Myiasis

Myiasis Basics - Buggy Intruders

• Infestation of live human/animal tissue by dipterous (fly) larvae (maggots).
• Causative agents: Various fly species; common ones include Dermatobia hominis (human botfly), Cordylobia anthropophaga (tumbu fly), Cochliomyia hominivorax (New World screwworm).
• Classification based on larval behavior:
  • Obligatory: Larvae require living tissue for development (e.g., D. hominis).
  • Facultative: Larvae can develop in living or dead tissue (e.g., some Sarcophagidae).
  • Accidental: Larvae ingested/enter via orifices, typically don't complete development.

⭐ Cochliomyia hominivorax (New World screwworm) causes obligatory myiasis and is a reportable disease due to its aggressive tissue destruction and potential for severe economic impact on livestock.

• Clinical forms: Furuncular, wound/traumatic, cavitary, migratory, intestinal, urogenital myiasis based on site of infestation and larval behavior.

Culprit Flies - The Buzzing Baddies

• Obligatory Parasites (Need Living Tissue):

  • Dermatobia hominis (Human Botfly): Furuncular lesions. Phoresis via mosquitoes.
  • Cordylobia anthropophaga (Tumbu Fly): African furuncular myiasis; eggs on soil/clothes.
  • Cochliomyia hominivorax (New World Screwworm): Destructive wound myiasis.
  • Chrysomya bezziana (Old World Screwworm): Old World screwworm; wound myiasis.

    ⭐ Dermatobia hominis larvae possess backward-pointing spines, aiding firm anchorage within the host's skin.

• Facultative Parasites (Usually Dead Tissue; Can Invade Wounds):

  • Lucilia spp. (Greenbottle), Calliphora spp. (Bluebottle), Sarcophaga spp. (Flesh fly).

• Specific Presentations:

  • Gasterophilus intestinalis: Creeping eruption (larva migrans cutanea).
  • Oestrus ovis (Sheep Botfly): Ophthalmomyiasis, nasopharyngeal myiasis.

Clinical Picture - Skin's Squirmy Story

• Furuncular Myiasis: Most common.
  • Boil-like, erythematous nodule.
  • Central punctum (breathing pore); serosanguinous discharge.
  • Movement sensation, pain, itching.
  • Agents: Dermatobia hominis (botfly), Cordylobia anthropophaga (tumbu fly).
• Wound (Traumatic) Myiasis: Larvae infest open wounds, ulcers, necrotic tissue.
• Creeping (Migratory) Myiasis:
  • Larva burrows; serpiginous, erythematous tracts.
  • Itchy, raised linear lesions.
  • Agents: Gasterophilus spp. (horse botfly), Hypoderma spp. (cattle botfly).
• Cavitary Myiasis: Infests body cavities (nasal, aural, oral, ocular, urogenital).
  • Destructive; site-specific symptoms.
• Sanguinivorous Myiasis: Larvae feed on blood (e.g., Auchmeromyia luteola - Congo floor maggot). Rare.

⭐ Furuncular myiasis often presents with a characteristic central punctum from which the larva's posterior spiracles may be visible, aiding diagnosis.

Spotting & Nabbing - Larva Eviction Plan

• Spotting:
  • Look for: Central punctum, visible larva/movement, serosanguinous discharge.
  • Tools: Dermoscopy, Ultrasound (confirms depth/viability).
• Nabbing (Eviction):
  • Occlusion: Apply petroleum jelly/liquid paraffin to block spiracles; larva surfaces.
  • Extraction: Gentle pressure, forceps. Surgical removal if needed.
  • Systemic: Oral Ivermectin (200 µg/kg) for extensive/cavitary myiasis.
  • Post-Op: Wound care, antibiotics if infected, tetanus prophylaxis. 📌 Mnemonic: "SOS" - Suffocate (Occlude), Operate (Extract), Systemic (Ivermectin if severe).

⭐ Dermatobia hominis larvae often require several hours of occlusion before emerging; patience is key during this step for successful non-invasive removal.

Prevention & Control - Fly-Free Zone Tactics

• Environmental hygiene:
  • Proper waste/carcass disposal.
  • Eliminate fly breeding sites (decaying matter).
• Personal protection:
  • Insect repellents (DEET).
  • Protective clothing in endemic areas.
  • Window/door screens.
• Animal husbandry:
  • Prompt wound care in animals.
  • Controlled insecticide use on livestock.
• Community measures:
  • Fly traps, baits.

⭐ Human botfly (Dermatobia hominis) uses mosquitoes as phoretic vectors for egg delivery to hosts.

High‑Yield Points - ⚡ Biggest Takeaways

• Myiasis: Infestation of live vertebrate tissue by dipterous larvae (maggots).
• Key types: Furuncular (boil-like, central punctum), wound/traumatic, and cavitary (nasal, aural).
• Caused by larvae of Dermatobia hominis (human botfly) and Cordylobia anthropophaga (tumbu fly).
• Screwworm myiasis (Cochliomyia, Chrysomya) is highly destructive, often in wounds.
• Diagnosis: Direct visualization of larvae; occlusion (e.g., petroleum jelly) aids emergence.
• Management: Mechanical removal of larvae is primary; oral ivermectin as adjunct_._