General Characteristics and Morphology
Pathogens causing bartonelloses belong to the family Bartonellaceae, class Alphaproteobacteria. These are Gram-negative rods characterized by marked pleomorphism (the ability to alter shape). The bacteria are motile, utilizing either a single polar flagellum or a tuft of flagella for movement.
Bartonellae are extremely fastidious regarding nutrient media. Complex blood-enriched media (such as chocolate agar) or embryonated eggs are used for their cultivation. Optimal incubation conditions are a temperature of 37 °C and a carbon dioxide-enriched atmosphere (5% CO₂). Bacterial growth is slow, taking up to 7 days. Biochemical activity is low; saccharolytic and proteolytic properties are practically absent.
Pathogenesis and Virulence Factors
Although the pathogenicity factors of Bartonella are not yet fully understood, their distinct tissue tropism is well-documented: they are intracellular parasites targeting erythrocytes, vascular endothelium, skin cells, and bone tissue.
Mechanism of cell invasion:
- The bacterium attaches to the membrane of a susceptible target cell.
- A specific water-soluble fraction termed the "deformin factor" is released.
- This factor induces deformation of the erythrocyte membrane, leading to its invagination.
- A vacuole containing the bacterium is formed inside the cell.
Microbes accumulate at the site of entry, prompting an inflammatory response. Characteristic pathological processes in bartonelloses include lymphadenopathy (enlarged lymph nodes) and angiomatosis (pathological proliferation of blood vessels). Microscopy of affected tissues reveals the bacteria arranged in chains.
Epidemiology and Clinical Forms
Depending on the species, bartonelloses can be zoonoses (with an animal reservoir) or anthroponoses (where the source is an infected human or carrier). Transmission occurs when the microbe enters the bloodstream through broken skin—either via direct contact (scratches) or vector-borne transmission (bites of hematophagous arthropods).
Three main clinical forms are associated with specific Bartonella species:
- B. henselae (Cat-scratch disease). Cats serve as the reservoir. Transmitted via bites and scratches, as well as cat fleas. Pathogenesis involves the skin and regional lymph nodes with the development of local lymphadenopathy.
- B. quintana (Trench fever). A classic anthroponosis. The vector is the body louse (Pediculus humanus humanus). Transmission occurs by rubbing infected louse feces into skin abrasions. The disease presents with relapsing fever, rash, myalgia, and neurological symptoms. The prognosis is favorable, but prolonged carriage is possible.
- B. bacilliformis (Carrion's disease). Found in South America. Rodents serve as the reservoir, and sandflies (Phlebotomus species) act as the vector. It features a biphasic course:
- Oroya fever (acute phase): characterized by severe anemia due to the direct hemolytic activity of the pathogen. Mortality can reach 40%.
- Verruga peruana (eruption phase): develops 1–2 months after the acute stage, manifesting as multiple bleeding skin papules.
Diagnosis, Treatment, and Prevention
The primary method of microbiological diagnosis is serological testing (detecting specific antibodies via ELISA or indirect immunofluorescence assay [IFA]).
Additional methods include:
- Bacteriological: blood cultures on specialized media, though informative only during the febrile phase.
- Histological: examination of tissue biopsies. Staining with Giemsa stain reveals Bartonella as bright red chains.
Treatment relies on targeted antimicrobial therapy. Tetracyclines, macrolides, and fluoroquinolones are commonly used.
Prevention is strictly non-specific, as vaccines against bartonelloses are unavailable. Measures include the veterinary care and de-fleaing of domestic cats, vector control (sandflies, lice, and fleas), and adherence to general sanitary and hygienic standards.