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is usually precluded by autolysis. Therapy for chronic Cryptosporidium infection consists of
paronomycin.[487]
Isospora belli is more common in tropical regions than in temperate climates. It may
produce a protracted watery diarrhea lasting for months, along with steatorrhea and abdominal
pain, similar to Cryptosporidium in patients with AIDS, and extraintestinal dissemination has
been documented. Diagnosis is typically made by finding large 20 to 30 micron oval oocysts in
stool, aided by acid fast staining. Eosinophilia may be present, and this suggests additional
helminthic infection. Biopsy of small intestine may show Isospora organisms within the
intestinal lumen or within cytoplasmic vacuoles in mucosal cells in mucosa with mild
inflammation and atrophy.[401,486,487,675] Isospora can be treated with trimethoprim-
sulfamethoxazole.[487]
Microsporidial infections (caused by Enterocytozoon species including E bieneusi, E
cuniculi, and E hellum, and by Encephalitozoon (Septata) intestinalis) have a similar clinical
presentation to Cryptosporidium. However, microsporidiosis is characterized by fewer watery
stools per day, a more gradual weight loss, maintenance of appetite, and lack of fever.
Microsporidial infections can be more frequent than cryptosporidial infections in AIDS when
diagnostic techniques are available and can best be diagnosed on small intestinal biopsy samples
using light microscopy with Giemsa staining or by transmission electron microscopy. Stool
examination can be more sensitive than intestinal biopsy for diagnosis. The organisms are most
numerous in the jejunum, but they have also been reported as a cause for cholangitis.
[486,487,667]
Grossly, microsporidial infections do not produce striking changes, though mucosal
erythema and granularity may be seen on endoscopy. By light microscopy, there may be partial
villous atrophy with blunted villous tips from mucosal cell destruction. Crypt hyperplasia and
lamina propria inflammation are variable. The 4 to 5 micron meronts and sporonts are clustered
in the supranuclear intracytoplasmic region of villous mucosal cells. The 1 to 2 micron spores
are acid fast, and can also be seen by light microscopy in smears of stool or duodenal aspirates
by use of a modified trichrome stain.[491,494,667] Treatment with albendazole has been
recommended for Septata infections, while no effective therapy exists for Enterocytozoon
infections.[487]
Infection with the small coccidian organism Cyclospora cayetansis produces an
appearance clinically similar to cryptosporidiosis.[494] Stool examination provides the
diagnosis with acid fast staining for organisms that resemble a large cryptosporidium; they are 8
to 10 micron with a double cyst wall and a central morula.[486] On small intestinal biopsy there
can be mild to moderate acute and chronic inflammation of lamina propria with prominent
plasma cells along with focal vacuolization of the brush border and mild to moderate partial
villous atrophy and crypt hyperplasia. Cyclosporiasis has a high recurrence rate. Treatment with
trimethoprim-sulfamethoxazole appears to be effective both for acute infections as well as for
prophylaxis.[487,491,494]
Giardia lamblia infections may occur with or without diarrhea, casting doubt about the
pathogenicity of this organism. By endoscopy, the small intestinal mucosa may appear mildly
erythematous. On biopsy, the mucosa demonstrates no significant changes, and the organisms
are mainly intraluminal, appearing as 3 by 8 micron amphophilic to eosinophilic pear-shaped
trophozoites with two indistinct nuclei. Stool examination can demonstrate cysts of G lamblia
for diagnosis.[667]