Fungi and parasites Practice Questions
20 free Fungi and parasites practice questions for the USMLE Step 1. Tap an option to answer — you get instant feedback, the correct answer, and a detailed explanation for every question.
A patient presents with pneumonia after traveling to the Ohio River Valley. Chest imaging shows calcified granulomas. Which organism is the most likely cause?
- A Blastomyces dermatitidis
- B Histoplasma capsulatum
- C Coccidioides immitis
- D Aspergillus fumigatus
Correct answer: Histoplasma capsulatum
Histoplasma is endemic to the Ohio and Mississippi River Valleys. It is often found in bird and bat droppings and causes granulomatous lung disease.
A diabetic patient presents with necrotic facial lesions and black eschar in the nasal cavity. Broad, non-septate hyphae are seen. Which fungus is responsible?
- A Aspergillus fumigatus
- B Mucor/Rhizopus species
- C Candida albicans
- D Cryptococcus neoformans
Correct answer: Mucor/Rhizopus species
Mucor and Rhizopus cause mucormycosis, especially in diabetics with ketoacidosis. They have broad, non-septate hyphae with right-angle branching.
A patient with HIV develops meningitis. CSF shows encapsulated yeasts that are India ink–positive. What is the most likely pathogen?
- A Cryptococcus neoformans
- B Candida albicans
- C Histoplasma capsulatum
- D Blastomyces dermatitidis
Correct answer: Cryptococcus neoformans
Cryptococcus produces a thick polysaccharide capsule visible on India ink stain. It commonly causes meningitis in HIV patients.
A 45-year-old farmer in Arizona develops fever, cough, and erythema nodosum. Spherules containing endospores are found in tissue biopsy. What is the diagnosis?
- A Blastomycosis
- B Coccidioidomycosis
- C Paracoccidioidomycosis
- D Sporotrichosis
Correct answer: Coccidioidomycosis
Coccidioides immitis is endemic to the Southwest U.S. It forms spherules filled with endospores and may cause erythema nodosum.
A patient has a slowly spreading ulcer on the hand after a thorn injury. Cigar-shaped budding yeasts are found. What is the organism?
- A Candida albicans
- B Sporothrix schenckii
- C Aspergillus flavus
- D Trichophyton rubrum
Correct answer: Sporothrix schenckii
Sporothrix schenckii causes sporotrichosis, often acquired from rose thorns. It grows as cigar-shaped yeasts in tissue.
A patient presents with tinea corporis. Which fungus is the most likely cause?
- A Malassezia furfur
- B Trichophyton species
- C Candida glabrata
- D Sporothrix schenckii
Correct answer: Trichophyton species
Dermatophytes such as Trichophyton cause tinea corporis (ringworm). They infect keratinized tissue.
A patient presents with hypopigmented patches on the skin. A KOH prep reveals “spaghetti and meatballs” appearance. Which organism is responsible?
- A Malassezia furfur
- B Microsporum canis
- C Sporothrix schenckii
- D Aspergillus fumigatus
Correct answer: Malassezia furfur
Malassezia furfur causes tinea versicolor. It shows characteristic hyphae and yeast forms on KOH prep.
A bone marrow transplant recipient develops pulmonary infiltrates. “Acute angle” septate hyphae are seen invading blood vessels. What is the organism?
- A Histoplasma capsulatum
- B Aspergillus fumigatus
- C Mucor species
- D Blastomyces dermatitidis
Correct answer: Aspergillus fumigatus
Aspergillus causes invasive aspergillosis in immunocompromised hosts. Its hyphae are septate and branch at acute angles.
A patient presents with pneumonia after visiting caves with bat droppings in Latin America. Large yeast cells with a “captain’s wheel” appearance are seen. What is the diagnosis?
- A Histoplasmosis
- B Blastomycosis
- C Paracoccidioidomycosis
- D Coccidioidomycosis
Correct answer: Paracoccidioidomycosis
Paracoccidioides brasiliensis forms large yeast with multiple budding daughter cells arranged like a ship’s wheel.
A patient develops thrush and vaginal infections after prolonged antibiotic use. Which organism is the most likely cause?
- A Cryptococcus neoformans
- B Candida albicans
- C Malassezia furfur
- D Sporothrix schenckii
Correct answer: Candida albicans
Candida albicans overgrows when normal flora are disrupted, causing oral and vaginal candidiasis.
A patient develops liver abscesses after traveling to India. Stool microscopy shows trophozoites with ingested RBCs. What is the organism?
- A Giardia lamblia
- B Entamoeba histolytica
- C Cryptosporidium parvum
- D Balantidium coli
Correct answer: Entamoeba histolytica
Entamoeba histolytica trophozoites containing RBCs are diagnostic. It can cause liver abscesses and dysentery.
A camper develops foul-smelling, watery diarrhea. Stool exam shows pear-shaped organisms with flagella. What is the most likely cause?
- A Giardia lamblia
- B Entamoeba histolytica
- C Cryptosporidium parvum
- D Cyclospora cayetanensis
Correct answer: Giardia lamblia
Giardia causes malabsorptive diarrhea and is pear-shaped with flagella. It is associated with contaminated water sources.
A patient with AIDS has chronic diarrhea. Acid-fast staining of stool shows oocysts. Which organism is responsible?
- A Giardia lamblia
- B Entamoeba histolytica
- C Cryptosporidium parvum
- D Trichinella spiralis
Correct answer: Cryptosporidium parvum
Cryptosporidium causes watery diarrhea, especially severe in AIDS patients. Oocysts are acid-fast positive.
A child develops perianal itching at night. Tape test shows oval eggs. What parasite is responsible?
- A Enterobius vermicularis
- B Trichuris trichiura
- C Strongyloides stercoralis
- D Taenia saginata
Correct answer: Enterobius vermicularis
Enterobius (pinworm) causes perianal itching and is diagnosed with a tape test showing eggs.
A patient infected with undercooked pork develops seizures. Brain imaging reveals cystic lesions. What parasite is the most likely cause?
- A Taenia saginata
- B Taenia solium
- C Echinococcus granulosus
- D Strongyloides stercoralis
Correct answer: Taenia solium
Taenia solium can cause neurocysticercosis when larvae invade the brain. It is associated with undercooked pork.
A patient develops hematuria from chronic parasitic infection. The eggs have terminal spines. What is the organism?
- A Schistosoma mansoni
- B Schistosoma japonicum
- C Schistosoma haematobium
- D Strongyloides stercoralis
Correct answer: Schistosoma haematobium
Schistosoma haematobium eggs have terminal spines and cause urinary schistosomiasis with hematuria.
A patient presents with a hydatid cyst in the liver after exposure to sheep and dogs. What is the causative organism?
- A Echinococcus granulosus
- B Taenia solium
- C Schistosoma japonicum
- D Fasciola hepatica
Correct answer: Echinococcus granulosus
Echinococcus granulosus causes hydatid cysts in the liver. It is associated with sheep and dog exposure.
A patient develops myalgias and periorbital edema after eating undercooked wild game. What parasite is the most likely cause?
- A Trichuris trichiura
- B Ancylostoma duodenale
- C Trichinella spiralis
- D Toxocara canis
Correct answer: Trichinella spiralis
Trichinella spiralis infects muscle tissue and causes myalgias after ingestion of larvae in undercooked meat.
A cat owner develops chorioretinitis. The pathogen is transmitted by oocysts in cat feces. What organism is responsible?
- A Toxoplasma gondii
- B Toxocara canis
- C Cryptosporidium parvum
- D Giardia lamblia
Correct answer: Toxoplasma gondii
Toxoplasma gondii is transmitted via cat feces and can cause chorioretinitis and encephalitis, especially in immunocompromised hosts.
A traveler to Africa develops cyclical fever, anemia, and splenomegaly. Blood smear shows ring forms in RBCs. What organism is responsible?
- A Babesia microti
- B Plasmodium falciparum
- C Trypanosoma brucei
- D Leishmania donovani
Correct answer: Plasmodium falciparum
Plasmodium falciparum causes malaria with ring forms in RBCs. It presents with periodic fever and anemia.