Parasitic Diseases

Parasitology Basics - Tiny Terrors Intro

• Parasitism: Symbiotic relationship; parasite benefits, host harmed.
• Host Types:
  • Definitive Host (DH): Harbors adult/sexual stage of parasite.
  • Intermediate Host (IH): Harbors larval/asexual stage.
  • Paratenic Host: Transport host; no parasite development.
  • Reservoir Host: Maintains infection in nature, source for human infection.
• Major Groups:
  • Protozoa: Unicellular eukaryotes (e.g., Plasmodium, Giardia).
  • Helminths (Worms): Multicellular.
    • Nematodes (roundworms).
    • Cestodes (tapeworms).
    • Trematodes (flukes).
  • Ectoparasites: Live on host surface (e.g., lice, mites).
• Zoonosis: Disease primarily of animals, transmissible to humans.

⭐ Many parasitic infections, especially helminthic, are associated with eosinophilia.

Protozoal Diseases - Single-Cell Saboteurs

• Malaria: Plasmodium spp. (P. falciparum, P. vivax, P. ovale, P. malariae). Vector: Female Anopheles mosquito.

  • Symptoms: Cyclical fever, chills, rigors, sweats. P. falciparum: cerebral malaria, blackwater fever.
  • Dx: Peripheral smear (ring forms, gametocytes), Rapid Diagnostic Tests (RDTs).
  • Rx: Artemisinin-based Combination Therapies (ACTs). Chloroquine (for sensitive areas). Primaquine for P. vivax/ovale hypnozoites (check G6PD status).

• Amoebiasis: Entamoeba histolytica. Transmission: Fecal-oral (cysts).

  • Symptoms: Amoebic dysentery (blood & mucus in stool), amoebic liver abscess ("anchovy sauce" pus).
  • Dx: Stool microscopy (trophozoites with ingested RBCs, quadrinucleate cysts), antigen detection.
  • Rx: Metronidazole or Tinidazole, followed by a luminal amoebicide (e.g., Paromomycin, Diloxanide furoate).

• Leishmaniasis (Kala-azar): Leishmania donovani complex. Vector: Sandfly (Phlebotomus).

  • Symptoms: Prolonged fever, hepatosplenomegaly, pancytopenia, weight loss, hypergammaglobulinemia.
  • Dx: Demonstration of LD bodies (Leishman-Donovan bodies) in macrophages from bone marrow/spleen aspirate; rK39 strip test.
  • Rx: Amphotericin B (liposomal), Miltefosine.

  ⭐ Post-Kala-azar Dermal Leishmaniasis (PKDL) can manifest as hypopigmented or nodular skin lesions months to 1-2 years after apparent cure of Visceral Leishmaniasis.

• Giardiasis: Giardia lamblia (G. intestinalis, G. duodenalis). Transmission: Fecal-oral (cysts), often via contaminated water.

  • Symptoms: Foul-smelling steatorrhea, diarrhea, abdominal cramps, bloating, malabsorption. Characteristic "falling leaf" motility of trophozoites.
  • Dx: Stool microscopy (cysts or trophozoites), antigen detection tests (ELISA).
  • Rx: Metronidazole, Tinidazole. 📌 Giardia Is Awful: Rotten Diarrhea, Infects All!

Helminthic Diseases - Wormy Woes

I. Nematodes (Roundworms)

• Intestinal:
  • Ascaris: Obstruction, Löffler's. Dx: Mammillated eggs.
  • Hookworms: IDA. Dx: Eggs. Cutaneous Larva Migrans.
  • Enterobius: Perianal itch. Dx: Scotch tape.
  • Trichuris: Rectal prolapse. Dx: Polar plug eggs.
  • Strongyloides: Autoinfection/hyperinfection (immunosuppressed). Dx: Larvae.
• Tissue/Blood:
  • Filarial:
    • Wuchereria/Brugia: Elephantiasis. Dx: Microfilariae (night).
    • Loa loa: Calabar swellings. Dx: Microfilariae (day).
    • Onchocerca: River blindness. Dx: Microfilariae (skin).
  • Dracunculus: Skin blister, worm.

II. Cestodes (Tapeworms)

• T. solium (Pork): Cysticercosis. Hooks.

  ⭐ Neurocysticercosis: most common parasitic CNS infection.

• T. saginata (Beef): Mild GI. No hooks. Dx: Proglottids/eggs.
• E. granulosus: Hydatid cysts. Anaphylaxis risk. Dx: Imaging.
• D. latum (Fish): Vit B12 def. anemia. Dx: Operculated eggs.

III. Trematodes (Flukes)

• Schistosoma: 📌 Eggs: S. mansoni (lateral), S. haematobium (terminal), S. japonicum (rudimentary).
  • S. haematobium: Hematuria, bladder Ca. Dx: Terminal spine egg (urine).
  • S. mansoni: Periportal fibrosis. Dx: Lateral spine egg (stool).
  • S. japonicum: Severe. Dx: Rudimentary spine egg (stool).
• F. hepatica: Biliary obstruction. Dx: Operculated egg.
• P. westermani: Hemoptysis. Dx: Operculated egg.

High‑Yield Points - ⚡ Biggest Takeaways

• P. falciparum: severe malaria (cerebral); P. vivax: relapses. ACT is drug of choice.
• Kala-azar (L. donovani) via sandfly: splenomegaly, pancytopenia. PKDL is a key sequela.
• Amoebiasis (E. histolytica): flask-shaped ulcers, liver abscess (anchovy sauce pus).
• Neurocysticercosis (T. solium larva): commonest parasitic CNS infection, causes seizures.
• Lymphatic Filariasis (W. bancrofti): mosquito vector, causes elephantiasis. DEC for treatment.
• Hydatid disease (E. granulosus): cysts in liver/lung; rupture risks anaphylaxis.