human itch or mange mites, are in the arthropod class Arachnida,
subclass Acari, family Sarcoptidae. The mites burrow into the skin but
never below the stratum corneum. The burrows appear as raised
serpentine lines up to several centimeters long. Other races of scabies
may cause infestations in other mammals such as domestic cats, dogs,
pigs, and horses. It should be noted that races of mites found on other
animals may establish infestations in humans. They may cause temporary
itching due to dermatitis but they do not multiply on the human host.
undergoes four stages in its life cycle; egg, larva, nymph and adult.
Females deposit eggs at 2 to 3 day intervals as they burrow through the
Eggs are oval and 0.1 to 0.15 mm in length
time is 3 to 8 days. After the eggs hatch, the larvae migrate to the
skin surface and burrow into the intact stratum corneum to construct
almost invisible, short burrows called molting pouches. The larval
stage, which emerges from the eggs, has only 3 pairs of legs
and this form lasts 2 to 3 days. After larvae molt, the resulting
nymphs have 4 pairs of legs
This form molts into slightly larger nymphs before molting into adults.
Larvae and nymphs may often be found in molting pouches or in hair
follicles and look similar to adults, only smaller. Adults are round,
sac-like eyeless mites. Females are 0.3 to 0.4 mm long and 0.25 to 0.35
mm wide, and males are slightly more than half that size. Mating occurs
after the nomadic male penetrates the molting pouch of the adult female
Impregnated females extend their molting pouches into the characteristic
serpentine burrows, laying eggs in the process. The impregnated females
burrow into the skin and spend the remaining 2 months of their lives in
tunnels under the surface of the skin. Males are rarely seen. They
make a temporary gallery in the skin before mating.
Transmission occurs by the transfer of ovigerous females during personal
contact. Mode of transmission is primarily person to person contact,
but transmission may also occur via fomites (e.g., bedding or
clothing). Mites are found predominantly between the fingers and on the
wrists. The mites hold onto the skin using suckers attached to the two
most anterior pairs of legs.
Scabies mites are
distributed worldwide, affecting all races and socioeconomic classes in
When a person is
infested with scabies mites for the first time, there is usually little
evidence of infestation for the first month (range 2 to 6 weeks). After
this time and in subsequent infestations, people usually become
sensitized to mites and symptoms generally occur within 1 to 4 days.
Mites burrowing under the skin cause a rash, which is most frequently
found on the hands, particularly the webbing between the fingers; the
folds of the wrist, elbow or knee; the penis; the breast; or the
shoulder blades. Burrows and mites may be few in number and difficult
to find in some cases. A papular "scabies rash" may be seen in skin
areas where female mites are absent, usually on the buttocks, scapular
region and abdomen; this may be a result of sensitization from a
previous infection. Most commonly there is severe itching, especially
at night and frequently over much of the body, including areas where
mites are undetectable. A more severe form of scabies that is more
common among immunocompromised persons is called Norwegian scabies,
characterized by vesicles and formation of thick crusts over the skin,
accompanied by abundant mites but only slight itching. Complications
due to infestation are usually caused by secondary bacterial infections
Most diagnoses of
scabies infestation are made based upon the appearance and distribution
of the rash and the presence of burrows. Whenever possible scabies
should be confirmed by isolating the mites, ova, or feces in a skin
scraping. Scrapings should be made at the burrows, especially on the
hands between the fingers and the folds of the wrist. Alternatively,
mites can be extracted from a burrow by gently pricking open the burrow
with a needle and working it toward the end where the mite is living.
are available to treat scabies. The treatment of choice is the topical
use of permethrin (5%). Crotamiton and ivermectin* are alternative
drugs. Ivermectin* is taken orally and is effective for treating
crusted scabies in immunocompromised persons. If a topical preparation
is used, a second treatment with the same product may be necessary 7-10
days later. All clothes, bedding, and towels used by the infested
person during the 2 days before treatment should be washed in hot water,
and dried in a hot dryer.
* This drug is
approved by the FDA, but considered investigational for this purpose.