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Broadly speaking, any organism that lives off another is a parasite. Some parasites cause no harm to the host while others may eventually kill it. Parasites come in all shapes and sizes from single celled organisms such as Amoeba to large roundworms to lice and bedbugs.

Amoeba (Amebiasis, Dysentery)
Arthropods (Bugs and Insects)
Chagas' Disease (Trypanosoma cruzi)

Cutaneous Larva Migrans (Creeping Eruption)
Onchocerciasis (River Blindness)


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Babesiosis Two Atypical Cases From Minnesota and a Review

Suman Setty, MD, PhD, Zena Khalil, MD, Pamela Schori, MT(ASCP), Miguel Azar, MD, and Patricia Ferrieri, MD
Am J Clin Pathol 2003;12):554-559 Abstract quote

We present 2 atypical cases of babesiosis and a review of babesiosis. The first patient was a 72-year-old man with an intact spleen, who had marked intravascular hemolysis. His RBCs were parasitized heavily with trophozoites of Babesia, and he had a large number of extracellular aggregates of Babesia. The infection did not respond to oral antibiotic therapy, and he required an RBC exchange transfusion. The second patient was a 29-year-old man who had undergone splenectomy and who had multiple episodes of fever and gastrointestinal symptoms for 4 months, with partial response to antibiotics.

Thin smears revealed both intraerythrocytic and extraerythrocytic forms in very low numbers. The infection responded promptly to clindamycin and quinine therapy. The varying clinical manifestations, from acute to chronic, at a wide range of ages and often the difficulty of detection by routine blood smears make it necessary that a high index of clinical suspicion be present for prompt diagnosis.

With increasing numbers of cases of transfusion-transmitted babesiosis being reported, protection of the blood supply is essential.
Screening for Giardia/Cryptosporidium infections using an enzyme immunoassay in a centralized regional microbiology laboratory.

Church D, Miller K, Lichtenfeld A, Semeniuk H, Kirkham B, Laupland K, Elsayed S.

Calgary Laboratory Services, Calgary, Alberta, Canada.
Arch Pathol Lab Med. 2005 Jun;129(6):754-9. Abstract quote  

CONTEXT: Stool parasitologic testing for Giardia and Cryptosporidium (G/C) previously relied on staining (ie, modified iron hematoxylin-kinyoun), ethyl acetate concentration procedures, and microscopy (the stool ova and parasite method). In April 1999, a microplate enzyme immunoassay (EIA) (ProSpecT G/C, Remel, Inc, Lenexa, Kan) for routine screening of all stool specimens was implemented.

OBJECTIVE: To determine the clinical and laboratory impact of this service change.

DESIGN: Changes were made to the regional microbiology requisition so that physicians could order either a G/ C EIA screen or stool ova and parasite examination. During a 3-year period (May 1999 through April 2002), changes in physician ordering practice, the rate of detection of G/ C infections, and test turnaround times were monitored. The economic outcomes have also been studied and compared annually since implementation and up to the current fiscal year (2004).

RESULTS: The following effects have been noted since G/ C EIA screening was implemented: (1) 70% of all stool parasite tests ordered were converted to G/C EIA screens versus stool ova and parasite tests, (2) stool parasitologic volumes decreased by up to 30% because of physicians ordering a single test per patient, (3) most stool parasite results (70%-80%) were reported within 24 hours of specimen receipt, and (4) the screening assay has improved detection of cryptosporidiosis cases. Although the G/C EIA tests cost more than stool ova and parasite examination, the equivalent of 1.8 full-time employees have been freed up to perform other duties.

CONCLUSIONS: Routine stool G/C EIA screening in our region is not only clinically relevant but also improves the timeliness and efficiency of detection of these important enteric parasite infections.
Point Prevalence of Cryptosporidium, Cyclospora, and Isospora Infections in Patients Being Evaluated for Diarrhea

Julie A. Ribes, MD, PhD, John P. Seabolt, EdD, MT(ASCP)SM, and Sue B. Overman, MA, SM(AAM)
Am J Clin Pathol 2004;122:28-32 Abstract quote

From March to September 2001, 315 specimens from "nonrepeat" patients that were submitted for ova and parasite examination were stained using the Kinyoun modified acid-fast stain to detect the intestinal coccidians.

Four patients (1.3%) were infected with coccidians, 2 with Cryptosporidium parvum and 2 with Cyclospora cayetanensis. No infections with Isospora belli were detected. In comparison, 15 patients (4.8%) had infections with one or more intestinal parasites detected by routine trichrome staining: 5 had Giardia lamblia; 2, Dientamoeba fragilis; 3, Strongyloides stercoralis; 1, Iodamoeba bütschlii; 3, Endolimax nana; 6, Blastocystis hominis; and 1, Entamoeba coli. Four patients were multiply infected. Coccidians made up 29% of the clinically significant parasitic infections. The coccidians were missed in all 4 cases because no special staining was ordered.

Clinicians need to be reminded that additional tests should be ordered to fully evaluate patients with chronic diarrhea in which no diagnosis is found by routine testing.
Gnathostomiasis: clinicopathologic study.

Magana M, Messina M, Bustamante F, Cazarin J.

*Hospital General de Mexico/Universidad Nacional Autonoma de Mexico, Mexico City, Mexico.
Am J Dermatopathol. 2004 Apr;26(2):91-5. Abstract quote  

Gnathostomiasis is a systemic parasitic disease that is caused by the ingestion of contaminated raw fish, the intermediate host. Involvement of the skin is a common event, and when it does happen, it can produce a superficial or creeping eruption, pseudofurunculosis, and nodular migratory panniculitis.

We carried out a retrospective study of 946 cases of gnathostomiasis; 66 of them had skin biopsies. The diagnosis was made based on clinical and epidemio-logic findings as well as the therapeutic response. The most common skin finding was nodular migratory panniculitis affecting the trunk. Most of the patients were males between 20 and 40 years of age.

Histopathologically, we were able to see the larva and make a definitive diagnosis in 15 cases, and in 12 cases, the worm was retrieved during the surgical procedure. In remaining cases, despite of our inability to identify the larva, the histopathologic changes were quite characteristic and included: dermal and hypodermal edema with dense mixed infiltrates composed of eosinophils admixed with lymphocytes and neutrophils, eosinophilic vasculitis, flame figures, areas of necrosis, and hemorrhage.

Thus, the presence of these histopathologic features in the context of a clinical picture suggestive of gnathostomiasis allows the pathologist to make the correct diagnosis.
Pneumocystis carinii infection. Update and review.

Wazir JF, Ansari NA.
Arch Pathol Lab Med. 2004 Sep;128(9):1023-7. Abstract quote  

OBJECTIVE: To review and update the literature on current trends with regard to Pneumocystis carinii (jiroveci ) diagnosis, treatment modalities, and its role in human disease processes.

DATA SOURCES: Bibliographic databases (PubMed and Ovid) were searched for material and data between 1980 and September 2003 relevant to the review. Indexing terms used were "Pneumocystis carinii pneumonia," and "Pneumocystis jiroveci," with the English language as a constraint. Other sources were the PhD thesis of one of the authors (J.F.W., London University, 1993) and the library at the Arabian Gulf University in the Kingdom of Bahrain.

STUDY SELECTION: Acquired immunodeficiency syndrome and organ transplant cases with Pneumocystis carinii pneumonia.

DATA EXTRACTION: Independent extraction by 2 observers.

DATA SYNTHESIS: We reviewed the major characteristics of P carinii (jiroveci ) with special emphasis on the more recently acquired data including the presence of a round pore in the cyst wall, which appears to be used for the release of sporozoites, supporting the hypothesis of sexual reproduction in P carinii (jiroveci ).

CONCLUSIONS: Opportunistic infection with P carinii (jiroveci ) remains a significant cause of morbidity and mortality in human immunodeficiency virus and non-human immunodeficiency virus-associated immunosuppressed patients. Diagnosis may be achieved in the majority of cases by routine cytochemical stains and specialized techniques such as immunocytochemistry and polymerase chain reaction. The incidence of P carinii pneumonia can significantly be reduced with effective use of prophylaxis and early detection of cases at high risk. Immunization for P carinii pneumonia is in the early stages and presents a challenging area for research.

Henry JB. Clinical Diagnosis and Management by Laboratory Methods. Twentieth Edition. WB Saunders. 2001.
Rosai J. Ackerman's Surgical Pathology. Ninth Edition. Mosby 2004.
Sternberg S. Diagnostic Surgical Pathology. Fourth Edition. Lipincott Williams and Wilkins 2004.
Robbins Pathologic Basis of Disease. Seventh Edition. WB Saunders 2005.
DeMay RM. The Art and Science of Cytopathology. Volume 1 and 2. ASCP Press. 1996.
Weedon D. Weedon's Skin Pathology Second Edition. Churchill Livingstone. 2002
Fitzpatrick's Dermatology in General Medicine. 6th Edition. McGraw-Hill. 2003.
Weiss SW and Goldblum JR. Enzinger and Weiss's Soft Tissue Tumors. Fourth Edition. Mosby 2001.

Commonly Used Terms

Stool O and P-This stands for stool ova and parasites. This is a frequently requested test if intestinal parasites are suspected. A stool sample is obtained and submitted to the laboratory and a microscopic slide is prepared.

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Last Updated September 8, 2005

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