Microbiology: Parasites

  1. Protozoa - GI infections
    • Giardia lamblia
    • Entamoeba histolytica
    • Cryptosporidium
  2. Giardia lamblia
    • Disease:
    • Giardiasis: bloating, flatulence, foul-smelling, fatty diarrhea (often seen in campers and hikers)

    Think fat rich Ghirardelli chocolates for fatty stools of Giardia

    Transmission: Cysts in water

    Dx: Trophozoits or cysts in stool

    Tx: Metronidazole
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    Giardia lamblia

    • A. Trophozoite
    • B. Cyst
  4. Entamoeba histolytica
    Disease: Amebiasis: bloody diarrhea (dyssentery), liver abscess (reddish brown), RUQ pain (histology shows flask-shaped ulcer if submucosal abscess of colon rputures

    Transmission: Cysts in water

    Dx: Serology and/or trophozoites with RBCs in the cytoplasm or cysts (with multiple nuclei) in the stool

    Tx: Metronidazole and iodoquinol
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    Entamoeba histolica

    • C. trophozoites (with RBCs in the cytoplasm)
    • D. cyst (with multiple nuclei)
  6. Cryptosporidium

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    • Disease: Severe diarrhea in AIDS
    • -Mild disease (watery diarrhea) in non-immunocompromised

    Transmission: Cysts in water

    Dx: Cysts on acid-fast stain

    Tx: Prevention (by filtering city water supplies); no treatment
  7. Protozoa - CNS infections
    • Toxoplasma gondii
    • Naegleria fowleri
    • Trypanosoma brucei
  8. Toxoplasma gondii

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    • Disease: Brain abscess in HIV (seen as ring-enhancing brain lesions on CT/MRI)
    • -congenital toxoplasmosis = "classic triad" of chorioretinitis, hydrocephalus, and intracranial calcifications

    Transmission: cysts in meat or cat feces; crosses placenta (pregnant women should avoid cats)

    Dx: serology, biopsy

    Tx: Sulfadiazine + pyrimethamine
  9. Naegleria fowleri
    Disease: rapidly fatal meningoencephalitis

    Transmission: Swimming in freshwater lakes (Think Nalgene bottle filled with freshwater containing Naelgeria); enter via cribiform plate

    Dx: Amoebas in spinal fluid

    Tx: Amphotericin has been effective for a few survivors
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    Naegleria amoeba
  11. Trypanosoma brucei
    • T. gambiense
    • T. rhodesiense

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

    Transmission: Tsetse fly, a painful bite

    Dx: Blood smear

    Tx: Suramin for blood-borne disease or melarsoprol for CNS penetration (it SURe is nice to go to sleep; MELAtonin helps with sleep)
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    Trypanosoma on blood smear
  13. Protozoa - Hematologic infections
    • Plasmodium
    • -P. vivax/ovale
    • -P. falciparum
    • -P. malariae

  14. Plasmodium
    Disease: Malaria: fever, headache, anemia, splenomegaly

    • -P. vivax/ovale
    • Presentation: 48-hr cycle (tertian; includes fever on first day and third day);
    •     - dominant form in liver

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

    • -P. malariae
    • Presentation: 72-hr cycle (quartan)

    Transmission: Mosquito (Anopheles)

    Dx: blood smear, trophozoite ring form, RBC shizont with merozoites

    • Tx: Chloroquine (blocks plasmodium heme polymerase); if resistant, use mefloquine
    • -vivax/ovale - add primaquine for dominant form in liver (hypnozoite)
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    Plasmodium (malaria)

    • A. blood smear, trophozoite ring form
    • B. RBC schizont with merozoites
  16. Babesia
    Disease: fever and hemolytic anemia; predominantly in northeastern US; asplenia pts have increase risk for severe disease

    Transmission: Ixodes tick (same as Borrelia burgdorferi of Lyme disease; may often co-infect humans)

    Dx: Blood smear, ring form, "Maltese cross"

    Tx: Quinine, clindamyacin
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    • Blood smear
    • 1. ring form
    • 2. "Maltese cross"
  18. Protozoa - other
    • Trypanosoma cruzi
    • Leishmania donovani
  19. Trypanosoma cruzi
    Disease: Chagas' disease (dilated cardiomyopathy, megacolon, megaesophagus); predominantly in South America

    Transmission: Reduviid bug ("kissing bug"), a painless bite (much like a kiss)

    • Dx: Blood smear
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    Tx: Nifurtimox
  20. Leishmania donovani
    Disease: Visceral leishmaniasis (kala-azar): spiking fevers, hepatosplenomegaly, pancytopenia

    Transmission: Sandfly

    Dx: Macrophages containing "amastigotes"

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    • Tx: Sodium stibogluconate
  21. STDs
    Trichomonas vaginalis

    Disease: Vaginitis: foul-smelling, greenish discharge; itching and burning; do not confuse with Gardnerella vaginalis, a gram-negative bacterium that causes bacterial vaginosis

    Transmission: Sexual (cannot exist outside human - cannot form cysts)

    Dx:  Trophozoites (motile) on wet mount

    Tx: Metronidazole for pts and partner
  22. Nematodes (roundworms)

    Routes of infection
    • Intestinal
    • Tissue

    • Ingestion - Enterobius, Ascaris, Trichinella
    • Cutaneus - Strongyloides, Ancylostoma, Necator

    • You'll get sick if you EAT these!
    • These get into your feet from the SANd.
  23. Nematodes
    • Enterobius vermicularis (pinworm)
    • Ascaris lumhricoides (giant roundworm)
    • Trichinella spiralis
    • Strongyloides stercoralis
    • Ancylostoma duodenale, Necator americanus (hookworms)
  24. Enterobius vermicularis
    Food contaminated with eggs; intestinal infection; causes anal pruritis (the Scotch tape test)

    Tx: bendazoles or pyrantel pamoate (worms are BENDy; treat with meBENDazole)
  25. Ascaris lumbricoides
    (giant roundworm)
    Eggs are visible in feces; intestinal infection

    Tx: bendazoles or pyrantel pamoate
  26. Trichinella spiralis
    Undercooked meat, usually pork; inflammation of muscle (larvae encyst in muscle); periorbital edema

    Tx: bendazoles
  27. Strongyloides stercoralis
    Larvae in soil penetrate the skin; intestinal infection; causes vomiting, diarrhea, and anemia

    Tx: bendazoles or ivermectin
  28. Ancylostoma duodenale,
     Necator americanus
    Larvae penetrate skin of feet; intestinal infection causes anemia (sucks blood from intestinal walls)

    Tx: bendazoles or pyrantel pamoate
  29. Nematodes - tissue
    • Dracunculus medinensis
    • Onchocerca volvulus
    • Loa loa
    • Wuchereria hancrofti
    • Toxocara canis
  30. Dracunculus medinensis
    In drinking water; skin inflammation and ulceration

    Tx: Niridazole, prolonged extraction
  31. Onchocerca volvulus
    Transmitted by female blackflies; causes hyperpigmented skin and river blindness (remember black flies, black skin nodules, "black sight"). Can have allergic reaction to microfilaria

    Tx: Ivermectin (IVERmectin for rIVER blindness)
  32. Loa loa
    Transmitted by deer fly, horse fly, and mango fly; causes swelling in skin (can see worm crawling in conjunctiva)

    Tx: Diethylcarbamazine
  33. Wuchereria bancrofti
    Female mosquito; causes blockage of lymphatic vessels (elephantiasis). Takes 9 months - 1 year after bite to get elephantiasis sx.

    Tx: Diethylcarbamazine
  34. Toxocara canis
    Food contamination with eggs; causes granulomas (if in retina --> blindness) and visceral larva migrans

    Tx: Albendazole or mebendazole
  35. Cestodes (tapeworms)
    • Taenia solium
    • Diphyllobothrium latum
    • Echinococcus granulosus

    • Treat most with Praziquantel
  36. Taenia solium
    • Ingestion of larvae encysted in undercooked pork leads to intestinal tapeworm.
    • Ingestion of eggs causes cysticercosis and neurocysticercosis, mass lesions in brain ("swiss cheese"" appearance)

    Tx: Praziquantel (use -bendazoles for neurocysticercosis)
  37. Diphyllobothrium latum
    Ingestion of larvae in raw freshwater fish. Causes vit B12 deficiency, results in anemia

    Tx: Praziquantel
  38. Echinococcus granulosus
    Eggs in dog feces when ingested can cause cysts in liver; causes anaphylaxis if echinococcal antigens are released from cyst (surgeons inject ethanol before removal to kill daughter cysts)

    Tx: Bendazoles
  39. Trematodes (flukes)
    • Schistosoma
    • Clonorchis sinensis
    • Paragonimus westermani

    • Tx: Praziquantel
  40. Schistosoma
    Snails are host; cercariae penetrate skin of humans

    • Causes granulomas, fibrosis, and inflammation of the spleen and liver. 
    • Chronic infection with S. haematobium can lead to squamous cell carcinoma of the bladder

    Tx: Praziquantel
  41. Clonorchis sinensis
    • Undercooked fish
    • causes inflammation of the biliary tract --> pigmented gallstones
    • Also associated with cholangiocarcinomas

    Tx: Praziquantel
  42. Paragonimus westermani
    • Undercooked crab meat
    • Causes inflammation and secondary bacterial infections of the lung, causing hemoptysis

    Tx: Praziquantel
  43. Parasite hints

    Findings --> organism
    • Brain cysts, seizures - Taenia solium (cysticercosis)
    • Liver cysts - Echinococcus granulosus
    • B12 deficiency - Diphyllobothrium latum
    • Biliary tract disease, cholangiocarcinoma - Clonorchis sinensis
    • Hemoptysis - Paragonimus westermani
    • Portal hypertension - Schistosoma mansoni
    • Hematuria, bladder cancer - Schistosoma haematobium
    • Microcytic anemia - Ancylostoma, Necator
    • Perianal pruritis - Enterobius (pinworm)
Card Set
Microbiology: Parasites
Parasitology First AID