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USMLE 1 > Microbiology- Parasitology > Flashcards

Microbiology- Parasitology Flashcards

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USMLE® Step 1 flashcards
1
Q

Protozoa—gastrointestinal infections

A

Giardia lamblia, Entamoeba histolytica, Cryptosporidium,

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2
Q

Giardia lamblia

  • Disease
  • Transmission
  • Diagnosis
  • Treatment
A

Giardiasis—bloating, flatulence, foul-smelling, fatty diarrhea (often seen in campers/hikers)— think fat-rich Ghirardelli chocolates for fatty stools of Giardia.

Cysts in water

Multinucleated trophozoites or cysts in stool, antigen detection.

Metronidazole

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3
Q

Entamoeba histolytica

  • Disease
  • Transmission
  • Diagnosis
  • Treatment
A

Amebiasis—bloody diarrhea (dysentery), liver abscess
(“anchovy paste” exudate), RUQ pain; histology of colon biopsy shows flask-shaped ulcers.

Cysts in water

Serology, antigen testing, and/or trophozoites (with
engulfed RBCs in the cytoplasm) or cysts with up to 4 nuclei in stool.

Metronidazole; paromomycin or iodoquinol for asymptomatic cyst passers.

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4
Q

Cryptosporidium

  • Disease
  • Transmission
  • Diagnosis
  • Treatment
A

Severe diarrhea in AIDS Mild disease (watery diarrhea) in
immunocompetent hosts.

Oocysts in water

Oocysts on acid-fast stain, antigen detection.

Prevention (by filtering city water supplies); nitazoxanide in immunocompetent hosts.

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5
Q

Protozoa—CNS infections

A

Toxoplasma gondii, Naegleria fowleri, Trypanosoma

brucei,

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6
Q

Toxoplasma gondii

  • Disease
  • Transmission
  • Diagnosis
  • Treatment
A

Reactivation in AIDS Žbrain abscesses usually seen as
multiple ring-enhancing lesions on MRI.

Cysts in meat (most common); oocysts in cat feces; crosses placenta (pregnant women should avoid cats)

Serology, biopsy (tachyzoite).

Sulfadiazine + pyrimethamine

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7
Q

Congenital toxoplasmosis:

A

classic triad of chorioretinitis, hydrocephalus, and intracranial calcifications.

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8
Q

Naegleria fowleri

  • Disease
  • Transmission
  • Diagnosis
  • Treatment
A

Rapidly fatal meningoencephalitis

Swimming in warm freshwater; enters via cribriform plate

Amoebas in CSF

Amphotericin B has been effective for a few survivors

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9
Q

Trypanosoma brucei

  • Disease
  • Transmission
  • Diagnosis
  • Treatment
A

African sleeping sickness— enlarged lymph nodes, recurring fever (due to antigenic variation), somnolence, coma

Tsetse fly, a painful bite

Trypomastigote in blood smear

Suramin for bloodborne disease or melarsoprol for CNS penetration.

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10
Q

Protozoa—hematologic infections

A

Plasmodium P vivax/ovale P falciparum P malariae, Babesia

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11
Q

Plasmodium

- Disease

A

Malaria—fever, headache, anemia, splenomegaly

P vivax/ovale—48-hr cycle (tertian; includes fever on first day and third day, thus fevers are actually 48 hr apart); dormant form (hypnozoite) in liver.

P falciparum—severe; irregular fever patterns; parasitized RBCs occlude capillaries in brain (cerebral malaria), kidneys, lungs.

P malariae—72-hr cycle (quartan)

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12
Q

Plasmodium

  • Transmission
  • Diagnosis
A

Anopheles mosquito

Blood smear: trophozoite ring form within RBC A , schizont containing merozoites; red granules (Schüffner stippling) throughout RBC cytoplasm seen with P vivax/ovale.

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13
Q

Plasmodium

- Treatment

A

Chloroquine (for sensitive species), which blocks Plasmodium heme polymerase;

if resistant, use mefloquine or atovaquone/ proguanil If life-threatening, use intravenous quinidine or artesunate (test for G6PD deficiency)

For P vivax/ovale, add primaquine for hypnozoite (test for G6PD deficiency)

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14
Q

Babesiosis

  • Disease
  • Transmission
  • Diagnosis
  • Treatment
A

fever and hemolytic anemia; predominantly in northeastern United States; asplenia  risk of severe disease

Ixodes tick

Blood smear: ring form, “Maltese cross”; PCR

Atovaquone + azithromycin

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15
Q

Protozoa Visceral infections

A

Trypanosoma cruzi, Leishmania donovani

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16
Q

Chagas disease

  • Disease
  • Transmission
  • Diagnosis
  • Treatment
A

dilated cardiomyopathy with apical atrophy, megacolon,
megaesophagus; predominantly in South America
Unilateral periorbital swelling (Romaña sign) characteristic of acute stage.

Triatomine (“kissing”) bug

Trypomastigote in blood smear

Benznidazole or nifurtimox;

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17
Q

Leishmania donovani

  • Disease
  • Transmission
  • Diagnosis
  • Treatment
A 
Visceral leishmaniasis (kala-azar)—spiking fevers, hepatosplenomegaly, pancytopenia.
Cutaneous leishmaniasis—skin ulcers.

Sandfly

Macrophages containing amastigotes

AmphotericinB, sodium stibogluconate

18
Q

Trichomonas vaginalis (protozoa)

  • Disease
  • Transmission
  • Diagnosis
  • Treatment
A

Vaginitis—foul-smelling, greenish discharge; itching and burning;

Sexual

Trophozoites (motile) on wet mount; “strawberry cervix”

Metronidazole for patient and partner (prophylaxis)

19
Q

Nematode routes of infection

  • Ingested
  • Cutaneous
  • Bites
A

EATTT: Enterobius, Ascaris, Toxocara, Trichinella, Trichuris

SANd: Strongyloides, Ancylostoma, Necator

LOW: Loa loa, Onchocerca volvulus, Wuchereria bancrofti

20
Q

Enterobius vermicularis (pinworm)

  • Disease
  • Transmission
  • Diagnosis
  • Treatment
A

Causes anal pruritus (diagnosed by seeing
egg via the tape test).

Fecal-oral

Pyrantel pamoate or bendazoles.

21
Q

Ascaris lumbricoides (giant roundworm)

  • Disease
  • Transmission
  • Diagnosis
  • Treatment
A

May cause obstruction at ileocecal valve, biliary obstruction, intestinal perforation, migrates from nose/mouth.

Fecal-oral; knobby-coated, oval eggs seen in feces under microscope.

Bendazoles

22
Q

Strongyloides stercoralis (threadworm)

  • Disease
  • Transmission
  • Diagnosis
  • Treatment
A

Autoinfection: rarely, some larvae may penetrate the intestinal wall to enter the bloodstream without leaving the body.

Larvae in soil penetrate skin; rhabditiform larvae seen in
feces under microscope.

Ivermectin or bendazoles

23
Q

Ancylostoma duodenale, Necator americanus (hookworms)

  • Disease
  • Transmission
  • Treatment
A

Cause anemia by sucking blood from intestinal wall.
Cutaneous larva migrans—pruritic, serpiginous rash from walking barefoot on contaminated beach.

Larvae penetrate skin

Bendazoles or pyrantel pamoate

24
Q

Trichinella spiralis

  • Disease
  • Transmission
  • Treatment
A

Larvae enter bloodstream, encyst in striated muscle Žmuscle inflammation.
Trichinosis—fever, vomiting, nausea, periorbital edema, myalgia

Undercooked meat (especially pork); fecal-oral (less likely).

Bendazoles

25
Q

Trichuris trichiura (whipworm)

  • Disease
  • Transmission
  • Treatment
A

Often asymptomatic; loose stools, anemia, rectal prolapse in children (heavy infection).

Fecal-oral

Bendazoles

26
Q

Toxocara canis

  • Disease
  • Transmission
  • Treatment
A 
Visceral larva migrans—nematodes migrate to blood through intestinal wall inflammation and damage. Often
affects heart (myocarditis), liver, eyes (visual impairment, blindness), and CNS (seizures, coma).

Fecal-oral

Bendazoles

27
Q

Onchocerca volvulus

  • Disease
  • Transmission
  • Treatment
A

Skin changes, loss of elastic fibers, and river blindness; allergic reaction to microfilaria possible.

Female blackfly

Ivermectin (ivermectin for river blindness)

(black flies, black skin nodules, “black sight”)

28
Q

Loa loa

  • Disease
  • Transmission
  • Treatment
A

Swelling in skin, worm in conjunctiva

Deer fly, horse fly, mango fly

Diethylcarbamazine

29
Q

Wuchereria bancrofti

A

Lymphatic filariasis (elephantiasis)— worms invade lymph nodesŽinflammation Žlymphedema; symptom onset after 9 mo–1 yr

Female mosquito

Diethylcarbamazine

30
Q

Cestodes (tapeworms)

A

Taenia solium, Diphyllobothriumn latum, Echinococcus

granulosus.

31
Q

Taenia solium

  • Disease
  • Transmission
  • Treatment
A

Cysticercosis, neurocysticercosis (cystic CNS lesions, seizures).

Ingestion of eggs in food contaminated with human feces.

Praziquantel; albendazole for neurocysticercosis.

32
Q

Diphyllobothrium latum

  • Disease
  • Transmission
  • Treatment
A

Vitamin B12 deficiency

Ingestion of larvae in raw freshwater fish

Praziquantel

33
Q

Echinococcus granulosus

  • Disease
  • Transmission
  • Treatment
A

Hydatid cysts (“eggshell calcification”) in liver; cyst rupture can cause anaphylaxis

Ingestion of eggs in food contaminated with dog feces
Sheep are an intermediate host

Albendazole

34
Q

Trematodes (flukes)

A

Schistosoma, Clonorchis sinensis,

35
Q

Schistosoma

- Disease

A

Liver and spleen enlargement (S mansoni, egg with lateral spine), fibrosis, inflammation, portal hypertension.

Chronic infection with Shaematobium (egg with
terminal spine) can lead to squamous cell carcinoma of the bladder (painless hematuria) and pulmonary hypertension

36
Q

Schistosoma

  • Transmission
  • Treatment
A

Snails are intermediate host; cercariae penetrate skin of
humans in contact with contaminated fresh water

Praziquantel

37
Q

Clonorchis sinensis

  • Disease
  • Transmission
  • Treatment
A

Biliary tract inflammation pigmented gallstones
Associated with cholangiocarcinoma

Undercooked fish

Praziquantel

38
Q

Ectoparasites

A

Sarcoptes scabiei, Pediculus humanus/ Phthirus pubis

39
Q

Sarcoptes scabiei

  • Disease
  • Transmission
  • Treatment
A

Mite burrow into stratum corneum and cause scabies—pruritus (worse at night) and serpiginous burrows (lines) in webspace of hands and feet.

transmission through skin-to-skin contact (most common) or via fomites.

Treatment: permethrin cream, washing/drying all clothing/bedding, treat close contacts.

40
Q

Pediculus humanus/ Phthirus pubis

A

Treatment includes pyrethroids, malathion, or ivermectin lotion, and nit combing.

Can transmit Rickettsia prowazekii (epidemic typhus), Borrelia recurrentis (relapsing fever), Bartonella quintana (trench fever).

41
Q

Parasite hints

A

Pag 161

USMLE 1 (73 decks)

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