Parasites MCQ

*The answer is C.* This patient presents with giardiasis, which is best treated with metronidazole. Giardiasis is an infectious disease caused by the protozoa Giardia lamblia. The organism attaches to the lining of the walls of the duodenum, and leads to malabsorption and diarrhea. The diarrhea is characteristically foul-smelling and fatty, and patients typically complain of bloating and flatulence. The infection is frequently seen in hikers and campers who consume water from natural sources such as fresh water rivers.

A 17-year-old male returns from a camping trip. He complains of abdominal bloating and flatulence. On further review, he reports foul-smelling diarrhea, which is difficult to flush. The results of staining a stool specimen with iodine are shown in Figure A. Which of the following treatment options is most appropriate? A. Penicillin B. Azithromycin C. Metronidazole D. Trimethoprim-sulfamethoxazole E. Ribavirin

*The answer is E.* The symptoms are consistent with the sexually transmitted infection caused by Trichomonas vaginalis. This protozoal flagellate is highly motile and easily distinguished from other sexually transmitted disease pathogens by light microscopy. The other protozoal pathogens listed do not cause diseases that present with genitourinary tract symptoms.

A 22 year old female visits her gynecologist complaining of a foul-smelling vaginal discharge and severe itching. A specimen was collected and examined it by light microscopy revealing highly motile, nucleated cells with multiple flagella. What is the most likely causative agent of this infection? A. Balantidium coli B. Plasmodium falciparum C. Toxoplasma gondii D. Giardia lamblia

*The answer is C.* The patient appears to be infected with one of the New World Leishmania organisms, probably L. braziliensis or L. mexicana. The sand fly is the vector. The insect bite will progressively evolve into a cutaneous ulcer. If untreated, the ulcer will spontaneously heal—after several weeks. Because the parasite attacks the reticuloendothelial system, it has the potential to reappear with a vengeance (i.e., as disseminated disease). Such is the case with this patient. T cell cytotoxicity is a major virulence component of all forms of leishmaniasis. Cercarial dermatitis is a schistosome disease, an accidental parasite of no real consequence. Tungiasis, although caused by a tropical parasite (specifically a flea that embeds in tissue), usually involves only the ankle or foot. The scabies mite will most often manifest as small, circumscribed, pruritic eruptions.

A 24-year-old emigrant from Belize presents with an insidious but nontender skin condition that on casual inspection appears to be lepromatous leprosy (shown in the photographs); however, scraping from the skin lesions do not produce acid-fast bacilli when stained. Consequently, the attending physician believes that his patient is infected with a parasite common to tropical areas of Central America. Of the following diseases, which is the most reasonable diagnosis? (A) Cercarial dermatitis (B) Chronic Chagas' disease (C) Disseminated cutaneous leishmaniasis (D) Scabies (E) Tungiasis

*The answer is A.* This patient is presenting with flatulence, bloating, and foul-smelling diarrhea suggestive of giardiasis. The first-line treatment for giardiasis is metronidazole. The clinical presentation of flatulence, bloating, and foul-smelling diarrhea following a hiking trip is characteristic of giardiasis. The stool sample demonstrating a flagellated trophozoite confirms the diagnosis of giardiasis. Giardia lamblia is an anaerobic protozoon that is usually transmitted to humans via waterborne cysts that are ingested by drinking water from mountain streams. They can be seen on histology as flagellated trophozoites that "look back at you." The first-line therapy for symptomatic giardiasis is metronidazole, an antibiotic and anti-protozoal agent. Of note, patients with IgA deficiency are at an increased risk of developing giardiasis due to an inability to mount an immune response against mucosal parasitic infections. Giardia rarely causes bloody diarrhea, so the blood on the toilet paper in this case likely stemmed from abrasion due to excessive wiping.

A 26-year-old male presents to his primary care physician complaining of diarrhea. He recently returned from a two-week hike in the Peruvian Andes mountains, during which time he ate undercooked chicken and beef. Since returning, he has experienced frequent bloating, flatulence, and several foul-smelling watery stools per day. He has recently noticed blood on the toilet paper after wiping. His past medical history is notable for asthma. He takes albuterol and low-dose budesonide. His temperature is 100°F (37.8°C), blood pressure is 120/70 mmHg, pulse is 90/min, and respirations are 20/min. A stool sample is shown in Figure A. What is the most appropriate treatment for this patient? A. Metronidazole B. Ciprofloxacin C. Amipicillin D. Vancomyin E. Sulfasalazine

*The answer is E.* In all probability, this is a case of pseudoappendicitis. Along with several types of bacteria (e.g., Yersinia, Campylobacter, and Salmonella), many parasitic roundworms (e.g., agents of anisakiasis, Enterobius, and Trichuris) have been implicated in pseudoappendicitis. The bacillary band, short muscle fi bers, and the stichosome esophagus are reliable morphological attributes consistent with T. trichiura. However, from the medical student's perspective, the point of the question is not so much worm morphology but rather if the appendix is able to sustain the growth of a parasite. Whipworms normally reside in the large intestine, hookworms (Necator and Ancylostoma) in the small intestine, B. malayi in the lymphatics, and D. medinensis in the skin. The vermiform appendix is considered large intestine by histologists and theoretically would support the physiological needs of a whipworm but not the other choices. In view of the clinical presentation, an appendectomy seems reasonable; however, healthcare professionals should recognize the possibility of parasites mimicking appendicitis, especially when dealing with patients who have recently lived in the tropical areas of the world. The clinical importance of T. trichiura should not be underestimated.

A 30-year-old male, who recently emigrated from Asia, presents at the emergency room with severe intestinal spasms and cramps. The abdominal pain has persisted for almost 2 days. Physical examination reveals bowel sounds and localized tenderness of the right lower quadrant with rebound tenderness. An appendectomy is performed. The pathology report does not describe associated inflammation but does mention that the anterior or head end of a parasitic worm is embedded in the mucosa. The cross section of the parasite at the level of its esophagus is shown in the image. Which of the following is the probable offending agent in this case? (A) Ancylostoma duodenale (B) Brugia malayi (C) Dracunculus medinensis (D) Necator americanus (E) Trichuris trichiura

*The answer is A.* In general, all species of malaria are transmitted via the bite of an anopheline mosquito.

A 40-year man, who recently returned from a vacation in Brazil, seeks medical care at an urgent care clinic because of an incapacitating febrile illness of 4 days duration. On examination, the patient has a temperature of 104 °F and complains of generalized body aches and pains. Laboratory blood work reveals pancytopenia and decreased hemoglobin. A blood smear is shown in the image. Chloroquine was prescribed and, within days, the patient made a dramatic recovery. How was the infection in the above case acquired? (A) Bite of an infected mosquito (B) Drinking contaminated water (C) Inhalation of agent shed in rodent urine (D) Person-to-person via respiratory droplets (E) Swimming in contaminated streams or lakes

*The answer is A.* Chloroquine by itself is considered incomplete therapy. Plasmodium vivax, due to the hypnozoite stage in the liver, will relapse every few months for 3 to 5 years. Primaquine targets this stage of the parasite. Although P. vivax, if left untreated, can lead to organ damage, cerebral malaria, and renal manifestations (blackwater fever) are typically associated with P. falciparum.

A 40-year man, who recently returned from a vacation in Brazil, seeks medical care at an urgent care clinic because of an incapacitating febrile illness of 4 days duration. On examination, the patient has a temperature of 104 °F and complains of generalized body aches and pains. Laboratory blood work reveals pancytopenia and decreased hemoglobin. A blood smear is shown in the image. Chloroquine was prescribed and, within days, the patient made a dramatic recovery. Why would the infectious disease resident caring for the patient in the above case recommend a combination therapy that included primaquine? (A) To treat the exoerythrocytic stages and reduce the chance of relapse (B) To prevent the emergence of resistant strains of this organism (C) To treat coinfection with a related organism (D) To prevent central nervous system manifestations (E) To prevent development of renal disease

*The answer is E.* Based on the clinical picture, the most reasonable diagnosis is a Plasmodium vivax infection. The intraerythrocytic trophozoite and Schüffner's dots are irrefutable evidence. Geographically, P. vivax is the most prevalent form of malaria in Latin America and possibly the world. P. ovale is an African parasite. Due to its small size, Babesia might be mistaken for P. falciparum but never P. vivax. Leishmaniasis and Chagas' disease are not characteristically intraerythrocytic.

A 40-year man, who recently returned from a vacation in Brazil, seeks medical care at an urgent care clinic because of an incapacitating febrile illness of 4 days duration. On examination, the patient has a temperature of 104 °F and complains of generalized body aches and pains. Laboratory blood work reveals pancytopenia and decreased hemoglobin. A blood smear is shown in the image. Chloroquine was prescribed and, within days, the patient made a dramatic recovery. What is the diagnosis? (A) Babesiosis (B) Chagas' disease (C) Ovale malaria (D) Visceral leishmaniasis (E) Vivax malaria

*The answer is A.* A person may be infected with a different strain of malaria if they move to another geographic area. This accounts for why the child was reinfected a year later. Falciparum malaria is nonrelapsing. Vivax malaria, because of the hypnozoite stage latent in the liver, may relapse for up to 5 years. Recrudescence, due to a subclinical infection, has been reported for P. malariae. Complement deficiencies are linked to recurring meningococcal infections.

A 5-year-old child, who lives with his missionary parents in a rural locality in Sierra Leone, Africa, contracts an illness that is initially characterized by vomiting and periods of moderate fever. Over the next few days, his condition dramatically worsens, he becomes markedly lethargic, and his fever intensifies to the point of delirium and convulsions. At the aid station, a blood smear reveals the infective agent (shown in the image). The child in the above case makes a full recovery following treatment. But, when the family is transferred to another region of Africa a year later, the child is again diagnosed with the same infection. What is the most likely explanation for the second infection? (A) The child was infected with a different strain of the same organism. (B) The child is deficient in complement components C5-C9 and could not clear the organism despite appropriate treatment. (C) The child was inadequately treated a year ago, and was not completely cleared of the organism. (D) The infection is chronic for up to 20 years, and an annual recrudescence is to be expected. (E) This is a relapse and is attributed to the activation of the dormant liver stage or hypnozoite.

*The answer is C.* Chloroquine is not recommended for falciparum malaria treatment in many areas of the world due to resistance of this organism to the drug. Resistant strains of Plasmodium falciparum express an energy-dependent effl ux pump which prevents accumulation of chloroquine in the parasite cell body. Malarone is one of the several agents that can be used for the treatment of chloroquine-resistant P. falciparum. Other treatment regimens include quinine sulfate plus either doxycycline, tetracycline, or clindamycin, or mefloquine. Carbapenems are β-lactam antibiotics; amphotericin is an antifungal drug and foscarnet is an antiviral drug used for the treatment of infections with cytomegalovirus.

A 5-year-old child, who lives with his missionary parents in a rural locality in Sierra Leone, Africa, contracts an illness that is initially characterized by vomiting and periods of moderate fever. Over the next few days, his condition dramatically worsens, he becomes markedly lethargic, and his fever intensifies to the point of delirium and convulsions. At the aid station, a blood smear reveals the infective agent (shown in the image). The child in the above case requires aggressive treatment. Which antimicrobial is suitable for treatment of this organism? (A) A carbapenem (B) Amphotericin B (C) Atovaquone plus proguanil (Malarone) (D) Chloroquine (E) Foscarnet

*The answer is E.* The double ring trophozoites seen in the red blood cells, and the lack of erythrocytic Schüffner's dots are consistent with P. falciparum. This is the most severe form of malaria and rapid diagnosis is critical. This type of malaria is wide spread in Africa and young children are extremely vulnerable to the disease largely because they are immunologically naive. Frequently, the manifestations of fever are experienced by children with a falciparum infection. Complications of this infection include renal failure and cerebral malaria. Babesia is a related organism that typically causes mild disease, and is transmitted by ticks in the northeastern United States. Brugia is a helminth parasite associated with elephantiasis. Cryptosporidium is an intestinal protozoan associated with severe diarrhea in the immune compromised and L. tropica is an intracellular protozoan causing skin ulcers.

A 5-year-old child, who lives with his missionary parents in a rural locality in Sierra Leone, Africa, contracts an illness that is initially characterized by vomiting and periods of moderate fever. Over the next few days, his condition dramatically worsens, he becomes markedly lethargic, and his fever intensifies to the point of delirium and convulsions. At the aid station, a blood smear reveals the infective agent (shown in the image). What is the cause of this child's illness? (A) Babesia microti (B) Brugia malayi (C) Cryptosporidium parvum (D) Leishmania tropica (E) Plasmodium falciparum

*The answer is D.* Although several nematode species have been linked to ocular parasitic infections in humans, T. canis is the most common cause of ocular toxocariasis or ocular larva migrans— a variety of visceral larva migrans. Children who suffer from pica, especially geophagy, are the ones at most risk. Dogs and cats naturally harbor the parasitic worm. Embryonated eggs are infective to children, even though the human is an unsuitable host for parasite maturation. Retinal involvement is simply a matter of chance as the worm has the potential to migrate to any visceral organ. Unfortunately, due to the inflammatory response, visually distinguishing the condition in situ from a retinoblastoma is difficult. Enucleation and subsequent histopathogenic examination might be required for an accurate diagnosis. Trichuris trichiura matures in the intestinal tract; A. caninum is an agent of cutaneous larva migrans; and, O. volvulus and L. loa are tropical fi larial worms that are transmitted by an arthropod vector.

A 6-year-old boy, who has a history of eating dirt while playing in a New York City park, develops a vision problem in one eye. An opaqueness of pupil or leukokoria is readily discernable by the parents, and this prompts a visit to the ophthalmologist. Funduscopic examination reveals a single granulomatous lesion of the retina. Assuming that his ocular condition is caused by a parasitic worm, what is most likely the etiologic agent? (A) Ancylostoma caninum (B) Loa loa (C) Onchocerca volvulus (D) Toxocara canis (E) Trichuris trichiura

*The answer is A.*This cestode, sometimes called the broad fish tapeworm, has the tendency to absorb large quantities of vitamin B12 from the intestinal tract of the human host—thus producing a tapeworm pernicious anemia. The species is common in parts of Finland, but similar species occur elsewhere in northern boreal regions and other areas of the world. Freshwater fi sh carry infective juvenile tapeworms, but cooking the fish will inactivate these encysted juveniles. The egg—noted in the stool concentration— features an anopercular knob, and the scolex is adorned with bothria (shown in the image) and not suckers or hooks. These are considered reliable markers in the identification of the species in the clinical laboratory.

A 65-year-old woman in Finland suffers from a macrocytic anemia. Her history is significant for frequent consumption of pickled fish. A stool sample reveals parasite ova like the one shown in the first image. Upon treatment, she expels a tapeworm similar to the stained specimen shown in the second image. With which tapeworm was she most likely infected? (A) Diphyllobothrium latum (B) Echinococcus granulosus (C) Hymenolepis nana (D) Taenia saginata (E) Taenia solium

*The answer is B.* Enterobius vermicularis, the causative agent of enterobiasis or human pinworm disease, is a common childhood parasitic infection in the United States, especially in middle-class families. The child becomes infected by ingesting embryonated eggs indoors, usually in a home or school setting. The human pinworm does not infect household pets; therefore, dogs and cats are not involved in the life cycle. Controversy still exists; however, as to the parasite's medical importance, but most microbiologists consider infections to be underrated. Treatment is almost always recommended.

A 9-year-old child is observed repeatedly scratching herself around the anal canal. Distinctive microscopic eggs (shown in the image) are detected via the cellophane tape technique. What is the correct diagnosis? (A) Ascariasis (B) Enterobiasis (C) Strongyloidiasis (D) Trichinosis (E) Trichuriasis

*The answer is B.* Diphyllobothrium latum and similar species are transmitted to people when raw or insufficiently cooked fish is consumed. The plerocercoid or the infective stage resides in the flesh of freshwater fish like trout and salmon. Although human sewage may play a role in the perpetuation of the life cycle, a person cannot become infected by ingesting the tapeworm eggs in drinking water.

A businessman who recently returned from a trip to Scandinavia goes to the clinic because of intestinal distress. Based on positive stools, a diagnosis of diphyllobothriasis is made. What is the most likely vehicle for infection in the above case? (A) Drinking water (B) Raw fi sh (C) Raw hamburger (D) Salad greens (E) Soil or sewage

The answer is E.* This is an imported case of cysticercosis. The daughter presumably acquired the infection from a household contact—her father being the likely candidate. Taenia solium eggs are infectious immediately when they are passed in feces. Further environmental development is unnecessary. Therefore, contaminated salad or possibly other uncooked vegetables is the most probable means of transmission. Since the child did not harbor the adult tapeworm, autoinfection will not occur. Although fairly common in Latin America, T. solium has a low-degree of endemicity in the United States. The disease is most prevalent in countries that are challenged with issues of poor hygiene and sanitation. Cysticercosis takes approximately 1 year to develop, which would discount the possibility of polluted drinking water and the recent eating of raw pork. Cysticercosis should not be viewed as merely a medical curiosity but an important and potentially life-threatening parasitic disease.

A 9-year-old patient—a daughter of a migrant farm laborer—experiences onset of epileptic seizures. The family has recently arrived in the United States from Mexico. A few pea-sized lipoma-like lesions are undeniably palpable in her subcutaneous tissue of her torso and limbs. Excision of two of these lesions reveals parasites (shown in the image). These parasites are active when placed in warm saline. MRI demonstrates similar lesions in the CNS, and an immunoblot assay is positive for the suspected parasitic disease. Of interest is the discovery of taeniid ova in the stool of her father. What was the probable source or vehicle of infection for the child in the above case? (A) Autoinfection from her own feces (B) Consuming rare hamburgers (C) Consuming undercooked pork (D) Drinking fecal contaminated water at the farm labor camp (E) Ingestion of fecal-contaminated salad vegetables

*The answer is D.* The diagnosis is cysticercosis. The condition is a result of cysticerci or bladderworms (sometimes referred to as juvenile tapeworms) infecting the tissue of the patient. Almost any tissue can be infected, but intraocular cysticercosis and neurocysticercosis pose grave challenges for the patient. Other serious infections involve cardiac and parenchymal brain tissue. Seizures are regularly reported in the CNS patient. Direct visualization of the juvenile parasites in biopsy or excised tissue can be done. The immunoblot assay is the test of choice to confirm the diagnosis of neurocysticercosis suggested by CT and MRI findings. Although the cystic form of the parasite is sensitive to the taeniacidal drugs like albendazole, the dead and dying worms may promote adverse inflammatory reactions. To minimize this situation, coadministration of an antiseizure medication and a corticosteroid is generally recommended.

A 9-year-old patient—a daughter of a migrant farm laborer—experiences onset of epileptic seizures. The family has recently arrived in the United States from Mexico. A few pea-sized lipoma-like lesions are undeniably palpable in her subcutaneous tissue of her torso and limbs. Excision of two of these lesions reveals parasites (shown in the image). These parasites are active when placed in warm saline. MRI demonstrates similar lesions in the CNS, and an immunoblot assay is positive for the suspected parasitic disease. Of interest is the discovery of taeniid ova in the stool of her father. Which parasite is most likely the cause of the child's illness? (A) Echinococcus granulosus (B) Onchocerca volvulus (C) Taenia saginata (D) Taenia solium (E) Toxocara canis

*The answer is E.* Hydroceles are perhaps the most common presentation of W. bancrofti, a filarial worm that is endemic to Brazil. The diagnostic microfilaria is described as being sheathed but is often not visible in Giemsa-stained material. Chyluria is an associated sign. Scrotal elephantiasis is successfully managed through surgery. The other nematodes listed are not associated with this presentation.

A Brazilian man presents with an enlarged scrotum (shown in the first photograph). The man reports that his scrotum is gradually "getting bigger." During the medical history, he also expresses alarm that his urine appears milky—giving the physician the impression that he is also suffering from chylous urine. A thick blood film stained with Giemsa is shown in the second image. With which organism is he most likely infected? (A) Ancylostoma brasiliense (B) Loa loa (C) Onchocerca volvulus (D) Trichinella spiralis (E) Wuchereria bancrofti

*The answer is B.* Clonorchiasis, a liver-bile duct parasitic disease, is endemic to Taiwan and many other regions of Southeast Asia. Millions of people harbor this parasite. Although not the intent of this question, there may be a more-than-causal connection between cholangiocarcinoma and Clonorchis. The important point here is the fact that this is a liver fluke. The cross-section of the parasite in the histological section clearly demonstrates the presence of twin intestinal caeca, a reliable morphological marker for flukes. Ascaris is a huge worm in comparison and appears round in cross section; Fasciola is also large and the fl uke is more endemic to North America; both the adult and juvenile stages of T. solium do not customarily involve the bile ducts; and, E. histolytica would present as a liver abscess.

A Taiwanese patient dies from complications of cholangiocarcinoma. Postmortem examination determines parasite bile duct involvement. Which of the following is the most likely species? (A) Ascaris lumbricoides (B) Clonorchis sinensis (C) Entamoeba histolytica (D) Fasciola hepatica (E) Taenia solium

*The answer is D.* Cutaneous leishmaniasis is the obvious diagnosis—based on the clinical presentation and the fact that New World leishmaniasis is endemic to tropical environments in Latin America. Direct microscopic or visualization of the amastigote diagnostic stage or the immunochromatographic procedure, which detects antibodies to Leishmania antigen K39, would be more conclusive, however. Both dermotropic and viscerotropic leishmaniasis are endemic to the Middle East. As a result of the Iraq and Afghanistan wars, hundreds of laboratory-confi rmed cases have been reported in GIs. Without question, this parasitic disease has military importance. Avoiding contact with water alludes to schistosomiasis, a disease that is not that common in Central America. There is no evidence of a louse (i.e., nits cemented to clothing fibers) or tick infestation. Targeting anopheline mosquito larva in water would have no relevance since the sandfly is the only reported vector and does not breed in water.

A US Army Special Forces unit is considering establishing a training center in a tropical forested region of Central America. A reconnoiter team of army physicians and public health officers note that a substantial number of children and young adults are afflicted with chronic sores like the ones shown in the photographs. Which of the following measures is most relevant in preventing this disease from becoming a problem in the US soldiers? A) Avoid swimming or wading in waters that contain snails (B) Control the anopheline mosquito larval population with insecticides (C) Frequent inspection of the body and prompt removal of tick (D) Soldiers protecting themselves from the bites of sand flies (E) Washing clothing in hot water to kill attached nits

*The answer is D.* Oftentimes light infections of the human whipworm (Trichuris trichiura) are only treated palliatively; however, a child who is symptomatic and who harbors heavy parasite burdens should be aggressively managed. Failure to treat with an anthelminthic could theoretically result in rectal prolapse. Hypochromic anemia is a possibility, but pernicious anemia (the choice here) refers to the broadfish tapeworm, Diphyllobothrium latum. The human whipworm is small and resides in the large intestine, which would eliminate choice C. Intestinal obstruction anywhere in the intestinal tract would be highly unlikely. The juvenile worms have no pulmonary phase like Ascaris and hookworms. Again, the adult worm resides in the large intestine and occasionally the appendix.

A child is taken to the doctor because of a 2-week bout of abdominal discomfort and diarrheic stools. A fecal concentration reveals scores of bipolar eggs like the one shown, indicating a heavy parasite burden. Which of the following complications might occur if the child is not treated for this parasite? (A) Asthmalike manifestations (B) Blockage of the duodenum (C) Extraintestinal infection (D) Prolapse of the rectum (E) Severe pernicious anemia

*The answer is B.* The consumption and the oozing of blood from the intestinal site where the worm attaches explains the iron-defi ciency anemia. Heavy infections of Trichuris trichiura or the human whipworm (not a choice in this question) has also been linked to anemia. Diphyllobothrium latum or the broad fish tapeworm has been noted to produce a type of pernicious or megaloblastic anemia.

A child with a helminth parasite is found to be anemic. Which parasitic worm is linked to microcytic anemia in children? (A) Broad fi sh tapeworm (B) Hookworm (C) Pinworm (D) Pork tapeworm (E) Schistosome blood fluke

*The answer is A.* The causative agent is Entamoeba histolytica. This is the most common extraintestinal manifestation. Amebic liver abscess develops as a result of a hematogenous spread (i.e., hepatoportal to the liver) and may grow to the size of a grapefruit. In the majority of the patients, leukocytosis occurs. The micrograph depicts a trophozoite.

A fl ight attendant, who works trips to Latin America, presents with fever, right upper abdominal pain, fever, and blood-streaked diarrhea. A stained sample under oil immersion reveals the diagnostic stage (shown in the image). If treatment were to be withheld, what would the fl ight attendant be in danger of developing? (A) A liver abscess (B) Aplastic anemia (C) Bladder cancer (D) Malignancy of the bile duct (E) Pancreatitis

*The answer is D.* This is a microscopic view of the scolex or holdfast organ of the ribbon stage of a taeniid tapeworm like T. solium. It routinely infects the small intestine. The suckers and crown of hooks are characteristic. E. granulosis (echinococcosis) is also a taeniid; however, it occurs as hydatid sand or protoscolices (shown in the image) within a liver or pulmonary cyst. Ascaris and Toxacara are roundworms, and Fasciola is a fluke. Roundworms and fluke do not possess scolices.

A medical student, who is completing a pathology rotation, is given an assignment to review the collection of parasite specimens taken from patients with gastrointestinal disease. On one of the slides, the label is faded and unreadable. Even so, the specimen (shown in the image) is well preserved and, according to the attending pathologist, easy to identify. What is the identification of this parasite? (A) Ascaris lumbricoides (B) Echinococcus granulosum (C) Fasciola hepatica (D) Taenia solium (E) Toxocara canis

*The answer is C.* The reduviid bug, Triatoma infestans, is responsible for transmitting most of the infections of Chagas' disease. The parasite (Trypanosoma cruzi) is passed in the feces of the bug, a process described as posterior station. A pseudocyst or a pocket of amastigotes, is clearly depicted in the micrograph and is characteristic of T. cruzi infection. Cardiac disease, including sudden death, is connected with chronic Chagas' disease. Toxoplasma is associated with litter boxes of cats. Tickborne diseases include Rocky Mountain spotted fever, Lyme disease, and babesiosis. Malaria is transmitted by anopheline mosquitoes, and sand fly species are vectors for leishmaniasis.

A middle-aged man who emigrated from South America unexpectedly dies of cardiac failure. A histological section of myocardial tissue reveals numerous bodies as shown in the image. How did the man most likely become infected with this disease? (A) A sand fly injected the parasite into the blood stream while feeding (B) An infected anopheline mosquito introduced the parasite during a blood meal (C) He inoculated himself by rubbing infected reduviid feces into the bite site (D) The man inadvertently ingested infected feces from a house cat (E) The parasite was transmitted to the man during a tick bite

*The answer is A.* Trophozoites that have engulfed red blood cells and quadrinucleate cysts are strongly suggestive of amebic dysentery or a case of Entamoeba histolytica. Untreated infections may lead to intestinal perforation (due to cysteine proteinases and other tissue-damaging enzymes), peritonitis, or a liver abscess. To complicate matters, nonpathogenic amebae, like E. dyspar, are difficult to distinguish from E. histolytica—except that that nonpathogenic species do not ingest erythrocytes. Parasite antigen detection by ELISA is more sensitive and specific than examination of stool smears.

A missionary returns home from South America because of health problems. Principally, the patient is suffering from weeks of acute colitis. The diarrheic stool sample submitted for analysis is positive for occult blood, trophozoites with ingested erythrocytes (shown in the first image), and quadrinucleate cysts (shown in the second image). Based on these clinical findings, what is the most likely diagnosis? (A) Amebiasis (B) Balantidiasis (C) Cryptosporidiosis (D) Cyclosporiasis (E) Giardiasis

*The answer is C.* Sometimes referred to as creeping eruptions, this is solely a dermal disease in people. The person becomes infected when the fi lariform larva, which is found in moist soil or sand, penetrates bare skin. Individuals who go barefoot in a tropical setting are prime targets. The linear or serpiginous lesion is primarily an infl ammatory response to the microscopic larval worm wandering through the skin. Ancylostoma braziliense, a hookworm that infects dogs and cats, is believed to be the most frequently encountered species, and the human is an unsuitable host for this particular hookworm species. Recommended therapy includes topical thiabendazole, albendazole, or ivermectin. Cercarial dermatitis or swimmer's itch is produced by an avian schistosome and the rash is widespread and produces pruritic papules. Chiggers and the Demodex mites both are capable of producing dermatitis, but the rash will usually not appear serpiginous. Dracunculus medinensis, a nematode that can cause skin lesions, is not found in the United States.

A mother becomes alarmed when she discovers a serpiginous reddish rash on the foot of her child who just returned from a 2-week summer camp ona beach in South Florida. The child reports that the lesion "itches a lot." Their family physician prescribes a topical preparation of thiabendazole and, within 2weeks, the condition resolved. What is the most likely diagnosis? (A) Cercarial dermatitis (B) Chigger dermatitis (C) Cutaneous larva migrans (D) Demodex follicularis infesation (E) Dracunculus medinensis infection

*The answer is B.* Giardia is not a tissue invader. It does not lyse epithelial cells, and therefore, blood in a stool sample cannot be attributed to giardiasis. Iron-deficiency anemias are signs of hookworm disease or diphyllobothriasis. Intestinal blockage is most often a result of ascariasis. The ventral adhesive disc of Giardia allows the parasite to firmly attach to the epithelial lining of the small intestine. Oftentimes, the parasitic burden is so great that this surface is nearly completely covered with protozoans, thus mechanically interfering with the digestive process. Steatorrhea and stools with mucus are reliable signs of a heavy infection.

A number of orphan children from a Third World nation are evaluated for failure to thrive. Some of these children present with debilitating parasitic diarrhea (representative stool sample shown in the image) and exhibit signs of malabsorption. Which of the following microbial virulence-producing attributes most accurately explains the pathology of this parasitic disease? A) Development of macrocytic iron-deficiency anemia (B) Heavy parasite burden covering the epithelial surface of the duodenum (C) Lysis of the epithelial lining in the colon, resulting in blood in the stools (D) Massive infections, resulting in intestinal blockage and peritonitis (E) Perforation of the small intestine and hepatic abscess formation

*The answer is B.* Distinctive clues with this case include the geographic location, socioeconomic conditions, the anemia, and most importantly the fragile nature of the egg. Ancylostoma and Necator hookworms are transmitted when the filariform larvae penetrate bare skin. Parasite eggs are passed in the stool and, under austere sanitary conditions, will contaminate soil. The warm moist soil of the South favors development of the infective stage or the filariform larva. Protein deficiency and mental dullness are clinical manifestations of severe disease.

A nurse who works part time in an elementary school in rural southern Mississippi notes loss of appetite, weakness, and poor school performance in a boy. The child's weight is below the second percentile, and a low hemoglobin level is noted in the laboratory findings. Of note, the child lives in a rural setting without adequate toilet or latrine facilities and customarily goes barefoot. Parasite eggs are observed in the stool sample (shown in the image). What is the diagnosis? (A) Ascariasis (B) Hookworm disease (C) Intestinal amebiasis (D) Strongyloidiasis (E) Taeniasis

*The answer is C.* Praziquantel is the drug of choice for most trematode infections.

A patient is diagnosed as having a trematode infection. Lacking a more specific identification of the causative organism, which of the following drugs would most likely be effective? A. Niclosamide B. Thiabendazole C. Praziquantel D. Diethylcarbamazine E. Tetracycline

*The answer is E.* Motility is a key factor in identifying trophozoites of Trichomonas vaginalis in a wet mount. The preparation should be fresh, however. No clue cells in the micrograph would eliminate the possibility of bacterial vaginosis. Also, the lack of specificity of a stain to distinguish Neisseria gonorrhoeae from normal reproductive tract flora, no budding yeast cells eliminating a vaginal candidiasis, and identifying Chlamydia trachomatis from a saline prep or Gram stain is open to question.

A patient presents with a malodorous vaginal discharge, which according to the patient is significantly worse during menstruation. A motile microbe that is considerably smaller than an epithelial cell is detected in the saline wet microscopic preparation and also a stained preparation (shown in the image). What is the diagnosis? (A) Bacterial vaginosis (B) Candidiasis (C) Chlamydia (D) Gonorrhea (E) Trichomoniasis

*The answer is A.* The intraerythrocytic parasites are similar to falciparum on causal glance; however, clinical presentation and the fact that the patient has not traveled to areas which are known to be endemic to malaria strongly point to babesiosis as the correct diagnosis. Babesia microti, the causative agent, is fairly common in this area of New York (also Massachusetts). It is transmitted to people via a deer tick. At this point in time, clindamycin plus quinine is considered the best possible treatment.

A patient, who lives on Long Island, presents with fever and hemoglobinuria. The lab reports that the CBC is remarkable for a parasite (shown in the image). Of note, the patient has not traveled abroad for at least 10 years, except for an occasional trip to Canada. What is the most likely diagnosis? (A) Babesiosis (B) Benign tertian malaria (C) Falciparum malaria (D) Ovale malaria (E) Quartan malaria

*The answer is C.* The diagnosis is African sleeping sickness—caused by the acute form of Trypanosoma brucei rhodesiense. The trypomastigote stage, seen in the micrograph, is able to hide from host defenses by regularly changing or switching its glycoprotein surface molecules. Cysteine proteinases, phospholipases, and lectin are virulence factors of the diarrheogenic ameba, Entamoeba histolytica. Schistosome blood flukes disguise themselves with a coating of host blood product (i.e., host antigenic mimicry). The occurrence of African sleeping sickness in the United States is extremely rare, but arguably, the real significance of this disease gives insight into a critical microbial mechanism that leads to successful invasion of the human host.

A wildlife photographer travels to a big game park in East Africa and returns home with intermittent fever and a painless chancre-like sore on his neck. A Giemsa-stained blood smear is positive for a flagellated microbe (shown in the image). Which of the following mechanisms gives the microbe the ability to evade humoral defense responses? (A) Cysteine proteinase production (B) Host antigenic mimicry (C) Glycoprotein switching (D) Lectin adhesion (E) Phospholipase activity

*The answer is B.* Based on the number of uterine branches stained by the India ink, the correct identifi cation is Taenia saginata or commonly referred to as the beef tapeworm (i.e., a steer or cow serves as the intermediate host). The bladderworm or Cysticercus—a juvenile tapeworm of sorts—is the infective stage for people, and the vehicle for transmission is insuffi ciently cooked beef. The parasite may only produce vague abdominal discomfort, and the patient becomes aware of an infection when proglottids are noticed in the undergarments or after a bowel movement. T. saginata rarely is transmitted in the United States, but endemicity is high in Asia, Africa, and Latin America.

A woman who emigrated from Asia undergoes a spontaneous abortion, and in the recovery room she passes numerous proglottids. The medical technologist injects one of the proglottids with India ink to delineate the uterus (shown in the image). How did she become infected with this tapeworm? (A) Person-to-person or direct fecal-oral exposure (B) Consumption of insufficiently cooked sirloin (C) Consumption of insufficiently cooked pork sausage (D) Consumption of sushi (E) Fecal contamination of food or drink

*The answer is D.* Praziquantel therapy has a high degree of efficacy. Chloroquine is an antimalarial drug; ivermectin is used in filarial worm infections; metronidazole is used for anaerobic bacterial infections as well as in some protozoal infections, and piperazine is used for infections with the nematodes Ascaris vermicularis and Enterobius vermicularis. Niclosamide is also used for Taenia infections.

A woman who emigrated from Asia undergoes a spontaneous abortion, and in the recovery room she passes numerous proglottids. The medical technologist injects one of the proglottids with India ink to delineate the uterus (shown in the image). What is an appropriate therapy for the woman in the above case? (A) Chloroquine (B) Ivermectin (C) Metronidazole (D) Praziquantel (E) Piperazine

*The answer is C.* The thick shell of the egg stage identifies the disease as ascariasis or an infection of Ascaris lumbricoides. The parasitic helminth is often described as a geohelminth (i.e., to be infective to people, the egg must first develop or embryonate in soil). Ingestion of the contaminated soil results in an infection. The egg stage is remarkably resistant to the environmental pressures and remains viable for years in the soil. Drinking polluted water is the vehicle of transmission for protozoans like the diarrheogenic organisms of Giardia and Entamoeba. Meat is the vehicle for a taeniid tapeworm infection, wading in water best describes the means of acquiring schistosomiasis, and barefoot exposure pertains to the transmission of hookworms.

A young Haitian boy is brought to an aide station by his mother. She is seeking vitamins for her son. She indicates that her son "does not eat" and sometimes complains of nausea. He apparently has no diarrhea and no significant gastrointestinal pain. A fecal concentration is positive for parasite ova (shown in the image). How did this child become infected? (A) Drinking water polluted with the cystic forms (B) Eating insuffi ciently cooked meat infected with cysticerci (C) Ingesting soil contaminated with embryonated eggs (D) Wading in streams that harbor snails and cercariae (E) Walking barefoot, thus allowing larvae to penetrate the skin

*The answer is C.* In this case, the detection of bipolar eggs in the stool and abdominal symptoms are highly suggestive of a Trichuris trichiura or a human whipworm infection. Even though the worm embeds in the mucosa of the large intestine, only patients with heavy worm burdens are treated. Such is apparently the case here.

A young child from Louisiana is seen because of lower abdominal pain and blood-streaked diarrhea. The stool sample shows an abundance of eggs, like the one in the micrograph, suggesting a heavy worm burden. Considering these findings, what is the correct course of action that should be taken by the physician? (A) Order a fresh sample to test for amebic dysentery (B) No treatment necessary since the infection will spontaneously resolve (C) Prescribe albendazole for trichuriasis (D) Prescribe metronidazole for hookworm disease (E) Treat for pernicious anemia but not intestinal parasites

*The answer is D.* Mature cysts of G. lamblia feature four nuclei; however, two of the nuclei are often not visible because of the limited depth of field of the micrograph (shown in the image). The axonemes and the hyaline cyst wall make the diagnosis irrefutable. The clinical presentation, especially the watery diarrhea without blood, is consistent with a giardiasis diagnosis. More than likely the child consumed water that was contaminated with Giardia cysts, a definite possibility in a rural setting.

A young child who lives in a rural community in the Appalachia and who has been ill for 10 days presents with abdominal pain, anorexia, steatorrhea, and watery diarrhea. There is no indication of blood in the stool, but a fecal smear stained with trichrome reveals an abundance of cyst-like structures like the one shown in the image. What is the agent responsible for the clinical manifestations? (A) Cryptosporidium parvum (B) Entamoeba histolytica (C) Enterotoxigenic Escherichia coli (D) Giardia lamblia (E) Rotavirus

*The answer is D.* The identification of a Strongyloides stercoralis infection is determined in part because of the presence of rhabditiform larvae in a fecal sample. On the other hand, the laboratory diagnosis of hookworms, Ascaris, Enterobius, and Trichuria are based on the recovery of parasite eggs in the feces. Once in a while, however, a pinworm egg will hatch on the perianeum and a larva may be seen in a stool sample. The presence of pinworm larvae in a stool sample, which has been properly stored and processed, is a very rare occurrence. A key word in the stem, therefore, is "abundance" and indicates the presence of numerous larvae in the stool. Strongyloides is a common parasite in children who reside in developing nations, especially children who are confined to an orphanage. A pulmonary phase of the Strongyloides life cycle has been linked with pneumonitis and also asthma-like manifestations. Enteritis is also a possibility. More than not, intestinal involvement will produce a benign infection. From time to time, this nematode is identified from patients in the United States.

A young child, who was adopted from an orphanage in Asia, routinely experiences loose stools. An abundance of microscopic worms (shown in the image) are noted in a fecal preparation smear. What is the correct diagnosis? (A) Ascariasis (B) Enterobiasis (C) Hookworm disease (D) Strongyloidiasis (E) Trichuriasis

*The answer is C.* Ascaris lumbricoides is a geohelminth, meaning that the eggs that are passed in the stool must first embryonate in the soil or the environment. The parasite is not commonly transmitted person-to-person via feces. Consequently, the embryonated egg—not the unembryonated egg in fresh feces (choice A)—is the infective stage. Ingesting food and drink contaminated with these embryonated eggs would be the most likely way for humans to become infected. Lack of proper hand washing before eating only compounds the problem. Choice C has reference to hookworm disease, D refers to schistosomiasis, and E hemorrhagic Escherichia coli.

An 8-year-old child, who recently emigrated with the family from Central America, is taken to the emergency department because of a stomach ache that has persisted for about 24 hours. In fact, the mother indicates that the pain did not lessen even after the child vomited up two worms (shown in the image) the night before. The mother further indicates that for the past several weeks the child has had little desire to eat and often complains of diarrhea. Physical examination reveals that the pain is more pronounced in the right upper quadrant region and directly radiates to the scapular area of the back. With reference to the above question, how did the child most likely become infected? (A) Direct fecal contamination from a sibling (B) Eating raw or insufficiently cooked hamburger (C) Ingestion of contaminated soil or water (D) Swimming in cercariae-infested lake water (E) Walking barefoot on moist soil or grass

*The answer is A.* More than 1 billion people worldwide are infected with Ascaris lumbricoides. Children are more likely candidates than adults to be infected. The worms commonly reside in the small intestine, but migration into the biliary tract is fairly common. Based on the exquisite radiating pain in this case, biliary involvement should be ruled out, probably though radiographic findings. It is not unusual for a child to spit up a worm upon being treated. Children in Latin America will harbor multiple worms—sometimes hundreds—and intestinal obstruction is a potential complicating factor. Usually, however, abdominal symptoms are vague with nothing more than a loss of appetite and occasional episodes of diarrhea.

An 8-year-old child, who recently emigrated with the family from Central America, is taken to the emergency department because of a stomach ache that has persisted for about 24 hours. In fact, the mother indicates that the pain did not lessen even after the child vomited up two worms (shown in the image) the night before. The mother further indicates that for the past several weeks the child has had little desire to eat and often complains of diarrhea. Physical examination reveals that the pain is more pronounced in the right upper quadrant region and directly radiates to the scapular area of the back. Based on these findings, what is the most likely diagnosis? (A) Ascariasis with biliary involvement (B) Disseminated strongyloidiasis (C) Hemolytic uremic syndrome (D) Intestinal and hepatic amebiasis (E) Salmonella enterocolitis

*The answer is D.* Certain parasites like the Asian liver fluke (e.g., Clonorchis sinensis) are associated with neoplastic disease. The patient emigrated from an endemic region of the world, which further supports the physician's supposition. Schistosoma haematobium, although not a response to this question, is a blood fluke that inhabits the veins around the bladder and is also believed to promote neoplastic disease, squamous cell carcinoma of the bladder in this case.

An immigrant from eastern Asia develops a cholangiocarcinoma. A fecal sample shows evidence of a parasitic infection which the physician believes to be linked to malignancy. What did the specimen reveal that led to this conclusion? (A) Ameba cyst (B) Cryptosporidium oocysts (C) Flagellated protozoan trophs (D) Fluke eggs (E) Nematode larvae

*The answer is C.* In many regions of Africa, O. volvulus is a leading cause of blindness; however, the helminth has migrated into areas of Central America and Ecuador. L. loa affects people of West Africa and parts of the Sudan; W. bancrofti is more commonly associated with elephantoid manifestations; D. medinensis has a completely different presentation and is currently confi ned to specific regions of Africa. Occasionally, cases are diagnosed in people immigrating into the United States. Juveniles of T. canis, an important agent of visceral larva migrans, provokes retinal granulomatous reactions.

An ophthalmologist makes the diagnosis of sclerosing keratitis in a patient who immigrated to the United States from a Pacific coastal community of Ecuador. Of note are many filariform juveniles (similar to the one shown in the image) in the chambers of the eye. Which of the following parasites is the causative agent? (A) Dracunculus medinensis (B) Loa loa (C) Onchocerca volvulus (D) Toxocara canis (E) Wuchereria bancrofti

*The answer is E.* The fumigant course of the disease and the lack of bacterial and fungal elements in the Gram stain are most consistent with amebic meningoencephalitis. Neurocysticercosis (Taenia solium) is a tapeworm disease and is statistically more likely to occur in a patient who emigrated from developing countries in Latin America, Asia, and Africa. Naegleria fowleri, the etiologic agent in this particular case, is transmitted during the summer months in warm ponds or streams. The ameba in reality is a free-living freshwater species that inadvertently invades the nasal passageways of swimmers. It craws up the olfactory nerve, a pathway of sorts that leads to the central nervous system. A number of tissue-damaging virulence determinants (e.g., cysteine protease, phospholipase A) have been identified, which account for the severe hemorrhagic meningoencephalitis seen in fatal infections. Mortality rates are especially high, largely because the disease is rare and progresses rapidly. A correct diagnosis may easily be unrecognized and made at autopsy. Motile trophozoites (directional movement) can be observed in a wet mount preparation of centrifuged CSF. Effective therapy includes amphotericin B.

In August, a previously healthy 12-year-old girl, who enjoys swimming in farm ponds in central Florida, is evaluated for meningitis. Gram stain of the CSF demonstrates no bacteria or yeast; however, there are indications of a PMN leukocytosis. A wet mount shows motile cells that resemble WBCs. Intravenous ceftriaxone therapy is initiated, but within 24 hours she slips into a coma. CT shows brain swelling or edema. Unfortunately, she is unresponsive to anticonvulsant drugs and dies the following day. Based on the available information, which diagnosis is the most plausible? (A) Bacterial meningitis (B) Cryptococcal meningitis (C) Disseminated coccidioidomycosis (D) Neurocysticercosis (E) Primary amebic meningoencephalitis

*The answer is B.* The children are infected with the Protozoan Giardia lamblia. Airborne transmission of dust most closely fits the clinical picture of certain fungal diseases (e.g., cryptosporidiosis, histoplasmosis). Urinating while wading in a stream is somewhat nonsensical since this is clearly an intestinal infection. Although it is theoretically possible for a patient to be introduced to Giardia through poor hygiene habits or via contaminated food, a preponderance of the cases occurs by ingesting the cystic stage in water. The micrograph is of the trophozoite (indicating that at least this sample was taken from a patient with significant diarrhea) and the cystic form of Giardia lamblia.

Over a 1-week period, several elementary age children, who are involved in a summer camp in the Pocono Mountains of Pennsylvania, contract a gastrointestinal illness (i.e., they all exhibit similar manifestations like painful bloating and the passage of loose stools). A common microbe is present in fresh stool smears (example shown under oil immersion). Of the following means of transmission, which one is the most likely way each of these children became infected? (A) Breathing (and swallowing) dust laden with bird droppings (B) Drinking contaminated lake or stream water (C) Eating rare or insuffi ciently cooked hamburger (D) Eating salad that contains dandelion flowers grown in nature (E) Poor hygiene practice of urinating while wading in streams

*The answer is B.* The sporozoans are also called apicomplexa because of the presence of a complex of organelles at the cell tip that facilitates penetration of the parasite into host tissue. A schizont is not a taxonomic group but a mass of trophozoites.

Plasmodium falciparum, which causes malaria, is an example of: A. an ameboid protozoan. B. a sporozoan. C. a flagellate. D. a ciliate. E. a schizont.

*The answer is D.* Echinococcosis or hydatid disease is transmitted to people via oral exposure to the egg stage in excrement from dogs. Sheep droppings are not involved in the life cycle. Proper hand washing is imperative after working with dogs, especially before eating a meal. The person does not become infected by eating sheep livers or mutton or by handling sheep.

Several dogs that work Native American sheep ranches in a community of New Mexico undergo their yearly purges for intestinal worms. Examination reveals that all the stools are positive for tapeworms, including a tiny tapeworm species that measures <10 mm (shown in the image). What is the means of transmission by which people become infected with this parasite? (A) Eating raw sheep liver (B) Eating insuffi ciently cooked mutton (C) Fecal-oral exposure of sheep droppings (D) Ingesting dog excrement (E) Poor hand washing after butchering sheep

*The answer is D.* Echinococcus granulosus is a tiny tapeworm of dogs, especially sheepdogs that have been fed sheep viscera. The dog harbors the ribbon stage in the small intestine, tapeworm eggs are passed in the excrement and contaminate pasture, the sheep inadvertently eats the egg, and the juvenile or metacestode stage (hydatid cyst) develops in the liver or lungs of the sheep. Echinococcus or the development of the hydatid cyst also can occur in humans. Dipylidiasis is a dog flea tapeworm that has minor medical importance; diphyllobothriasis is transmitted to people via raw fi sh; cysticercosis occurs with the pork tapeworm; and, taeniasis refers to intestinal infections with the tapeworms Taenia solium and T. saginatus.

Several dogs that work Native American sheep ranches in a community of New Mexico undergo their yearly purges for intestinal worms. Examination reveals that all the stools are positive for tapeworms, including a tiny tapeworm species that measures <10 mm (shown in the image). Which medically important disease is linked to this worm? (A) Cysticercosis (B) Diphyllobothriasis (C) Dipylidiasis (D) Echinococcosis (E) Intestinal taeniasis

*The answer is B.* Simply stated, if the dog is denied access to the sheep offal, the life cycle is broken.

Several dogs that work Native American sheep ranches in a community of New Mexico undergo their yearly purges for intestinal worms. Examination reveals that all the stools are positive for tapeworms, including a tiny tapeworm species that measures <10 mm (shown in the image). Which of the following practices is most effective in order to prevent these sheepdogs from becoming infected with the same tapeworm species next year? (A) Periodically worm the sheep (B) Stop feeding raw sheep livers to dogs (C) Vaccinate dogs against round worms (D) Vaccinate dogs against tapeworms (E) Vaccinate sheep against intestinal worms

*The answer is C.* Imported raspberries from Central America have also been linked to cluster cases of cyclosporiasis in the United States. More than likely the use of contaminated river water to wash the berries or to apply fungicide and insecticide prior to shipping is a contributing factor. Cyclosporan oocysts are noticeably larger than those of Cryptosporidium. Although both Cyclospora and Cryptosporidium have oocysts that are acid-fast, the sensitivity to the antimicrobial TMP-SMZ is the distinguishing attribute.

Several individuals present with explosive watery diarrhea, mild fever, and profound fatigue. Epidemiologically, the common link is the eating of imported salad greens. Acid-fast preparations of fresh stools reveal large oocysts. Furthermore, the illness responds to TMP-SMZ treatment. What is the most likely pathogen? (A) Blastocystis (B) Cryptosporidium (C) Cyclospora (D) Entamoeba (E) Giardia

*The answer is B.* The tapeworm egg is the infective stage for echinococcosis or hydatid disease and sheepdogs are the usual source of the infection in people. The finding of protoscolices within the liver is proof of hydatid disease. Cysticerci in raw pork has reference to the intestinal form of the pork tapeworm, anisakiasis and diphyllobothriasis are associated with raw fish, and contaminated fruit like raspberries is a vehicle for transmission for Cyclospora.

Surgical removal of a liver cyst about the size of a tennis ball from a 45-year-old man reveals the presence of protoscolices, allowing for a definitive diagnosis. The patient likely acquired this infection by ingesting what? (A) Cyst-contaminated raspberries grown in Guatemala (B) Food or water contaminated with tapeworm eggs (C) Undercooked calf liver containing hydatid sand (D) Undercooked fish or shellfi sh containing larvae (E) Viable cysticerci in pork or pork products

*The answer is C.* The trophozoite is, generally speaking, the active phase, in contrast to the cyst, which is the dormant phase. In some species, several varieties of trophozoites are recognized, such as the tachyzoites and bradyzoites of Toxoplasma gondii.

The protozoal trophozoite phase is characterized by: A. metabolic dormancy. B. toxin production. C. active feeding and reproduction. D. flagellar locomotion. E. residence in the intermediate host.

*The answer is E.* The micrograph is of the cercarial stage or the infective stage of schistosomiasis, a fl uke disease that involves veins near the intestinal tracks or bladder. Chlorine treatment and heating the water will kill this stage—highly unlikely with this scenario. Cercariae emerge from snails and remain viable in the water for more than 24 h. Even a brief exposure like wading in the water is ample time for the cercaria to penetrate intact skin. This water source appears to be regularly contaminated with human waste, and drinking from it would also pose a risk for acquiring other microbial diseases.

Tourist backpackers, visiting a primitive tropical island, are assured that the untreated water supply is safe for bathing because it originates from a pristine river. However, water analysis reveals infestation with the organism shown in the image. Based on the photo, what are tourists who bathe in unheated water from this river at risk for? (A) Amebiasis (B) Ascariasis (C) Fasciolopsiasis (D) Giardiasis (E) Schistosomiasis

*The answer is A.* Chagas' disease is endemic to many countries in Central and South America. The acute phase is defined when motile trypanosomes are detected in the anticoagulated blood or the buffy coat (layer of white blood cells and platelets just above the erythrocyte zone). The trypomastigote stage, often C-shaped (see micrograph), is readily visualized in a fixed Giemsa-stained blood smear. The clinical manifestations in this case clearly pertain to the acute phase of the disease. Sleeping sickness is endemic to Africa and not South America, blackwater fever is linked to falciparum malaria. Malaria is an intraerythrocytic life cycle, and leishmaniasis is characterized with amastigotes and not tryptomastigotes.

While completing a public health rotation in an urban clinic in Peru, a US medical student is given an academic assignment to study a cluster of acute febrile cases in young children. Incident to each case is an acute regional lymphadenitis, myalgia, and a characteristic bloodborne parasite (shown in the image). Which of the following diseases is the most reasonable diagnosis? (A) Acute Chagas' disease (B) Benign tertian malaria (C) Blackwater fever (D) Chronic sleeping sickness (E) Disseminated leishmaniasis

*The answer is A.* Most people who are indigenous to West Africa are resistant to P. vivax infections because they lack the Duffy glycoprotein receptor for the merozoite stage on the erythrocyte. This receptor ordinarily serves as the receptor for interleukin-8. Lacking the receptor gives the person protection against vivax malaria. Other forms of genetically determined resistance to malaria—specifically, P. falciparum—include sickle cell trait, thalassemia, and deficiency of glucose-6-phosphate dehydrogenase.

With the exception of one, all peace corps volunteers assigned to a remote village in African contract vivax malaria. Which of the following volunteers is the person who did not become infected with Plasmodium vivax? (A) West African man (B) Italian-American woman (C) Mexican-American man from Texas (D) Asian-American woman (E) Central American man

*The answer is D.* Schistosome cercariae released from snails in fresh water are capable of penetrating human skin. Filariasis is transmitted by mosquitoes. Onchocerciasis is transmitted by the bite of the blackfly. Dracunculiasis is transmitted by drinking water containing the intermediate host copepods in which the larvae live. Visceral larva migrans is transmitted by ingestion of eggs from dog feces.

Which of the following helminthic diseases is transmitted by direct skin penetration by helminth larvae? A. Filariasis B. Onchocerciasis C. Dracunculiasis D. Schistosomiasis E. Visceral larva migrans

*The answer is A.* Mosquitoes ingest filarial embryos (microfilariae) from infected blood. In the insect, the embryos develop into infective filariform larvae that are injected into the human host. Onchocerciasis is transmitted by the bite of the blackfly. Taeniasis is transmitted by ingestion of larvae in undercooked pork. Schistosomiasis is transmitted by direct skin penetration. Visceral larva migrans is transmitted by ingestion of eggs from dog feces.

Which of the following helminthic diseases is transmitted by the bite of a mosquito? A. Filariasis B. Onchocerciasis C. Taeniasis D. Schistosomiasis E. Visceral larva migrans

*The answer is E.* Enterobiasis is known as pinworm disease.

Which of the following is the most common helminthic infection in the United States? A. Schistosomiasis B. Diphyllothriasis C. Clonorchiasis D. Trichinosis E. Enterobiasis

*The answer is D.* Ingesting the eggs of the pork tapeworm (Taenia solium) in fecalcontaminated food items is the likely means for transmission of cysticercosis. Because of the shape, the cysticercus is sometimes referred to as bladderworm (a type of metacestode) and is the stage responsible for the pathogenesis of neurocysticercosis. To minimize the possibility of an autoinfection, it is critical that the infection be aggressively managed. Ascaris is a geohelminth and must first embryonate in soil to be infective, Cyclospora and Toxoplasma produce protozoan infections, and raw beef is the vehicle for transmission of another tapeworm that is not believed to be associated with neurocysticercosis.

Which of the following modes of transmission accounts for the development of neurocysticercosis in humans? (A) Ascarid eggs from soil (B) Bladderworms in raw beef (C) Cyclosporan oocysts in water (D) Fecal-oral taeniid eggs (E) Toxoplasma zoitocysts in raw pork

*The answer is B.* Albendazole therapy is most effective in a patient who is experiencing the intestinal phase of the disease. Usually, this patient will have significant relief within a few weeks following completion of the anthelminthic drug. Patients with encapsulated disease could possibly experience residual myalgia, at least until the larvae are calcified. Corticosteroid will help the person cope with the adverse hypersensitivity reactions that invariably occur when the larvae are killed.

Within 2 weeks of eating jerky that is made from a mountain lion, a Montana man develops intense vomiting and diarrhea, followed shortly by a fever of 103 °F, throbbing headache, and achy muscles. After a few more days of these unrelenting symptoms, he seeks medical attention. His white blood cell count at presentation is 16,100/mm3, with 22% eosinophils. What is the best therapeutic option available for the patient? (A) Mebendazole (B) Albendazole plus a corticosteroid (C) Corticosteroid alone (D) Metronidazole (E) Praziquantel plus a hydrochlorothiazide