Section 2 -

Diagnosis of Select Parasitic Infections in the Immunocompromised Host Ronald C. Neafie Chief, Parasitic Disease Pathology Branch Department of Environmental and Infectious Disease Sciences Armed Forces Institute of Pathology

Case 1 An elderly man with Hodgkin Disease for several years had been treated with chemotherapy. Terminally, he developed clinical evidence of central nervous system disease that was thought to be progressive multifocal leukoencephalopathy (PML). His condition gradually deteriorated, and he died. Autopsy was limited to examination of the brain. Grossly, there were 2 foci suggestive of areas of softening and necrosis. Diagnosis: Toxoplasmosis Toxoplasma gondii The tachyzoites of Toxoplasma gondii are free in tissue or in groups. In fresh preparations and smears, they are crescentric-shaped with a maximum size of 7 mm by 1-3 mm and have a prominent nucleus near the middle of the parasite. In tissue sections, they are round or oval and 2-3 m m in diameter, have a prominent spherical nucleus, and divide by binary fission. Bradyzoites occur in cysts, which have a maximum diameter of 100 mm and a thin cyst wall. Individual bradyzoites are morphologically nearly identical to tachyzoites. The differential diagnosis of toxoplasmosis includes histoplasmosis, leishmaniasis, Chagas disease, cytomegalovirus (CMV) infection, sarcocystosis, and microsporidiosis. Histoplasma capsulatum is GMS-positive, shows budding, and contains vacuoles. Amastigotes have kinetoplasts. The intracytoplasmic inclusions of CMV lack nuclei. The cysts of Sarcocystis are larger and have septa. Microsporidia are elongate, birefringent, and variably staining. Case 2 A 34 year-old man from Colorado with AIDS presented with a 4 month history of fever, night sweats, intractable cough and weight loss. He was treated with trimethoprim-sulfamethoxazole prophylaxis for pneumocystosis. Previous biopsies of bone marrow, tongue ulcer and maxillary sinus contents were unrewarding. Open lung biopsy was performed, and small ovoid unidentified structures were observed. Diagnosis: Microsporidiosis Encephalitozoon cuniculi The spores of Encephalitozoon cuniculi are ovoid to elongate and 2-3 mm by 1.0-1.5 mm. They stain poorly with hematoxylin-eosin. Frequently there is a thin band across the spore. Some spores are birefringent, acid-fast, and gram positive. Case 3 A 38 year-old man from Maine had a history of AIDS for 1 year when he developed viral hepatitis and pneumocystosis. He was admitted to hospital with weakness, anorexia, bloody stools, vomiting, and extreme weight loss. His course was steadily downhill, and the patient expired about 2 months after hospitalization. Diagnosis: Cryptosporidiosis Cryptosporidium parvum Cryptosporidium parvum oocysts lie within a p arasitophorous vacuole that is within the microvillous border just below the plasma membrane. It is intracellular but extracytoplasmic. Oocysts are spherical and 2-6 m m in diameter. Oocysts in stool specimens are acid-fast when stained with modified Kinyoun, but are not acid-fast in tissue sections. The differential diagnosis of cryptosporidiosis includes Cyclospora sp. and Isospora belli. In tissue, variable morphologic forms of Cyclospora sp. or Isospora belli are within vacuoles of enterocytes. In stool specimens, oocysts of Cyclospora sp. are 8-10 m m in diameter, and oocysts of Isospora belli are 20-33 mm in length. Both are acid-fast with modified Kinyoun stain. Case 4 A 38 year-old HIV-positive man from El Salvador residing in Virginia was admitted to hospital semicomatose. A laboratory technician saw moving organisms during routine cell count of his cerebrospinal fluid. The patient developed AIDS and died shortly thereafter. Diagnosis: Chagas Disease Trypanosoma cruzi Amastigotes of Trypanosoma cruzi are found in myofibers and brain. They are spherical, and 1-5 mm in diameter, and have cytoplasm with a round nucleus and a rod-shaped kinetoplast. The trypomastigote form is found in peripheral blood. It is elongate (frequently C-shaped) and 16-22 m m long and has cytoplasm with an oval nucleus and a round terminal kinetoplast, an undulating membrane and a free flagellum. The differential diagnosis of Chagas disease includes other trypanosomiasis and leishmaniasis. The trypomastigotes of Trypanosoma rangeli are larger than those of T. cruzi (25-50 mm), have a small kinetoplast, are not C-shaped, and divide in peripheral blood. The trypomastigotes of Trypanosoma rhodesiense/gambiense are also larger (14-33 mm), have a small kinetoplast, are not C-shaped, and divide in peripheral blood. The amastigotes of Leishmania sp. are smaller (2-3 mm) and are usually in different anatomic sites and host cells. Case 5 A 42 year-old Lebanese man with AIDS had been residing in the U.S.A. for 2 years when he developed multiple nodular masses of his arms and legs. Clinically, the nodules were suggestive of Kaposi sarcoma. The patient also had a clinical history of CMV infection and presumptive toxoplasmosis encephalitis. A skin biopsy was taken of the left upper arm. Diagnosis: Granulomatous Amebic Encephalitis (GAE) Acanthamoeba sp. Acanthamoeba sp. trophozoites are round to oval and 15-45 mm in diameter. They have foamy cytoplasm and are uninucleate with a large dense central karyosome. They divide by binary fission. The cysts are spherical and 16-30 mm in diameter. They also have foamy cytoplasm and are uninucleate with a large dense central karyosome. They are double-walled with an outer wrinkled ectocyst and an inner round endocyst. The differential diagnosis of GAE includes infection by Naegleria fowleri or Entamoeba histolytica. The trophozoites of N. fowleri are smaller (9-14 mm) and uninucleate. The trophozoites of E. histolytica are similar in size (15-25 mm) to those of Acanthamoeba sp., but have anucleus with a tiny karyosome. Neither N. fowleri or E. form cysts in tissue Case 6 A 56 year-old man living in Kentucky presented with chills, fever, and headache. Splenectomy had been performed 8 years previously. He had recently killed a deer that had ticks, but had no known tick bites. During his work-up, the contributor noticed numerous intracellular organisms within erythrocytes. Diagnosis: Babesiosis Babesia divergens Babesia sp. are malaria-like parasites found in normal-sized erythrocytes. On Giemsa stained blood smears, they have blue cytoplasm and red chromatin material. They may be spherical, oval, pyriform, and rod-shaped. They are 1-5 m m and are frequently in pairs or rarely in tetrads. The differential diagnosis of babesiosis includes malaria. Compared to Plasmodium sp. parasites, Babesia sp. are smaller, more pleomorphic and occur within normal sized erythrocytes. Case 7 A 60 year-old man living in California was diagnosed with asthma and treated with steroids. Duodenal biopsy revealed unidentified nematodes. The pathologist notified the pulmonologist and suggested a possible relationship between the nematodes and his asthma. The pulmonologist responded that the patient was improving on steroids. He then developed lower gastrointestinal tract bleeding, and colectomy was performed. Nematodes were found in the colon, appendix and ileum. Diagnosis: Strongyloidiasis Strongyloides stercoralis The adult parasitic female is parthenogenic, 2-3 mm by 30-60 m m, and contains eggs in uteri. The eggs are oval, 50-60 mm by 30-35 mm, thin-shelled, and embryonated. Rhabditiform larvae are 200-400 mm by 10-20 mm and have an esophagus with a bulb and no alae. Filariform larvae are 300-600 mm by 10-20 mm and have an esophagus without a bulb, minute double lateral alae, and a notched tail. The differential diagnosis of strongyloidiasis includes intestinal capillariasis, angiostrongyliasis costaricensis, toxocariasis and ancylostomiasis (hookworm infection). The adult worms of Capillaria philippinensis have astichosome in a long anterior end, bacillary bands, and eggs with bipolar plugs. The larvae of C. philippinensis have a stichosome in a long anterior end and no alae. The larvae of Angiostrongylus costaricensis have single lateral alae and are 8-11 mm in diameter. The larvae of Toxocara canis have single lateral alae and are 8-21 mm in diameter. The eggs of hookworms are indistinguishable from those of S. stercoralis. References Beattie JF, Michelson ML, Holman PJ. Acute babesiosis caused by Babesia divergens in a resident of Kentucky . N Engl J Med. 2002 Aug 29;347(9):697-8. De Groote MA, Visvesvara G, Wilson ML, Pieniazek NJ, Slemenda SB, daSilva AJ, Leitch GJ, Bryan RT, Reves R. Polymerase chain reaction and culture confirmation of disseminated Encephalitozoon cuniculi in a patient with AIDS: successful therapy with albendazole. J Infect Dis. 1995 May;171(5):1375-8. Dubey JP, Lindsay DS, Speer CA. Structures of Toxoplasma gondii tachyzoites, bradyzoites, and sporozoites and biology and development of tissue cysts. Clin Microbiol Rev. 1998 Apr;11(2):267-99. Ferreira MS, Nishioka Sde A, Silvestre MT , Borges AS, Nunes-Araujo FR, Rocha A. Reactivation of Chagas' disease in patients with AIDS: report of three new cases and review of the literature. Clin Infect Dis. 1997 Dec;25(6):1397-400. Gutierrez Y, Bhatia P, Garbadawala ST, Dobson JR, Wallace TM, Carey TE. Strongyloides stercoralis eosinophilic granulomatous enterocolitis. Am J Surg Pathol. 1996 May;20(5):603-12. Horsburgh CR Jr., Nelson AM. Pathology of Emerging Infections. 1997, ASM Press, Washington , DC. Karp CL, Neva FA. Tropical infectious diseases in human immunodeficiency virus-infected patients. Clin Infect Dis. 1999 May;28(5):947-63; quiz 964-5. Kayembe KP, Nelson AM, Colebunders RL. Chapter 17. Opportunistic Infections and Diseases. in Essex M, Mboup S, Kanki PJ, Kalengayi MR, (Eds.) AIDS in Africa. 1st ed., 1994, Raven Press, Ltd., New York. Lewin-Smith MR, Klassen MK, Frankel SS, Nelson AM. Pathology of human immunodeficiency virus infection: infectious conditions. Ann Diagn Pathol. 1998 Jun;2(3):181-94. Nelson AM, Horsburgh CR Jr. Pathology of Emerging Infections 2. 1998, ASM Press, Washington , DC.