Bartonella is a genus of bacteria that causes bartonellosis in humans and animals. This bacterium is blood-borne and can persist in the bloodstream for long periods in a host. Because the infection circulates in the blood, questions have arisen about the potential for direct human-to-human transmission. This article examines whether Bartonella can be transmitted through sexual contact, based on the current understanding of its primary transmission routes.
Current Scientific Consensus on Sexual Transmission
The current scientific literature does not support that Bartonella species are transmitted between humans through sexual contact. Bartonella is a Gram-negative bacterium that primarily targets red blood cells and the cells lining blood vessels. Its nature as a blood-borne pathogen raises questions about its potential presence in other bodily fluids exchanged during sexual activity.
Detecting a pathogen’s DNA in a body fluid, such as blood, saliva, or semen, does not equate to successful transmission and subsequent infection. The primary established method for human-to-human spread of Bartonella quintana is through the human body louse. This process involves the louse’s feces being rubbed into a break in the skin, meaning this human-to-human route is mediated by a specific vector, not direct contact.
For Bartonella henselae, the most common species affecting humans, there is no accepted evidence for direct human-to-human spread, including sexual contact. The primary modes of acquiring this infection involve exposure to an infected animal and an arthropod vector. While Bartonella can be transmitted through blood transfusions, this direct inoculation of a large bacterial load differs fundamentally from contact during sexual intercourse. The lack of established cases or supporting epidemiological data means sexual transmission is not a recognized route of infection.
Established Zoonotic and Vector-Borne Transmission
The established methods for acquiring bartonellosis center on zoonotic transmission (from animals to humans) or vector-borne transmission via arthropods. These bacteria circulate between a mammalian reservoir host and a blood-feeding insect vector. The domestic cat is the most well-known reservoir, often harboring B. henselae without showing symptoms.
Infected cats transmit B. henselae to humans primarily through a scratch or bite. The bacteria are inoculated into the wound from the cat’s saliva or claws contaminated with flea feces. The cat flea, Ctenocephalides felis, is the main arthropod vector that spreads the bacteria between cats. This vector-mediated cycle maintains the bacteria’s presence and facilitates the occasional jump to a human host.
Other Bartonella species are spread by different vectors with specific host reservoirs. Bartonella quintana, which causes Trench Fever, is spread between humans by the human body louse. Bartonella bacilliformis, which causes Carrion’s disease, is transmitted exclusively by the bite of the infected sand fly (Lutzomyia species) in specific regions of South America.
The potential for ticks to serve as vectors for various Bartonella species is a topic of ongoing research. While Bartonella DNA has been detected in multiple tick species worldwide, a definitive transmission cycle from ticks to humans has not been clearly demonstrated for most species. Transmission of Bartonella in nature relies heavily on an arthropod intermediary that facilitates the movement of the bacteria from an infected reservoir to a new host.
Common Clinical Presentations of Bartonellosis
Infection with Bartonella species leads to various clinical presentations, collectively termed bartonellosis, ranging from self-limiting to severe. The most frequently recognized illness in the United States is Cat Scratch Disease, caused by B. henselae. This is characterized by the development of a small lesion, such as a papule or pustule, at the site of the scratch or bite.
The hallmark sign of Cat Scratch Disease is the subsequent swelling of lymph nodes, or lymphadenopathy, usually occurring in the area closest to the initial inoculation site. These enlarged lymph nodes can be painful and may persist for several weeks or months. Patients might also experience non-specific systemic symptoms, including a low-grade fever, general malaise, and fatigue.
Other Bartonella species cause distinct illnesses with differing symptoms. B. quintana is responsible for Trench Fever, an infection marked by recurrent episodes of high fever, chills, and severe body aches that typically last about five days per cycle. In contrast, B. bacilliformis causes Carrion’s disease, which has an acute phase called Oroya fever, characterized by severe anemia and fever due to the destruction of red blood cells.
In immunocompromised individuals, Bartonella infections can manifest as more severe conditions. These include bacillary angiomatosis, which involves the proliferation of blood vessels leading to tumor-like lesions on the skin or internal organs. Another serious complication is peliosis hepatis, where blood-filled cysts develop in the liver.