NAVMED P-5010-8 - Navy Medicine - U.S. Navy

8-40 CHAPTER 8. NAVY ENTOMOLOGY AND PEST CONTROL TECHNOLOGY 8-40
8-40. Mites
a. Relationship to Man. Based upon their
habitats, mites of medical importance may be
classified into four groups: nest-inhabiting
mites parasitic on birds and rodents, and which
occasionally bite man, mites parasitic on animals
and which occasionally bite man, mites parasitic
on man, and food-infesting mites that occasionally
bite man.
(1) Nest Inhabiting Mites. All of these
mites live within the nests of birds and rodents
and only bite man when deprived of their normal
hosts. Medically, the house mouse mite is the
most important member of this group, since it
vectors rickettsial pox from mouse to man.
(2) Mites Parasitic on Birds and
Rodents. These mites are parasitic on rodents,
birds, and reptiles and the larvae may occasionally
bite man. The term “chigger” is applied to
the larvae of certain species of this group. Many
of these species cause dermatitis to man, and a
few transmit scrub typhus (Tsutsugamushi
disease), a severe and debilitating rickettsial
disease of man endemic to some land areas of
the Far East.
(3) Mites Parasitic on Man. This
group includes the well-known scabies or itch
mite. The scabies mite is transmitted through
close body contact and may appear wherever
social conditions cause excessive crowding of
people. This mite burrows in the horny layer of
the dermis, causing an intense itching, especially
at night, and occasionally erythema.
(4) Food-Infesting Mites. Many
species of mites infest dry foods (e.g., bread,
cheese, cereals, and smoked meats). Some of
them can also cause a contact dermatitis to
workers handling infested materials. These
mites also have been associated with respiratory
complications (e.g., asthma exacerbation or
bronchial inflammation) when they or their byproduct
antigens are inhaled. There are also
reports of urinary tract infestations that cause
irritation, urethral stricture, and a predisposition to
secondary infection. Ingestion of mite-infested
food may lead to gastrointestinal disturbances.
b. Biological Characteristics. Mites can
be recognized by the fact that they lack distinct
body segmentation. They are usually very
small, some being less than 0.5 microns (1/2000
of an inch) long. After hatching from the eggs,
mites pass through three developmental stages:
larva, nymph, and adult. The larva has six legs,
while the nymph and adult forms have eight. In
the species that transmit scrub typhus, the larval
forms are parasitic on rodents, and incidentally
parasitic on man. These larvae are quite small
and usually red or pinkish in color. They feed
on lymph and serous fluids and epidermal
tissues, which are partially predigested by secretion
of salivary fluids into the host's skin during
feeding. The nymph and adult stages of these
mites are free-living and feed on eggs of small
insects and related invertebrates. The adult
females oviposit on the ground. The larval
chiggers are found most often in damp areas
covered with vegetation such as margins of lakes
or streams shaded woods and high grass or
weeds.
c. Control
(1) Nest-Inhabiting Mites. Elimination
of the house mouse mite and other important
species of this group is principally dependent on
host control. It may be necessary, in the case of
infested structures, to apply residual sprays in
the manner recommended for the interior control
of flies and mosquitoes. If man regularly
inhabits the structure, the application of residual
insecticide should be restricted to infested areas
only.
(2) Mites Parasitic on Birds and
Rodents. The chiggers of these mites are of
primary importance to man. Most are not disease
vectors, but may be extremely pestiferous.
9 Nov 2004
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