Bartonella bacilliformis is a proteobacterium, Gram negative aerobic, pleomorphic, flagellated, motile, coccobacillary, 2–3 μm large and 0.2–0.5 μm wide and facultative intracellular bacterium.
The bacterium was discovered by the Peruvian microbiologist Alberto Barton in 1905, but it was not published until 1909. Barton originally identified them as endoglobular structures, which actually were the bacteria living inside red blood cells. Until 1993, the Bartonella genus contained only one species; there are now more than 23 identified species, all of them within family Bartonellaceae.
Bartonella bacilliformis is found only in Peru, Ecuador, and Colombia. It is endemic in some areas of Peru,occurring outbreaks of the disease in new epidemic areas. The bacterium is transmitted by sandflies of genus Lutzomyia.
For its isolation, special cultures are required containing complemental soy agar, proteases, peptones, some essential amino acids and blood. The optimum growing temperatures is 19–29°C. Colonies grow in Colombia blood agar supplemented 10% defibrinated bovine blood incubated at 19–25°C for 2 weeks.
The bacteria is inoculated by the sandflies bit to the capillaries where in a variable period of time (around 21 days) the bacteria produce a massive invasion of human red blood cells and a severe intravascular hemolytic anemia (acute phase of Carrion's disease). This phase is potentially a life-threatening infection and is associated with high fever anemia, and transient immunosuppression. The acute phase typically lasts two to four weeks. Peripheral blood smears shows anisomacrocytosis with many coccobacilli adherent to red blood cells. Thrombocytopenia is also seen and can be very severe. Neurologic involvement is sometimes seen (neurobartonellosis) and the prognosis in this case is very guarded. The most feared complication is overwhelming infections by mainly enterobacterias such as Salmonella, and also other parasites such as Toxoplasma gondii or Pneumocystis.
It is known when the bacterium invade Endothelial cells, producing the chronic manifestation of the disease (Verruga Peruana). This phase consists of a benign skin eruption with raised, reddish-purple nodules (angiomatous tumours). Visualization of the bacterium is possible using a silver stain (the Warthin–Starry method) of biopsy.
Bartonella bacilliformis is the etiologic agent of Carrion´s disease or Oroya fever (acute phase of infection) and Verruga peruana or Peruvian wart (chronic phase of infection). The acute phase of the disease is a life threatening disease characterized by massive invasion of bartonella to human red blood cells and consequently an acute hemolysis and fever. If the infection is not treated the case fatality rate is 40 to 85% Patients in this phase of the infection can be complicated by overwhelming infections primarily by enterobacterias (Salmonella spp) and parasites (Toxoplasma gondii, Pneumocystis jirovecci). The chronic phase is characterized by benign eruptive lesions that are pruritic and bleeding, and other symptoms like malaise and osteoarticular pain. Bartonella can be isolated from blood cultures and secretion of the lesions in people from endemic areas.
Before the antibiotic era, the only treatment for the acute phase was blood transfusion, but the effectiveness of this treatment was poor and the mortality rate was high. Later, with the discovering of new antibiotics, Penicillin, chloramphenicol, tetracycline, and erythromycin have been used successfully. However, because of the risk of overwhelming infections by enterobacteria, quinolones are preferred. Therapeutic failures and persistent bacteremia have been reported with chloramphenicol, and successful treatment with this drug does not appear to eliminate the patient's risk for development of the eruptive phase. So, the drug of choice is Ciprofloxacin.
In the chronic phase, the treatment used traditionally has been streptomycin for 10 days. Since 1975, Rifampin has become the drug of choice for Verruga Peruana. However, failures of Rifampin treatment have also been reported and resistance can develop. Recently Macrolides have been used with similar effectiveness.
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