Clinical Features

In both immunocompetent and immunocom-promised hosts, a non-specific watery diarrheal illness accompanied by abdominal cramps, nausea, malaise, anorexia and weight loss is the most common presentation of I. belli infection. Most infections in immunocompetent individuals are expected to be short-lived, whereas individuals with defects in cell-mediated immunity, such as AIDS, are predominantly reported to experience chronic diarrheal illnesses (DeHovitz et al., 1986; Forthal and Guest, 1984; Whiteside et al., 1984). However, the illness may be severe, resulting in dehydration. Up to 6 liters of stool output has been reported in an apparent immunocompetent host (Brandborg et al., 1970). This general pattern of illness makes this infection clinically indistinguishable from C. parvum infection. One of the notable features of I. belli infection is the ability of the parasite to cause strikingly protracted illnesses in immunocompetent hosts (Brandborg et al., 1970; Shaffer and Moore, 1989; Trier et al., 1974). Intermittent diarrheal illnesses of several months to possibly years in duration have been reported in immunocompetent individuals, including travelers. Dysentery or high fevers are not features of I. belli infection but, as indicated above, malabsorption is likely. Extraintestinal dissemination of infection has been reported in an AIDS patient (Restrepo et al., 1987).

intermittent, stool concentration and examination of multiple stools are advised to improve diagnostic sensitivity. The optimum number of stools necessary to establish a diagnosis is unknown, but examination of two unconcen-trated stools had a diagnostic sensitivity of approximately 80% in AIDS patients (Pape et al., 1989). Similar to C. parvum, I. belli oocysts are acid-fast and will be detected using the rhodamine-auramine stain (Ma and Soave, 1983; Ng et al., 1984). The distinct morphology of I. belli oocysts permits them to be readily distinguished from either C. parvum or Cyclo-spora cayetanensis oocysts (Figure 6.4). Typically, the excreted unsporulated I. belli oocysts contain two sporoblasts. I. belli oocysts do not stain with hematoxylin, trichrome or iodine. In the absence of effective antibiotic treatment, oocyst excretion post-infection can be very protracted, often lasting 1-2 months with as long as 4 months reported (Henderson et al., 1963). The developmental stages of the parasite can be demonstrated in the epithelium of small bowel biopsies but this should only rarely be necessary for diagnosis (Brandborg et al., 1970; Trier et al., 1974). Neither fecal leukocytes nor blood are clearly reported in stools of patients infected with I. belli, although sensitive (but nonspecific) assays for intestinal inflammation, such as the fecal lactoferrin test, have not been evaluated (DeHovitz et al., 1986; Matsubayashi and Nozawa, 1948; Soave and Johnson, 1988). A notable feature of I. belli infection is its propensity to stimulate an eosinophilic response in the lamina propria, with concomitant Charcot-Leyden crystals detectable in stool samples. In addition, mild to moderate systemic eosinophilia in the absence of leukocytosis is commonly reported, although not always clearly attributable to I. belli infection (Brandborg et al., 1970; Matsubayashi and Nozawa, 1948; Trier et al., 1974).

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