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USMLE STEP 1 > Parasites > Flashcards

Parasites 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
Cryptosporidium- virulence
Lectin (binding), superficial invasion of cytoplasm (intracellular organisms, so no lysis)
26
Strongyloides stercoralis- reservoir
humans
27
Strongyloides stercoralis- location
Affects small intestine but may disseminate.
28
Strongyloides stercoralis- lifecycle/spread
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.
29
Strongyloides stercoralis- biology
Nematode. 2 forms of larvae: rhabditiform and filariform (infectious).
30
Strongyloides stercoralis- complications
Hyperinfection if immunocompromise allows maturation to infectious filariform. Associated gram-negative sepsis or candidemia may also be seen.
31
Strongyloides stercoralis- normal presentation
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
Strongyloides stercoralis- hyperinfection
Diarrhea, GI hemorrhage, pneumonia, gram-negative meningitis (otherwise uncommon in adults), sepsis
33
Strongyloides stercoralis- treatment
Ivermectin, thiabendazole. Treat even after clear.
34
Enterobiasis (pinworm)- reservoir
Humans
35
Enterobiasis (pinworm)- presentation
Affects colon. Pruritis (itchy butt) may occur.
36
Enterobiasis (pinworm)- spread
Ingestion of ova. Classically in children or their parents.
37
Enterobiasis (pinworm)- lifecycle
Nematode. After ingestion, ova hatch. Adults live in cecum. Gravid females lay ova on skin. Risk of autoinfection.
38
Enterobiasis (pinworm)- treatment
Mebendazole
39
Enterobiasis (pinworm)- diagnsosis
Demonstration of ova on perianal skin. Adhesive tape.
40
Taeniasis- reservoir and intermediate hosts
Reservoir is humans. Intermediate hosts are pigs and cattle.
41
Taeniasis- spread
Ingestion of infected beef/pork
42
Taeniasis- causal organisms
Taenia solium (pork tapeworm) and Taenia saginata (beef tapeworm)
43
Taeniasis- lifecycle
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
Taeniasis- presentation
Affects small intestine. May be asymptomatic. May be mild mucosal inflammation.
45
Taeniasis- diagnosis
Ova or proglottids in stool.
46
Taeniasis- treatment
Praziquantel or niclosamide
47
Cystircercosis- spread
Ingestion of Taenia solium ovum by the human, rather than the intermediate host (pig). Burrows into intestine and accesses bloodstream. Autoinfection is possible.
48
Cystircercosis- presentation
Cystic lesions in brain, muscle, and skin. Often without inflammation if organism is viable. Inflammation, fibrosis, and calcification if dead.
49
Schistosomiasis- causal organisms
Schistosoma mansoni, haematobium, and japonicum
50
Schistosomiasis- spread
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
Schistosomiasis- virulence
Mature organisms incorporation of host proteins into their own membranes (antigenic mimicry). Ova are highly immunogenic, causing granulamatous inflammation, fibrosis, and even allergy.
52
Schistosomiasis- presentation
Intestinal, liver, bladder, and skin penetration site symptoms
53
Schistosomiasis- treatment
Antihistamines, corticosteroids for snail fever. Praziquantel.
54
Most common nematode infection worldwide
Ascariasis
55
Ascariasis- spread
Contact with contaminated soil or ingestion of eggs (fecal-oral route)
56
Ascariasis- presentation
Abdominal pain, nausea/vomiting, cough/wheezing/dyspnea, jaundice, peripheral eosinophilia. May cause small bowel obstruction.
57
Enteropathogenic E. coli- presentation
Noninflammatory diarrhea in infants in developing countries
58
Enteropathogenic E. coli (EPEC)- virulence
Adherence to M cells, rearrangement of actin and effacement of brush border villi
59
Echinococcus granulosus- spread
Cestode, usually ingested as eggs from dog feces in rural settings
60
Echinococcus granulosus- presentation
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
Echinococcus granulosus- treatment
Surgical intervention (may cause anaphylaxis) or albendazole
62
Schistosoma mansoni and japonicum venous location and presentation
mesenteric veins and portal veins, causing portal hypertension leading to cirrhosis and even liver failure
63
Schistosoma haematobium venous location and presentation
Veins of bladder, leading to hematuria and bladder cancer
64
Schistosoma mansoni O&P findings
Egg with large lateral spine
65
Schistosoma japonicum O&P findings
Egg with small spine, round
66
Schistosoma haematobium
Egg with large terminal spine
67
Clonorchis sinesis- spread
Trematode. Snails are intermediate hosts. Larvae are ingested by humans from undercooked fish. Worms mature and reside in biliary system.
68
Clonorchis sinesis- presentation
Biliary tract fibrosis, pigmented gallstones, choleangiocarcinoma
69
Clonorchis sinesis- O&P findings
Operculated eggs
70
Clonorchis sinesis- treatment
Praziquantel
71
Paragoniumus westermani- spread
Snails are intermediate host. Larvae are ingested by humans in undercooked crab meat. Affect the lungs.
72
Paragonimus westermani- presentation
Chronic cough with bloody sputum
73
Paragonimus westermani- O&P findings
Operculated eggs
74
Paragonimus westermani- treatment
Praziquantel

USMLE STEP 1 (24 decks)

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