Notes on Common Medical Parasites

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Entamoeba histolytica:

• Amebiasis; dysentery; inverted flask-shaped lesions in LI and also in liver, lungs, brain, heart.

• Blood and pus in stools; liver abscesses.

• Fecal-oral; fresh fruits, vegetables, water.

• Trophozoites present in stool.

• Treatment: metronidazole.

Giardia lamblia:

• Giardiasis.

• Fatty, foul smelling diarrhea; malabsorption.

• Transmitted by water, food, oral-anal sex; fecal-oral transmission.

• Trophozoites present in stool; fecal antigen test.

• Treatment: metronidazole.

Cryptosporidium:

• Cryptosporidiosis.

• Mild diarrhea in normal; severe in IC patients.

• Undercooked meat; water.

• Acid-fast oocysts in stool and intestinal glands.

Balantidium coli:

• Dysentery.

• Colon infected.

• Contaminated food or water.

• Ciliated trophozoites present in stool.

• Treatment: tetracycline.

Trichomonas vaginalis:

• Trichomoniasis.

• Asymptomatic; frothy vaginal discharge.

• Sexual contact.

• Motile trophozoites in methylene blue wet mount.

• Treatment: metronidazole.

Naegleria:

• Primary amebic meningoencephalitis (PAM).

• Headache, nausea, fever, altered sense of smell, fatal.

• Motile trophozoites in CSF; they leave trails on agar plates.

• Swimming in fresh water.

• Amphotericin B (rarely succesful).

Acanthamobea:

• Keratitis; granulamatous amebic encephalitis.

• Contact lens solution.

• Star-shaped cysts on biopsy; rarely seen in CSF.

• Treatment: keratitis (topical miconazole and propamidine isothionate); GAE: sulfadiazine.

Plasmodium cycle in mosquito:

1. Gametocysts are ingested by mosquitoes.

2. Mature cysts divide in stomach, rupture, then travel to mosquito salivary gland.

3. Mosquito bites human and cysts enter human blood stream.

4. Sporozoites invade parenchymal cells in liver.

5. In there, they divide, are released, then invade RBCs.

6. Relapsing chills, fever spike whenever infected RBCs are lysed releasing a new generation of merozoites.

P. vivax (48 hour fever cycle), P. ovale (48 hour fever cycle), P. malariae, P. falciparum.

Trypanosoma cruzi:

• Chagas disease.

• Swelling around eye.

• Spread by (Reduviid bug) kissing bug.

• Found in cats, dogs, armadillos, etc.

• Seen in blood films.

• Treat with nifurtimox.

Trypanosoma brucei gambiense; Trypanosoma b. rhodesiense:

• African sleeping sickness.

• Tsetse fly.

• Blood film.

• Treatment: suramin (acute); melarsoprol (chronic).

Leishmania donovani:

• Visceral leishmaniasis; kalazar.

• Sandfly bite.

• Found in rodents, wild animans.

• Treatment: stibogluconate sodium.

Babesia:

• Causes Babesiosis.

• Spread by Ixodes tick.

• Co-infection with Borrelia.

• Giemsa stain.

• Treatment: clindamycin and quinine.

Toxoplasma gondi:

• Disease in AIDS patients, pregnant women.

• Can lead to blindness in infants of infected mothers.

• Cat is essential host.

• High IgM seen with acute infection.

• Treat with pyrimethamine + sulfadiazine.

Additional Readings:

Basic Parasitology

1. Common Medical Parasites

Medical Images

Useful Medical Images & Diagrams (link opens in a new window)

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