Bartonella is not Lyme disease. They are two separate infections caused by entirely different bacteria, spread by different vectors, and producing different symptoms. The confusion arises because the two infections are often discussed together in tick-borne illness communities, and some people may carry both at the same time. But medically, they are distinct conditions that require different approaches to diagnosis and treatment.
Two Different Bacteria
Lyme disease is caused by a spirochete bacterium called Borrelia burgdorferi, the most frequently tick-transmitted pathogen in the Northern Hemisphere. It enters the body through the bite of a blacklegged tick and spreads through connective tissues, joints, and sometimes the nervous system.
Bartonella is a completely separate genus of bacteria. The most common species affecting humans, Bartonella henselae, causes cat-scratch disease. Unlike Borrelia, Bartonella species are intracellular parasites that infect red blood cells directly, living inside them for prolonged periods. This ability to hide within blood cells is central to how Bartonella causes disease and evades the immune system.
They Spread Through Different Vectors
Lyme disease has a well-established transmission route: the bite of an infected Ixodes tick (commonly called a deer tick or blacklegged tick). This is not disputed.
Bartonella, on the other hand, spreads primarily through fleas, body lice, and sand flies, depending on the species. Bartonella henselae reaches people through cat scratches or bites from cats that carry infected fleas. Bartonella quintana spreads through the feces of human body lice. Bartonella bacilliformis is transmitted by sand fly bites.
The question of whether ticks can transmit Bartonella to humans remains unresolved. The CDC states there is currently no evidence that Bartonella spreads to people through tick bites. One laboratory study showed Bartonella could transfer from ticks to animals in controlled conditions, but whether this happens in nature is unknown. This is an important distinction: finding Bartonella DNA inside a tick is not the same as proving that tick can transmit it to a human during a bite.
How Symptoms Differ
Lyme disease typically begins with an expanding circular rash called erythema migrans (the “bull’s-eye” rash), appearing days to weeks after a tick bite. It progresses to joint pain, fatigue, and neurological symptoms like facial paralysis or memory problems if untreated.
Bartonella infections look quite different. Cat-scratch disease, the most common form, usually causes swollen lymph nodes near the scratch site, along with fever and fatigue. Small raised bumps called papules often appear at the site of the scratch about a week after contact. In most healthy people, cat-scratch disease resolves on its own within a few weeks.
More severe Bartonella infections can affect the heart valves, liver, spleen, and eyes. The bacteria can also produce neuropsychiatric symptoms. A study from North Carolina State University enrolled 33 participants with neuropsychiatric complaints ranging from sleep disorders and migraines to depression and anxiety. Of those who tested positive for Bartonella, 83% had developed unusual skin lesions during their illness, described as red, irregular linear marks on various parts of the body. In one striking case published in 2019, an adolescent boy diagnosed with rapid-onset schizophrenia was found to have Bartonella henselae infection. After antimicrobial treatment, all of his psychiatric symptoms resolved.
The “Stretch Mark” Rash Controversy
You may have seen images online of reddish streaked marks attributed to Bartonella, sometimes called “Bartonella striae.” These look similar to stretch marks, and dermatologists have pushed back on the connection. A dermatological review found that horizontal stretch marks on the lower back are associated with growth spurts, tall stature, and family history, not with bacterial infections. A Google image search for “rash bartonella” returns many photos that are likely ordinary stretch marks rather than true skin manifestations of infection. Confirmed Bartonella skin lesions tend to be papules or cutaneous eruptions, not the streaked marks commonly shared in online communities.
Why Both Are Hard to Diagnose
Part of the reason these two infections get conflated is that both can be frustratingly difficult to confirm with lab tests, and both can cause fatigue, pain, and neurological symptoms that overlap.
Lyme disease is typically diagnosed with a two-step blood test: an initial screening followed by a confirmatory test. This system works reasonably well for established infections but can miss early cases before the immune system has produced enough antibodies.
Bartonella testing is even less reliable. Standard antibody tests for Bartonella have poor sensitivity. In one study, the IgM antibody test caught only 43% of confirmed cases. A more detailed Western Blot method did somewhat better at 53% sensitivity, while a conventional antibody assay detected only 28% of cases. PCR testing, which looks for bacterial DNA directly, performs well on infected tissue (92% sensitivity on heart valve tissue, for example) but poorly on blood samples, catching only about 33 to 58% of confirmed infections. This means a negative Bartonella test does not reliably rule out infection, which contributes to diagnostic uncertainty and the temptation to attribute unexplained symptoms to a hidden Bartonella infection.
Co-infection: When Both Are Present
Some people do carry both Borrelia and Bartonella simultaneously, which is one reason the two get lumped together. Ticks can harbor multiple pathogens, and a single tick bite can potentially deliver more than one infection. Other co-infections associated with tick bites include Babesia (a parasite that infects red blood cells) and Anaplasma (another type of bacteria).
When someone with Lyme disease doesn’t improve as expected with standard antibiotic treatment, clinicians sometimes consider whether a co-infection could be complicating the picture. However, because Bartonella’s role as a tick-transmitted pathogen is not confirmed, its status as a true “Lyme co-infection” remains debated in mainstream medicine. The Lyme disease community and some clinicians treat the two as related threats, while the CDC and most infectious disease specialists maintain that Bartonella’s primary vectors are fleas and lice, not ticks.
Different Treatment Approaches
Lyme disease is treated with antibiotics, and most people recover fully when treated early. The specific antibiotics used and the duration of treatment differ from what works against Bartonella, which is another reason it matters to distinguish between the two.
Most cases of cat-scratch disease in healthy people clear without antibiotics. More serious Bartonella infections, particularly those involving the heart or nervous system, require targeted antibiotic therapy that can last weeks to months. The choice of antibiotics is different from Lyme treatment because the bacteria behave differently: Bartonella lives inside red blood cells, making it harder for certain drugs to reach.
If you suspect you have either infection, the distinction matters for getting the right treatment. Telling your doctor about specific exposures, whether that’s a tick bite in a wooded area or a scratch from a cat with fleas, helps narrow down which pathogen is more likely and which tests to order.