Scabies
More details/Information for students
Definition
Causative Organism
Transmission of Scabies
Incubation Period
Clinical Features
Investigation and Diagnosis
Management
Scabies is a contagious skin disease caused by the itch
mite Sarcoptes scabiei.
Fertilised female mites burrow into the horny layer of
the skin, advance some 2 mm each day, deposit eggs (2-3 per day for 10
days) and then die.
The transfer of the female mite requires close personal
contact rather than transient personal contact.
Transmission can occur while:
- sleeping with, or
- having sexual intercourse with an infected person;
- between members of families and households
- and in body contact.
Primary infection: symptoms will appear around 4 weeks
after infestation.
In people who have previously had scabies, the symptoms
will appear more rapidly, often within hours of infestation. (Due to
increased sensitivity.)
The primary lesion, the burrow, is often difficult to
see. It is a thread-like furrow or ridge 5-15 mm long. Burrows mostly
occur on the medial and flexor (inside) surfaces of the wrists, the sides
and webs of the fingers and sometimes around the nipples, penis, scrotum
and buttocks. A vesicle (small blister) may appear at the end of a burrow.
In sexually acquired scabies the lesions are often
confined to the lower trunk, thighs and genitals.
After about a month the lesions become papular (raised)
and irritable, presumably through host sensitisation. Intense itching
occurs, especially when the person becomes warm in bed, after
exercise, a hot shower or bath.
Usually by the time people seek attention, the eruption
has been scratched, burrows disrupted and secondary infection has
occurred.
In males, penile or scrotal lumps can be the main or
only complaint. The lumps, which may or may not itch, are seen as
inflamed, reddish-brown, indurated nodules up to 12mm across. They are
commonly seen on the penis, especially the glans, and on the scrotum.
Careful searching may reveal scabetic lesions in some of the usual sites.
In people who shower frequently, the clinical signs of
scabies may be minimal and not typical, and burrows especially difficult
to find.
The prior use of topical applications containing
steroids frequently masks the clinical features and hinders accurate
diagnosis.
The distribution of the rash, the presence of burrows,
the multiplicity of lesions, the intense irritation (especially when in
bed or while warm) and the possible infestation of those in close personal
contact make for a clinical diagnosis of scabies.
The diagnosis is confirmed by finding a whole acarus, an
identifiable part or some eggs. Preferably using good natural light and a
binocular loupe, a search should be made among the lesions for burrows. If
the overlying epidermis is thin, the mite can sometimes be seen at the
anterior end of a burrow. The burrow should be opened with a triangular,
cutting-edge needle on the point of which the mite can be transferred to a
glass slide for low power microscopic examination.
If no burrows can be found and a mite cannot be
isolated, microscopy of skin scrapings taken over old burrows or papules,
under a drop of potassium hydroxide 10% solution, will sometimes show
parts of an acarus or some eggs.
See Diagnosis and management
guidelines entry for scabies |
Pamphlet
Health
on the Net Code of Conduct for health-related sites