Myiasis Overview - Maggot Mayhem
- Definition: Tissue infestation by dipterous larvae (maggots) of flies.
- Causative Flies (Order: Diptera):
- Families: Calliphoridae (e.g., Chrysomya), Sarcophagidae (e.g., Sarcophaga), Oestridae (e.g., Hypoderma, Dermatobia).
- Key Indian Example: Chrysomya bezziana (Old World screwworm).
- Mode of Infestation:
- Accidental: Larvae ingested/enter orifices (e.g., intestinal from Musca domestica).
- Facultative: Larvae develop in decaying tissue or existing wounds.
- Obligatory: Larvae require living tissue for development (most pathogenic).
⭐ Chrysomya bezziana is a significant cause of obligatory wound myiasis in India, where larvae invade living tissue.
Myiasis Classification - Invasion Sites
| Type | Common Sites | Key Larvae Examples | Clinical Hint |
|---|---|---|---|
| Cutaneous | Skin | ||
| - Furuncular | Exposed areas | Dermatobia hominis, Cordylobia anthropophaga | Boil-like lesion, central punctum, movement |
| - Creeping/Migratory | Epidermis/Dermis | Gasterophilus spp., Hypoderma spp. | Serpiginous, erythematous tracts |
| - Wound/Traumatic | Neglected wounds, ulcers | Cochliomyia hominivorax, Wohlfahrtia spp., Chrysomya bezziana | Larvae in wound, tissue destruction |
| Cavity | Nasopharynx, Orbit, Ear, Urogenital, Intestinal | Oestrus ovis, Fannia spp., Musca domestica | Site-specific (e.g., epistaxis, otorrhea, dysuria) |
| Systemic (Rare) | Internal organs | Hypoderma spp. (visceral migration) | Vague, severe systemic illness; often incidental |
⭐ Wound myiasis, often caused by screwworm flies like Cochliomyia hominivorax, critically signals neglected wounds and can cause rapid tissue destruction.
Myiasis Clinicals - Spotting Squatters
-
Furuncular (e.g., Dermatobia hominis):
- Painful, itchy, erythematous nodule.
- Central pore (punctum) with serosanguinous discharge.
- Sensation of movement; larva sometimes visible.
-
Creeping / Migratory (e.g., Gasterophilus, Hypoderma):
- Serpiginous, erythematous, intensely pruritic linear tracts.
- Larva migrates within epidermis.
-
Wound / Traumatic (e.g., Cochliomyia hominivorax):
- Larvae infest pre-existing wounds or necrotic tissue.
- Foul smell, pain, significant tissue destruction.
-
Cavitary (e.g., Oestrus ovis - nasal):
- Site-specific symptoms:
- Nasal: Obstruction, epistaxis, pain, foreign body sensation.
- Auricular: Otalgia, discharge, sensation of crawling, tinnitus.
- Ophthalmomyiasis: Interna (visual disturbance, pain) or Externa (foreign body sensation, redness, chemosis).
- Site-specific symptoms:
⭐ The characteristic central punctum in furuncular myiasis often intermittently extrudes serosanguinous fluid or the posterior end of the larva (the "breathing spiracles").
Myiasis Dx & Rx - Eviction Notice
- Dx: Clinical (travel Hx, visualize larvae); larval ID (entomologist).
- Rx: 📌 'Suffocate, Sedate, Snatch'
- Occlusion (petroleum jelly) → Manual/Surgical extraction.
- Wound care; antibiotics for secondary infection.
- Oral Ivermectin (200 mcg/kg) for extensive/cavitary/difficult cases.
- Prevention: Fly control, wound hygiene, protective clothing.
⭐ Occlusive therapy works by depriving the larva of oxygen, forcing it to migrate towards the surface for easier removal.
High‑Yield Points - ⚡ Biggest Takeaways
- Myiasis: Infestation of live human/animal tissue by dipterous larvae (maggots).
- Furuncular myiasis (e.g., Dermatobia hominis, Tumbu fly): Boil-like lesion with a central punctum for larval respiration.
- Wound myiasis (e.g., Screwworms like Cochliomyia): Larvae infest open wounds/cavities, causing aggressive tissue destruction.
- Creeping myiasis (e.g., Gasterophilus): Characterized by migratory serpiginous erythematous tracts.
- Diagnosis: Clinical by visualizing larvae (movement, bubbles at punctum); dermoscopy aids.
- Treatment: Occlusion (petroleum jelly), surgical extraction, or oral ivermectin for extensive cases.
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