, and the question remains under investigation. |
| It occurs alongside Lyme in patients | Observed, rate unsettled | The two turn up together often enough to warrant checking. The exact co-occurrence rate is not settled. |
| It causes serious disease (heart valves, retina) | Established | Bartonella is a recognized cause of blood-culture-negative endocarditis and can infect the retina. |
| It causes sudden mood and cognitive symptoms | Investigational | Early, small studies suggest a possible link. It is not proven to be a cause, and the researchers have testing-lab ties. |
Bartonella and Lyme keep turning up in the same patients with the same symptoms, so a workup that skips it can leave real illness untreated. The overlap is fatigue, brain fog, joint pain, and mood changes, the same picture that sends people from specialist to specialist. Someone who spends time outdoors and around animals can be exposed to both, through different routes.
How often the two occur together is not settled. Bartonella co-occurs with Lyme, and is missed, often enough to warrant testing in the right context.
At Indigo Integrative Health Clinic, we evaluate for co-infections like Bartonella when we work up a suspected Lyme case. We do not lean on narrow guidelines that reserve co-infection testing for the sickest patients.
Bartonella can affect the skin, eyes, heart, nerves, and mood, and its symptoms overlap heavily with Lyme, which is part of why it gets missed. The evidence behind them varies. Some are well documented in the medical literature, some are reported associations, and some are still investigational. Symptoms can include:
The skin, mood, and chronic-pain symptoms lower on this list come from patient reports and small studies. Many of these symptoms overlap with Lyme and other co-infections, which is how one infection gets treated while another is missed.
Bartonella persists inside red blood cells and blood-vessel walls at low levels, and it cycles in and out of the bloodstream, so a single blood test misses it often. The infection rises and falls in the blood in waves, which means a draw can land on a low-level day and read negative. Antibody testing for Bartonella has limited and variable sensitivity. It can support the diagnosis in some forms of infection, but a negative result does not settle the question.
A negative result is not proof you are clear. It can mean the sample was taken on a low-level day, or that the method was not sensitive enough to catch a low-level infection.
Bartonella testing has limits, and no single test rules the infection in or out. PCR looks for the bacteria's DNA directly, but a negative blood PCR does not rule out infection, especially when bacterial levels are low. Antibody testing can support the diagnosis in some forms of Bartonella infection, though results vary by species, timing, and assay. The right test depends on the symptoms, the suspected species, and the type of illness.
What matters more than any brand is what the test does and where it runs. Look for a CLIA-certified laboratory and a testing plan that matches the suspected species and form of illness. A clinician may use serology, PCR, or both, depending on the case. At Indigo Integrative Health Clinic, we use more sensitive antibody testing and direct DNA testing when we evaluate for co-infections. We choose the method that fits the case.
Documented Bartonella infection is treated with a specific combination of antibiotics, and the single-drug course used for a routine Lyme case does not reliably clear it. Mild cat scratch disease in an otherwise healthy person often resolves without treatment. Serious or spreading infection is different. It calls for more than one drug, given longer, in a regimen built for Bartonella rather than for the Lyme bacteria.
The lingering cases are where the medical societies disagree. Mainstream guidelines treat infection that is clearly documented. The Lyme-literate approach considers longer treatment for a presumed chronic infection that standard testing struggles to confirm, and that approach goes beyond what current guidelines endorse. A Lyme-literate provider can walk you through where your own case falls.
A prior negative Bartonella test does not clear you, because the testing has limits, so symptoms that linger after Lyme treatment deserve a second look. A short appointment and a single test cannot catch everything a complex case can hold. If you followed your Lyme treatment and still feel unwell, a co-infection like Bartonella may have been missed. The medicine used for Lyme may also have done nothing for it.
At Indigo Integrative Health Clinic, we evaluate for co-infections like Bartonella when we work up a suspected Lyme case across Washington DC, Maryland, and Virginia. A complimentary 20-minute Discovery Call is where every Indigo patient starts. A team member reviews your symptom history, your past testing, and what you have already tried. You get a clear read on whether a closer look makes sense, and what a fuller workup would check for. It costs nothing and commits you to nothing. Visits are virtual, so you can work with us from anywhere in the DMV. You can book a free Discovery Call here.
This content is provided by Indigo Integrative Health Clinic for educational purposes only. It does not constitute medical advice, a diagnosis, or a treatment recommendation, and does not establish a provider-patient relationship. Individual health conditions vary — information presented here may not apply to your specific situation. Always consult a qualified, licensed healthcare provider before making decisions about your health, medications, supplements, or treatment plan.
Bartonella is a bacterial infection that often appears alongside Lyme. In the US there is no current evidence that ticks transmit it, and the question is still under investigation. The proven routes are cat scratches and bites, cat-flea feces, and body lice. It is hard to detect, which is why a thorough Lyme workup checks for it properly.
Babesia is a malaria-like parasite carried by the same tick that carries Lyme. Because it is a parasite and not a bacterium, the antibiotics typically used for Lyme have no effect on it. It is seldom tested for, so people can finish Lyme treatment, still feel sick, and not understand why.
The CDC classifies Washington DC, Maryland, and Virginia as high-incidence areas for Lyme. Standard two-tier blood testing catches only 22 to 36 percent of early infections, so a negative result does not rule Lyme out when symptoms are present. Free state and county programs identify a tick's species but do not test it for disease, and broader co-infection testing is not routinely ordered.
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