General characteristics and morphology
The causative agents of bartonelloses belong to the family Bartonellaceae, class Alphaproteobacteria. These are Gram-negative rods characterized by pronounced pleomorphism (the ability to change shape). The bacteria are motile: they move using either a single polar flagellum or a tuft of flagella.
Bartonellae are extremely fastidious regarding nutrient media. Their cultivation requires complex media enriched with blood (e.g., chocolate agar) or embryonic chicken eggs. Optimal incubation conditions are a temperature of 37 °C and a carbon dioxide-enriched atmosphere (5% CO₂). Bacterial growth is slow and takes up to 7 days. Their biochemical activity is low: saccharolytic and proteolytic properties are practically unexpressed.
Pathogenesis and virulence factors
Although the pathogenicity factors of Bartonella are not yet fully understood, their clear tissue tropism is well established: they are intracellular parasites affecting erythrocytes, vascular endothelium, as well as skin and bone tissue cells.
Mechanism of cell invasion:
- The bacterium attaches to the membrane of a susceptible target cell.
- A specific water-soluble fraction, the "deformin factor", is released.
- This factor causes 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 pathogen entry, and an inflammatory response develops. Characteristic pathological processes in bartonelloses include lymphadenopathy (enlarged lymph nodes) and angiomatosis (pathological proliferation of blood vessels). Microscopy of affected tissues reveals bacteria arranged in chains.
Epidemiology and clinical forms
Depending on the species, bartonelloses can be zoonoses (with animals as the reservoir) or anthroponoses (with an infected human or carrier as the source). Infection occurs when the microbe enters the bloodstream through damaged skin—either by direct contact (scratches) or vector-borne transmission (through bites of blood-sucking arthropods).
There are three main clinical forms associated with specific Bartonella species:
- B. henselae (Cat scratch disease). Cats serve as the source. It is transmitted through bites and scratches, as well as cat flea bites. Pathogenesis involves the skin and regional lymph nodes with the development of local lymphadenitis.
- B. quintana (Trench fever, Volhynian fever, or quintan fever). A classic anthroponosis. The vector is the body louse. Infection occurs by rubbing the feces of infected lice into skin excoriations. The disease presents with recurring bouts of 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 are the vector. It is characterized by a biphasic course:
- Oroya fever (acute phase): characterized by severe anemia due to the direct hemolytic activity of the pathogen. Mortality reaches 40%.
- Verruga peruana (cutaneous phase): develops 1–2 months after the acute stage and manifests as multiple bleeding skin papules.
Diagnostics, treatment, and prevention
The main method of microbiological diagnostics is serological (detection of specific antibodies using ELISA or indirect immunofluorescence assay [IFA]).
Additional methods:
- Bacteriological: blood culture inoculation on specialized media, though it is informative only during the febrile period.
- Histological: examination of tissue biopsy specimens. When stained with Romanowsky-Giemsa, bartonellae appear as bright red chains.
Treatment is based on targeted antibiotic therapy. Drugs from the tetracycline, macrolide, and fluoroquinolone groups are used.
Prevention is exclusively non-specific, as vaccines against bartonelloses have not been developed. It includes treatment (sanitation) of domestic cats, vector eradication (sandflies, lice, and fleas), and adherence to general sanitary and hygienic standards.
Briefly: answers to topical questions
What virulence factors do Bartonellae have?
The virulence factors of Bartonellae are not yet fully understood, but specific mechanisms ensuring their invasion are known. The main factors include:
- "Deformin factor" — a water-soluble fraction that causes erythrocyte membrane deformation, its invagination, and subsequent formation of an intracellular vacuole containing the bacterium.
- Hemolytic activity (in B. bacilliformis) — the ability to directly destroy erythrocytes.
Vectors are easy to remember using the triad: the cat (B. henselae) scratches, the louse (B. quintana) lives in the trenches, and the sandfly (B. bacilliformis) bites in South America.
Class and exam questions
Why does Oroya fever lead to severe anemia with high mortality?
This is because the causative agent of Carrion's disease (B. bacilliformis) possesses direct hemolytic activity, meaning it is capable of directly destroying the patient's erythrocytes.
What do Bartonellae look like upon histological examination of affected tissues?
Upon tissue microscopy and Romanowsky-Giemsa staining of the biopsy, the bacteria are arranged in chains and stained bright red.
Are there vaccines against cat scratch disease or other bartonelloses?
No, specific prophylaxis (vaccines) against infections caused by Bartonellae has not been developed to date.
What else to study on this topic
- Mechanism of action of the "deformin factor" on the erythrocyte membrane
- The process of angiomatosis development in Bartonella infection
- Peculiarities of blood collection for blood culture during the febrile period
- Histological picture of verruga peruana
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