Scabies

Question 1

sarcoptes scabiei

Answer 1

mite that infests the skin

• mates on the skin with male which dies
• female crawls 2-3 mm per day, lays 2-3 eggs per day and 25 in total
• female survives 4-6 weeks in host
• symptoms develop within 1-4 days if have scabies before
• 2-6 weeks if never had scabies before

Question 2

Life cycle

Answer 2

• male one stage (nymph stage)
• female two stages (nymph and adult stage)
• larvae hatch within one week of laying
• leave burrow and head to surface of skin
• dig their own burrows, and develop
• males enter mating burrows
• females come out of burrow and dig their own
• ## whole cycle 2 weeks

Question 3

immune compromised patients

Answer 3

• crusted scabies

- can exceed over 1 million in number (population explosion) when usually it is only 10-15

Question 4

transmission

Answer 4

only humans

skin skin contact or through clothing etc

Question 5

Host immune response

Answer 5

type 1 Hypersensitivity reaction:

• increased antibodies (IgE)
• binds to mast cells on fc portion
• releases histamine induces degranulation

Type 4 hypersensitivity reaction

• T cells migrate to antigen area
• secrete cytokines, that recruit and activate lymphocytes and phagocytic cells
• they carry out cell-mediated immune response
• leads to visible lesions

Question 6

Topical medication

Answer 6

Permethrin

• acts on voltage gated sodium channel and prolongs depolarization of action potentials (of mites)
• results in paralysis and death due to excitation of neurons
• slightly permeable to human skin, low toxicity but some effects
• rinse after 8-14 hours
• reapply 1-2 weeks

Question 7

Oral medication

Answer 7

ivermectin

• single dose repeat after 14 days
• antiparasitic, more specific
• broad spectrum activity against nematodes and arthropods
• binds invertebrate specific glutamate gated chloride channels
• increase in chloride permeability to cell membrane
• excessive hyperpolarization of nerves/muscle
• paralysis and death