πͺ€ TRAP: Chronic foul fatty (steatorrhea) diarrhea after camping/hiking with well water β Giardia. "Crypto in HIV" has no great treatment; restore CD4 with ART.
LO 2
ON EXAM β Leishmania (visceral = kala-azar, cutaneous); Trypanosoma cruzi = Chagas (cardiomyopathy, megaesophagus/colon, kissing bug); Plasmodium (P. falciparum vs vivax/ovale vs malariae); Toxoplasma; Babesia
Leishmania
Trypanosoma cruzi β Chagas disease
Plasmodium species
Species
Fever periodicity
Key feature
P. falciparum
P. vivax
P. ovale
P. malariae
P. knowlesi
Malaria β key treatment
Toxoplasma gondii
Babesia
πͺ€ TRAP: "Maltese cross" = Babesia (intraerythrocytic, tetrad). "Ring form" and banana gametocyte = P. falciparum.
πͺ€ TRAP: Always screen at-risk patients for Strongyloides BEFORE steroids or other immunosuppression to prevent lethal hyperinfection.
LO 4
ON EXAM β Taenia solium (neurocysticercosis), Taenia saginata (beef), Diphyllobothrium (B12 deficiency), Echinococcus (hydatid cyst), Schistosoma (S. mansoni/japonicum vs haematobium β bladder cancer)
Cestode framework β definitive vs intermediate host
Match cestode β exposure β signature disease
Cestode
Exposure
Signature
Treatment
Taenia solium (pork)
Taenia saginata (beef)
Diphyllobothrium latum (fish)
Echinococcus granulosus
Neurocysticercosis β high-yield
Echinococcus (hydatid cyst) β high-yield
Diphyllobothrium latum β the fish tapeworm
Schistosoma β species differences
Species
Geography
Primary site
Chronic complication
S. mansoni
S. japonicum
S. haematobium
Schistosoma β general
πͺ€ TRAP: S. haematobium β squamous cell carcinoma of the bladder (not TCC!). Eggs with terminal spine β S. haematobium. Lateral spine β S. mansoni.
LOs 1β4
Q1: Hikers and foul fatty diarrhea
A 32-year-old returns from a camping trip where she drank untreated stream water. For 3 weeks she has had foul-smelling, greasy, floating stools, bloating, and weight loss. Which organism + treatment?
A) Cryptosporidium; nitazoxanide
B) Giardia lamblia; metronidazole (or tinidazole)
C) Entamoeba histolytica; metronidazole + paromomycin
D) Cyclospora; TMP-SMX
E) Rotavirus; supportive
Correct Answer: B
Giardia is classic for prolonged foul fatty diarrhea after untreated water (hikers, daycare, travel). Diagnosis: stool antigen or ova & parasite (pear-shaped trophozoites, "owl-eyes"). Treat with metronidazole or tinidazole.
Q2: HIV + CD4 <100 + watery diarrhea
A 38-year-old man with AIDS (CD4 = 42) has 3 weeks of profuse watery diarrhea. Modified acid-fast stain of stool shows 4β6 ΞΌm oocysts. Organism?
A) Giardia lamblia
B) Entamoeba histolytica
C) Cryptosporidium parvum
D) Cyclospora cayetanensis
E) Isospora (Cystoisospora) belli
Correct Answer: C
Cryptosporidium β small (4β6 ΞΌm) modified acid-fast oocysts; severe chronic diarrhea in AIDS. Treatment is limited (nitazoxanide); best therapy is CD4 recovery with ART. Cyclospora oocysts are larger (~10 ΞΌm); Cystoisospora (Isospora) are oval and acid-fast, treated with TMP-SMX.
Q3: Chagas cardiomyopathy
A 52-year-old Bolivian man presents with progressive CHF and dysphagia. ECG: RBBB + LAFB. Echo: apical aneurysm. Dilated megaesophagus on barium swallow. Which organism + vector?
A) T. brucei; tsetse fly
B) T. cruzi; reduviid (kissing) bug
C) Leishmania donovani; sandfly
D) Babesia microti; Ixodes tick
E) P. falciparum; Anopheles mosquito
Correct Answer: B
Chagas disease (Trypanosoma cruzi) is transmitted by the reduviid ("kissing") bug in Latin America. Chronic sequelae: dilated cardiomyopathy with apical aneurysm and conduction disease (RBBB + LAFB), megaesophagus and megacolon. Treatment: benznidazole or nifurtimox.
Q4: Malaria relapse
A patient treated 3 months ago for uncomplicated P. vivax malaria with chloroquine returns with recurrent fever and parasitemia. Which drug should have been added initially to prevent relapse?
A) Atovaquone-proguanil
B) Mefloquine
C) Primaquine (after G6PD testing)
D) Doxycycline
E) Artesunate
Correct Answer: C
P. vivax and P. ovale produce hypnozoites (dormant liver forms) β relapse. Add primaquine (or tafenoquine) to eradicate hypnozoites, AFTER checking G6PD status (risk of hemolysis).
Q5: Strongyloides hyperinfection
A 60-year-old Vietnamese man is started on high-dose prednisone for asthma. One week later he develops bloody sputum, abdominal pain, sepsis, and gram-negative bacteremia (E. coli). Filariform larvae are seen in sputum. What should have been done prior to steroids?
A) Stool ova & parasite and empiric ivermectin
B) Nothing β Strongyloides is rare in the US
C) Blood smear for malaria
D) Colonoscopy
E) Chest X-ray only
Correct Answer: A
Strongyloides can persist asymptomatically for decades via autoinfection. Steroids/immunosuppression trigger hyperinfection with massive larval dissemination, bacteremia from gut translocation (polymicrobial GNR sepsis), and ARDS. Screen with serology and stool; treat with ivermectin.
Q6: Neurocysticercosis
A 28-year-old recent immigrant from rural Mexico presents with new-onset seizures. MRI shows multiple small cystic lesions with scolex visible inside. Most likely organism + transmission route?
A) Taenia saginata; ingestion of undercooked beef
B) Taenia solium; ingestion of eggs (fecal-oral, often from a human tapeworm carrier)
C) Echinococcus; ingestion of dog eggs
D) Toxocara; ingestion of dog eggs
E) Toxoplasma; ingestion of cat oocysts
Correct Answer: B
Neurocysticercosis = cysts in the CNS from ingestion of Taenia solium EGGS (not larvae in undercooked pork, which causes intestinal taeniasis). Humans become an accidental intermediate host. Treatment: albendazole + steroids + anticonvulsants.
Q7: B12 deficiency from fish
A 40-year-old sushi enthusiast is found to have macrocytic anemia with elevated MMA and hypersegmented neutrophils. Stool O&P: operculated eggs. Organism and mechanism?
A) Diphyllobothrium latum; competes for dietary B12
B) Ascaris; intestinal malabsorption
C) Giardia; villous blunting
D) Tropheryma whipplei; enteritis
E) Schistosoma; chronic blood loss
Correct Answer: A
Diphyllobothrium latum (fish tapeworm) competes for dietary B12 β megaloblastic anemia. Exposure: raw/undercooked freshwater fish (sushi, sashimi, smoked salmon). Treat with praziquantel.
Q8: Hydatid cyst
A 45-year-old sheep rancher has a large cystic liver lesion with "eggshell" calcification and daughter cysts. Serology: Echinococcus positive. Best management?
A) Percutaneous aspiration alone
B) Albendazole + careful surgical resection or PAIR (Puncture-Aspirate-Inject-Reaspirate) β avoid uncontrolled spillage (anaphylaxis/spread)
C) Metronidazole
D) Observation only
E) Ivermectin
Correct Answer: B
Echinococcus (hydatid cyst): albendazole Β± PAIR or surgical resection. Do NOT simply aspirate β uncontrolled spillage can cause anaphylaxis and seeding of daughter cysts.
Q9: Pinworm
A 6-year-old has nocturnal perianal itching. Scotch-tape test shows oval eggs flattened on one side. Best management?
A) Topical hydrocortisone
B) Metronidazole
C) Albendazole or mebendazole for patient AND household contacts; repeat dose in 2 weeks
D) Ivermectin for patient only
E) Praziquantel
Correct Answer: C
Enterobius (pinworm): classic nocturnal perianal pruritus. Diagnose with Scotch-tape test (morning). Treat patient + household contacts with albendazole or pyrantel pamoate; repeat in 2 weeks to kill newly hatched eggs.
Q10: Schistosoma and bladder cancer
A 35-year-old Egyptian man has painless hematuria. Urinalysis: RBCs + eggs with a terminal spine. Cystoscopy: squamous cell carcinoma of the bladder. Which Schistosoma species?
A) S. mansoni
B) S. japonicum
C) S. haematobium
D) S. mekongi
E) S. intercalatum
Correct Answer: C
S. haematobium β bladder (terminal-spined eggs) β chronic inflammation β squamous cell carcinoma (NOT transitional). Mansoni/japonicum affect mesenteric veins β chronic liver fibrosis (pipestem) and portal hypertension. Treat all with praziquantel.
Q11: Toxoplasma in AIDS
A 45-year-old with AIDS (CD4 = 50) has headache and hemiparesis. MRI: multiple ring-enhancing lesions. Serology: Toxoplasma IgG positive. Best initial therapy?
A) Radiation therapy
B) Pyrimethamine + sulfadiazine + leucovorin
C) Amphotericin B
D) Artesunate
E) Ganciclovir
Correct Answer: B
AIDS + ring-enhancing brain lesions + Toxo IgG+ β treat empirically with pyrimethamine + sulfadiazine + leucovorin. TMP-SMX for PJP prophylaxis also prevents toxoplasmosis reactivation.
Q12: Babesia
A 65-year-old splenectomized man from Nantucket develops fever, hemolytic anemia, and fatigue. Smear: small intraerythrocytic ring forms and a "Maltese cross." Vector?
A) Reduviid bug
B) Ixodes scapularis tick
C) Anopheles mosquito
D) Sandfly
E) Tsetse fly
Correct Answer: B
Babesia microti is transmitted by the Ixodes scapularis tick (same vector as Lyme and anaplasmosis). Maltese cross = pathognomonic. Especially severe in asplenic/elderly. Treat with atovaquone + azithromycin (or clindamycin + quinine for severe disease).