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USMLE STEP 1 > Parasites > Flashcards

Parasites Flashcards

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USMLE® Step 1 flashcards
1
Q

Trypanasoma cruzi- spread

A

South America; reduviid (kissing bug) via feces in bite

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2
Q

Trypanasoma cruzi- presentation

A

Chagas disease: megacolon, dilated cardiomyopathy, and megaesophagus

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3
Q

Trypanasoma cruzi- diagnosis

A

Blood smear (acute), serology (chronic), heart biopsy (rare)

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4
Q

Trypanasoma cruzi- treatment

A

Nifurtimox

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5
Q

Giardia lamblia- spread

A

Water contaminated with cysts, fecal-oral route. “camping, hiking.”

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6
Q

Giardia lamblia- presentation

A

Affects small intestine. Bloating, flatulence, foul-smelling steatorrhea (or watery diarrhea)

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7
Q

Giardia lamblia- diagnosis

A

stool O&P (cysts), ELISA stool antigen test (usually required before stool O&P)

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8
Q

Giardia lamblia- treatment

A

Metronidazole. Furazolidone may be used in children.

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9
Q

Entamoeba histolytica- spread

A

Water contaminated with cysts, anal-oral route. “men who have sex with men.”

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10
Q

Entamoeba histolytica- presentation

A

Affects colon. Bloody diarrhea, “flask-shaped” intestinal ulcerations, liver abscess (usually right lobe; pus smells like “anchovy paste”), right upper quadrant pain, hepatomegaly

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11
Q

Entamoeba histolytica- diagnosis

A

Stool O&P (trophozoites with endocytosed RBCs), ELISA stool/serum antigen tests. Serology should only be used in cases of suspected invasion.

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12
Q

Entamoeba histolytica- treatment

A

Metronidazole and luminal agents (paramomycin, iodoquinol)

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13
Q

Cryptosporidium- spread

A

Oocysts (containing 4 motile sporozoites) released in water. Fecal-oral route. “campers, swimmers, etc.” Common in HIV/AIDS.

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14
Q

Cryptosporidium- presentation

A

Targets small intestine. Severe diarrhea in AIDS/immunocompromised patients. Mild watery diarrhea in immunocompetent patients. Sporozoites attach to intestinal wall- usually the small intestine but can also cause colitis.

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15
Q

Cryptosporidium- diagnosis

A

Acid-fast staining in stool, antigen test, demonstration in tissue

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16
Q

Cryptosporidium- treatment

A

Nitazoxanide (immunocompetent only), spiramycin (a macrolide; not FDA-approved)

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17
Q

How to rule out non-pathogenic Entamoeba dispar in favor of Entamoeba histolytica?

A

Phagocytosed RBC in the trophozoite (hard to tell in smear). Normally, use clinical findings.

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18
Q

Entamoeba histolytica cysts transform into trophozoites in what organ?

A

Ileum; primarily affects the colon

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19
Q

Entamoeba histolytica- stool O&P findings

A

Fulminant diarrhea will contain trophozoites. More formed stool (slower movement) may have more cysts.

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20
Q

Entamboeba histolytica- virulence

A

Chitin wall (temps up to 55’C, stomach acid, chlorine), proteinase (invasion), surface lectins (binding), channel-forming proteins (host cell lysis)

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21
Q

Giardia lamblia- other name

A

Giardia duodenalis

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22
Q

Giardia lamblia virulence

A

Lectin-based sucker disc

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23
Q

Crytosporidium- reservoir

A

Humans and some animals, like cows

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24
Q

Cryptosporidium- life cycle

A

Alternating asexual and sexual reproductive cycles. Oocysts exit via feces or may cause autoinfection.

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25
Q

Cryptosporidium- virulence

A

Lectin (binding), superficial invasion of cytoplasm (intracellular organisms, so no lysis)

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26
Q

Strongyloides stercoralis- reservoir

A

humans

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27
Q

Strongyloides stercoralis- location

A

Affects small intestine but may disseminate.

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28
Q

Strongyloides stercoralis- lifecycle/spread

A

They live in soil. Larvae penetrate the skin directly and travel to the lungs via circulation. They then climb up the respiratory tree and are swallowed. They mature in the small intestine and lay ova, which are excreted in the feces and hatch. Autoinfection is possible.

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29
Q

Strongyloides stercoralis- biology

A

Nematode. 2 forms of larvae: rhabditiform and filariform (infectious).

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30
Q

Strongyloides stercoralis- complications

A

Hyperinfection if immunocompromise allows maturation to infectious filariform. Associated gram-negative sepsis or candidemia may also be seen.

31
Q

Strongyloides stercoralis- normal presentation

A

Larvae may cause pneumonitis or eosinophilia. Adult worms cause mild/moderate mucosal inflammation. Rash/pruritis at site of entrance may be seen. Often asymptomatic.

32
Q

Strongyloides stercoralis- hyperinfection

A

Diarrhea, GI hemorrhage, pneumonia, gram-negative meningitis (otherwise uncommon in adults), sepsis

33
Q

Strongyloides stercoralis- treatment

A

Ivermectin, thiabendazole. Treat even after clear.

34
Q

Enterobiasis (pinworm)- reservoir

A

Humans

35
Q

Enterobiasis (pinworm)- presentation

A

Affects colon. Pruritis (itchy butt) may occur.

36
Q

Enterobiasis (pinworm)- spread

A

Ingestion of ova. Classically in children or their parents.

37
Q

Enterobiasis (pinworm)- lifecycle

A

Nematode. After ingestion, ova hatch. Adults live in cecum. Gravid females lay ova on skin. Risk of autoinfection.

38
Q

Enterobiasis (pinworm)- treatment

A

Mebendazole

39
Q

Enterobiasis (pinworm)- diagnsosis

A

Demonstration of ova on perianal skin. Adhesive tape.

40
Q

Taeniasis- reservoir and intermediate hosts

A

Reservoir is humans. Intermediate hosts are pigs and cattle.

41
Q

Taeniasis- spread

A

Ingestion of infected beef/pork

42
Q

Taeniasis- causal organisms

A

Taenia solium (pork tapeworm) and Taenia saginata (beef tapeworm)

43
Q

Taeniasis- lifecycle

A

Cestode. Intermediate host ingests ova. Embryo travels to tissue. Human eats undercooked meat and ingests cystircerci, which are then liberated. Evaginate scolex and attach to small intestine. Ova and gravid proglottids may be passed in feces.

44
Q

Taeniasis- presentation

A

Affects small intestine. May be asymptomatic. May be mild mucosal inflammation.

45
Q

Taeniasis- diagnosis

A

Ova or proglottids in stool.

46
Q

Taeniasis- treatment

A

Praziquantel or niclosamide

47
Q

Cystircercosis- spread

A

Ingestion of Taenia solium ovum by the human, rather than the intermediate host (pig). Burrows into intestine and accesses bloodstream. Autoinfection is possible.

48
Q

Cystircercosis- presentation

A

Cystic lesions in brain, muscle, and skin. Often without inflammation if organism is viable. Inflammation, fibrosis, and calcification if dead.

49
Q

Schistosomiasis- causal organisms

A

Schistosoma mansoni, haematobium, and japonicum

50
Q

Schistosomiasis- spread

A

Trematode. Underdeveloped countries (e.g. Sub-Saharan Africa), inadequate water supplies (dams and irrigation systems increase risk). Ova in water mature into miracidium, which infect snail.. Cercaria from snails (intermediate host) go into contaminated water. Direct skin penetration of human. Travel to venous plexuses and mature in pairs, then lay eggs which are excreted.

51
Q

Schistosomiasis- virulence

A

Mature organisms incorporation of host proteins into their own membranes (antigenic mimicry). Ova are highly immunogenic, causing granulamatous inflammation, fibrosis, and even allergy.

52
Q

Schistosomiasis- presentation

A

Intestinal, liver, bladder, and skin penetration site symptoms

53
Q

Schistosomiasis- treatment

A

Antihistamines, corticosteroids for snail fever. Praziquantel.

54
Q

Most common nematode infection worldwide

A

Ascariasis

55
Q

Ascariasis- spread

A

Contact with contaminated soil or ingestion of eggs (fecal-oral route)

56
Q

Ascariasis- presentation

A

Abdominal pain, nausea/vomiting, cough/wheezing/dyspnea, jaundice, peripheral eosinophilia. May cause small bowel obstruction.

57
Q

Enteropathogenic E. coli- presentation

A

Noninflammatory diarrhea in infants in developing countries

58
Q

Enteropathogenic E. coli (EPEC)- virulence

A

Adherence to M cells, rearrangement of actin and effacement of brush border villi

59
Q

Echinococcus granulosus- spread

A

Cestode, usually ingested as eggs from dog feces in rural settings

60
Q

Echinococcus granulosus- presentation

A

Asymptomatic at first. Later, they develop vague abdominal symptoms, weight loss, vomiting, diarrhea, fatigue, hepatomegaly. Hydatid cysts found in liver, but may be found in kidney and spleen as well.

61
Q

Echinococcus granulosus- treatment

A

Surgical intervention (may cause anaphylaxis) or albendazole

62
Q

Schistosoma mansoni and japonicum venous location and presentation

A

mesenteric veins and portal veins, causing portal hypertension leading to cirrhosis and even liver failure

63
Q

Schistosoma haematobium venous location and presentation

A

Veins of bladder, leading to hematuria and bladder cancer

64
Q

Schistosoma mansoni O&P findings

A

Egg with large lateral spine

65
Q

Schistosoma japonicum O&P findings

A

Egg with small spine, round

66
Q

Schistosoma haematobium

A

Egg with large terminal spine

67
Q

Clonorchis sinesis- spread

A

Trematode. Snails are intermediate hosts. Larvae are ingested by humans from undercooked fish. Worms mature and reside in biliary system.

68
Q

Clonorchis sinesis- presentation

A

Biliary tract fibrosis, pigmented gallstones, choleangiocarcinoma

69
Q

Clonorchis sinesis- O&P findings

A

Operculated eggs

70
Q

Clonorchis sinesis- treatment

A

Praziquantel

71
Q

Paragoniumus westermani- spread

A

Snails are intermediate host. Larvae are ingested by humans in undercooked crab meat. Affect the lungs.

72
Q

Paragonimus westermani- presentation

A

Chronic cough with bloody sputum

73
Q

Paragonimus westermani- O&P findings

A

Operculated eggs

74
Q

Paragonimus westermani- treatment

A

Praziquantel

USMLE STEP 1 (24 decks)

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