A delayed hypersensitivity (allergic) response resulting in a
papular eruption (red, elevated area on skin) often occurs 30-40
days after infestation. While there may be hundreds of papules,
less than 10 burrows are typically found. The burrow appears as
a fine, wavy and slightly scaly line a few millimeters to one
centimeter long. A tiny mite (0.3 to 0.4 mm) may sometimes be
seen at the end of the burrow. Most burrows occur in the webs
of fingers, flexing surfaces of the wrists, around elbows and
armpits, the areolae of the breasts in females and on genitals
of males, along the belt line, and on the lower buttocks. The
face usually does not become involved in adults.
The rash may become secondarily infected; scratching the rash
may break the skin and make secondary infection more likely. In
persons with severely reduced immunity, such as those with HIV
infection, or people being treated with immunosuppressive drugs
like steroids, a widespread rash with thick scaling may result.
This variety of scabies is called Norwegian scabies.
Scabies is frequently misdiagnosed as intense pruritis (itching
of healthy skin) before papular eruptions form. Upon initial pruritus
the burrows appear as small, barely noticeable bumps on the hands
and may be slightly shiny and dark in color rather than red. Initially
the itching may not exactly correlate to the location of these
bumps. As the infestation progresses, these bumps become more
red in color.
Generally diagnosis is made by finding burrows, which often may
be difficult because they are scarce, because they are obscured
by scratch marks, or by secondary dermatitis (unrelated skin irritation).
If burrows are not found in the primary areas known to be affected,
the entire skin surface of the body should be examined.
The suspicious area can be rubbed with ink from a fountain pen
or alternately a topical tetracycline solution which will glow
under a special light. The surface is then wiped off with an alcohol
pad; if the person is infected with scabies, the characteristic
zigzag or S pattern of the burrow across the skin will appear.
When a suspected burrow is found, diagnosis may be confirmed
by microscopy of surface scrapings, which are placed on a slide
in glycerol, mineral oil or immersion in oil and covered with
a coverslip. Avoiding potassium hydroxide is necessary because
it may dissolve fecal pellets. Positive diagnosis is made when
the mite, ova, or fecal pellets are found.
