Etiology and Epidemiology

B. bacilliformis are pleomorphic bacteria, well stained with the Romanovsky stain. In the red blood cells and in the histiocytic cells, the bartonella assumes a rodlike (bacillus) or coccoid shape, 1 to 3 microns in size (Figure VIII.22.1). The electron microscope shows the flagella of the bartonella. It grows well in liquid and in semisolid blood media. The human bartonella is closely related to the animal bacteria Hemobartonella, Eperythrozoon, and Grahamella.

In 1913 Charles Townsend identified the sandfly Phlebotomus verrucarum as the insect vector of the disease. The female is the only transmitter, and the transmission occurs during the night. Carrion's disease is a rural disease, and, like yellow fever, it does not need a human reservoir because the bartonella lives in the small animals in the area.

Figure VIII.22.1. Bartonella bacilliformis within red blood cells stained by Giemsa and Romanovsky stains. (From O. Urteaga-Ballón and J. Calderón. 1972. Dermatología Clínica, by permission of the author.)

Immunology (Experimental Transmission) Between 1948 and 1950, the author and collaborators conducted a series of experimental transmission on human volunteers. Thirty healthy men were inoculated with parasitic blood through subcutaneous, intramuscular, and intravenous routes. None of the volunteers developed the disease, and the blood culture remained negative after more than 120 days. Another four volunteers who had been splenecto-mized for other reasons were infected with the same inoculum. All of them developed the disease, with bartonellas evident in the erythrocytes and blood cultures positive. Antibiotics halted the parasitism, and the volunteers recovered immediately.

After our experiments, three of the former healthy volunteers were exposed to the bite of the insect in the verrucogenous zone. None of them developed the disease. They appeared to have developed immunity as a result of the previous live inoculation. Later on, 10 workers out of a group of 100 were inoculated with attenuated live bartonellas in order to test a vaccine against the disease. None of them developed any symptoms, and the blood cultures remained negative. Meanwhile 45 of their companions who were not vaccinated developed the disease.

Our conclusions were as follows: First, the natural infection of the bartonellosis occurs only through the sandfly vector. Second, the inoculation from a sick person to a healthy person does not effect transmission of the disease. Rather the inoculation of a live germ appears to produce immunity. Third and last, direct inoculation of the B. baciliformis into a splenectomized patient produces the disease, with bartonellas evident within the erythrocytes and blood cultures testing positive.

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