Q. What is Loa loa?
- Loa loa = filarial nematode, causes loiasis (African eye‑worm disease)
Q. Causative agent & transmission
- Parasite = Loa loa (adult worm) → transmitted by bite of infected Chrysops (deer/mango fly)
Q. Types / related filariae (exam point)
- Loa loa – subcutaneous filaria
- Other human filariae (for comparison) → Wuchereria bancrofti, Brugia malayi
Q. Morphology of adult worm
- Length 4–6 cm, width 1–2 mm, white‑yellow, smooth cuticle
- Female larger than male, both dioecious
Q. Pathogenesis – step‑wise sequence
- Chrysops lands → probes skin for blood → deposits third‑stage larvae (L3) on skin surface →
- L3 larvae penetrate bite wound → enter subcutaneous tissue →
- Larvae mature → become adult male & female (≈4–6 cm) →
- Adults migrate freely in subcutaneous connective tissue → speed up to 1–2 cm/min →
- Mechanical movement → tissue irritation, micro‑trauma → inflammation, edema, pain →
- Adult female releases microfilariae → enter peripheral blood (diurnal periodicity, peak midday) →
- Microfilariae circulate → can be taken up by another Chrysops → continue cycle
Q. Clinical features
- Calabar swellings = transient, itchy, painful subcutaneous nodules where adult worm moves
- Conjunctival/ocular migration → worm seen moving across eye (visible “eye worm”)
- Pruritus, localized urticaria, low‑grade fever (immune response)
Q. Complications
- Ocular inflammation → keratitis, conjunctivitis, possible vision loss if worm damages cornea
- Severe allergic reactions (hypersensitivity to worm antigens) → eosinophilia, urticaria, anaphylaxis (rare)
Q. Diagnosis
- Direct visualization of adult worm in subconjunctival tissue or skin nodule → definitive
- Blood smear (mid‑day) → microfilariae (sheathed, nuclei not extending to tip) → stained with Giemsa
- Concentration techniques (Knott’s) for low parasitemia
- Serology (ELISA) – supportive, not routine
- Imaging (high‑frequency ultrasound) can show moving adult worm in subcutaneous tissue
Q. Management
- Surgical removal → adult worm from eye or palpable nodule (first‑line for visible worms)
- Pharmacotherapy for microfilariae → diethylcarbamazine (DEC) 6 mg/kg daily for 12 days OR albendazole 400 mg daily for 21 days (if DEC contraindicated)
- Ivermectin alone not recommended (may cause severe reactions)
- Antihistamines & corticosteroids → control allergic symptoms
Q. Life cycle – simplified numbered steps with arrows
- Adult worms live in human subcutaneous tissue →
- Female releases microfilariae into peripheral blood (diurnal) →
- Chrysops bite → ingests microfilariae →
- In fly, microfilariae develop → first‑stage → second‑stage → third‑stage larvae (L3) in mouthparts →
- Infective L3 deposited on skin during next bite →
- L3 penetrate skin → mature to adult → cycle repeats
Memory trick for pathogenesis (rhyming)
“Fly bites, larvae slip, grow and zip, worm walks, blood talks, micro‑filariae hop, next fly stop!”
Memory trick for life cycle (fun)
“Adult’s nest → blood‑fest → fly’s feast → larva’s beast → bite‑release → start the peace‑to‑piece!”