MITES
Mites that attack
humans with some frequency in the U.S. originate in a variety of habitats.
Some,
including the
chicken mite and the tropical fowl mite, migrate to humans from birds. Others,
such as grain
mites and mushroom
mites, are found in food materials or stored products. The straw itch mite and
furniture mite come
from plant material, and the chigger mite is found in lawns and open woodlands.
The
tropical rat mite
and the mouse mite come from rodents, whereas the itch mite and follicle mite
are
permanent residents
on humans. Mites develop by gradual metamorphosis.
Bionomics
Chicken
mite (Dermanyssus gallinae).
Best-known of the mites infesting poultry, the chicken
mite is found on
the birds only when it is feeding, which is normally at night. In the daytime
it hides in
cracks and crevices
in the vicinity of the roost. The chicken mite will feed freely on many other
birds,
including pigeons,
canaries, sparrows, swallows, doves and wrens. When the mite attacks humans it
causes mild
dermatitis and itching. Cases of dermatitis caused by this mite are common in
rural areas, but
infestations also
occur in urban areas. These include instances where the infestations can be
traced to pet
canaries, pigeons
and nests of other wild birds or in which the death of the bird host or its
departure from
the nest instigated
the attack on humans. It is believed that this species can live for several
months
without food.
Northern
fowl mite (Ornithonyssus sylvarium).
Although very
similar to the
chicken mite in appearance, the northern fowl mite differs in that it breeds
among the feathers of the host and may
complete
development without leaving the host. It is not necessary for this
mite to stay on the
host, however, and it may be found in nests, or roost
areas, and in
surrounding cracks and crevices. It can survive for two or
three weeks away
from the host. This mite may bite humans, causing some
annoyance but
infrequently dermatitis. The problem most frequently is
irritation from the
occasional bites inflicted by wandering mites. The mite
is a general parasite
of birds, being found on domestic fowl, sparrows,
swallows and many
other avian species throughout the temperate region. Human annoyance is
frequently
associated with the
absence of the normal host bird, leaving an infestation of mites in the nest
area
without a convenient source of food.
Tropical
rat mite (Ornithonyssus bacoti).
This mite is associated with rats throughout the
U.S., where it
feeds also on humans and many other warm-blooded animals. The bite is painful,
causing
intense itching and
a skin irritation known as rat-mite dermatitis. This mite has not been proven
to be a
transmitter of
typhus or other diseases, although its habits appear to suit it well for such a
role. Attacks on
humans are almost
always associated with rats in buildings, and complaints are common from areas
that
may be infested
with rats, such as warehouses, stores, theaters and apartments. Rat control may
intensify
the attack on
humans, but this mite will bite humans even when there is an abundance of host
rats on
which they can
feed. The mite drops from its host after each feeding and may be found on a
variety of
surfaces near
rat-infested areas. It can survive for several days without a blood meal.
House
mouse mite (Liponissoides sanguineus).
This mite in the U.S. is primarily a parasite of
mice. It tends to
leave its rodent host to wander throughout buildings and bite people. Its major
importance is that
it has been identified as the vector of rickettsial pox, a mild and nonfatal
human
disease.
Grain
mite. Grain mites (including the furniture mite and the mushroom
mite) are commonly
found infesting all
types of grain flour, stored foods, cheese and mushroom beds. They prefer a
moist
location and under
favorable conditions develop rapidly and in great numbers, completing the life
cycle in
as little as 17
days. Under adverse conditions this period may be considerably extended. In
some species
the second nymphal
form may be replaced by a special stage known as the hypopus.
In this stage the mite
is highly resistant
to unfavorable conditions, insecticides and fumigation, and may exist for
several
months without
feeding. The hypopus is transported from place to place by clinging to small
animal
forms such as
insects or mice. When it encounters favorable conditions it sheds its skin and
resumes
normal growth and
development. The peculiar adaptation through the hypopus stage makes control
very
difficult.
Grain mites are
reported to have been the cause of mild dermatitis in humans, known under
various names as
“grocers’ itch,” “vanillism” (from infestations on vanilla beans), and “copra
itch.” These
cases are reported
where products infested with the mites are handled by humans. These mites are
not
bloodsucking forms
and thus are the cause of only mild irritations, very easily remedied once the
source
of exposure is
identified.
Straw
itch mite (Pyemotes ventricosis).
The straw itch mite normally lives on other arthropods. Common hosts are the
larvae of several
insects, including
the wheat jointworm; the wheat strawworm; the Angoumois
grain moth; the rice,
granary, bean and pea weevils; and the pink bollworm. It
reproduces rapidly
and in enormous numbers. This mite has an unusual
development in
which the eggs hatch and the young are matured within the body
of the female. They
are released as sexually mature adults. It is reported that a
single female may
give birth to more than 200 adult mites and that in one week
the females of this
brood will have produced another brood in the same manner.
Homes with
beetle-infested beans or cereals in cupboards often have problems
with this mite. Pyemotes
causes severe bite reactions.
People engaged in
threshing straw or handling grains or other material infested with the insect
hosts often are
overrun by these mites. Their bites produce a rashlike dermatitis that may cover
large areas
of the body. The
rash appears about 12 hours after the attack and is accompanied by severe
itching. The
attack is often so intense that vomiting, headache, sweating and
fever follow.
Chiggers
(Eutrombicula alfreddugesi).
Larvae
of chiggers,
commonly called redbugs, attack humans and dogs
during the larval
stage. These mites are distributed over
approximately the
eastern half of the country. They are most common
in the southern
states where breeding may be continuous but
frequently are
abundant during the summer in the more northern
states with one to
three generations per year. They infest a variety of
areas ranging from
overgrown brush to well-kept lawns. Adults
overwinter in
earthen cells in the soil, scavenge on decaying matter
and emerge from the
soil in the spring to lay their eggs. These hatch
into tiny, oval,
orange-colored larvae that normally feed on snakes,
turtles, rabbits,
birds and other wildlife. These larvae, barely visible
to the naked eye,
are very active. When humans come in contact with infested vegetation, the
larvae
swarm over the
entire body and it might be several hours before they settle down to feed.
Their attack
seems to be
concentrated at points where the clothing is pressed against the skin, such as
under belts or
garters.
They attach,
frequently near a hair follicle, by their mouthparts and first pair of
appendages. The
mites inject a
fluid that liquefies the immediately adjacent tissues, which are then ingested.
The
surrounding tissues
become hardened and, as feeding progresses, form a tiny tube through which
further
liquefied tissue
may be withdrawn. The larvae become fully fed in four to six days when they
drop off the
host, leaving
behind the tubes that have developed from the feeding activity. The digestive
fluid of the
mites causes a
severe itching and a definite dermatitis. Itching may last for a week or more.
Scratching
these areas may
lead to secondary infection. After leaving the host, the larvae transform into
nymphs and
later into adults.
Neither of these forms attacks humans or other animals. Both feed on vegetable
matter.
Chiggers are not
associated with disease transmission in the U.S.
Itch
mite This mite causes scabies or itch in humans and is
parasitic on dogs,
pigs, horses and sheep. There are several closely
related forms on
animals that may sometimes transfer to humans, but
usually close
contact is required. Favored sites are in the skin between
the fingers, the
folds at the wrists, at the bend of the elbow or knee,
and under the
breasts. Crowded conditions encourage the spread of
scabies
infestations. The female mite cuts into the skin, makes a
burrow under the
skin and lays eggs. The larvae return to the surface
of the skin to
molt, and the nymphal and adult stages then live on the
surface. Unnoticed
at first in newly infested people, sensitivity and
itching build up at
the end of the first month of infestation.
Follicle
mite (Demodex folliculorum).
This mite is found in the skin pores of humans, especially
around the nose and
eyelids. It is likely that most people harbor this species. The mite is
entirely parasitic,
spending the entire
life cycle on the host.
House
dust mite (Dermatophagoides spp.).
House dust mites can be a problem in any building
occupied on a
regular basis. They are generally found in mattresses, pillows, overstuffed
furniture, rugs,
floors or other
protected places where people sleep or sit for long periods. They require a
damp
environment and are
often found in floors where moist air may enter a room. Eggs are laid singly
and the
life cycle takes
about a month. Adults live for one to three months, feeding on a variety of
foods including dog food, cereals, yeast and especially the scaling of the skin
of humans and their pets. In some
sensitive people,
they cause an allergic reaction.
Detection
and Control
Detection.
Survey methods vary with the habits of the species being investigated. Various
household ectoparasites
can generally be found in structures.
To survey for
chigger mites, use 12-inch squares of black or white paper placed on the ground
for
one to five minutes
at intervals of 100 feet, perhaps, throughout the area, or in 400x400-foot
grids. Count
and record the
number of mites aggregating at the upper edge of the squares. Collect the mites
with a finepointed
brush and vials of
alcohol for later identification. Use Berlese funnels to collect flour and
grain
mites and other
free-ranging species, such as bird mites in nesting material.
Estimates of
chigger, bird and rodent mite population densities can be based on data
gathered by
stunning or killing
the ectoparasites (with ether or chloroform) on dead or trapped animals, and
combing
(or beating) the
parasites into a white enameled pan or picking them off with forceps.
Alternatively, live
hosts in cages with
hardware cloth bottoms can be placed so that mites will drop into a pan of
water after
engorging, or the
ectoparasites can be floated from a dead animal by immersion in water
containing
detergent and then
collected on filter paper.
Scabies mites are
detected by making skin scrapings for microscopic examination.
Control.
Do not attempt control for the scabies (human itch) mite. This pest is
controlled by
laundering bedding
and underwear and use of pesticide ointments prescribed by a physician. These
may
be recommended for
application from the neck down for all family members.
For mites that
migrate from bird nests or coops, remove the nests or caulk to exclude mite
movement into
dwellings. Wear protective clothing (gloves, eyeglasses, etc.) to prevent mites
and nest
debris from
contaminating workers. Apply approved pesticide sprays or dusts indoors to
cracks and
crevices near or
leading to mite sources, and outside at nest areas. Habitat alteration to
remove birds from
nest areas coupled
with pesticide application should immediately eliminate the problem.
For chigger mites,
avoid infested locations or use repellents on pants legs and shoes and tuck
trousers into
boots. When possible, keep vegetation cut low. Not only does this remove
chigger
harborage,
it also eliminates harborage for rodents and other animals that serve as wild
hosts. These
sanitation
practices are especially important for chigger management in fields, vacant
lots, recreational
areas and parks.
Chiggers can also be controlled in lawns and other infested areas by careful
and thorough
treatment with
granules or sprays of residual pesticides that are effective against mites. The
miticides will
work best if applied after the infested area has been mowed.