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trombiculidae

Harvest mite

Harvest mite (genus Trombicula; also known as red bugs, trombiculid mites, scrub-itch mites, berry bugs or, in their larval stage, as chiggers) are mites in the family Trombiculidae that live in forests and grasslands. In their larval stage they attach to various animals including humans and feed on skin, often causing itching. These relatives of ticks are nearly microscopic measuring 0.4 mm (1/100 of an inch) and have a chrome-orange hue. A common species of harvest mite in Northern America is Trombicula alfreddugesi; in the UK the most prevalent harvest mite is Trombicula autumnalis.

Harvest mite larvae are tiny, irritating, red immatures between the egg and nymph stages, which have not yet become adult mites. They are usually microscopic. The larvae often live in berry patches, tall grass and weeds, woodland edges, pine straw, leaves, and treebark, or in typical habitats of their hosts (especially rodents).

The larval mites feed on the skin cells, but not blood, of animals, including humans. The six-legged parasitic larva feeds on a large variety of creatures including humans, rabbits, toads, box turtles, quail, and even some insects. After crawling onto their host, they inject digestive enzymes into the skin that break down skin cells. They do not actually "bite," but instead form a hole in the skin and chew up tiny parts of the inner skin, thus causing severe irritation and swelling. The severe itching is accompanied by red pimple-like bumps (papules) or hives and skin rash or lesions on a sun-exposed area. For humans, itching usually occurs after the larvae detach from the skin.

After feeding on their hosts, the larvae drop to the ground and become nymphs, then mature into adults which have 8 legs and are harmless to humans. In the post larval stage, they are not parasitic and feed on plant materials. The females lay 3-8 eggs in a litter, usually on a leaf or under the roots of a plant, and die by autumn.

Where harvest mites are found

Harvest mites are found throughout the world. In Europe and North America, they tend to be more prevalent in the hot and humid parts. In the more temperate regions, they are found only in the summer (in French, harvest mites are called aoûtat, or "August" flies). In the United States, they are found mostly in the southeast, the south, and the midwest. They are not present, or barely found, in far northern areas, in high mountains and in deserts.

Chiggers

Chigger or chigoe can refer to either of two parasitic arthropods that bite humans. In North America, chigger refers to the harvest mite, the bite of which results in an intensely itchy red bump in humans (who are accidental hosts). The name chigger originated as a corruption of chigoe. Also called scrub mite, red mite and several other names, they are found throughout temperate and tropical zones. In Asia and Australia, chiggers may carry Scrub typhus.

Chigger is also an alternate term for the chigoe flea (Tunga penetrans), a sand flea found in tropical and subtropical climates in the Americas and Africa

Description

Chiggers attach to the host, inject digestive enzymes into the bite wound, and then suck up the digested tissue. They do not burrow into the skin or suck blood, as is commonly assumed. Itching from a chigger bite may not develop until 24-48 hours after the bite, so the victim may not associate the specific exposure with the bite itself. The red welt/bump on the skin is not where a chigger laid eggs, as is sometimes believed.

Warm, rainy days make these parasitic and predatory mites reproduce into large populations. Once the ground temperature is regularly above 60°F (~16°C), the harvest mite lays eggs. Therefore, from April through early autumn up until the first frost, humans are susceptible to chigger bites . It is the larval stage that feeds on humans (as accidental host) or more commonly on other animals (small mammals, birds, reptiles, and amphibians).

Chiggers do not like sunlight or humidity. During the wet season, chiggers are usually found in tall grass and other vegetation. During dry seasons, chiggers are mostly found underneath brush and shady areas.

When carrying the parasite Orientia tsutsugamushi, chigger bites can cause scrub typhus.

Prevention and treatment

Keep grass short, and remove brush and wood debris where potential mite hosts may live. Keep major hosts away from the area, such as rodents and other small mammals. Secure trash cans to discourage wildlife from coming near your home. Sunlight that penetrates the grass will make the lawn drier and make it less favorable for chigger survival.

For personal protection, apply insect repellent to feet, legs, and mid-section.

To reduce the itching, an application of anti-itch cream containing hydrocortisone, calamine, or benzyl benzoate is often used. Applying fingernail polish to the affected area does not kill the chigger; the chigger is actually no longer present by the time a rash is noticed.

Chiggers as disease vectors

Although the harvest mite chigger usually does not carry diseases in North American temperate climates, the mites are considered a dangerous pest in East Asia and the South Pacific because they often carry Rickettsia tsutsugamushi (Orientia tsutsugamushi), the tiny parasite that causes scrub typhus, which is known alternatively as the Japanese river disease, scrub disease, or tsutsugamushi. The mites are infected by the Rickettsia passed down from parent to offspring before eggs are laid in a process called transovarial transmission. Symptoms of scrub typhus in humans include fever, headache, muscle pain, cough, and gastrointestinal symptoms.

Myth versus fact

Contrary to popular belief, the larvae do not burrow deep into the skin and live there. Rather, the larvae pierce the skin and inject powerful enzymes that digest cellular contents, which become liquified and are consumed by the larvae.

Treatment

The most effective way of removing chiggers is by washing the affected areas with warm water and soap. This must be done as soon as possible after exposure or possible exposure. Carefully wash the ankles, feet, behind the knees, and under the arms and chest. An Epsom salt bath may help alleviate itching. If one is near the seashore, wading for a few minutes in salt water will both get rid of the mites on one's skin and clothing and also alleviate the itching from their bites. Clothing, especially pants and socks, should be immediately discarded after returning from areas where exposure may have occurred. Another good way of removing chiggers is to cover the chiggers with scotch tape and pull them off that way. However, once symptoms appear, it may be too late to prevent further bites. Taking a hot bath when already covered with chigger bites may in fact be very uncomfortable and increase itching symptoms.

Do not rub and scratch the skin aggressively, which can break the skin and leave it vulnerable to a more serious infection.

Some claim that the chigger is still in the bite, perhaps mistaking the tiny red center of the bite for the chigger itself. In some cases, by the time the bite appears, the chigger is still there. Using a 10X magnifier one can easily see a chigger and then remove it with fine-tipped tweezers. Once it is gone, covering the bite with nail polish, calamine lotion, Vaseline or other petroleum jelly, baby oil, or anything else may help the pain and itching, but will neither suffocate the chigger nor help the bites heal any faster.

Medication such as antihistamines or corticosteroid creams may be prescribed by doctors, and might help in some instances.

Prevention

Chiggers seem to affect warm covered areas of the body more than drier areas. Thus, areas covered by socks and shoes, behind the knees and around the groin are often trouble spots. Special attention should be given to small children, as areas higher in the body (chest, back, waist-band, and under-arms) may be affected more easily than in adults, since children are shorter and may be more likely than adults come in contact with low-lying vegetation and dry grass where chiggers thrive.

To avoid being afflicted by chiggers, always wear a tight weave, protective clothing, and long pants. Spray insect repellent on your skin for further protection. Application of repellent to the shoes and lower trousers is helpful. Staying on trails, roads, or paths can help prevent contact.

Dusting sulfur is used commercially for mite control and can be used to control chiggers in yards. The dusting of shoes, socks and trouser legs with sulfur can be highly effective in repelling chiggers.

People who pick wild blueberries in the summer have traditionally been very vulnerable to chigger bites and have suggested applying deodorant soap to the skin and letting it dry without rinsing may help prevent bites.

Another helpful avoidance is to recognize the chigger habitat to avoid exposure in the first place. Chiggers in North America thrive late in summer, in dry tall grasses and other thick, unshaded vegetation.

Insect repellents containing one of the following active ingredients are recommended: DEET, Catnip oil extract - Nepetalactone, Citronella or eucalyptus oil extract. However, in 1993 issue a study reported on tests of two commercial repellants: DEET and citrus oil: "All chiggers exposed on the filter papers treated with DEET died and did not move off the treated papers. None of the chiggers that were placed on papers treated with citrus oil were killed. It was concluded that DEET was more effective than citrus oil.

Chiggers can also be treated using common household vinegar (5% acetic acid).

See also

References

External links

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