Parasitic Skin Infections Flashcards
What is scabies?
-Intensely itchy infestation with the sarcoptes scabiei mite, which only affects humans.
-Under half a millimetre in size, and with the naked eye is therefore barely visible
-Itchy rash due to the development of a delayed type hypersensitivity reaction to mite eggs and faeces
-As scabies is a cell mediated response, the immune response that produces the clinical symptoms will only be apparent approximately ~3 weeks or later following infestation
Clinical features of scabies
-Can affect 30-40% of children at any one time
-Intensely itchy, an itch which is markedly worse at night
-Burrows, are linear structures in which the female mite burrows before laying eggs. Most common on the palms / soles and finger-webs
-Nodules are particularly common around the nipples and genitalia
-There is widespread excoriation with a secondary dermatitis reflecting the cell mediated immune response to the mite.
-You only catch scabies from close physical contact. In practice, this usually means parent-child or child-child transmission, and for adults, sexual liaisons.
Describe crusted scabies
-Severe variant: skin is massively hyperkeratotic, with widespread crusting resembling severe psoriasis.
-The skin is teeming with mites.
-Downs Syndrome/ immunosuppressed patients/ people who are unable to scratch
=Crusted scabies is highly infectious
Diagnosis of scabies
-Intense itch and the involvement of family members.
-Examine whole patient (doesn’t usually involve head)
-Clinical diagnosis and ideally relies on identification of the mite (fine needle, pushed along the burrow, which the mite then attaches itself to)
=examined under the microscope and, most sensibly, the patient is shown the mite as many people are reluctant to
believe they have scabies
=Alternatively, dermatoscopy can be used to try and identify the mite in vivo.
=Failure to identify the mite leads to both under and over treatment, as whole families are needlessly treated with agents that may induce itch in normal person
Treatment of scabies
-Depends on local patterns of resistance of the mite.
-Permethrin or malathion are commonly used.
=Both are applied after a warm bath, left on overnight, and the treatment repeated 7 days later.
-Bedding and clothing should be washed in a hot cycle of a washing machine, but other precautions are not necessary.
-All individuals with close contact with the affected individual need to be treated at the same time otherwise, given the incubation period, there will be a continual ‘re-cycle’ of reinfection
-Apparent treatment failure may reflect the fact that the patient never had scabies in the first place and that the treatment-induced-dermatitis is causing persistent itch or, there is a cycle of reinfection.
-An alternative to topical treatments is the use of the systemic agent ivermectin, which is used particularly for Crusted / Norwegian scabies.
Overview of pediculosis capitis (head lice)
-Lice are insects (6 legs), that use strong glue to attach to your hairs and feed on your blood.
-The louse is 2-3mm long and the nits are the eggs stuck to hairs.
-The presence of nits after treatment does not mean treatment has failed.
-Clinical features are an itchy eruption on the scalp and nape of the neck with secondary excoriation and potentially, secondary infection.
-The physical signs reflect the nits (the eggs that the mites have hatched from), as well as mites on the scalp.
-Nits are easy to over-diagnose or misdiagnose — simply put, scalp scales can stick to hair, and be mistaken for nits.
-Treatment: malathion or permethrin are widely used. Because there are nits present does not mean there is active infection as treatment will not remove the nits, but just kill off the mites.
Overview of pediculosis corporis (body lice)
-Itching, with scratching and excoriation, and is usually found in those with poor personal hygiene.
=You need to examine the clothes as well as the patient, because the lice and nits will be evident on the clothes.
-Treatment is of the clothes not the patient.
=Disinfection with hot washes and ironing, usually suffices, but often replacement of all clothing may be sensible in those who cannot easily comply.
=The patient will get better as long as the lice have been killed from the clothes (you treat the patient by treating the clothes)
