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USMLE Step 1 > Microbiology - Fungi and Parasites > Flashcards

Microbiology - Fungi and Parasites Flashcards

1
Q

Anaplasma phagocytophilum

A

Gram -

Obligate intracellular in granulocytes (vs. monocytes for erhliciosis)

Deer tick (Ixodes)

Granulocytic ehrlichiosis

Granulocytes with morulae in cytoplasm

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2
Q

Ancylostoma duodenale

Necator americanus

A

Intestinal nematode (hookworm) parasite

Larvae penetrate skin → lungs → GI tract

Drinks blood and digests hemoglobin → microcytic anemia

More likely to infect adults; pregnancy complications

Rx: mebendazole, albendazole, pyrantel pamoate

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3
Q

Angiostrongylus cantonesis

A

Ingestion of snails, slugs Rat lungworm disease –> peripheral and CSF eosinophilia

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4
Q

Anisakis simplex

A

Ingestion of raw or undercooked seafood Inhabits stomach Kill larvae by freezing

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5
Q

Ascaris lumbricoides

A

Intestinal nematode (roundworm) parasite

Eggs ingested –> lungs (Loeffler’s syndrome) –> bowel

Causes intestinal, biliary, or pancreatic obstruction

Tx: mebendazole, albendazole, pyrantel pamoate

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6
Q

Aspergillus fumigatus

A

Mold fungus (not dimorphic)

Catalase +

Septate hyphae branch at acute angles (see picture)

Types:

  • Invasive aspergillus in immunosuppressed, neutropenic
  • Allergic bronchopulmonary aspergillosis (Type 1 hypersensitivity a/w asthma, CF; high IgE, eosinophilia, proximal bronchiectasis)
  • Aspergillomas - colonization of old lung cavities (esp. after TB)

a/w hepatocellular carcinoma (via aflatoxins)

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7
Q

Babesia

A

Protozoa parasite causes babesiosis (fever, myalgias, headache, hemolytic anemia, thrombocytopenia, increased LFTs); asplenia increases risk of severe disease

Deer tick (Ixodes)

Dx: blood smear may show Maltese cross (see picture), PCR

Tx: atovaquone + azithromycin

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8
Q

Blastomyces dermatiditis

A

Dimorphic fungus that causes blasomycosis

Yeast have “double-contoured” wall, broad-based budding (see picture)

Causes pneumonia → granuloma formation, cutaneous warts, genitourinary tract infections, osteomyelitis

Endemic in states east of the Mississippi and Central America

Tx (local): itroconazole

Tx (systemic): amphotericin B

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9
Q

Candida albicans

A

Dimorphic fungus

Pseudohyphae with blastoconidia, true hyphae, germ tubes, and budding yeasts

Catalase +

Can cause candidiasis (oral, esophageal) in immunocompromised patients and candidemia in patients receiving parenteral nutrition through a central venous catheter

Can cause vaginal yeast infections in women –> thick white discharge; diagnose by pseudohyphae on wet prep and normal pH; treat with OTC azole-based ointments or oral fluconazole

Treat disseminated candida with fluconazole, amphotericin B, or caspofungin

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10
Q

Clonorchis sinsensis

A

Intestinal trematode parasite

Chinese liver fluke

Transmitted from ingestion of metacercarie in undercooked fish

Fluke lives in bile ducts and causes biliary tract inflammation → pigmented stones, and cholangiocarcinoma

Rx: prazinquantel

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11
Q

Coccidioides immitis

A

Dimorphic fungus that causes coccidioidomycosis (San Joaquin Valley Fever)

Infection by inhalation of arthroconidia → spherules filled with endospores (see picture)

Endemic in southwest U.S.

May have eosinophilia

Causes pneumonia and disseminated disease (meningitis, rash, symmetric arthralgia)

Tx (local): fluconazole, itroconazole

Tx (systemic): amphotericin B

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12
Q

Cryptococcus neoformans

A

Yeast (not dimorphic)

Budding yeast with a thick capsule → stains with india ink and mucicarmine

Found in soil, pigeon droppings

Urease +

Can cause meningitis in AIDS, pneumonia

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13
Q

Cryptosporidium parvum

A

Intestinal protozoa parasite

Transmitted from ingestion of oocysts from contaminated water (chlorine resistant)

Causes mild to severe diarrhea (esp. in immunocompromised)

Dx: acid fast stain for oocysts

Tx: filtering water supply, nitazoxanide in immunocompromised hosts

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14
Q

Diphyllobothrium latum

A

Intestinal cestode (tapeworm) parasite

Ingestion of larvae in raw freshwater fish

Causes B12 deficiency → macrocytic anemia

Tx: Praziquantel

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15
Q

Echinococcus granulosus

A

Intestinal cestode (tapeworm) parasite

Ingestion of eggs from dog feces

Causes hydatid cysts in the liver causing antiphylaxis if antigens released (surgeon preinjects with ethanol to kill cysts before removal)

Tx: albendazole

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16
Q

Echinococcus granulosus

A

Intestinal cestode (tapeworm) parasite Ingestion of eggs from dog feces Causes liver cysts with internal daughter cysts Rx: albendazole

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17
Q

Entamoeba histolytica

A

Intestinal protozoa parasite

Transmitted from ingestion of cysts from contaminated food or water

Causes dysentery, liver abscess (anchovy-paste), flask-shaped ulcers

Dx: serology, trophozoites containing RBCs, cysts (with up to 4 nuclei) in stool

Rx: metronidazole

18
Q

Enterobius vermicularis

A

Intestinal nematode (pinworm) parasite

Fecal-oral transmission

Causes peri-anal itching

Diagnose with “scotch tape test”

Rx: mebendazole, pyrantel pamoate

19
Q

Giardia lamblia

A

Intestinal protozoa parasite

Transmitted from ingestion of cysts from contaminated water (chlorine resistant)

Causes bloating, flatulence, steatorrhea

Dx: trophozoites or cysts in stool

Tx: metronidazole

20
Q

Histoplasma capsulatum

A

Dimorphic fungus that causes histoplasmosis

Endemic in the Ohio and Mississippi River Valleys

Risk factors: exposure to bird or bat droppings, cave diving

Histoplasma hides in macrophages (see picture)

Causes pneumonia but can become systemic

Tx (local): fluconazole, itroconazole

Tx (systemic): amphotericin B

21
Q

Leishmania

A

Protozoal parasite with kinetoplast, live in WBCs

Transmitted from bite of female sand fly

Cutaneous, mucosal, or visceral forms

Dx: macrophages containing amastigotes (see picture)

Tx: amphotericin B, sodium stibogluconate

22
Q

Loa loa

A

Tissue invasive nematode

Larvae enter wound from Chrysops fly

Adults: subcutaneous nodules (swelling of the skin), worms in conjunctiva

Microfilaria: blood during DAY

Causes calabar swelling, can be in eye

Tx: diethylcarbamazine unless high microfilaria load

23
Q

Malassezia furfur

A

Cutaneous mycoses that causes tinea versicolor

Degradation of lipids produces acids that damage melanocytes → hypo or hyperpigmented patches

Occurs in hot, humid weather

Tx: topical miconazole, selenium sulfide

Spaghetti and meatballs appearance (see picture)

24
Q

Mucor and Rhizopus

A

Mold

Large non-septate hyphae branch at obtuse angles (see picture)

Causes mucormycosis (facial and paranasal pain and ischemia, headache) in diabetics and leukemic patients –> fungi proliferate in blood vessels when glucose and ketones are high

Can penetrate brain

Tx: surgical debridement of necrotic tissue, amphotericin B, poscanazole

25
Naegleria fowleri
Protozoa parasite Transmitted by swimming in freshwater lakes → amoebas enter cribriform plate Causes rapidly fatal meningoencephalitis Dx: amoebas in spinal fluid Tx: amphotericin B
26
Onchocerca volvulus
Larva enter wound of female black fly bite Adults and microfilaria live in subcutaneous nodules Causes river blindness (hyperpigmented skin, blindness) → "black flies, black skin nodules, black sight" Tx: ivermectin + doxycycline to kill Wolbachia bacteria
27
Paracoccidoides brasiliensis
Dimophic fungus that causes paracoccidioidomycosis Budding yeast with "captain's wheel" formation Endemic in tropical and subtropical central and south America Causes pneumonia, chronic mucocutaneous ulcers
28
Pneumocystis jirovecii
Yeast that can't be cultured Can cause pneumocystic pnemonia (PCP) in immunosuppressed patients Ground-glass appearance on CXR Treatment and prophylaxis (CD4 count \< 200) with TMP-SMX Disc-shaped yeast form on methenamine silver stain
29
Schistosoma
Intestinal trematode parasite Blood fluke NOT hermaphroditic Snails release cercariae into water that can penetrate skin Can cause liver and spleen granulomas, fibrosis → portal HTN (S. mansoni, S. japonicum) S. haematobium can lead to squamous cell carcinoma of the bladder (painless hematuria) Tx: praziquantel
30
Sporothrix schenckii
Dimorphic, cigar-shaped budding yeast Lives on vegetation and introduced to the skin (_rose thorn_) Causes sporotrichosis (local pustule or ulcer with ascending lymphangitis) Biopsy shows granulomas surrounded by plasma cells Tx: itraconazole or potassium iodide
31
Strongyloides stercoralis
Intestinal nematode (roundworm) parasite Larvae from soil penetrate skin → lungs → GI tract (vomiting, diarrhea, epigastric pain) _Larvae in stool, not eggs_ Autoinfection possible Hyperinfection syndrome in immunocompromised states → test before starting steroids Rx: ivermectin, albendazole
32
Taenia solium
Intestinal cestode (tapeworm) parasite Ingestion of encysted larvae in undercooked pork → intestinal disease Ingestion of eggs from infected human stool → cystericosis, neurocysticercosis Rx: prazinquantel, albendazole for neurocystericosis
33
Tinea infections
Tinea versicolor → malassezia furfur Tinea pedis (foot), cruris (groin), corporis (body), capitis (head/scalp), unguium (fingernails) → dermatophytes Mirosporum, Trichophyton, Epidermophyton
34
Toxocara canis and toxocara catis
Ingestion of eggs in dog or cat feces Visceral larva migrans Tx: albendazole or mebendazole
35
Toxoplasma gondii
Obligate intracellular protozoan parasite Trasmitted from cysts in meat or oocysts in cat feces May cause TORCH congenital infection (hydrocephalus, scattered intracranial calcifications, chorioretinitis), brain abscess in HIV (multiple ring-enhancing lesions on imaging) Dx: culture, serology Tx: pyrimethamine + sulfadiazine
36
Trichinella spiralis
Tissue invasive nematode Ingestion of cysts in raw or undercooked meat Encysts in striated muscle
37
Trypanosoma brucei gambiense
Protozoal parasite with kinetoplast Bite of Tsetse fly Found in W. Africa (rivers) African trypanosomiasis (sleeping sickness): enlarged lymph nodes, recurring fever, somnolence, coma More common among endemic population Chronic presentation Mott cells (unsecreted IgM) Dx: blood smear (see picture) Tx: suramin (for blood-borne disease) or melarsoprol (for CNS penetration)
38
Trypanosoma brucei rhodesiense
Protozoal parasite with kinetoplast Bite of Tsetse fly Found in E. Africa (savannah) African trypanosomiasis (sleeping sickness): enlarged lymph nodes, recurring fever, somonolence, coma More common among travelers Acute presentation Mott cells (unsecreted IgM) Dx: blood smear (see picture) Tx: suramin (for blood-borne disease) or melarsoprol (for CNS penetration)
39
Trypanosoma cruzi
Protozoal parasite that enters the host from the feces of the kissing bug (Reduviid bug) Causes Chagas disease/American trypaosomiasis Acute: Romana's sig (unilateral, painless, periorbital edema) Chronic: dilated cardiomyopathy, GI disease (megacolon, megaesophagus) Dx: blood smear Tx: benznidazole or nifurtimox
40
Wuchereria bancrofti
Larvae enter skin through female mosquito bite Adults: lymphatics Microfilaria: lymph and blood at NIGHT Lymphatic filariasis, elephantitis, tropical pulmonary eosinophilia Tx: diethylcarbamazine
41
What CSF findings are consistent with fungal/TB meningitis?
↑ opening pressure ↑ lymphocytes ↑ protein ↓ glucose

USMLE Step 1 (20 decks)

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