scabies

This article is about scabies in humans. For scabies in dogs, see mange.

Scabies is a transmissible ectoparasite skin infection characterized by superficial burrows, intense pruritus (itching) and secondary infection. The word 'scabies' is Latin for 'itch'.

Etiology

Caused by the mite Sarcoptes scabiei, variety hominis, 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 motion of the mite in and on the skin produces an intense itch which may resemble an allergic reaction in appearance. The presence of the eggs produces a massive allergic response which, in turn, produces more itching.

Scabies is transmitted readily, often throughout an entire household, by prolonged skin-to-skin contact with an infected person (e.g. bed partners), and thus is sometimes classed as a sexually transmitted disease. Spread by clothing, bedding or towels is a less significant risk, though possible.

Onset

It takes approximately 4-6 weeks to develop symptoms after initial infestation. Therefore, a person was contagious at least a month before they were diagnosed. This means that person could have passed scabies to anyone at that time with whom they had close contact. Someone who sleeps in the same room with a person with scabies has a high possibility of having scabies as well although they show no symptoms.

The symptoms are caused by an allergic reaction that the body develops over time to the mites and their by-products under the skin, thus the 4-6 week "incubation" period. There are usually relatively few mites on a normal, healthy person--about 11 females in burrows. Scabies are microscopic although sometimes they are visible as a pinpoint of white, but most people can't see them. The females burrow into the skin and lay eggs there. Males roam on top of the skin, however, they can and do occasionally burrow. Both males and females surface at times, especially at night. They can be washed or scratched off (however scratching should be done with a washcloth to avoid cutting the skin as this can lead to infection), which, although not a cure, helps to keep the total population low. Also, humans create antibodies to the scabies mites which do kill some of them.

Signs, symptoms, and diagnosis

A delayed hypersensitivity (allergic) response resulting in a papular eruption (red, elevated area on skin) often occurs 30-40 days after infestation. While there may be hundreds of papules, fewer than 10 burrows are typically found. The burrow appears as a fine, wavy and slightly scaly line a few millimeters to one centimeter long. A tiny mite (0.3 to 0.4 mm) may sometimes be seen at the end of the burrow. Most burrows occur in the webs of fingers, flexing surfaces of the wrists, around elbows and armpits, the areolae of the breasts in females and on genitals of males, along the belt line, and on the lower buttocks. The face usually does not become involved in adults.

The rash may become secondarily infected; scratching the rash may break the skin and make secondary infection more likely. In persons with severely reduced immunity, such as those with HIV infection, or people being treated with immunosuppressive drugs like steroids, a widespread rash with thick scaling may result. This variety of scabies is called Norwegian scabies.

Scabies is frequently misdiagnosed as intense pruritus (itching of healthy skin) before papular eruptions form. Upon initial pruritus the burrows appear as small, barely noticeable bumps on the hands and may be slightly shiny and dark in color rather than red. Initially the itching may not exactly correlate to the location of these bumps. As the infestation progresses, these bumps become more red in color.

Generally diagnosis is made by finding burrows, which often may be difficult because they are scarce, because they are obscured by scratch marks, or by secondary dermatitis (unrelated skin irritation). 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, which are placed on a slide in glycerol, mineral oil or immersion in 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.

Compromised Immune Systems

People with compromised immune systems do not develop antibodies to the mites and may develop crusted Norwegian scabies, where many form scabs or have very red skin especially in the elderly and the mentally handicapped where white or gray crusted areas develop with little itching and little or no red bumps and mite population numbers soar to hundreds, thousands, or in AIDS patients millions. These cases require additional treatment options to ensure a complete kill. Ivermectin is the treatment of choice in these patients combined with any other topical treatment.

Treatment

Medications

Treatments basically fall into a few different categories: topical "pesticide" applications, systemic "tablet" doses which have the advantage of ensured total coverage, and the least toxic treatment is 10% sulfur ointment, a cost-effective treatment with the least long-term side-effects.Topical (surface) medications are often effective and must be applied thoroughly to all skin from the face down, especially to areas known to be primarily affected (skin folds, etc.). The topical medication of choice is 5% permethrin because it is safe for all age groups: it should be applied for eight to twelve hours (overnight is the most convenient) then washed off.

Lindane (hexachlorocyclohexane) creams or lotions are considered historical treatments, and should be avoided because they have been shown to have neurotoxic effects in children and infants; Lindane is no longer available in the UK or Australia, but is still available in the U.S.. Similarly, 5–10% sulfur ointments are considered historical. should only be started four weeks after treatment.

Although the mites are rapidly killed by treatment, itching can last for up to four weeks after treatment. A single dose of ivermectin (dosing: 200 µg/kg) has been reported to cure, but is an off-label use; some authorities recommend repeating treatment at 14 days.

Additional topical treatments include 10% crotamiton (except to eyes, nose, mouth), 25% benzyl benzoate cream or lotion.

A person can be reinfected with scabies: all household contacts must be treated simultaneously, even if asymptomatic.

The following is a treatment list in the order from most harmful to safest.

1. Lindane: (Kwell, Kwellada). It has been linked to 17 deaths by the US government FDA (3 were positively caused by lindane, although lindane was not used as prescribed in those cases).[1]
2. Malathion: Common pesticide, nervous system toxin in high quantities, no known mutagenic or carcinogenic properties in humans have been confirmed.[2]
3. Permethrin: Another pesticide, lacks carcinogenic testing in humans although animals test showed negative, toxicity may resembles allergic reactions. [3]
4. Crotamiton (Eurax ®): Less toxic, but less effective. Must use for roughly 3 days. [4]
5. Benzyl benzoate: Less toxic, but can cause asthmatic and allergic reactions. Must use for a week on 1st, 4th, and 7th day.^{citation needed]}
6. Ivermectin (Stromectol ®): Oral dewormer. Newest scabies treatment. Safer than all of the above and easiest and quickest to use.^{citation needed]}
7. 10% sulfur ointment: Safest treatment. Non-toxic. Used in pregnant women and infants under two months of age but effective in everyone if used for 7 days. Cheapest treatment. Over-the-counter treatment. May be used as often as one likes with no toxicity. Drawbacks: messy, stains clothes, therefore one shouldn't use white sheets and T-shirts.^{citation needed]}

Steroids or corticosteroids should not be used to combat itching. These can cause a weakened immune system creating various new diseases and the worst type of scabies. Options include antihistamines such as cetirizine. Prescription: Doxepin (oral or topical).

Without a host, scabies mites survive for a few hours in the environment (the mites rapidly dry out). Therefore it is recommended, after treatment, to wash all material (such as clothes and bedding) that has been in prolonged contact with the infested in the last four days.

Approximately 300 million cases of infestation with scabies occur worldwide annually.

Scabies also occurs in dogs; see article at Mange. Dog mites can easily be transferred to humans. Although mites that infect dogs are not able to complete their life cycle on humans, they will cause quite a bit of itching before they finally die. Dogs with mange should be treated to avoid continuously re-infecting humans.

Bird mites have also be noted to cause a similar disease.^[1]

Follow Up

After treatment has been applied or taken, (or directly before treatment if you are careful and wear gloves) cleaning of environment should occur. The key is timing. All household members should be treated at the same time and cleaning must be thorough and simultaneous. Expect increased itching and red bumps for the first week after taking any medication for scabies. The dead mites remain in the skin for 30 days. They are removed with the body's natural shedding process. During those 30 days expect new bumps and itching.

Home Cleaning

• Wash in hot water and dry in a hot dryer:

1. Recently worn clothing
2. Towels and bedding should be removed and washed daily for at least three days after each treatment, including mattress pad and pillow covers.

• Dryclean

1. Things that cannot be washed can be dry cleaned.

• Dryer Only OK

1. Pillows can be tossed in hot dryer for 30 minutes and mattresses can be vacuumed.

• "Quarantine" in Plastic Bag, Two Weeks:

1. Stuffed animals and pillows or freeze these items and shoes in the freezer overnight in a plastic bag with twist tie. This will kill any mites.
2. Don't forget about things like coats, gloves, hats, slippers, robes, kitchen towels, wetsuits, etc. Either isolate long enough for the mites to die in a plastic bag (at least 2 weeks) or clean or freeze overnight.

• Vacuum

1. Vacuum all carpets, rugs and upholstered furniture daily.

• Mop

1. Mop all floor surfaces and clean bathroom surfaces (this only needs to be done after the first treatment).

• Miscellaneous Cleaning

1. Thoroughly clean brushes and combs too (this is extra precaution and may not be necessary). This routine needs to be repeated at the time of the second follow-up treatment to ensure a thorough kill.
2. If there are pets in the house, they should be either treated with a permethrin shampoo at the same time as the humans or isolated and treated with Revolution. There are other herbal treatments if desired. Ivermectin products are also available for pets.
3. Don't forget about things like coats, gloves, hats, slippers, robes, kitchen towels, wetsuits, etc. Either isolate long enough for the mites to die in a plastic bag (at least 2 weeks) or clean or freeze overnight.

References

• The Merck Manual of Diagnosis and Therapy, 17th edition, 1999
• Clinician's Pocket Reference, 9th edition, 2002
• Taber's Cyclopedic Medical Dictionary, 17th edition, 1993
• United States Centers for Disease Control and Protection
• World Health Organization Essential Medicines Library
• American Social Health Association
• Chosidow O. "Scabies". New Engl J Med 354 (16): 1718–1727.

Numbered references

1. ^ Kong TK, To WK (2006). "Bird-Mite Infestation". New Engl J Med 354 (16): 1728.

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