Bartonella is a genus of bacteria that infects humans and animals, causing illnesses collectively known as Bartonellosis. These bacteria often reside within red blood cells and the lining of blood vessels. Transmission is complex, typically involving intermediary organisms or direct contact with an animal reservoir. The possibility of human-to-human spread, particularly through sexual contact, is a point of ongoing discussion and scientific inquiry.
Established Transmission Pathways
The established routes of Bartonella transmission are primarily zoonotic, meaning the infection is passed from animals to humans through a vector. These vector-borne pathways involve blood-feeding arthropods like fleas, lice, and sandflies. Bartonella henselae, the cause of Cat Scratch Disease, is commonly transmitted to humans following a scratch or bite from a cat infected with flea feces. The infection occurs when contaminated flea material is rubbed into a break in the skin.
Another species, Bartonella quintana, which causes Trench Fever, is spread from person to person by the human body louse (Pediculus humanus), making humans the main reservoir for this specific bacterium. Bartonella bacilliformis, the agent of Carrion’s Disease, is spread by the bite of infected sandflies in specific regions of South America. Although Bartonella DNA has been detected in ticks globally, the Centers for Disease Control and Prevention (CDC) states there is no definitive evidence proving ticks can transmit the infection to people. The established transmission cycle relies on transfer via blood-sucking arthropods or direct inoculation from an animal reservoir.
Sexual Transmission Research and Consensus
Bartonella is currently not classified as a sexually transmitted infection (STI) by major public health organizations. There is a lack of definitive epidemiological data supporting sexual transmission as a standard route of spread. Scientific investigation into non-vector, human-to-human transmission, including sexual contact, remains limited. The core challenge is the lack of clinical studies that specifically track infection spread between sexual partners.
Research has focused on whether the bacteria can be found in human reproductive fluids, as the presence of a pathogen in semen or vaginal secretions is a prerequisite for sexual transmission. However, there is no widely published research confirming the detection of viable Bartonella in human semen or vaginal secretions. The bacteria’s preference for residing in red blood cells and the lining of blood vessels means they are primarily blood-borne, which makes their sustained presence in reproductive fluids less likely than for certain other bacteria.
A parallel is sometimes drawn to other vector-borne diseases that can cause chronic bacteremia, where the question of sexual transmission is also debated. In those cases, the mere detection of a pathogen’s DNA in a fluid does not automatically prove it can be transmitted and cause disease in a partner. The current public health consensus maintains that prevention methods for Bartonellosis should remain focused on avoiding exposure to arthropod vectors and infected animal reservoirs, particularly cats and their fleas.
Clinical Picture of Bartonellosis
The diseases caused by Bartonella species, collectively termed Bartonellosis, present a wide and often non-specific spectrum of clinical manifestations. The severity of the illness depends on the specific Bartonella species involved and the immune status of the infected individual. The most common form in the United States is Cat Scratch Disease, which typically begins with a papule at the site of inoculation, followed by localized swelling of the lymph nodes (lymphadenopathy).
More serious, systemic forms of the infection can occur, particularly in individuals with compromised immune systems. These include Bacillary Angiomatosis, which causes the proliferation of blood vessels leading to tumor-like lesions on the skin and internal organs. Another serious condition is Peliosis Hepatis, characterized by blood-filled cysts in the liver and spleen. A significant complication seen across several species is endocarditis, a severe infection of the heart lining and valves that can be difficult to diagnose because blood cultures often remain negative.
Patients may also experience non-localized symptoms, such as chronic or relapsing fevers, persistent fatigue, muscle aches, and joint pain, which can lead to misdiagnosis. Some individuals develop neurological issues, including headaches, dizziness, and eye problems like neuroretinitis. A hallmark skin manifestation for some chronic infections is the appearance of stretch mark-like lesions, or subcutaneous nodules.