SECTION III. MITE-BORNE DISEASES
Mites, like ticks, are arachnids. They are too small to see with the naked eye, but
may be readily observed with a low-power magnifying glass. They are found throughout
most of the world in practically all climates. Many mites feed on plants, but some feed
on man and animals. Mites lay eggs that hatch into six-legged larval mites. Certain
mites feed on man and animal only in this larval stage. The larvae are commonly called
chiggers. Chiggers often occur in tall grass or in scrub vegetation. Larval mites
develop into nymphs that, in turn, develop into adult mites (figure 5-5). Both the
nymphs and adults have eight legs.
Figure 5-5. Life cycle of a mite (note six-legged larva or chigger).
a. Scrub Typhus. In Southeast Asia, some kinds of chiggers transmit a
dangerous disease called scrub typhus. It has a fatality rate of up to 40 percent in
untreated cases. It is often accompanied by a "punched out" skin ulcer at the point of
attachment of an infected mite. Other symptoms include headache, profuse sweating, a
sudden fever, and a dull red eruption (rash) on the trunk. The rash usually develops
about four or five days after the person becomes infected.
b. Scabies. The scabies itch mite (Sarcoptes scabiei) burrows and lives in the
skin of man. It causes a condition called scabies, which is characterized by intense