Chapter 28: Diagnostic Parasitology. Answers Explained

MULTIPLE CHOICE 1. A 4-year-old child has been complaining of a stomachache and has had intermittent episodes of diarrhea. Physical examination reveals an apparently healthy child with a mildly distended abdomen. Bec ...

MULTIPLE CHOICE 1. A 4-year-old child has been complaining of a stomachache and has had intermittent episodes of diarrhea. Physical examination reveals an apparently healthy child with a mildly distended abdomen. Because of the diarrhea, a fecal sample is sent for culture and for O&P. What is the identity of that found in the child’s fecal sample? (Courtesy CDC Public Health Image Library (PHIL); http://phil.cdc.gov/phil/home.asp.) a. Ascaris lumbricoides b. Strongyloides stercoralis c. Hookworm d. Schistosoma haematobium A The usual diagnostic stage is the egg. Fertile Ascaris eggs are oval, measure 45 to 75 by 35 to 50 m, and have thick hyaline walls surrounding a one-cell-stage embryo. Most eggs have a brown, bile-stained mammillated outer layer. CDC PHIL #410 REF: 676 OBJ: Level 3: Synthesis 2. A 15-year-old boy spent most of the summer at the northern Minnesota family cabin on a lake in a densely wooded area. After returning to school in the fall, he was frequently tired and listless with periods of fever and chills. A blood sample taken at the physician’s office revealed the following organism. The most likely identification is: (Courtesy CDC Public Health Image Library (PHIL); http://phil.cdc.gov/phil/home.asp.) a. Plasmodium ovale. b. Babesia microti. c. Plasmodium malariae. d. Trypanosoma cruzi. B The diagnosis of babesiosis is made from a Wright-Giemsastained thin blood smear. The organisms appear as small, delicate, ring-form trophozoites, about 1 to 2 m, with a prominent chromatin dot and faintly staining cytoplasm. More mature trophozoites may appear as pyriform organisms in single, double, or the classic tetrad (Maltese cross) formation within the red blood cells. CDC PHIL #5944 REF: 656 OBJ: Level 3: Synthesis 3. What is the organism shown below? (Courtesy CDC Public Health Image Library (PHIL); http://phil.cdc.gov/phil/home.asp.) a. Brugia malayi b. Loa loa c. Wuchereria bancrofti d. Onchocerca volvulus C Diagnosis of W. bancrofti should include the examination of a blood specimen obtained at night (10 p.m. to 2 a.m.) for the presence of microfilariae. The blood may be examined immediately for live microfilariae. If examined on a Wright’s-stained smear, the microfilariae of W. bancrofti are sheathed, and the nuclei do not extend to the tip of the tail. CDC PHIL #3010 REF: 681 OBJ: Level 3: Synthesis 4. A woman who just returned from a trip to Southeast Asia has signs of biliary obstruction, which is confirmed by CT scan. Due to her recent travel history, the physician orders an O&P examination before considering surgical intervention. The following element is found in her fecal sample. The most likely identity of this organism is: (Courtesy CDC Public Health Image Library (PHIL); http://phil.cdc.gov/phil/home.asp.) a. Schistosoma mansoni. b. Opisthorchis sinensis. c. Fasciola hepatica. d. Heterophyes heterophyes. B The Chinese liver fluke, Clonorchis (Opisthorchis) sinensis, is geographically limited to the Far East, where dogs and cats serve as reservoir hosts. The adults live in the distal bile ducts. Repeated or heavy infections cause inflammation because of mechanical irritation, fever, diarrhea, pain, fibrotic changes, or obstruction of the bile duct. The diagnosis is made by finding the egg in a stool specimen. The egg is 29 to 35 m long, embryonated when passed, flash shaped, and operculated with prominent shoulders at the operculum and a knob at the opposite end. CDC PHIL #5248 REF: 665 OBJ: Level 3: Synthesis 5. A young man from rural Brazil is visiting family in the United States when he becomes ill with muscle pains, high fever, and hepatosplenomegaly. A blood sample taken in the emergency room reveals the following organism. The most likely identification of this organism is: (Courtesy CDC Public Health Image Library (PHIL); http://phil.cdc.gov/phil/home.asp.) a. Leishmania donovani. b. Babesia microti. c. Plasmodium falciparum. d. Trypanosoma cruzi. D The primary diagnostic stage in the blood is the trypomastigote. It is an elongated structure 15 to 20 m long that often appears in a C or U shape. Individuals in the acute phase may be asymptomatic or have local symptoms including the presence of a chagoma (ulcerative skin lesion at the site of the insect bite) or a unilateral edema around the eye (Romaña sign) if the bite is on the ocular conjunctiva. Systemic manifestations include fever, lymphadenitis, hepatosplenomegaly, malaise, muscular pains, and diarrhea and vomiting. The latent phase can last 10 to 40 years after infection, but only about 30% to 40% of patients develop the chronic form of Chagas disease. CDC PHIL #3013 REF: 649 OBJ: Level 3: Synthesis 6. Five members of a family develop a sudden onset of watery diarrhea, nausea, vomiting, headache, and cramps. They go to the family physician who orders fecal cultures and complete ova and parasites (O&P) analysis. Each sample reveals the presence of organisms seen below. The most likely cause of the infection is: (Courtesy CDC Public Health Image Library (PHIL); http://phil.cdc.gov/phil/home.asp.) a. Cryptosporidium parvum. b. Isospora belli. c. Cyclospora cayetanensis. d. Encephalitozoon intestinalis. A The recommended detection methods when Cryptosporidium infection is suspected are the modified Ziehl-Nielsen acid-fast stain and an immunofluorescent antibody test using a monoclonal antibody directed against Cryptosporidium. With the acid-fast stain, the organism stains as a bright red sphere that distinguishes it from yeasts, which stain green. CDC PHIL #5242 REF: 659 OBJ: Level 3: Synthesis 7. A housewife from the Great Lakes area comes to her family physician with fatigue and malaise. Blood tests show that she has enlarged but pale red blood cells (RBCs) (megaloblastic anemia) along with a vitamin B12 deficiency. Her history includes a dietary habit of making pickled fish, a family favorite. Because of this, an O&P is also requested and reveals the following parasite egg. What is the identity of this parasite? (Courtesy CDC Public Health Image Library (PHIL); http://phil.cdc.gov/phil/home.asp.) a. Hymenolepis nana b. Taenia saginata c. Diphyllobothrium latum d. Taenia solium C D. latum, the fish tapeworm, is found worldwide in areas where the population eats pickled or raw fresh water fish. In the United States, it is primarily seen in the areas around the Great Lakes. The organism may cause a vitamin B12 deficiency, especially in persons of northern European descent, and long-term infection may lead to a megaloblastic anemia. The egg is operculated and yellow-brown, about 58 to 76 m by 40 to 50 m and has a small, knoblike protuberance at the end opposite the operculum. CDC PHIL #1541 REF: 668 OBJ: Level 3: Synthesis 8. The following organism was found in the fecal sample of a patient with diarrhea and elevated liver enzymes. This organism is most likely: (Courtesy CDC Public Health Image Library (PHIL); http://phil.cdc.gov/phil/home.asp.) a. Entamoeba histolytica. b. E. hartmanni. c. Giardia lamblia. d. E. coli. A The size of the organism ranges from 10 to 50 m, averaging 15 to 25 m. The organism is refractile, and the characteristic “bull’s-eye” nucleus, consisting of a small central karyosome. Even, fine peripheral chromatin may be only slightly visible. The average size of the E. histolytica cyst is 10 to 20 m and may have one to four nuclei each with a small central karyosome and fine, evenly distributed peripheral chromatin. CDC PHIL #607 REF: 634 OBJ: Level 3: Synthesis 9. Several children at a daycare center are having trouble sleeping and are showing increasing signs of restlessness. Because one child was recently diagnosed with a parasite, the parents are informed that other children should be tested. The organism below is found during examination. This organism is: (Courtesy CDC Public Health Image Library (PHIL); http://phil.cdc.gov/phil/home.asp.) a. Trichuris trichiura. b. Enterobius vermicularis. c. Ascaris lumbricoides. d. hookworm. B Enterobius vermicularis (pinworm) is a worldwide parasite commonly detected in children. Key risk factors for this infection are inadequate personal and/or community hygiene. The cellophane tape preparation is routinely used for detection of suspected pinworm infections. This procedure involves swabbing the child’s perianal area with a tongue blade covered with cellophane tape (sticky side out). The egg is oval, colorless, and slightly flattened on one side. It measures approximately 50 to 60 m by 20 to 30 m. CDC PHIL #5229 REF: 674 OBJ: Level 3: Synthesis 10. A recent emigrant from Somalia develops high fever, chills, and severe headache. Blood work on admission to the hospital reveals the following in his blood smear. This patient is most likely infected with: (Courtesy CDC Public Health Image Library (PHIL); http://phil.cdc.gov/phil/home.asp.) a. Plasmodium ovale. b. P. malariae. c. P. falciparum. d. P. vivax. C P. falciparum invades RBCs of any age and, for this reason, often exhibits the highest parasitemia—reaching 50% in some cases. The ring forms of P. falciparum are more delicate than those of other species, often have two chromatin dots, and may show multiple ring forms in a single RBC. Gametocytes have a characteristic banana or crescent shape. CDC PHIL #5941 REF: 655 OBJ: Level 3: Synthesis 11. A farmer who raises sheep and cattle shows signs of jaundice. Along with elevated liver enzymes, he also has an elevated eosinophil count. A fecal sample for O&P shows the parasite form seen below. The organism causing this infection is: (Courtesy CDC Public Health Image Library (PHIL); http://phil.cdc.gov/phil/home.asp.) a. Wuchereria bancrofti. b. Brugia malayi. c. Loa loa. d. Fasciola hepatica. D Fasciola hepatica, the sheep liver fluke, is seen in the major sheep-raising areas of the world, including parts of the southwestern United States. In addition, the organism is found in some cattle-raising areas. The unembryonated and operculated eggs of Fasciola hepatica are carried in the bile to the intestinal tract and are passed in the feces. The size range is 130 to 150 m by 60 to 90 m. They are virtually indistinguishable from eggs of F. buski. CDC PHIL #4846 REF: 664 OBJ: Level 3: Synthesis 12. A woman patient with history of travel to tropical Africa was noncompliant with her antimalarial medications. She now has a cyclical fever and paroxysm every 72 hours. The following organism is seen in her peripheral blood smear consistent with an infection caused by: (Courtesy CDC Public Health Image Library (PHIL); http://phil.cdc.gov/phil/home.asp.) a. Plasmodium ovale. b. P. vivax. c. P. falciparum. d. P. malariae. D Plasmodium malariae usually invades older RBCs, perhaps accounting for the occasional darker appearance of the invaded RBC. The life cycle is characterized as quartan, with reproduction occurring every 72 hours and invasion of new RBCs every fourth day. The trophozoite of P. malariae is compact and may assume a characteristic “band” appearance, in which it stretches across the diameter of the RBCs. The mature schizont contains 6 to 12 merozoites with an average of 8. Merozoites may be arranged in a characteristic loose daisy petal arrangement around the clumped pigment. CDC PHIL #5130 REF: 650 OBJ: Level 3: Synthesis 13. An international male student from Egypt comes to the campus clinic complaining of blood in his urine. A urinalysis reveals the parasite seen below. This organism is: (Courtesy CDC Public Health Image Library (PHIL); http://phil.cdc.gov/phil/home.asp.) a. Schistosoma mansoni. b. S. japonicum. c. S. haematobium. d. S. madurella. C S. haematobium, which is primarily found in the Nile Valley, the Mideast, and East Africa, lives in the veins surrounding the bladder. Diagnosis is made by finding embryonated eggs in the urine. S. haematobium eggs are elongated and 110 to 170 m by 40 to 70 m, and have a terminal spine. The best time to collect the eggs in urinary schistosomiasis is during peak excretion time in early afternoon (12 p.m. to 2 p.m.). CDC PHIL #4843 REF: 666 OBJ: Level 3: Synthesis 14. A patient with recent history of travel to the Philippines has bloody diarrhea. An O&P sample shows the following parasite egg. What is this called? (Courtesy CDC Public Health Image Library (PHIL); http://phil.cdc.gov/phil/home.asp.) a. Schistosoma mansoni b. S. japonicum c. S. haematobium d. S. madurella B S. japonicum, which is commonly found in the Far East, including Japan, China, and the Philippines, lives in venules of the small intestine. The egg spines cause trauma to the tissues and walls of the vessels during the early stage of acute infections and can result in diarrhea. S. japonicum eggs are round and 60 to 95 m by 40 to 60 m; they have a small, curved, rudimentary spine. CDC PHIL #4842 REF: 666 OBJ: Level 3: Synthesis 15. A patient who has traveled to the Puerto Rico comes to clinic with a history of diarrhea for the past 2 weeks. A fecal sample collected for O&P shows the following parasite. This organism is most likely: (Courtesy CDC Public Health Image Library (PHIL); http://phil.cdc.gov/phil/home.asp.) a. Schistosoma mansoni. b. S. japonicum. c. S. haematobium. d. S. madurella. A S. mansoni, which is most commonly found in Africa, parts of South America, the West Indies, and Puerto Rico, lives in venules of the mesentery and large intestines. The egg of S. mansoni is yellowish, elongated and 115 to 175 m by 45 to 75 m, and has a prominent lateral spine. CDC PHIL #4841 REF: 666 OBJ: Level 3: Synthesis 16. A patient finds a small ribbon-like piece in his stool sample and reports this to his physician. The physician orders a fecal O&P analysis that reveals the following egg in the sample. The most likely identity of this parasite is: (Courtesy CDC Public Health Image Library (PHIL); http://phil.cdc.gov/phil/home.asp.) a. Hymenolepis nana. b. Taenia spp. c. Diphyllobothrium latum. d. Paragonimus westermani. B Laboratory diagnosis of Taenia spp. infection can be made by finding the egg, scolex, or proglottid in the feces. The egg is yellow-brown and surrounded by a thick wall with radial striations; it measures 30 to 43 m. The egg is embryonated with a six-hook oncosphere when passed in the feces. Eggs of this species are indistinguishable and must be reported as “Taenia spp.” eggs. CDC PHIL #906 REF: 669 OBJ: Level 3: Synthesis 17. A patient with a history of eating wild game comes to the physician with a history of diarrhea over the past 3 weeks. In addition he complains of fever, muscular pain and tenderness, headache, and general weakness. The patient also has a significant eosinophilia. A biopsy of a nodular area on his forearm is seen in the image below. This is consistent with a diagnosis of: (Courtesy CDC Public Health Image Library (PHIL); http://phil.cdc.gov/phil/home.asp.) a. Leishmania donovani. b. Wuchereria bancrofti. c. Trichinella spiralis. d. Loa loa. C Trichinosis is the infection of muscle tissue with the larval form of T. spiralis, a helminth whose adult stages live in the human intestine. Humans acquire the infection by eating undercooked meat, particularly pork that contains the larval forms. In recent years ingestion of wild game has led to infection by other species of Trichinella. Because it is difficult to recover adults or larvae in a stool sample, the diagnosis is often based on clinical symptoms and the patient’s history. Biopsy of muscle tissue and identification of encapsulated, coiled larva is the definitive diagnostic method. CDC PHIL #10142 REF: 679 OBJ: Level 3: Synthesis 18. A young man who returned a week ago from a family vacation to Kenya, develops a high fever and delirium. Although he was compliant with his antimalarial medications, a blood sample is taken to rule out malaria. The laboratory scientist sees the following on the blood smear. This organism is most likely: (Courtesy CDC Public Health Image Library (PHIL); http://phil.cdc.gov/phil/home.asp.) a. Trypanosoma brucei. b. Leishmania donovani. c. Wuchereria bancrofti. d. Loa loa. A Trypanosoma brucei rhodesiense and Trypanosoma brucei gambiense are the causative agents of human African trypanosomiasis, commonly called sleeping sickness, which is seen primarily in central Africa. The diagnostic stage of trypanosomes in humans is the trypomastigote, which is usually seen in a Wright’s-stained blood smear. The trypomastigote is 15 to 20 m, with a single large nucleus and a posterior kinetoplast to which is attached the flagellum of the undulating membrane. CDC PHIL #3017 REF: 647 OBJ: Level 3: Synthesis 19. A patient comes to the emergency room stating that he has fever and chills every 48 hours. The patient has a history of travel to Central America in the past month and did not take any preventative measures against malaria. A complete blood count (CBC) shows the following RBC inclusions. This organism is most likely: (Courtesy CDC Public Health Image Library (PHIL); http://phil.cdc.gov/phil/home.asp.) a. Plasmodium malariae. b. P. ovale. c. P. falciparum. d. P. vivax. D P. vivax has the widest geographic distribution and is the one most likely to be found in temperate climates. A fine pink stippling, known as Schüffner’s stippling, may be present in the cell. The young trophozoite of P. vivax is characterized by its ameboid appearance; by maturity, it usually fills the red blood cell, and golden brown malarial pigment is present. CDC PHIL #5927 REF: 650 OBJ: Level 3: Synthesis 20. When a request is submitted to examine a blood sample for malaria, which of the following procedures should be performed? a. A thick smear for maximum detection and to determine morphology b. A PVA trichrome-stained blood smear c. A Giemsa thick blood smear preparation for maximum detection and a thin smear for speciation d. A formalin-ethyl acetate concentration for detection and a thin smear for speciation C History of travel to an endemic area and the presence of classic clinical symptoms, including the malarial paroxysm of fever and chills, should alert a health care provider to request Giemsa-stained thick and thin smears for malaria. The thick smear is used to detect malarial parasites; however, distortions of parasite morphology and the lack of intact RBCs require that a thin smear be examined to identify the species. REF: 653 OBJ: Level 1: Recall