Ectoparasites

Ectoparasite Essentials - Bug Basics 101

• Ectoparasites: Organisms that live on the external surface of a host.
• Key Classes:
  • Insecta: 3 pairs of legs; 3 body segments (head, thorax, abdomen). Examples: Lice, Fleas, Bedbugs.
  • Arachnida: 4 pairs of legs; 2 body segments (cephalothorax, abdomen). Examples: Ticks, Mites.
• Disease Causation:
  • Direct effects: Bites (irritation, dermatitis, blood loss), infestation (e.g., scabies, myiasis).
  • Indirect effects: Act as vectors transmitting pathogens (bacteria, viruses, protozoa).

⭐ Ticks (Arachnida) are major vectors for diseases like Lyme disease and Rocky Mountain Spotted Fever.

• Many are obligate parasites; host specificity varies greatly among species.

Lice & Scabies - The Itch Factors

• Lice (Pediculosis)

  • Types:
    • P. humanus capitis (Head): Pruritus, nits.
    • P. humanus corporis (Body): Pruritus, poor hygiene link. Disease vector. 📌 Diseases: RBT (Relapsing fever, Bartonellosis, Typhus).
    • Pthirus pubis (Pubic/Crab): Pruritus, maculae ceruleae.
  • Transmission: Direct contact, fomites.
  • Diagnosis: See lice/nits.
  • Treatment: Permethrin 1%, Ivermectin. Clean environment.

  ⭐ Body lice (P. humanus corporis) are vectors for epidemic typhus (Rickettsia prowazekii), trench fever (Bartonella quintana), and relapsing fever (Borrelia recurrentis).

• Scabies

  • Agent: Sarcoptes scabiei var. hominis (mite).
  • Pathogenesis: Mite burrows, hypersensitivity reaction.
  • Symptoms: Nocturnal pruritus. Burrows (interdigital, wrists, axillae, genitals), papules.
    • Crusted (Norwegian) Scabies: Immunocompromised, hyperinfestation, contagious.
  • Diagnosis: Clinical; skin scraping microscopy.
  • Treatment: Permethrin 5% cream, Ivermectin. Treat contacts, fomites.

Ticks - Tiny Terrors, Big Threats

• Overview: Arachnid ectoparasites; significant disease vectors.
• Types & Key Differences:

  Feature	Hard Ticks (Ixodidae)	Soft Ticks (Argasidae)
  Scutum	Present (hard dorsal shield)	Absent
  Capitulum	Anterior, visible dorsally	Ventral, not visible dorsally
  Feeding	Prolonged (days)	Rapid (minutes-hours), often repeated

• Diseases Transmitted:
  • Hard Ticks (Ixodidae):
    • Lyme Disease (Ixodes spp.)
    • Kyasanur Forest Disease (KFD) (Haemaphysalis spp.)
    • Rocky Mountain Spotted Fever (RMSF) (Dermacentor spp.)
    • Babesiosis (Ixodes spp.)
    • Anaplasmosis/Ehrlichiosis (Amblyomma, Ixodes spp.)
  • Soft Ticks (Argasidae):
    • Tick-Borne Relapsing Fever (TBRF) (Ornithodoros spp.)
• Tick Paralysis: Ascending flaccid paralysis from neurotoxin in saliva (esp. Dermacentor, Ixodes). Reversible upon tick removal.

⭐ Kyasanur Forest Disease (KFD), a viral hemorrhagic fever, is transmitted by Haemaphysalis ticks, endemic to parts of Karnataka, India.

• Prevention: DEET repellents, protective clothing, careful tick removal (grasp close to skin, pull steadily).

Fleas & Other Foes - Pesky Perpetrators

• Fleas (Siphonaptera): Laterally compressed, wingless, powerful jumping legs. Piercing-sucking mouthparts.
  • Xenopsylla cheopis (Oriental rat flea):
    • Vector: Bubonic Plague (Yersinia pestis), Murine Typhus (Rickettsia typhi).
  • Pulex irritans (Human flea): Plague transmission (less efficient).
  • Ctenocephalides spp. (Dog/Cat flea): Host for Dipylidium caninum; causes flea allergy dermatitis.
  • Control: Insecticides, environmental sanitation, rodent control.
• Bed Bugs (Cimex spp.): Nocturnal, hematophagous (blood-feeding) ectoparasites.
  • Bites: Characteristic linear pattern ("breakfast, lunch, dinner"). 📌 Mnemonic: Bed bugs dine in a LINE.
  • Impact: Intense pruritus, papular urticaria, anxiety; not significant disease vectors.
  • Control: Insecticides (check resistance), heat treatment, mattress encasements.

⭐ Xenopsylla cheopis is the most important vector for Yersinia pestis (plague).

High‑Yield Points - ⚡ Biggest Takeaways

• Scabies (Sarcoptes scabiei): Intense nocturnal itching, burrows (interdigital, wrists). Dx: skin scraping. Rx: Permethrin.
• Pediculosis (lice): Capitis, corporis, pubis. Nits (eggs) on hair shafts. Rx: Permethrin.
• Ticks: Vectors for Kyasanur Forest Disease (KFD), Rickettsial diseases (e.g., RMSF). Hard ticks (Ixodidae) are key.
• Fleas: Xenopsylla cheopis (rat flea) transmits Plague (Yersinia pestis). Also Murine typhus.
• Myiasis: Tissue invasion by fly larvae (maggots), e.g., wound myiasis.
• Trombiculid mites (chiggers): Larvae cause intense pruritus (scrub itch); vector for Scrub Typhus.