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Category: Clinical Microbiology
Parasites, Page 1 of 2
< Previous page | Next page > /docserver/preview/fulltext/10.1128/9781555815455/9781555813970_Chap14-1.gif /docserver/preview/fulltext/10.1128/9781555815455/9781555813970_Chap14-2.gifAbstract:
This chapter includes some of the opportunistic parasites that can cause disease in immunocompromised patients. Although most parasitic infections are known to cause more severe symptoms when a host's immune system is impaired, the representative organisms presented in this chapter have been identified as causing the most severe disease in this population group. Malaria, Trypanosoma spp., Toxoplasma gondii, and Leishmania spp. are the principal parasites that may be transmitted with bone marrow, kidney, or liver homografts, and microsporidia are the principle parasites transmitted with xeno-transplants. The organisms discussed in the chapter are Entamoeba histolytica, free-living amebae, Giardia lamblia, T. gondii, Cryptosporidium spp., Cyclospora cayetanensis, Isospora belli, Sarcocystis spp., microsporidia, Leishmania spp., Strongyloides stercoralis, and Sarcoptes scabiei (crusted scabies). It is important for the laboratorian and clinician to be aware of problems that these organisms can cause in immunocompromised patients and of the proper diagnostic techniques and their clinical relevance. Organism eradication is effective using cotrimoxazole, trimethoprimsulfamethoxazole (TMP-SMX), pyrimethaminesulfadiazine, primaquine phosphate-nitrofurantoin, and primaquine phosphate-chloroquine phosphate. The drug of choice is TMP-SMX, which is classified as an investigational drug for treatment of Isospora belli infection. The diagnosis can be confirmed by demonstration of the mites, eggs, or scybala (fecal pellets).
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(Top left) Entamoeba histolytica trophozoite (true pathogen; note the ingested RBCs in the cytoplasm); (top right) Entamoeba histolytica/E. dispar cyst (unable to differentiate the true pathogen E. histolytica from the nonpathogen E. dispar); (bottom) gross specimen of amebic liver abscess. (Courtesy of Armed Forces Institute of Pathology.)
(Top left) Giardia lamblia trophozoite (note two nuclei, curved median bodies, and linear axonemes); (top right) Giardia lamblia cyst; (bottom) Giardia lamblia cyst (large) and Cryptosporidium sp. oocysts (small) (demonstrating fluorescence using the fecal fluorescent-antibody immunoassay; some will use a counterstain, while others will not).
(Top left) Cryptosporidium sp. oocysts stained using modified acid-fast stain (note the spherical shape; oocysts measure 4 to 6 μm); (top right) Cryptosporidium sp. oocysts (note that sporozoites are visible in some of the oocysts, which are infective when passed, regardless of whether the sporozoites are visible or not); (bottom) histologic section of intestinal tissue showing organisms within parasitophorous vacuoles at the brush border. (Courtesy of Armed Forces Institute of Pathology.)
Cyclospora cayetanensis oocysts stained using modified acid-fast stain (note the spherical shape; oocysts measure 8 to 10 μm; some oocysts do not stain, and thus the organisms are said to be “modified acid-fast variable”). These oocysts are not infectious when passed, regardless of the stool consistency.
Isospora (Cystoisospora) belli. (Top) Immature oocyst (contains single sporocyst) stained using modified acid-fast stain; (bottom) more mature oocyst (contains two sporocysts) in a saline wet mount of stool concentration sediment.
Sarcocystis sp. in muscle tissue (note the bradyzoites contained within the sarcocyst).
Microsporidia. (Top) Microsporidial spores seen in fecal specimen (concentration sediment) stained with Ryan blue modified trichrome stain (note the horizontal line through some of the spores, representing the presence of the polar tubule); (middle) spores stained with Gram stain reagents for the detection of intra-cellular spores; (bottom) spores within a urine sediment after being stained with an optical brightening agent (note that some of the spores are intracellular, while some are outside the cells).
Naegleria fowleri trophozoites within brain tissue (note the large karyosome within the nucleus). (Courtesy of Armed Forces Institute of Pathology.)
(Top left) Acanthamoeba sp. trophozoites (note the sharp, spiky pseudopodia); (top right) Acanthamoeba sp. cysts (note the hexagonal double wall); (bottom) skin lesion caused by Acanthamoeba sp. infection in an immunocompromised host.
Balamuthia mandrillaris in brain tissue; both trophozoites and cysts are found in many of the same CNS tissues as those which harbor Acanthamoeba organisms. (Courtesy of Armed Forces Institute of Pathology.)
(Top) Toxoplasma gondii in tissue culture (note the somewhat crescent-shaped tachyzoites); (bottom) organisms in tissue.
(Top left) cutaneous leishmaniasis (typical lesion); (top right) same lesion after therapy; (bottom left) Leishmania donovani in bone marrow (note the individual amastigotes, with each one containing a bar and nucleus); (bottom right) promastigotes from culture (specimen was stained using Giemsa stain).
(Top) Trypanosoma cruzi trypomastigote (note the large kinetoplast at one end and the large central nucleus); (bottom) T. cruzi amastigotes in cardiac tissue.
Strongyloides stercoralis. (Top) Rhabditiform larvae seen in fecal concentration sediment (note the short mouth opening/buccal capsule and the packet of genital primordial cells at the bottom left of the image); (middle) notched tail (“slit in tail”) seen in filariform/infectious larvae; (bottom) larvae in tissue (disseminated infection at a higher magnification).
Sarcoptes scabiei “itch mite” (note the egg and immature and mature mites).
Parasitic infections: clinical findings in immunocompetent and immunocompromised patients
Parasitic infections in the compromised host: diagnostic options a,c