Myiasis

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

⭐ 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).

⭐ 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.