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11 : Cryptosporidium parvum: Minuscule but Mighty

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Abstract:

This chapter demonstrates the power of tiny parasite to alter human health. It focuses on recent observations and highlights current areas of uncertainty. Regardless of the exact taxonomy of species, numerous studies now indicate that isolates exhibit considerable molecular heterogeneity. A study by researchers indicates that bovine genotype isolates do have variable virulence for humans and makes it perfectly clear that is a very infectious parasite. In this study, healthy human volunteers serologically negative for anti- antibodies were infected with one of three bovine genotype isolates. Studies of waterborne disease, children in developing countries, and AIDS patients as well as data examining the course of infection in healthy volunteers illustrate the complexity of clinical cryptosporidiosis. The understanding of the mechanisms by which infection stimulates intestinal secretion to cause diarrheal disease remains incomplete. However, a variety of observations have facilitated one's ability to develop a working model of disease pathogenesis due to . Only effective highly active antiretroviral therapy has been clearly shown to result in the resolution of disease in AIDS patients due to improved host immune function.

Citation: Sears C. 2000. Cryptosporidium parvum: Minuscule but Mighty, p 149-163. In Scheld W, Craig W, Hughes J (ed), Emerging Infections 4. ASM Press, Washington, DC. doi: 10.1128/9781555816971.ch11
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Figures

Image of Figure 1.
Figure 1.

Acid-fast stain of stool containing C. parvum or Cyclospora cayetanensis. This figure illustrates the size difference between the oocysts of C. parvum (left panel) and C. cayetanensis (right panel), which are approximately 5 and 10 µm, respectively. Magnification, ×436.

Citation: Sears C. 2000. Cryptosporidium parvum: Minuscule but Mighty, p 149-163. In Scheld W, Craig W, Hughes J (ed), Emerging Infections 4. ASM Press, Washington, DC. doi: 10.1128/9781555816971.ch11
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Image of Figure 2.
Figure 2.

Proposed phylogeny of C. parvum species. A recent proposal based on neighbor-joining analysis of small-subunit rRNA sequences of C. parvum and other proposed Cryptosporidium species suggests that closely related strains from humans, monkeys, calves, mice, guinea pigs (c. wrairi), geese (c. meleagridis), and cats (c. felis) be considered a C. parvum group. Of interest, C. felis has recently been identified in AIDS patients. Adapted from reference .

Citation: Sears C. 2000. Cryptosporidium parvum: Minuscule but Mighty, p 149-163. In Scheld W, Craig W, Hughes J (ed), Emerging Infections 4. ASM Press, Washington, DC. doi: 10.1128/9781555816971.ch11
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Image of Figure 3.
Figure 3.

C. parvum infection predicts enhanced diarrheal disease morbidity in children infected when less than 1 year of age. (A) Distribution over time of the post-Co parvum infection diarrheal disease burden in children who acquired C. parvum infection when less than 1 year of age. After C. parvurn infection, case children experienced a significant increase in diarrheal disease burden lasting 21 months in comparison with age-matched controls. *, P < 0.005; §, P < 0.03 for cases versus controls. (B) Similar data for children who acquired C. parvum infection when older than 1 year of age. In these older children, any excess diarrheal disease burden after the C. parvurn infection episode resolved within 6 months. The episode of C. parvurn- related diarrhea lasted a mean of 8.8 ± 1.8 days in the children younger than 1 year of age and 8.0 ± 1.8 days in children older than 1 year of age at time of first infection and is included in the 3-month time point on both panels. Reproduced from reference 2 with permission.

Citation: Sears C. 2000. Cryptosporidium parvum: Minuscule but Mighty, p 149-163. In Scheld W, Craig W, Hughes J (ed), Emerging Infections 4. ASM Press, Washington, DC. doi: 10.1128/9781555816971.ch11
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Image of Figure 4.
Figure 4.

Model of pathogenesis of diarrheal disease caused by C. parvum. Adhesion and invasion of C. parvum sporozoites and merozoites to the apical membrane of intestinal epithelial cells appear to stimulate the activity of several cellular kinases which participate in the cytoskeletal rearrangement associated with C. parvum invasion of the cell. Cellular invasion also stimulates the intestinal epithelial cells to produce prostaglandin synthase, interleukin-8 and tumor necrosis factor alpha. Recruitment of polymorphonuclear leukocytes (by interleukin-8), activation of macrophages (by tumor necrosis factor alpha), production of prostaglandins (by prostaglandin synthase), and alteration in the function of ion transporters (by cellular kinases) would be predicted to stimulate intestinal secretion in response to cellular infection with C. parvum. A subset of cells infected by C. parvum appear to undergo apoptotic cell death, also likely contributing to the pathophysiology of the disease. Abbreviations: PGE2, 12, prostaglandins E2 and I22 ; PMNs, polymorphonuclear leukocytes; MacroØ, macrophages; ENS, enteric nervous system. See tcxt for references.

Citation: Sears C. 2000. Cryptosporidium parvum: Minuscule but Mighty, p 149-163. In Scheld W, Craig W, Hughes J (ed), Emerging Infections 4. ASM Press, Washington, DC. doi: 10.1128/9781555816971.ch11
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Tables

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Table 1.

a very infectious parasite

Citation: Sears C. 2000. Cryptosporidium parvum: Minuscule but Mighty, p 149-163. In Scheld W, Craig W, Hughes J (ed), Emerging Infections 4. ASM Press, Washington, DC. doi: 10.1128/9781555816971.ch11

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