Bartonella is not rare. A 2014 study at Duke University and North Carolina State University found Bartonella DNA in 28% of veterinary workers — people in regular contact with cats and dogs. A significant proportion of people with chronic Lyme-like illness test positive for Bartonella at specialist labs. Yet mainstream medicine recognises bartonellosis almost exclusively as a self-limiting condition from a cat scratch. The reality is considerably more complex.
An intracellular bacterium that hides inside your cells
Bartonella are gram-negative, facultative intracellular bacteria — meaning they live and replicate inside the cells of their host, particularly inside red blood cells and endothelial cells lining blood vessels. This intracellular strategy is central to understanding why Bartonella is so difficult to detect, treat, and clear. Hidden inside cells, it is largely invisible to the immune system and to standard blood tests.
The genus has over 45 named species, of which at least 14 cause disease in humans. Three are the most clinically significant:
The most common Bartonella in humans and domestic animals. Primarily transmitted through cat scratches or bites contaminated with flea faeces. Causes cat scratch disease in most people — but also endocarditis, neuroretinitis, encephalitis, and chronic neuropsychiatric illness. Endemic worldwide; present in cats on every continent.
Historically associated with soldiers and crowded conditions. Transmitted by human body lice. Today primarily found in homeless urban populations. Causes relapsing fevers, severe shin bone pain, bacteremia, and culture-negative endocarditis — the most dangerous manifestation, frequently missed by standard cardiac workup.
Endemic to the Andes. Transmitted by sand flies. Two distinct phases: Oroya fever — severe haemolytic anaemia with historically high mortality — and verruga peruana, a later phase with vascular skin nodules. Regionally significant but rarely encountered outside South America.
Beyond these three species, research continues to document additional Bartonella species in both animals and humans. Dogs can carry at least six Bartonella species — all of which are human pathogens. Rodents, deer, rabbits, and other wildlife serve as reservoir hosts. As the research grows, so does the recognition that bartonellosis in humans is a significantly underappreciated public health problem — particularly in the context of tick-borne co-infections.
How Bartonella reaches humans
Bartonella is transmitted by arthropod vectors. The primary route is through flea faeces: when a flea bites and defecates on skin, bacteria in the faeces enter through the bite wound or through scratching. This is why cat scratches transmit Bartonella — the cat's claws are contaminated with flea faeces from grooming, not because the cat itself carries bacteria in its claws.
The CDC currently states there is "no evidence that Bartonella is spread to people through tick bites." This position reflects the absence of large-scale human studies — not the absence of evidence. Laboratory research has demonstrated Bartonella transfer from ticks to animals. Dermacentor ticks have been implicated in at least three documented human cases of B. henselae transmission. Multiple studies have detected Bartonella DNA in Ixodes ticks. Researchers across several institutions have identified ticks as probable vectors. The scientific picture suggests tick transmission occurs — the question is how frequently. Given that Bartonella is regularly found co-occurring with Lyme disease in the same patients, the relationship between tick bites and Bartonella deserves far more rigorous investigation than it currently receives.
Beyond arthropod vectors, transmission can also occur through direct animal contact. Cat and dog bites transmit Bartonella through saliva. A 2010 study concluded that "a history of an animal scratch or bite is not necessary for disease transmission" — suggesting that contact with flea-infested animals may be sufficient without a visible wound.
What Bartonella actually does to the body
Bartonella invades endothelial cells — the cells lining blood vessels throughout the body. This vascular tropism explains why its symptoms are so diverse and system-wide. It also infects red blood cells, creating cycles of bacteremia and tissue invasion. The result is an infection that can present very differently depending on the person's immune status, the species involved, and which organs are affected.
A key clinical pattern: symptoms cycle. Flares and remissions, waxing and waning — this cyclical behaviour is characteristic of Bartonella and is frequently mistaken for many other conditions or dismissed as psychosomatic.
- Anxiety — often severe and seemingly unprovoked
- Rage episodes disproportionate to triggers
- OCD-like behaviours and intrusive thoughts
- Treatment-resistant depression
- Brain fog and memory issues
- Panic attacks
- Hallucinations in severe cases
- Personality changes noted by family
- Stretch-mark-like streaks in unusual locations
- Bacillary angiomatosis — raised reddish-purple nodules
- Easy bruising or unusual skin fragility
- Swollen or tender lymph nodes
- Vascular headaches
- Peliosis hepatis — blood-filled liver cysts (severe)
- Culture-negative endocarditis (missed by standard testing)
- Burning foot pain — particularly characteristic
- Shin pain (especially B. quintana)
- Bone and joint pain
- Muscle aches
- Tender lymph nodes — head, neck, upper limbs
- Osteomyelitis in more severe cases
- Recurrent low-grade fever — cyclic pattern
- Profound fatigue
- Persistent headaches
- Night sweats
- Eye problems — neuroretinitis, uveitis
- Sore throat, general malaise
- Loss of appetite, weight changes
The skin clue — stretch marks that are not stretch marks
One of the most overlooked physical signs of Bartonella is the appearance of skin streaks (striae) closely resembling stretch marks — but appearing in places where stretch marks don't normally occur: upper arms, upper back, flanks, and torso sides, in people who have not gained or lost significant weight.
Research by Dr. Edward Breitschwerdt has documented these Bartonella-associated cutaneous lesions (BACL) in multiple studies. Biopsies confirmed a higher bacterial load in these lesions compared to surrounding skin, with disrupted vascularisation beneath them. They do not follow the plane of skin tension the way normal stretch marks do. They may appear quite suddenly.
In patients with neuropsychiatric symptoms, the presence of these unusual streaks in unexpected locations is a significant clinical clue worth photographing and bringing to a knowledgeable practitioner's attention.
Multiple peer-reviewed case reports document patients with Bartonella infection who were initially diagnosed with OCD, panic disorder, treatment-resistant depression, or psychosis — and who improved significantly when treated with antibiotics. A 41-year-old man developed complete personality change after a camping trip, with rage, irritability, and a swollen lymph node after removing three deer ticks. Lyme test was negative. After Bartonella-targeted treatment, his symptoms resolved. In children, acute-onset OCD, rage, and regression linked to Bartonella infection has been associated with PANS (Paediatric Acute-Onset Neuropsychiatric Syndrome). These are not isolated anecdotes — they represent a consistent pattern across independent researchers and clinical settings.
A stealth pathogen — designed to hide
Bartonella is not hard to miss by accident. It is well-adapted to evading detection at every level: from the immune response to standard laboratory testing.
Bartonella hides inside red blood cells and endothelial cells. Standard blood cultures look for bacteria floating freely in plasma — Bartonella is not there. Special enrichment culture media are required to detect it. A standard culture negative for Bartonella tells you almost nothing about whether the infection is present.
Even when Bartonella does circulate in the bloodstream, it does so intermittently. A blood draw on the wrong day may show nothing. Galaxy Diagnostics addresses this by using an enrichment medium to amplify bacterial load from a blood sample before running PCR — dramatically improving detection compared to direct PCR testing.
Bartonella actively modulates the host immune response. It suppresses inflammatory signals that would normally alert the immune system. This is why many infected people show completely normal inflammatory markers on routine bloodwork — and why standard antibody tests have poor sensitivity. The bacteria can be present and active while the immune response remains weak or delayed.
Medical education presents Bartonella almost exclusively as a self-limiting condition in children. A doctor who learned this is not looking for it as a cause of treatment-resistant depression in adults, unexplained rage episodes in teenagers, or culture-negative endocarditis. The narrow framing systematically excludes the broader clinical spectrum — and leaves countless patients without answers.
How to detect it — and what standard tests miss
Standard hospital laboratory testing for Bartonella is largely inadequate for chronic infection. A negative result at a standard lab cannot rule out infection. For chronic illness patients — particularly those with Lyme — specialist laboratory testing is the appropriate approach.
Given the limitations of all available Bartonella tests, clinical diagnosis remains important. A pattern of cycling neuropsychiatric symptoms, burning foot pain, unusual skin streaks, lymph node tenderness, and a history of tick bites, animal contact, or flea exposure — taken together — can justify a treatment trial even without a confirmed positive test. Many Lyme-literate physicians approach Bartonella diagnosis the same way they approach Lyme: by assessing the whole clinical picture, not waiting for a definitive lab result that may never come.
Treatment — what works and what doesn't
Bartonella treatment is more complex than treating standard acute bacterial infections. Its intracellular nature means antibiotics must penetrate cells to be effective — not all antibiotics do this. And because Bartonella can establish chronic infection, short treatment courses may suppress but not clear the infection, leading to relapse.
Rifampin (rifampicin) combined with doxycycline or azithromycin is the most commonly used combination in Lyme-literate practice. Rifampin has excellent intracellular penetration and is effective against Bartonella. Treatment duration is typically 4–6 weeks minimum for chronic infection; many ILADS clinicians treat for significantly longer depending on clinical response.
Bartonella treatment can provoke a Herxheimer reaction as bacteria die and release inflammatory compounds. This can temporarily worsen neuropsychiatric symptoms — increased anxiety, rage, or cognitive impairment. This reaction, unpleasant as it is, can itself be a diagnostic signal confirming active infection. Careful management of the die-off response is part of treatment.
Bartonella can relapse after antibiotic courses end, particularly in immunocompromised patients or those co-infected with Lyme. The cyclic nature of the infection means monitoring for several months after treatment completion is important. Some patients require multiple treatment courses before achieving sustained improvement.
The mainstream guidance for cat scratch disease — often no antibiotics at all, or a short course of azithromycin — is appropriate for a healthy person with mild lymphadenopathy who will recover on their own. It is not appropriate for chronic Bartonella infection with neurological involvement, co-infection with Lyme disease, or any patient whose immune system is struggling. These are different clinical situations that require different treatment approaches.
Bartonella and Lyme — when they occur together
Bartonella and Lyme disease co-infection is common in tick-borne illness patients. The presence of both infections simultaneously changes the clinical picture in important ways — and has direct implications for treatment.
Borrelia and Bartonella respond to different antibiotics. Doxycycline is a cornerstone of Lyme treatment but is only moderately effective against Bartonella. Rifampin is effective against Bartonella but not Lyme. A treatment protocol that adequately addresses Lyme may not touch Bartonella — and vice versa. This is why some patients improve on standard Lyme treatment and then plateau or relapse: the Bartonella co-infection is not being addressed.
In Lyme-Bartonella co-infection, the neuropsychiatric component is often driven more by Bartonella than by Borrelia. Research suggests that Lyme with Bartonella co-infection produces psychiatric syndromes more consistently than Lyme alone. If a patient has significant psychiatric or neurological symptoms that are not responding to Lyme-targeted treatment, adding Bartonella-targeted antibiotics sometimes produces dramatic improvement. This pattern — improvement of psychiatric symptoms with antibiotic treatment — is itself diagnostically informative.
Sources & further reading
- Breitschwerdt EB et al. — Bartonella-associated cutaneous lesions (BACL) in people with neuropsychiatric symptoms. Pathogens, 2020
- Breitschwerdt EB — Bartonellosis: One Health Perspectives for an Emerging Infectious Disease. ILAR Journal, 2014
- Schaller JL, Burkland GA, Langhoff PJ — Do Bartonella Infections Cause Agitation, Panic Disorder, and Treatment-Resistant Depression? MedGenMed, 2007
- AVMA — Bartonellosis: A zoonosis hidden in plain sight, 2021
- Galaxy Diagnostics — From Cat Scratch Disease to Bartonellosis
- IGeneX — Overview of Bartonella species and testing
- Cameron D — Bartonella and Lyme Disease: Symptoms and Treatment, danielcameronmd.com
- LymeDisease.org — The Bartonella clue hidden in plain sight, 2026
- Human Bartonellosis: An Underappreciated Public Health Problem? PMC6630881
Last updated: April 2026