Harvest mite

Harvest mites (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 small, 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. Chiggers are known for never spreading from host to host.

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 mite are found
Many areas of the world are plagued by chiggers, or some form thereof. 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 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 usually are infected by the disease by their infected rodent hosts. The disease is transmitted to the next generation of offspring by breeding mites. Symptoms of scrub typhus in humans include fever, headache, muscle pain, cough, and gastrointestinal symptoms.

The North American genus and species can cause severe illness in children. This only occurs when the infestation is particularly heavy. Symptoms include a hallucinatory sense of floating outside one's body, fatigue, fever and general malaise.

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.

Another myth is that application of rubbing alcohol kills the chiggers or helps with symptoms. This method serves only to cause great burning pain and discomfort to the victim.

Treatment
The most effective way of removing chiggers is by taking a hot shower and washing the affected areas with mildly hot 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 pruritus. 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. 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, but instead gently but firmly rub the irritated skin with warm soapy water.

Clothing, especially pants and socks, should be immediately discarded after returning from areas where exposure may have occurred.

Try not to scratch the affected regions. Scratching could scrape off chigger larvae, but it may also cause increased irritation by breaking the skin and leaving it vulnerable to a more serious infection.

A covering to reduce air exposure over the itchy area, such as calamine lotion, petroleum jelly, or baby oil, may help relieve the pain (but does not cure the bites).

The application of a small drop of finger nail polish (usually clear nail polish) is one of the most popular remedies and is claimed to reduce itching and dry the itchy sores in the fewest number of days. This has a better chance of being effective if done early. Later, people sometimes may end up mistaking the red dot in the middle of the bite as the chigger itself (the chigger is long gone). There is a misconception that the mite has burrowed into the skin, and that coating their bites with vaseline, nail polish, or some other air-inhibiting seal will "suffocate" the chigger.

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 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 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, a study reported in the March 1993 issue of the Southeast Asian Journal of Tropical Medicine & Public Health (volume 24, issue 1: pp165-169) tested 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). This was reported in the March 12, 2001 issue of the Archives of Internal Medicine.