Diagnosis of Parasitic Infestations

Clinical Clues & Microscopy - Bug Hunt Basics

• Patient Clues:
  • Intense itching (esp. nocturnal for scabies).
  • Contact history (family, sexual, pets).
  • Travel.
• Lesion Examination:
  • Morphology: Burrows (scabies), papules, vesicles, excoriations.
  • Distribution: Interdigital (scabies), scalp (lice), pubic (phthiriasis).
• Microscopy Essentials:
  • Skin Scraping:
    • Use: Mineral oil or 10% KOH.
    • Find: Mites, eggs, scybala (fecal pellets).
  • Hair Pluck/Comb: For lice, nits.
  • Cellophane Tape Test: For mites, ova.
  • Dermoscopy: In-vivo visualization.

⭐ Identification of the mite, eggs, or scybala (fecal pellets) in skin scrapings is diagnostic for scabies.

Dermoscopy in Parasitology - Magnified Views

• Non-invasive, in-vivo visualization of parasites, burrows, nits.
• Improves diagnostic accuracy; reduces need for biopsy.
• Scabies:
  • "Delta-wing jet" sign (mite head).
  • S-shaped burrows (whitish lines).
  • Mite (dark dot).
• Pediculosis (Lice):
  • Nits (oval, translucent/white globules) on hair shafts.
  • Viable nits: dark, near scalp. Empty: white, distal.
  • Lice: elongated, grey-brown insects.
  • ⭐ > Dermoscopy differentiates viable from non-viable nits, guiding treatment efficacy.
• Tungiasis:
  • Central black dot (flea's posterior, eggs, feces) in whitish halo.
  • "Rosette" sign (eggs).
• Cutaneous Larva Migrans (CLM):
  • Serpiginous tracks.
  • May show larva (dark structure) or empty burrow_

Biopsy & Specialized Tests - Tissue Truths

• Skin Biopsy (Histopathological Examination - HPE):
  • Key for: Uncertain diagnoses, atypical presentations (e.g., crusted scabies, deep myiasis), confirming suspected leishmaniasis.
  • Findings: Direct visualization of parasites/ova/larvae; specific inflammatory patterns (e.g., eosinophilic infiltrates, granulomas).
• Specialized Laboratory Tests:
  • PCR: Detects parasite DNA/RNA. High sensitivity & specificity (e.g., Leishmania species, Sarcoptes scabiei in crusted scabies).
  • Serology: Antibody detection (IgG, IgM). Useful for systemic infections (e.g., cysticercosis, strongyloidiasis, toxocariasis, echinococcosis).
  • Culture: For specific parasites (e.g., Leishmania on NNN medium).
  • Antigen Detection: e.g., Immunochromatographic test (ICT) for filariasis.

⭐ Leishman-Donovan (LD) bodies, amastigotes of Leishmania, are typically found intracellularly within macrophages in skin biopsy specimens (Giemsa stain).

Key Parasites: Diagnostic Snapshots - ID Parade

⭐ In Scabies, the "hanging drop" sign on dermoscopy (mite suspended in fluid at burrow's end) is highly specific for diagnosis when present.

High‑Yield Points - ⚡ Biggest Takeaways

• Scabies diagnosis: Microscopy of skin scrapings for mites/eggs; burrow ink test helps.
• Pediculosis: Visual detection of lice/nits; Wood's lamp for nits.
• Cutaneous Larva Migrans: Clinical diagnosis from characteristic serpiginous tracks.
• Myiasis: Identification of larvae in lesions; imaging for deep cases.
• Leishmaniasis: Slit-skin smear, biopsy, culture, or PCR for LD bodies.
• Tungiasis: Clinical identification of embedded flea with its posterior end visible.
• Dermoscopy aids in visualizing parasites and burrows non-invasively for many conditions.