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Ectoparasites 217

contribute up to two million organisms in a human
infection. Both varieties of scabies will spread rap-
idly in households and among playmates as well as
those who are intimate partners or have extremely
close contact.
Source: Centers for Disease Control and Prevention (CDC) consciousness such as senility or retardation fre-
Those with deficient immune systems or reduced
■

quently fall victim to a more severe form of scabies,
but the same species of mite is responsible for
both conditions. Treatment is a topical chlorinated
hydrocarbon insecticide called “lindane,” a benzene
hexachloride toxic to both the blood and nervous
systems. These medications should not used on
children, pregnant women, or those with a history
of seizure disorders where the central nervous sys-
tem is affected. Recently, some resistance to lindane
FIGURE 10-4 Ventral view of a Sarcoptes scabei mite, has been found in some populations of the “itch
prepared specimen
mite” called scabies.
■ Another drug administered orally is “ivermectin,”
Mites usually burrow into the skin, in opposition to lice, but this medication has been blamed for increased
and cause intense itching, resulting in inflamed areas of death rates in nursing home patients who have this
the skin. Mites that are prevalent as inhabitants of the medication prescribed. Fortunately there are less
human body may live for only a few days away from toxic treatments that include home remedies based
humans or other animals and birds that they typically upon plant extracts that have been found to be
infest. Discussions of some of the more common species effective. Systemic antibiotics and steroidal prepara-
that affect humans by order of prevalence and health im- tions as well as antihistamines may be used to treat
pact include the following: the symptoms and to prevent the secondary bacte-
■ Itch mites (Sarcoptes scabiei) cause a condition rial infections that almost invariably come from vig-
of the skin commonly known as scabies and un- orous scratching. Mange in dogs and other animals
dergo all of their developmental stages in the skin are also caused by a mite belonging to two different
(Figure 10-5). This species of mite lays its eggs in families, Sarcoptidae and Psoroptidae. It is possible
tunnels in the skin, where it takes about 2 weeks for that humans have an inherited immunity against
them to hatch. these two organisms.
■ Diagnosis is often made by a medical professional ■ Two types of dust mites, Dermatophagoides ptero-
who observes the skin tunneling prominently vis- nyssinum and D. farinae, ingest human skin cells
ible to the naked eye. Symptoms and signs include that have been shed or dislodged by scratching.
intense itching, especially at night, and usually Face mites and follicle mites (Demodex brevis and
accompanied by a rash (Figure 10-6). This rash D. folliculorum) are also found as a normal part
may be seen most often on the hands and arms, but of the normal flora (microorganisms) of the face.
other common areas are in the armpits and genitalia These organisms are quite small and can only be
of both males and females. Commonly, a person seen with a microscope or magnifying glass and
infected by the S. scabiei organism will harbor only reside in hair follicles, pores, or sebaceous glands.
around a dozen adult mites who can cause a great They may cause mild allergic reactions and also
deal of torment for the victim. But a subspecies may contribute to or exacerbate an asthmatic condi-
called the Norwegian scabies, which is rare and in- tion in humans.
distinguishable from the other type in morphology, ■ Chiggers, caused most commonly by the Trom-
presents a more severe form of the disease as it may bicula autumnalis variety, but sometimes by