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What people say makes us excited::
These chappies belong to the Group Arachnid...yep..! they're spiders...ish. They in fact belong to the Order Acarina as also do ticks. In Europe it is only the itch mite which can be regarded as an important parasite of man, but other mites may occasionally cause trouble. In particular the Harvest mite (Trombicula autumnalis) often bites people in late summer. Mite larva have six legs and moult three or four times before the adult stage is reached. Some mites suck blood, while others are responsible for hypersensitive reactions. We are going to have a brief look at three varieties starting with the itch mite..
Sarcoptes scabiei
(The Itch Mite)
This mite, which is only 1/3 mm long and is very seldom seen, lives actually in and on the skin, with the female burrowing tunnels in the upper horny layer, particularly on the front of the wrists, the sides and webs of the fingers, the buttocks, the genitals and the feet. Eggs are deposited in the small tunnels she makes whilst the male remains on the surface of the skin. The development from egg to adult can take a good two weeks. The burrowing activities of the parasites cause intense itching and the original blister like lesions may be made much worse by scratching. Infection is usually by females with eggs being transferred from one person to another by direct contact. Have a look at the close- up below....
You can see from the drawing how well these insects are able to cling on.
Dermatophagoides spp
(Bed /Dust Mites)
Bed mites feed on the scales which are continually falling from our skin. The most common species of dust mite isolated in Britain is Dermatophagoides pteronyssinus from the family Pyroglyphidae, but there are other species of dust mite as well as predatory mites that share the same dusty environment. Dust mites live in the fine layer of minute dust particles that continually settles on household items. They are found almost world wide but their numbers are considerably reduced at high altitudes and dry climates. House dust mites have been known to be associated with allergies since the 1960's and have become a focus over the years for their involvement with respiratory ailments. They do not bite or sting but harbour strong allergens in their bodies as well as in their secretions, excreta and shed skins. Constant contact with these allergens can trigger respiratory and dermatological complaints in some humans.
Dust mites favour homes with high humidity levels and constant warm temperatures, and under these conditions mite populations explode, although there are some seasonal fluctuations. The mites are known to concentrate in high traffic areas in homes and on certain furniture items, especially beds, upholstered lounges, chairs, and in carpets with long fibres. They are attracted to these areas for food, and they feed on shed human skin scales and secretions, house dust, fungal spores, pollen grains, plant fibres, and insect scales. Dust mites dislike strong light and will take harbourage in the seams, ledges, and framework of furniture when exposed. Due to their light weight, dust mites can become airborne during activities such as bed making, and in this way can be distributed throughout the room or house. They prefer a high humidity (c. 80%) and a temperature (c. 25C), and so are particularly common in beds. Recent researches in to the causes of asthma found that it is the dust containing them which causes the more intense attacks of asthma in sensitive patients. Apart from sprays it has been found that the best method to get rid of these mites is frequent and thorough vacuuming of the mattresses.
There is not one single clinical symptom that can readily identify mite-allergic asthmatic patients. This makes a clinical diagnosis difficult, and is therefore dependent on the reporting of other associated features. There is a proliferation of allergy clinics that specialise in testing for allergic responses to different materials including dust mites using skin prick tests. Medical conditions that are attributable to the presence of dust mites include allergic rhinitis, asthma, childhood eczema and other allergic conditions. Dust mites do not transmit any disease-causing pathogens.
Treatment and Control
Allergies from house dust mite can be managed by immunotherapy using mite extracts in conjunction with reducing the mite population in the home of the patient. It is virtually impossible to eliminate all dust mites from a household, but areas where mites tend to congregate can be targeted. Wall to wall carpet should be reduced, and replaced where possible with smooth hard surfaces that are easy to clean. Upholstered furniture can be avoided, mattresses and pillows should be encased in especially manufactured (‘plastic’) products that aid in the exclusion of mites. Bedding and curtains should be selected on their ability to withstand frequent laundering. Thorough vacuuming on a regular basis, including all mattresses, especially the seams and framework of the bed, will also help. A reduction in humidity levels by increased air circulation and ventilation throughout the house will assist in maintaining mites at a lower level.
Glycyphagus domesticus
(House Mite)
These small mites are very similar to those found in foodstuffs, but under a lens they can be recognised by the long hairs at their rear end. They may occasionally occur in foodstuffs, but they are primarily found in old fashioned upholstered furniture, which has been kept in a damp area for some time so that the stuffing has rotted. House mites then feed on the fungus, and multiply in large numbers. They occur particularly in upholstery stuffed with fibres derived from palm leaves. Nowadays these mites don't present a problem with modern furnishings and central heating, because like all other mites they quickly die if they become desiccated.
For problems caused in late summer, the Harvest Mite seems to be the biggest culprit. I hope the information that follows is of some use...
Trombicula autumnalis
(Harvest Mite)
It is not the adult stage of the Harvest mite which causes the problems, but the six-legged larval stage which can send people and animals crazy scratching which then leads on to secondary infection. These are white to orange red in colour, that is before they have a good feed on you...and very small something like 1/100 of an inch, just about visible. To understand what is going on we need to know a bit of biology:
Lifecycle:
Adult harvest mite overwinter near or slightly below the soil and in other protected places. Females become active in the spring and lay up to 15 eggs per day in vegetation when soil temperatures are 60°F. The larvae congregate in groups on small clods of earth, in matted vegetation and even on low bushes and plants, where they have more access to a prospective host. The first active stage in the life of the harvest mite is the six-legged larva and this is the only stage to attack warm-blooded animals. A drawing (courtesy of Ohio State University) shows the difference between the adult and the larvae.
The life cycle is about 50 to 70 days, with adult females living up to one year and producing offspring during this time. Multiple generations occur in warmer climates, whereas only two to three develop each season in some northern areas/countries. They are active only during the day and their movements appear to be controlled chiefly by the weather, aren't we all, they are most active when it is dry and sunny and least active when the day is cold and wet, as is the case with most insects. When the larvae come into contact with any warm-blooded animal (dogs are particularly susceptible), they swarm onto it and wander in search of a place to attach themselves. Infestation in human beings generally occurs by way of the ankles when walking in areas where the mite is common; sitting or lying on infested ground offers even better opportunities to the mite.
The thickness of the skin is probably the most important factor because the harvest mite feeds by thrusting its small hooked chelicerae (fangs) into the surface layers of the skin. Where the skin is unusually thick they attach with difficulty and may be brushed off by the movements of the host. Young harvest mite larvae attach themselves to the skin of people, domestic animals, wild animals (including reptiles), poultry and birds. The preferred feeding locations on people are parts of the body where clothing fits tightly over the skin such as around the belt line, waistline, under girdles and under socks, or where the flesh is thin, tender or wrinkled such as the ankles, in the armpits, back of the knees, in front of the elbow, or in the groin, especially around hair follicles (see below again courtesy of Ohio State).
The insertion of the small fangs into the skin is painless, and is merely intended to puncture the skin so that the feeding process can begin. Harvest mite larvae do not burrow into the skin, nor suck blood. They pierce the skin and inject into the host a salivary secretion containing powerful, digestive enzymes that break down skin cells that are ingested (tissues become liquefied and sucked up). Also, this digestive fluid causes surrounding tissues to harden, forming a straw-like feeding tube of hardened flesh (stylostome) from which further, partially-digested skin cells may be sucked out. After a larva is fully fed in four days, it drops from the host, leaving a red welt with a white, hard central area on the skin that itches severely and may later develop into dermatitis. Any welts, swelling, itching, or fever will usually develop three to six hours after exposure and may continue a week or longer. If nothing is done to relieve itching, symptoms may continue a week or more. Scratching a bite may break the skin, resulting in secondary infections. However, harvest mites are not known to transmit any disease in this country.
Once the larva has finished feeding it drops to the ground to complete its lifecycle. It descends into the soil and, after a period of five or six weeks, changes into an eight-legged nymph. This stage is sexually immature like the larva, but it resembles far more closely the adult male or female into which it eventually develops. Both the nymph and the adult live in the soil and feed on plant juices or small insects. They are never parasitic. They prefer moist conditions (as do all mites as otherwise they would desiccate) and are especially numerous in the vicinity of rabbit warrens. Thus the lifecycle of the harvest mite is completed. The eggs laid by the adult in the spring and summer hatch into the six-legged harvest mites which are most abundant in late summer and autumn. These, after they have fed on warm-blooded animals, develop through the nymph stage to the adult.
Distribution:
The harvest mite is widely distributed in the British Isles and is particularly abundant on chalk downs. The geological origin of the soil and the climate does not affect its abundance. Heavy infestations, however, are often found to be sharply localised; a heavy infestation may occur in the gardens of one or two houses in a village which is otherwise free from the pest. They may also be found in town gardens and parks.
After returning from a chigger/harvest mite-infested area, launder the field clothes in soapy, hot water (125°F.) for about half an hour (this applies to any insect infestation, washing clothes on cool wash does not work, so if your Amani jacket....well you know). Infested clothes should not be worn again until they are properly laundered and/or exposed to hot sunshine. Unlaundered clothes or those laundered in cool water will contain the biting chiggers to again reinfest your skin. As soon as possible, take a good hot bath or shower and soap repeatedly. The chiggers may be dislodged, but you will still have the stylostomes, causing the severe itch. Scratching deep to remove stylostomes can cause secondary infections. For temporary relief of itching, apply ointments of benzocaine, hydrocortisone, calamine lotion, or others recommended by your pharmacist or medical doctor. Some use Vaseline, cold cream, baby oil, or fingernail polish. (The sooner the treatment, the better the results.)
Mowing of briars, weeds, and thick vegetation and close clipping of lawns, to eliminate shade and moisture, will reduce harvest mite larvae populations, and permit sunlight and air to circulate freely. Harvest mite larvae can penetrate many types of clothing, but high boots and trousers of tightly woven fabric tucked into stockings or boots help deter them.
Before going into an area where harvest mite larvae may be present, protect yourself by using a repellent or permethrin available at many chemists or hardware stores. Deet-based repellents are effective for only a few hours, whereas permethrin-based repellents are for use only on clothing and effective for several days. Apply the repellent to both the skin and clothing, especially on hands, arms, or legs, if uncovered, and to clothing openings at cuffs, neck, waistband, and upper edges of socks. Follow label directions since repellents may damage plastics, nail polish, and painted or varnished surfaces. Do not use indiscriminately as severe human allergies can develop. Keep moving since the worst harvest mite infestations occur when sitting or laying down in a sunny spot at midday with temperatures above 60°F. If possible, stick to roads and trails.
Treating known harvest mite larvae trouble spots is quicker and less expensive than treating an entire area. Place six-inch squares of black cardboard (black is a heat sink and will become warmer than the surrounding grass) on edge in the grass and observe for a few minutes (obviously on a dry day....!). Any small, yellowish or pinkish harvest mite larvae present will climb rapidly to the top of the square and congregate there. Make tests in 10 to 12 different spots such as grass, dead leaves, briars, weeds, etc. Unless the entire area is infested, treat only the spots where control is desired such as grass around picnic tables, lawn chairs, or recreational equipment (Always remember, when you are spraying insecticide none target species are also at risk...poor old ladybirds). Harvest mite larvae tend to concentrate in "mite islands" while nearby spots are free of them. They become rather inactive at temperatures below 60°F.
I am not going to make a recommendations on which insecticide that you can use. Those preparations that pest controllers and farmers use are not normally available to the general public in this country (Gt. Britain). I would also not advise to go getting too much information from American sites on treatments as the laws on pesticides are different to ours.
Do not wear dog or cat flea collars on your ankles or cattle ear tags on your shoes to ward off harvest mite larvae. It is very dangerous resulting in chemical skin burns and toxic effect to the wearers.
by Barb Ogg, Ph.D., Extension Educator
This educational resource guide, based on Chapter 10, "Mites," in Common-Sense Pest Control by Olkowski, Daar and Olkowski, will discuss biology of dust mites and will emphasize non-chemical control tactics. An allergist, a medical doctor specially trained to treat allergies, should be consulted for proper diagnosis and treatment of allergies.
House dust mites primarily live on dead skin cells regularly shed from humans and their animal pets. Skin cells and scales, commonly called dander, are often concentrated in lounging areas, mattresses, frequently used furniture and associated carpeted areas, may harbor large numbers of these microscopic mites.
For most people, house dust mites are not harmful. The medical significance of house dust mites arises because their microscopic cast skins and feces are a major constituent of house dust that induces allergic reactions in some individuals (Figure 1).
For those individuals, inhaling the house dust allergen triggers rhinitis allergica or bronchial asthma. People with allergies to house dust usually also have allergic reactions to house dust mite fecal material and cast skins. Studies have shown that the most potent house dust allergens can be extracted from the organic debris produced by dust mites. Other important allergen-producing organisms that are found in house dust are found in Figure 1.
There are two species of house dust mites, belonging to the genus Dermatophagoides, that are found in North America. These mites are so tiny that they are virtually invisible without magnification. They pass through six developmental stages, and the adult form may also molt once. Adult female mites lay cream-colored elliptical eggs coated with a sticky fluid that helps them adhere to the substrate. Under optimal conditions, the cycle from egg to adult mite takes about one month.
Both species of house dust mites feed on human skin scales, pollen, fungi, bacteria, lepidopteran (moth and butterfly) scales, animal dander, and skin scales of birds. Human, cat, dog, and horse dander have been used to raise these species in a laboratory. Dust mites do not drink free water, but they absorb water fro the air and the environment. The food consumption of these mites and development increases at higher relative humidities. Mites survive best at relative humidities of 70-80% and temperatures of 75-80 degrees F. House dust mites do not survive well at low relative humidities, especially at higher temperatures. Temperatures of 140 degrees F for one hour is lethal to these mites.
Integrated pest management (IPM) means that several tactics should be used at the same time to alleviate a pest problem. Complete elimination of house dust mites is not a realistic goal, but integrated mite management should revolve around reducing human exposure to allergens as well as making the environment inhospitable to house dust mites. Sleeping areas deserve the most attention.
Select appropriate furnishings. Avoid furniture that collects dust, like overstuffed furniture made of fuzzy textiles. Also avoid wool fabrics/rugs, because wool shed particles and is eaten by other insects. Use washable curtains or blinds that can be vacuumed and small rugs that can be washed instead of wall-to-wall carpeting. Keep surfaces free of clutter and knickknacks that collect dust. Enclosing mattresses in plastic covers decreases populations of mites in the bed. Replace feather pillows and down quilts with synthetic fibers.
Avoid Furry or Feathered Pets. Pets that have fur or feather contribute dander to the dust and increase the food source for mites. If you are a pet lover, locate their sleeping quarters as far from yours as possible and furnish their sleeping quarters so they can be cleaned easily. Hardwood or vinyl floors with washable area rugs are ideal.
This drawing shows the important allergen-producing organisms and relative amounts of their body parts and by-products found in one gram of house dust.
Constituents of House Dust: ash, cigarette; ash, incinerator; combustion products; fiber, synthetic textile; fibers: wool, cotton, paper and silk; fingernail filings; food crumbs; glass particles; glue; graphite; hair, human and animal; insect fragments; oil soot; paint chips; plant parts; pollen; polymer foam particles; salt and sugar crystals; skin scales, humans; skin scales, pets; soil; spores, fungal; stone particles; tobacco; wood shavings
*Drawn primarily from van Bronswijk, 1981.
Control Other Insect Pests. Other insect pests in the home may contribute to allergies and mite populations so suppressing populations of fleas, cockroaches, and silverfish will minimize additional allergens in the home. Store grains and crackers in glass containers with good rubber seals that close by pressure. You may wish to store these containers in the freezer. Information on these pests and their control can be obtained by contacting the Lancaster County Extension Office.
Low Humidity. The humidity in the house should be kept below 70%. During humid times of the year, it might be useful to run dehumidifiers in bedrooms and/or particularly damp areas of the home. In addition, bathroom and laundry rooms can be vented to remove humid air to the outside with a fan.
Reducing Air Infiltration. Airing out the house with open windows allows the entry of pollen, which is another major allergen for many people as well as a food source for dust mites. Minimize incoming air by caulking cracks around windows, doors and other openings like you would weatherize your house.
Dust Management: Getting rid of allergy-inducing dust mites and other allergy-inducing constituent of dust is related to eliminating dust from the environment. The most important tool for managing house dust mites is the vacuum cleaner. Regular, thorough vacuuming of carpets, furniture, textiles and other home furnishings such as draperies will help keep dust mite populations low. Avoid wet-mopping because it increases moisture in the air. Where wet-mopping is necessary, as in kitchens and bathrooms, vacuum thoroughly first. Vacuums with a water filter are preferable to those with a disposable paper bag because a water vacuum removes a greater range of particle sizes than paper-bag types. There are a number of vacuums with highly efficient filters designed for use by people with allergies to dust. It is better to vacuum thoroughly once a week rather than lightly on a daily basis. Vacuum mattresses and padded furniture thoroughly; 20 minutes for each mattress is not too long. Dust furniture before you vacuum so the dust has time to settle on the floor, where it can be picked up by the vacuum. Special dust cloths or other cleaning implements that are treated chemically to hold rather than scatter dust may be helpful. You may also wish to use an electrostatic precipitator to help reduce small particles in the air.
Cleaning/Heat Treatments. Shampoo, steam clean, or beat non-washable carpets once a year. This removes large particles missed by the vacuum cleaner. Wash sheets in soapy water at 140 F every one or two weeks to kill all mites. Take blankets to the dry cleaner, hang them outdoors once a year, or wash them frequently. In the wintertime in Nebraska, the house, furniture (mattresses, overstuffed furniture), or bedding can be exposed to the outside cold for one or two days to kill the dust mites. Alternatively, a study has shown that using an electric blanket for eight hours every day reduced mites in mattress by 50% in one month. Another study documented that heating blankets in a clothes dryer for several hours killed mites. If this is done each month with one annual dry cleaning or wash, house dust mites can be held to a minimum.
According to Common-Sense Pest Control, cleaning and nontoxic approaches listed above should give adequate control, except in humid, tropical regions of the world. For more information, the following references contain technical information on house dust mites that may be of interest:
Alexander, J.O. 1984. Arthropods and human skin. Berlin: Springer-Verlag. 442 pp.
Bronswijk, J.H., van. 1981. House dust biology, for allergists, acarologists and mycologists. Zeist, The Netherlands: NIB Publishers, Box 144, 3700 AC Zeist, The Netherlands.
Olkowski, W., S. Daar, and H. Olkowski. 1991. Common-sense pest control. The Taunton Press, Newtown, CT.
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