Mites and Scabies

Mites, along with ticks, belong to the subclass Acarina (also known as Acari) and the class Arachnida. Mites are among the most diverse and successful of all the invertebrate groups. They have exploited an incredible array of habitats, and because of their small size (most are microscopic) go largely unnoticed. Many live freely in the soil or water, but there are also a large number of species that live as parasites on plants, animals, and some that feed on mold.

Some of the plant pests include the so-called spider mites (family Tetranychidae), thread-footed mites (family Tarsonemidae), and the gall mites (family Eriophyidae). Among the species that attack animals are members of the Sarcoptic Mange mites (family Sarcoptidae), which burrow under the skin. Demodex mites (family Demodicidae) are parasites that live in or near the hair follicles of mammals, including humans. Perhaps the best-known mite, though, is the house dust mite (family Pyroglyphidae).

Insects may also have parasitic mites. Examples are Varroa destructor, which attaches to the body of the honeybee, and Acarapis woodi (family Tarsonemidae), which lives in the tracheae of honey bees. There are hundreds of species of mites associated with other bee species, and most are poorly described and understood. Some are thought to be parasites, while others beneficial symbionts.

There are over 45,000 described species of mites. Scientists believe that we have only found 5% of the total diversity of mites. Mites are believed to have existed for around 400 million years.

The scientific discipline devoted to the study of ticks and mites is called acarology.

The tropical species Archegozetes longisetosus is one of the strongest animals in the world, relative to its mass (100 μg): It lifts up to 1182 times its own weight, over five times more than would be expected of such a minute animal (Heethoff & Koerner 2007).

Allergy

Mites cause several forms of allergic diseases, including hay fever, asthma and eczema and are known to aggravate atopic dermatitis. Mites are usually found in warm and humid locations, including beds. It is thought that inhalation of mites during sleep exposes the human body to some antigens that eventually induce hypersensitivity reaction. Dust mite allergens are thought to be among the heaviest dust allergens.

Like most of the other types of allergy, treatment of mite allergy starts with avoidance. There is a strong body of evidence showing that avoidance should be helpful in patients with atopic dermatitis triggered by exposure to mites. Regular washing of mattresses and blankets with hot water can help in this regard. Antihistamines are also useful; Cetirizine, for example, is shown to reduce allergic symptoms of patients. However not all types of mites are infectious including the Alaskozetes antarcticus an arctic inhabiting mite.

Scabies

Scabies, also known as the itch, is a contagious ectoparasite skin infection characterized by superficial burrows and intense pruritus (itching). It is caused by the mite Sarcoptes scabiei. The word scabies itself is derived from the Latin word for "scratch" (scabere). Other names or variants of the condition include Mite, Itch Mite, Mange, Crusted Scabies, Norwegian Scabies, Sarcoptes scabiei, or The Seven-Year Itch.

Signs and symptoms

The characteristic symptoms of scabies infection include superficial burrows, intense pruritus (itching), a generalized rash and secondary infection. Acropustulosis, or blisters and pustules on the palms and soles of the feet, are characteristic symptoms of scabies in infants.

S-shaped tracks in the skin are often accompanied by small, insect-type bites called nodules that may look like pimples. These burrows and nodules are often located in the crevices of the body, such as the webs of fingers, toes, feet, buttocks, elbows, waist area, genital area and axilla, and under the breasts in women.

The intense itching and rash characteristic of scabies infection is caused by an allergic reaction of the body to the burrowed microscopic scabies mites. The rash can be found over much of the body, especially in immunocompromised people (HIV positive or elderly); the associated itching is often most prevalent at night.

Secondary infection of impetigo, a Streptococci or Staphylococci bacterial skin infection, may occur after scratching. Cellulitis may also occur, resulting in localized swelling, redness and fever (DermNet).

In immuno-compromised, malnourished, elderly or institutionalized individuals, infestation can cause a more severe form of scabies known as crusted scabies or Norwegian scabies. This syndrome is characterized by a scaly rash, slight itching and thickened crusts of skin containing thousands of mites. Norwegian scabies is the form of scabies that is hardest to treat.

In individuals never before exposed to scabies, the onset of clinical signs and symptoms is 4–6 weeks after infestation. Some people may not realize that they have it for years; in previously exposed individuals, onset can be as soon as 2–4 days after infestation.

Cause

Scabies is highly contagious and can be spread by scratching, picking up the mites under the fingernails and simply touching another person's skin. They can also be spread onto other objects like keyboards, toilets, clothing, towels, bedding, furniture, and anything else that the might may be rubbed off onto, especially if a person is heavily infested. The parasite can survive up to 14 days away from a host, but often do not survive longer than two or three days away from human skin. Scabies is caused by the mite Sarcoptes scabiei, variety hominis, as shown by the Italian biologist Diacinto Cestoni in the 18th century. It produces intense, itchy skin rashes when the impregnated female tunnels into the stratum corneum of the skin and deposits eggs in the burrow. The larvae, which hatch in 3–10 days, move about on the skin, molt into a "nymphal" stage, and then mature into adult mites. The adult mites live 3–4 weeks in the host's skin.

The action of the mites moving within the skin and on the skin itself produces an intense itch which may resemble an allergic reaction in appearance. The presence of the eggs does not in fact produce more itching, that is a myth. It is rather the feces of the mites which cause the allergic reaction.

Scabies can be transmitted readily throughout an entire household, by skin-to-skin contact with an infected person (e.g. bed partners, schoolmates, daycare). It can be spread by clothing, bedding, or towels. Washing clothing in very hot water and dry on high heat will help prevent the transmission. Alternatively, permethrin sprays can be used for items that cannot be laundered.

The symptoms of itching and rash are caused by an allergic reaction that the human body develops over time to the mites and their by-products under the skin. As such, there is usually a 2-6 week incubation period between infestation and presentation of symptoms. However, in individuals with prior exposure to scabies, the incubation period is much shorter: as little as 1–4 days.

There are usually relatively few mites on a normal, healthy person (who is infested with scabies) — about 11 females in burrows. Scabies are microscopic although sometimes they are visible as a pinpoint of white. The females burrow into the skin and lay eggs there. Males roam on top of the skin, although can also occasionally burrow.

Diagnosis

Signs and symptoms of early scabies infestation mirror other skin diseases, including dermatitis, syphilis, allergic reactions, and other ectoparasites such as lice and fleas.

Generally diagnosis is made by finding burrows – which often may be difficult because they are scarce, and because they are obscured by scratch marks. If burrows are not found in the primary areas known to be affected, the entire skin surface of the body should be examined.

The suspicious area can be rubbed with ink from a fountain pen or alternately a topical tetracycline solution which will glow under a special light. The surface is then wiped off with an alcohol pad; if the person is infected with scabies, the characteristic zigzag or S pattern of the burrow across the skin will appear.

When a suspected burrow is found, diagnosis may be confirmed by microscopy of surface scrapings with scalpel or curette are placed on a slide in glycerol or mineral oil and covered with a coverslip. Avoiding potassium hydroxide is necessary because it may dissolve fecal pellets. Positive diagnosis is made when the mite, ova, or fecal pellets are found. Although this sounds simple in practice, actual detection of scabies sites is very difficult – requiring the scraping of dozens of suspicious lesions down to the superficial dermis. This will result in minor bleeding in spots. Even a negative (not finding any mites) scraping will not completely rule out scabies. Sometimes, the best diagnosis is by the history, physical findings and noticing response to effective topical treatment. The diagnosis of Crusted Scabies is not as elusive and a scraping under the fingernail is often diagnostic.

Management

Medications

Sulphur has been used since around 25 AD to treat Scabies. You can find bar soap with sulfur in the ranges of 1%-10% to kill scabies, it's recommended you go with 6% or above. Wash whole body once daily for 4 days. It is still recommended that you wash all clothing and bedclothes in hot water and tumble dry on hot as with Permethrin. However, this treatment is largely ineffective.

Topical drugs

• Permethrin 5% is topical medication of choice. Toxicity may resemble allergic reactions. It is usually applied to the skin before bedtime and left on for about 8 to 14 hours, then showered off in the morning. Package directions or doctor's instructions should be followed, but one application is normally sufficient to cure an infection.
• Eurax (USP Crotamiton) This is not a cure but helps to relieve itch (pruritis)
• Malathion: Applied for 24 hours; effective in killing both adults and eggs.
• Lindane lotion is approved in the U.S. for use as a second-line treatment where first-line medications like permethrin have either failed, are not well tolerated or otherwise contraindicated. It is illegal in 17 other countries, and 33 more countries have restricted its use. Though rare, serious side effects have resulted from product misuse. The FDA has confirmed 3 deaths that all involved use of lindane not in accordance with the label, including excessive topical applications and oral ingestions.
• There is some evidence that a 10% sulfur ointment in petroleum jelly applied topically is effective. It is cheap and readily available over-the-counter. It also has the advantage of being able to be used in pregnant women and infants under two months of age.
• Neem oil is deemed very effective in the treatment of scabies although only preliminary scientific proof exists which still has to be corroborated, and is recommended for those who are sensitive to permethrin, a known insecticide which might be an irritant. Also, the scabies mite has yet to become resistant to neem, so in persistent cases neem has been shown to be very effective.
• Tea tree oil at 5% was only partially effective and does not seem to be a viable solution for treatment. In one study, it was more effective than commercial medications against the scabies mite in an in vitro situation.

Oral

A single dose of Ivermectin has been reported to reduce the load of scabies but another dose is required after 2 weeks for full eradication. In 1999, a small scale test comparing topically applied Lindane to orally administered Ivermectin found no statistically significant differences between the two treatments. As Ivermectin is easily administered (not requiring a rub down of the whole body like lindane or permethrin twice per treatment), compliance is much better. Ivermectin is used in eradication programs of many parasites of both human and animal. Side effects may include mild abdominal pain, nausea, vomiting, myalgia and/or arthralgia, which subside. The product is considered safe for use in children over five months of age.

Public health and prevention strategies

There is no vaccine available for scabies, nor are there any proven causative risk factors. Therefore, most strategies focus on preventing re-infection. All family and close contacts should be treated at the same time, even if asymptomatic. Cleaning of environment should occur simultaneously, as there is a risk of reinfection. Therefore it is recommended to wash and hot iron all material (such as clothes, bedding, and towels) that has been in contact with scabies infestation.

Cleaning the environment should include:

• Treatment of furniture and bedding.
• Vacuuming floors, carpets, and rugs.
• Disinfecting floor and bathroom surfaces by mopping.
• Cleaning the shower/bath tub after each use.
• Daily washing of recently worn clothes, towels and bedding in hot water, drying in a hot dryer and steam ironing.

Itchiness during treatment

Options to combat itchiness include antihistamines such as chlorpheniramine. Prescription: Hydroxyzine (Atarax).