Description Of The Organism

The taxonomy of babesias was recently described in a review by Telford et al. (1993) as phylum Apicomplexa, class Aconoidasida, order Piroplas-midora, family Babesdiidae and genus Babesia. A listing of the many species and their hosts is included in the review. However, only a few species are known to cause disease in humans. The organisms are intracellular parasites which are piriform, round or oval, depending upon the species. B. microti, normally found in rodents, measures 2.0 x 1.5 pm. Of species found in cattle which infect humans, B. bovis measures 2.4x1.5 ^ and B. divergens measures 1.5x0.4 These organisms are frequently mistaken for Plasmodium falciparum, one of the agents that causes malaria, because of their intracellular ring forms and the peripheral location of the parasite in the erythrocyte. However, in contrast to the appearance of the developing intraerythrocytic Plasmodium, intraerythrocytic Babesia contain no

Principles and Practice of Clinical Parasitology

Edited by Stephen Gillespie and Richard D. Pearson © 2001 John Wiley & Sons Ltd

Fig. 4.1 (A) Wright-Giemsa stained blood smear of a patient with B. microti. Numerous merozoite ring forms are seen (arrow) within erythrocytes. The ring forms resemble P. falciparum, but are large, clear and devoid of the brown (hemozoin) pigment seen with P. falciparum. The absence of gametocytes and schizonts further distinguishes B. microti from P. falciparum. Courtesy of Philip R. Daoust MD. (B) Wright-Giemsa stained human blood smear. Ring form merozoites are seen (arrows) but one erythrocyte contains five immature merozoites, characterized by sparse cytoplasm and small nucleus. As these develop, they form rings. The presence of parasites at different stages is consistent with the asynchronous schizogeny that characterizes babesial infection. Smear courtesy of Philip R. Daoust MD

Fig. 4.1 (A) Wright-Giemsa stained blood smear of a patient with B. microti. Numerous merozoite ring forms are seen (arrow) within erythrocytes. The ring forms resemble P. falciparum, but are large, clear and devoid of the brown (hemozoin) pigment seen with P. falciparum. The absence of gametocytes and schizonts further distinguishes B. microti from P. falciparum. Courtesy of Philip R. Daoust MD. (B) Wright-Giemsa stained human blood smear. Ring form merozoites are seen (arrows) but one erythrocyte contains five immature merozoites, characterized by sparse cytoplasm and small nucleus. As these develop, they form rings. The presence of parasites at different stages is consistent with the asynchronous schizogeny that characterizes babesial infection. Smear courtesy of Philip R. Daoust MD

hemoglobin-derived pigment. The appearance of the tetrad form of B. microti, the result of division by budding rather than schizogeny, is diagnostic of babesiosis (Figure 4.1A,B).

Was this article helpful?

0 0

Post a comment