Microbiology- Parasitology Flashcards
Protozoa—gastrointestinal infections
Giardia lamblia, Entamoeba histolytica, Cryptosporidium,
Giardia lamblia
- Disease
- Transmission
- Diagnosis
- Treatment
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
Entamoeba histolytica
- Disease
- Transmission
- Diagnosis
- Treatment
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.
Cryptosporidium
- Disease
- Transmission
- Diagnosis
- Treatment
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.
Protozoa—CNS infections
Toxoplasma gondii, Naegleria fowleri, Trypanosoma
brucei,
Toxoplasma gondii
- Disease
- Transmission
- Diagnosis
- Treatment
Reactivation in AIDS brain 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
Congenital toxoplasmosis:
classic triad of chorioretinitis, hydrocephalus, and intracranial calcifications.
Naegleria fowleri
- Disease
- Transmission
- Diagnosis
- Treatment
Rapidly fatal meningoencephalitis
Swimming in warm freshwater; enters via cribriform plate
Amoebas in CSF
Amphotericin B has been effective for a few survivors
Trypanosoma brucei
- Disease
- Transmission
- Diagnosis
- Treatment
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.
Protozoa—hematologic infections
Plasmodium P vivax/ovale P falciparum P malariae, Babesia
Plasmodium
- Disease
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)
Plasmodium
- Transmission
- Diagnosis
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.
Plasmodium
- Treatment
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)
Babesiosis
- Disease
- Transmission
- Diagnosis
- Treatment
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
Protozoa Visceral infections
Trypanosoma cruzi, Leishmania donovani
Chagas disease
- Disease
- Transmission
- Diagnosis
- Treatment
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;
Leishmania donovani
- Disease
- Transmission
- Diagnosis
- Treatment
Visceral leishmaniasis (kala-azar)—spiking fevers, hepatosplenomegaly, pancytopenia. Cutaneous leishmaniasis—skin ulcers.
Sandfly
Macrophages containing amastigotes
AmphotericinB, sodium stibogluconate
Trichomonas vaginalis (protozoa)
- Disease
- Transmission
- Diagnosis
- Treatment
Vaginitis—foul-smelling, greenish discharge; itching and burning;
Sexual
Trophozoites (motile) on wet mount; “strawberry cervix”
Metronidazole for patient and partner (prophylaxis)
Nematode routes of infection
- Ingested
- Cutaneous
- Bites
EATTT: Enterobius, Ascaris, Toxocara, Trichinella, Trichuris
SANd: Strongyloides, Ancylostoma, Necator
LOW: Loa loa, Onchocerca volvulus, Wuchereria bancrofti
Enterobius vermicularis (pinworm)
- Disease
- Transmission
- Diagnosis
- Treatment
Causes anal pruritus (diagnosed by seeing
egg via the tape test).
Fecal-oral
Pyrantel pamoate or bendazoles.
Ascaris lumbricoides (giant roundworm)
- Disease
- Transmission
- Diagnosis
- Treatment
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
Strongyloides stercoralis (threadworm)
- Disease
- Transmission
- Diagnosis
- Treatment
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
Ancylostoma duodenale, Necator americanus (hookworms)
- Disease
- Transmission
- Treatment
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
Trichinella spiralis
- Disease
- Transmission
- Treatment
Larvae enter bloodstream, encyst in striated muscle muscle inflammation.
Trichinosis—fever, vomiting, nausea, periorbital edema, myalgia
Undercooked meat (especially pork); fecal-oral (less likely).
Bendazoles
Trichuris trichiura (whipworm)
- Disease
- Transmission
- Treatment
Often asymptomatic; loose stools, anemia, rectal prolapse in children (heavy infection).
Fecal-oral
Bendazoles
Toxocara canis
- Disease
- Transmission
- Treatment
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
Onchocerca volvulus
- Disease
- Transmission
- Treatment
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”)
Loa loa
- Disease
- Transmission
- Treatment
Swelling in skin, worm in conjunctiva
Deer fly, horse fly, mango fly
Diethylcarbamazine
Wuchereria bancrofti
Lymphatic filariasis (elephantiasis)— worms invade lymph nodesinflammation lymphedema; symptom onset after 9 mo–1 yr
Female mosquito
Diethylcarbamazine
Cestodes (tapeworms)
Taenia solium, Diphyllobothriumn latum, Echinococcus
granulosus.
Taenia solium
- Disease
- Transmission
- Treatment
Cysticercosis, neurocysticercosis (cystic CNS lesions, seizures).
Ingestion of eggs in food contaminated with human feces.
Praziquantel; albendazole for neurocysticercosis.
Diphyllobothrium latum
- Disease
- Transmission
- Treatment
Vitamin B12 deficiency
Ingestion of larvae in raw freshwater fish
Praziquantel
Echinococcus granulosus
- Disease
- Transmission
- Treatment
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
Trematodes (flukes)
Schistosoma, Clonorchis sinensis,
Schistosoma
- Disease
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
Schistosoma
- Transmission
- Treatment
Snails are intermediate host; cercariae penetrate skin of
humans in contact with contaminated fresh water
Praziquantel
Clonorchis sinensis
- Disease
- Transmission
- Treatment
Biliary tract inflammation pigmented gallstones
Associated with cholangiocarcinoma
Undercooked fish
Praziquantel
Ectoparasites
Sarcoptes scabiei, Pediculus humanus/ Phthirus pubis
Sarcoptes scabiei
- Disease
- Transmission
- Treatment
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.
Pediculus humanus/ Phthirus pubis
Treatment includes pyrethroids, malathion, or ivermectin lotion, and nit combing.
Can transmit Rickettsia prowazekii (epidemic typhus), Borrelia recurrentis (relapsing fever), Bartonella quintana (trench fever).
Parasite hints
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