Parasitology Flashcards
Giardia - Morphology
Trophozoite: Pear shaped, with two nuclei and 4 pairs of flagellae
Cyst: 4 nuclei
Chilomastix
Non-pathogenic.
Trophozoite: Pear-shaped, flagellated. One nucleus, with adjacent cytostome
Cyst: Lemon-shaped with anterior hyaline knob. “Shepherd’s hook”
Dientamoeba
Non-pathogenic.
Only trophozoite: 1-2 nuclei, each with 4 clumps of chromatin (resembles die pips)
Entamoeba histolytica
Fecal-oral cyst transmission. Causes amebic dysentery, sometimes liver abscesses.
Cyst: 1-4 nuclei, with “chromatoid bar” cigar-shape
Trophozoite: 1 nucleus with central karyosome. RBCs!
Entamoeba dispar
Non-pathogenic; resembles E. Histolytica except without erythrophagocytosis.
Entamoeba hartmannii
Resembles E. Histolytica, only smaller (<9um)
Entamoeba coli
Resembles entamoeba histolytica, except larger, has 1-8 nuclei, and eccentric karyosome
Iodamoeba butschlii
Cyst has large central glycogen vacuole and one nucleus.
Blastocystis
Unclear pathogen status
Huge central vacuole, compresses nuclei peripherally
Cryptosporidium parvum
Fecal-oral oocyst, immediately infective. Resists chlorine.
Tiny (1-3um), acid-fast. Diagnosable with histology.
Cyclospora
Fecal-oral oocyst, delayed infectivity. Resists chlorine.
8-10um, modified acid-fast. Thick wall?
Cystisospora
Fecal-oral oocyst (delayed infectivity). Rare.
The only oocyst that can be observed on O&P. Round/ovoid with 2 sporozoites. 20-33um?
Microsporidia
Protozoan (or fungus) that is actually an enormous phylum of OBLIGATE INTRACELLULAR parasites.
Best diagnosed on histology. “Belt-like stripe”
Malaria transmission & diagnosis
Transmitted by anopheline mosquitoes, transmission, needles, or vertically
Diagnosed by BinaxNow (rapid Ag; has T1 for falciparum, T2 for common plasmodium antigen), 200-300 thick smear fields (but use thin smear to quantify).
Plasmodium falciparum
Malignant tertian fever (48 hours). Cerebral symptoms, often fatal.
High parasitemia, including multiple organisms per RBC (all stages). Crescent (“banana”) gametocytes (DO NOT COUNT TOWARDS PARASITEMIA LOAD). No schizonts.
Plasmodium malariae
Causes quartan (72hr) fever. Mild? Indolent.
Infects mature RBCs (smaller). 6-12 merozoites.
Plasmodium vivax
Schizont can infect liver»_space; hypnozoites cause true dormancy & relapses.
Infects reticulocytes (larger). Schuffner stippling. 12-24 merozoites, ameboid trophozoite.
Most common malaria overall
Plasmodium ovale
Schizont can infect liver»_space; hypnozoites cause true dormancy & relapses.
Infects reticulocytes (larger). Schuffner stippling. Up to 16 merozoites.
Plasmodium knowlesi
Zoonotic (often infects rhesus monkeys). Asia.
Morphologically indistinguishable from P. Malariae, but clinically worse.
Babesia microti
Ixodes tick (NE US / anterior anal groove). 1-4wk incubation»_space; malaria-like illness. TTI.
Maltese cross, ring forms, extracellular merozoites.
Dx: Serology, smear, PCR
Trypanosoma brucei
Transmitted by Tsetse (Glossina) fly. Rhodesiense (west), Gambiense (east)
Triphasic disease: Chancre»_space; Hemolymphatic involvement»_space; CNS involvement (fatal)
Large trypomastigotes with SMALL POSTERIOR KINETOPLAST and dividing forms
Trypanosoma Cruzi
Transmitted by Reduviid bug.
Chagoma / Romana»_space; Systemic symptoms including megacolon/megaesophagus and cardiomyopathy.
Amastigotes on tissue sections. Trypomastigote on smear with LARGE SUBTERMINAL KINETOPLAST and no dividing.
Leishmania donovani
Transmitted by sandfly. Promastigote transforms to amastigote within macrophages.
Cutaneous ulcer»_space; visceral involvement (especially in immunocompromised)
Resembles histoplasmosis. Look for kinetoplast. No budding, no PAS.
Toxoplasma Gondii
Cats, infected meat, transplacental, transfusion. Direct transmission of oocyst.
Immunocompetent: Asymptomatic, sometimes mono-like.
Immunocompromised: Ring-like brain abscesses, carditis.
Congenital: Severe chorioretinitis, hydrocephalus with calcifications, death.
Dx with serology (follow IgM to seroconversion). Cysts with bradyzoites on H&E. Tachyzoites indicate active infection.
Trichomonas
1 STD. Underrecognized. Only trophozoite (no cysts)
Undulating membrane covers 1/2 of body. 1 nucleus.
What features are common to all nematodes?
True gut (coelom) and cuticle.
Most cause high morbidity but low mortality infections.
Enterobius vermicularis (pinworm)
1 nematode in US. Children, often autoinfection.
No O&P. Eggs are oval, 50-60um, asymmetric.
Can directly observe worms at night.
Trichuris trichiura (whipworm)
Fecal-oral transmission. Produces 1000s of eggs per day.
May cause prolapse with severe burden.
Ova are barrel-shaped, brown, with bipolar mucus plugs.
Ascaris lumbricoides
1 nematode worldwide. Fecal-oral egg transmission but lung maturation (eosinophilic pneumonitis). 100,000s of eggs.
Huge worms (up to 40cm), often many»_space; obstruction, perforation.
Ova: Unfertilized are mammillated/bumpy. Fertilized are round with ruffled shell.
Necator/Ancylostoma (hookworms)
Skin-penetrating filaria (larva migrans)»_space; lung maturation (eosinophilic pneumonitis).
Causes severe iron deficiency anemia.
Ova are ~65um with early embryo inside (grape-like).
*Cannot differentiate species by eggs; but ancylostoma has “4 fangs” while necator has “2 plates”
Strongyloides
Skin-penetrating filaria (larva migrans)»_space; lung maturation (eosinophilic pneumonitis). Autoinfection!
Adults 2mm long; rhabditiforms in stool. Can move on agar plate»_space; may “carry” gram-neg bacteria in disseminated infection
Dx by O&P, serology, often histology.
Wuchereria Bancrofti
Many vectors (Culex, Anopheles). Causes lymphedema, elephantiasis.
Pulmonary tropical eosinophilia syndrome.
Nighttime collection»_space; Sheathed worm with nuclei that do not extend to tail.
Brugia
Many vectors (Culex, Anopheles). Causes lymphedema, elephantiasis.
Pulmonary tropical eosinophilia syndrome.
Nighttime collection»_space; Sheathed worm with 2 terminal nuclei
Loa loa filariasis
Horse/deer fly vector. Occupies visceral lymphatics?
Worm classically infects conjunctivae. Periocular “Calabar swelling”
Nighttime harvest»_space; Sheathed worm with nuclei that extend to end of tail.
Onchocerciasis
Transmitted by black fly.
Subcutaneous nodules, river blindness.
No specific harvest-time»_space; Unsheathed worm that does not have nuclei to end of tail
Diphyllobothrium latum
Fish tapeworm, huge. “Bothrium” folded scolex. 1Mil eggs/day!
Proglottids are wider than long.
Ova have operculum and abopercular knob. 70um.
Taenia solium
Pig tapeworm. Can cause neurocysticercosis (egg ingestion) or GI parasite (larva ingestion).
Proglottids have 7-13 uterine branches per side.
Eggs are 30um, round, with thick shell and visible hooklets.
Taenia saginata
Beef tapeworm.
Proglottids have 15-30 uterine branches per side.
Eggs are 30um, round, with thick shell and visible hooklets.
Echinococcus granulosis
Infects sheep & dogs (humans incidental). Actually a tiny cestode (3 segments).
Hydatid cysts are thick-walled with scolical debris.
Risk of anaphylaxis»_space; inject and aspirate.
Echinococcus multilocularis
Rats, rodents etc. Humans incidental host.
More severe liver cyst burden than granulosus…
Hymenolepis nana & diminuta (dwarf tapeworm)
1 cestode in US.
Nana: Worms are 4cm long. Ova have thick shell with polar filaments (“silly string”)
Diminuta: No polar filaments
Dipylidium caninum
Dogs & cats. “Rice-grain” proglottids in stool.
Ova are actually packets/sachets of 5-15 eggs.
What are some general characteristics of trematodes?
Flatworms; have ventral sucker and oral cavity with no true coelom. All are hermaphroditic and rely on 1-2 intermediate hosts, of which one is always a snail.
Clonorchis sinensis
Asia, uncooked fish secondary (smoking, pickling do not kill).
Bile duct obstruction, cholangiocarcinoma…
Ova have operculum and abopercular knob with shoulders. 30um.
Fasciola hepatica
Raw water cress. Bile duct obstruction.
Small operculum, no shoulders. 140um.
Fasciolopsis buski
Raw water chestnut. Bile duct obstruction.
Small operculum, no shoulders. 140um.
Paragonimus Westermani
Oriental lung fluke; crayfish/crab.
Acute infection involves GI but chronic infection involves lungs.
Ova have operculum, thickened abopercular end. 100um.
Schistosoma mansoni
Colon polyposis, bloody diarrhea, portal HTN.
Prominent lateral spine, 120um.
Schistosoma japonicum
Portal hypertension.
Small-round ova with wimpy lateral spine (80um)
Schistosoma hematobium
Cystitis, squamous metaplasia, urothelial carcinoma.
Terminal spine. 120um.
Balantidium coli
The only ciliated parasite of humans. Quite large (70um). Pigs.
Ixodes tick
Anterior anal groove
Transmits borrelia, anaplasma
Stool preservatives
Sodium acetate / acetic acid / formalin (SAF)
Polyvinyl alcohol (PVA)
Merthiolate iodine formalin (MIF)
Blood smear preservative
Use EDTA (heparin distorts morphology)
Trichinella
Pork-encysted larvae»_space; adult worms in human GI tract»_space; larvae re-encyst. One host with no eggs!
GI symptoms, muscle pain/weakness, fever, periorbital edema.
Diagnosed with serology or H&E.
Acanthamoeba
Wrinkled double-wall. Causes keratitis and granulomatous encephalitis.
