Description Of The Organism And Taxonomy

With the conclusive documentation of the sporulation of Cyclospora (Ashford, 1979; Ortega et al., 1993), its classification as an eimerian member of the order Eucoccidiida and phylum Apicomplexa as a distant relative of Plasmodium sp. became clear (Guerrant and Thielman, 1998). Key to its potential modes of spread is the obligatory requirement for the excreted oocysts to mature outside the host before it is infectious (see Figure 7.1). Recent phylogenetic analyses of ribosomal DNA demonstrate that human Cyclospora spp. are closely related to species of Eimeria

Fig. 7.1 Life-cycle of Cyclospora cayetanensis

Principles and Practice of Clinical Parasitology

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

Fig. 7.2 Cyclospora oocytes in stool x 640

severity and protracted course in patients with AIDS suggests that, like Cryptosporidium, cellular immunity likely plays an important role in containing the infection (Long et al., 1990; Pape et al., 1994). In addition, the predominance of infections in children and its relative rarity in adults living in endemic areas like Peru and Haiti further suggests that protective immunity develops relatively early in life (Ortega et al., 1997; Eberhard et al., 1999).

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