Scabies is a transmissible ectoparasite skin infection characterized by superficial burrows, intense pruritus (itching) and secondary infection. The word 'scabies' is Latin for 'itch'.
Contents
- 1 Etiology
- 2 Signs, Symptoms, and Diagnosis
- 3 Treatment
- 4 Practical Information
- 5 References
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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.
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 there may be hundreds of papules, less 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 pruritis (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.
Treatment
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.). Medication should remain on for more than 12 hours, and preferably 24, and then washed off.
Although the mites may be rapidly killed, improvement is sometimes slow and residual inflammation may take some time to finally subside. The topical medication of choice is 5% Permethrin because it is safe for all age groups. 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. Similarly, 5–10% sulfur ointments are considered historical.
A single dose of Ivermectin (dosing: 200 µg/kg) has been reported to cure, but is an off-label use, and thus considered experimental. Additional topical treatments include 10% crotamiton (except to eyes, nose, mouth), 25% benzyl benzoate cream or lotion; permethrins offer a simpler, one-application treatment which may be applied with in a 5% cream that remains on overnight or for 8-14 hours.
A person can be reinfected with scabies. Without a host, scabies mites survive for a few days. 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.
To prevent reinfestation, all social contacts and members of the family, even if not infested, should be treated similarly and most importantly at the same time.
Approximately 300 million cases of infestation with scabies occur worldwide annually.
Scabies also occurs in dogs; see Mange. Note: Although the mange mites are not able to complete their life cycle on humans, they will cause quite a bit of itching before they finally die.
Practical Information
Scabies 101--What you need to know about scabies--copyright researcher Janeen Hunt
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 can burrow and do, but both males and females surface at times especially at night. They can be washed off 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.
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.
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 which is also the cheapest treatment and has the least long-term side-effects.
U.S. doctors normally prescribe topical applications of a chemical called Permethrin 5%, a poisonous pesticide. Brand names include Acticin and Elimite. Never use these topical pesticides twice in the same week as this can produce pesticide poisoning which can be lethal. Application of these creams should be made from the top of the head if you live in a humid climate or have had scabies misdiagnosed for several months to tips of toes, all crevices. Other climates may use them from the neck down. Leave the cream on at least 12 hours but up to 24. The optimal duration of application is 16 hours for a kill. Repeat the process in seven days to ten days if necessary.
The systemic approach involves a drug called Ivermectin, generic name Stromectol. A dosage is prescribed according to weight at least 12 mg for an adult, taken all at once and repeated in seven days if necessary. This is the easiest and quickest method although most doctors are as yet unfamiliar with this treatment.
After treatment has been applied or taken, (or directly before treatment if you are careful and wear gloves) cleaning of environment should occur. Wash all recently worn clothing in hot water and dry in a hot dryer. There is no need to wash clean clothes that haven't been touched in the past week. Place clean clothes on a clean sheet out of the dryer. Things that cannot be washed can be dry cleaned. Place other stuffed animals and pillows in a plastic bag for two weeks or freeze these items and shoes in the freezer overnight in a plastic bag with twist tie. This will kill any mites. Towels and bedding should be removed and washed daily for at least three days after each treatment, including mattress pad and pillow covers. Pillows can be tossed in hot dryer for 30 minutes and mattresses can be vacuumed. Vacuum all carpets, rugs and upholstered furniture daily. 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. Mop all floor surfaces and clean bathroom surfaces (this only needs to be done after the first treatment). 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.
If there are pets in the house, they should be either treated with a pemethrin 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.
The key is timing. All household members should be treated at the same time and cleaning must be thorough and simultaneous.
Sulfur treatment is a little messier, but many have found complications later by taking Permethrin treatments (Acticin or Elimite) due to the pesticide content. Sometimes the effects of too much pesticide can cause bad complications for a year or more. 10% sulfur ointment needs to be left on the body 24/7 for a week. This is effective and the least toxic method.
However, the topical pesticide called Lindane should not be used (Kwell or Kwellada--however Kwellada-P with the "-P" is Permethrin) as this has caused 17 deaths in the US according to the FDA and will probably soon be taken off the market. Australia already has a ban on Lindane use for scabies along with 7 other countries. There are several other countries that have banned Lindane for agricultural use (i.e. the entire EU).
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.
Do not use topical pesticides more than directed.
The following is a treatment list in the order from most harmful to safest.
1. Worst: Lindane (Kwell, Kwellada). Up to 40% of this pesticide is absorbed into the bloodstream. It has been linked to 17 deaths by the US government FDA (3 were positively caused by Lindane).
2. Malathion: Toxic pesticide, damages genes in the body
3. Permethrin: Toxic pesticide but 2% absorption into bloodstream so slightly safer than above
4. Crotamiton (Eurax): Less toxic, but less effective. Must use for a week minimum to 10 days.
5. Benzyl Benzoate: Less toxic, but can cause asthmatic and allergic reactions. Must use for a week on 1st, 4th, and 7th day.
6. Ivermectin: Oral dewormer. Newest scabies treatment. Safer than all of the above and easiest and quickest to use. (generic name Stromectol)
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 use white sheets and T-shirts.
For itching:
Use of steroids or corticosteroids should be avoided. These can cause a weakened immune system creating various new diseases and the worst type of scabies.
Options: Benadryl over-the-counter or other antihistamine. Prescription: Doxepin
(oral or topical).
Information on sulfur ointment should you choose to use it:
All topical treatments to the skin should be tested on a small area first for allergic reaction including sulfur ointment.
As regards the sulfur treatment, one study done in an orphanage in Mexico used 10% sulfur in cold cream (which it appears they mixed together themselves) was applied once a day at night for three days straight to every child (a total 58 were treated this way). The cold cream would spread in a thinner layer than would the the normal petrolatum-based sulfur ointments. Three days were let pass then one additional night of ointment was applied. Nothing was applied during the day. Clothing and bedding were changed on the third day. So in total the treatment was carried out only four times at once a day. All those treated with this cold cream-sulfur mixture were evaluated on the tenth day after initial treatment began and considered free of scabies by the researchers in the study. However, if you are an adult with scabies that was misdiagnosed for several months, it is highly suggested that 10% sulfur ointment be applied every day for a week if you find it comfortable. If not, then 3 days on, 3 days off, 3 days on, 3 days off, 3 days on. This will ensure a kill. Reapply sulfur each day after bathing.
For persons exposed to scabies and yet do not have symptoms and are undiagnosed, it is safe to use a 3-day sulfur ointment treatment and then wait for the appearance of symptoms. A three day sulfur treatment is what most manuals recommend.
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 Associationda:Fnat
Search Term: "Scabies"
Categories: Parasitology | Sexually-transmitted diseases | Infectious skin diseases
