18. Ectoparasites - Ectoparasites Ectoparasites live on or...

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Ectoparasites Ectoparasites • live on or in the skin of its host including lice, scabies, fly larva, and fleas Lice (Pediculosis) • small 2 - 4 mm in size • >200 species - only 2 genera are parasitic for humans: 1) Pediculus humanis var. corporis (body louse), Pediculus humanis var. capitus (head louse) 2) Phthirus pubis (pubic or crab louse) Lice (Pediculosis) • fertilized female lays 250 - 300 eggs over 20 - 30 days then dies • eggs are firmly glued to body hairs or fibres of clothing called “nits” • 7 - 10 days later small nymphs emerge that must feed after 2 - 3 weeks, mature adults mate • lice pierce the skin, inject saliva, defecate and obtain blood meal • hypersensitivity reactions to antigens in saliva results in pruritic papules Pediculosis - Epidemiology • worldwide • may serve as vectors for other infectious diseases (eg. typhus, trench fever) Pediculosis capitis: • affects all social and economic groups • transmission via close personal contact and possibly sharing of hats, combs, brushes
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18. Ectoparasites - Ectoparasites Ectoparasites live on or...

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