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.