Advice for students

SIGNS, SYMPTOMS, AND DIAGNOSIS 
A scabies burrow under magnification. The scaly patch at the left is due to scratching of the 
original papule. The mite traveled from there to the upper right, where it can be seen as a dark spot at the end 
of the burrow. 
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, fewer 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 0.9.08 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 pruritus (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.