Tissue Nematodes

Lymphatic Filariasis - Elephant Legs & Blocked Drains

• Causative Agents: Wuchereria bancrofti (90%), Brugia malayi, Brugia timori.
• Vector: Mosquitoes (Culex, Anopheles, Aedes, Mansonia).
• Pathogenesis: Adult worms in lymphatics → inflammation, obstruction → lymphedema, hydrocele, elephantiasis.
• Clinical Features:
  • Asymptomatic microfilaremia.
  • Acute: Adenolymphangitis (ADL), filarial fever.
  • Chronic: Lymphedema → Elephantiasis (legs, scrotum, arms), hydrocele, chyluria.
• Diagnosis:
  • Peripheral blood smear (PBS): Microfilariae (thick smear, Giemsa stain, nocturnal sample for W. bancrofti).
  • Antigen detection: Immunochromatographic card test (ICT) for W. bancrofti antigen.
  • Ultrasound: Filarial dance sign (FDS) of adult worms in lymphatics.
  • DEC provocation test (daytime sample after 2 mg/kg DEC).
• Treatment: Diethylcarbamazine (DEC) - kills microfilariae & adult worms. Ivermectin + Albendazole for Mass Drug Administration (MDA). 📌 "Dogs Eat Cats" (DEC).

⭐ W. bancrofti microfilariae exhibit nocturnal periodicity (peak 10 PM - 2 AM); B. malayi can be nocturnal or subperiodic. Blood collection timing is crucial for diagnosis via PBS.

Onchocerciasis - River Blindness & Skin Bumps

• Agent: Onchocerca volvulus (filarial nematode).
• Vector: Female Simulium blackfly; breeds near fast-flowing rivers.
• Pathogenesis: Microfilariae migrate through skin & eyes, causing inflammation. Adults reside in subcutaneous nodules (onchocercomas).
• Clinical Features:
  • Skin: Intense itching ("craw-craw"), papular dermatitis, lichenification ("lizard skin"), depigmentation ("leopard skin"), onchocercomas, "hanging groin".
  • Ocular ("River Blindness"): Punctate keratitis, sclerosing keratitis, iridocyclitis, chorioretinitis, optic atrophy.
• Diagnosis:
  • Skin snips (demonstrate microfilariae).
  • Nodule biopsy (adult worms).
  • DEC (diethylcarbamazine) patch test.
• Treatment:
  • Ivermectin: Drug of choice (microfilaricidal). Given every 6-12 months.
  • Doxycycline: Targets Wolbachia endosymbionts, leading to adult worm sterility/death.
  • Nodulectomy.
• Prevention: Vector control, mass Ivermectin distribution (MDA).

⭐ Ivermectin primarily kills microfilariae of O. volvulus; doxycycline targets the endosymbiotic Wolbachia bacteria, which are essential for adult worm survival and embryogenesis, thus leading to adult worm death.

Trichinellosis & Dracunculiasis - Pork Worms & Fiery Serpents

• Trichinellosis (Trichinella spiralis - Pork Worm)

  • Transmission: Ingestion of undercooked pork containing encysted larvae.
  • Pathogenesis: Larvae mature in intestine → new larvae migrate to striated muscles, forming nurse cells.
  • Clinical: Myalgia, fever, periorbital edema, marked eosinophilia, splinter hemorrhages.
  • Diagnosis: Muscle biopsy (larvae), serology.
  • Treatment: Albendazole/Mebendazole; corticosteroids for severe cases.

• Dracunculiasis (Dracunculus medinensis - Guinea Worm/Fiery Serpent)

  • Transmission: Drinking water contaminated with copepods (Cyclops) containing L3 larvae.
  • Pathogenesis: Larvae mature → gravid female migrates to subcutaneous tissue (lower limbs) → painful blister → ulcer → larval release on water contact.
  • Clinical: Localized pain, blister, visible emerging worm.
  • Diagnosis: Clinical visualization of worm.
  • Treatment: Slow, mechanical extraction (e.g., on a stick); wound care. No curative drug.

⭐ Trichinellosis: Periorbital edema and marked eosinophilia are highly suggestive clinical features; nurse cell formation in muscle is pathognomonic on biopsy.

Loiasis & Toxocariasis - Eye Worms & Wandering Larvae

• Loiasis (Loa loa)
  • Vector: Chrysops spp. (deer/mango fly).
  • Clinical: Fugitive Calabar swellings (transient angioedema), adult worm migration in subconjunctiva ("eye worm").
  • Dx: Microfilariae in blood (diurnal periodicity), adult worm ID.
  • Rx: Diethylcarbamazine (DEC).
• Toxocariasis (Toxocara canis/cati)
  • Source: Ingestion of embryonated eggs from soil contaminated with dog/cat feces.
  • Clinical:
    • Visceral Larva Migrans (VLM): Fever, hepatomegaly, marked eosinophilia.
    • Ocular Larva Migrans (OLM): Unilateral vision loss, strabismus, leukocoria.
  • Dx: Serology (ELISA), marked eosinophilia. (No eggs in human stool).
  • Rx: Albendazole; corticosteroids for inflammation.

⭐ OLM due to Toxocara can mimic retinoblastoma (leukocoria), a critical differential.

High‑Yield Points - ⚡ Biggest Takeaways

• Wuchereria bancrofti & Brugia malayi cause lymphatic filariasis; microfilariae show nocturnal periodicity.
• Loa loa (eye worm) causes Calabar swellings; microfilariae show diurnal periodicity; vector Chrysops.
• Onchocerca volvulus causes river blindness, dermatitis; diagnosed by skin snips; vector Simulium.
• Dracunculus medinensis (Guinea worm) emerges from painful skin ulcers; intermediate host Cyclops.
• Trichinella spiralis from undercooked pork; causes myalgia, periorbital edema, eosinophilia.
• Toxocara spp. cause Visceral Larva Migrans (VLM) and Ocular Larva Migrans (OLM).