Scabies

Scabies is a contagious affection of the skin characterized by the development of vesicles, pustules, and other lesions on the skin, and caused by the presence of an animal parasite, known as the Acarus scabiei.

The affection usually commences by the appearance of small, non-umbilicated vesicles on the hands and between the fingers, accompanied with severe itching. The itching leads to scratching, and as a consequence transfer of the affection to other parts of the body with which the hands are brought in contact. Very early in the disease, then, we will find it appearing on the penis, on the breasts in women, and on the feet in children. From these parts it may spread over the greater part of the surface, more profoundly on the anterior than posterior parts and avoiding the face and scalp.




The vesicles above mentioned may be termed the primary lesions of the disease, but are usually followed in a few days by others secondary to the irritation produced by the insect, and to the effects of the finger nails. These new lesions may be papular or pustular in character, and may even assume distinctly eczematous characters, or develop into a true eczema in those predisposed to this affection. On the penis the lesions are usually papular. None of these features are absolutely pathognomonic. There is, however, a lesion which is met with in no other disease, and which when found renders the diagnosis absolute. This is a fine, grayish line frequently terminating in a vesicle, and found between the fingers more frequently than elsewhere. It is called the acarian burrow. When an impregnated female acarus finds lodgment on the skin, she immediately seeks a place in which to deposit her eggs. This she accomplishes by boring beneath the epidermis and laying an egg, and then advancing in a straight or slightly curved line for several days until ovulation is complete. She then dies, and her decomposing remains give rise to a vesicle or pustule. When the eggs hatch, the young find their way to the surface, and as soon as they assume the adult form copulate, and the impregnated females commence to burrow as did their mother before them. A sharp needle-point, if guided by a sharper eye, will sometimes extract the acarus from her nest. The male acarus never burrows, and is very rarely detected.