Scabies infestation | causes, symptoms and management

Scabies infestation

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Scabies infestation

Scabies is caused by the mite, Sarcoptes scabiei var. hominis, which burrows into the upper layer of the skin – the stratum corneum. The female lays eggs in the tracks of the burrows. The eggs and mite proteins produce an allergic reaction and this reaction, is responsible for the characteristic itching and rash. 

Scabies is normally acquired from skin-to-skin contact with another individual who has scabies. It is frequently acquired among children and can also be sexually transmitted.  

  It is sometimes transmitted from care providers or beddings. 

The incubation period for those without previous exposure to scabies is 2 to 6 weeks. Individuals who have been previously infested with scabies develop symptoms within 1 to 5 days of re-exposure. 

scabies infestation

Transmission

Scabies is usually passed from one person to another through close skin-to-skin contact. It takes about three to four weeks for signs or symptoms of a first scabies infection to develop after infection. People who have been infected with scabies previously may develop symptoms within a few days after another exposure.

The most common mode of transmission between young adults is sexual contact, although the infection can be passed without sexual activity.

The mites that cause scabies only survive for 24 to 36 hours once they are no longer in contact with the skin; however, they may survive longer in colder conditions. As a result, scabies tends to be more common in the winter than in the summer.

Although uncommon, it is possible for a person to get scabies by wearing or handling heavily infected clothing, or sleeping in an unchanged bed recently occupied by an infected individual. 

Animals can also become infected with scabies (a condition called mange), although animals are affected by a different type of mite. This mite can tunnel under the skin and cause itching in humans, but it does not reproduce and does not require treatment because symptoms resolve when the mite dies (usually within a few days). People who suspect that their pet has mange should have the animal evaluated by a veterinarian. Getting the proper treatment for the pet will prevent new mites from infecting the human. 

Symptoms

The primary symptom of scabies is widespread itching, which may be severe and is usually worse at night. Scabies also causes visible lesions (reddish bumps or blisters) on the skin; however, these are often very small and can be difficult to see. These bumps or blisters if you scratch frequently.

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A person may also notice a “burrow” or tunnel sign, a thin, visible line in the skin that extends from 2 to 15 millimeters (0.08 to 0.6 inches). Although not everyone with scabies has visible burrows, the presence of such marks strongly suggests scabies. 

The following parts of the body are more likely than others to be affected by scabies

●The fingers and webbing between the fingers

●The skin folds around the wrists, elbows, and knees

●The armpits

●The area surrounding the nipples (particularly in women)

●The waist

●The male genitalia (penis and scrotum)

●The lower buttocks and upper thighs

●The sides and bottoms of the feet

The back is usually not affected, nor is the head. 

Scabies lesions can become more irritated and inflamed with scratching, which may lead to infection.  

Physical Examination

• Presence of small erythematous papulovesicular lesions predominantly over anterior axillary folds, nipple area, periumbilical skin, elbows, volar surface of the wrists, interdigital web spaces, belt line,  thighs, buttocks, penis, scrotum, ankles and typically except for  the head, face, and neck in adults. 

• Infants and young children may develop similar lesions diffusely, but unlike adults, lesions are common on the face, scalp, neck, palms and soles.

• Scabies burrows are most easily found on the hands, especially finger webs and on the wrists; other sites of predilection are the feet, axillae, umbilicus, male genitalia and breast areolas in women. 

• In infants, burrows are common on the palms and soles, and sides of the feet. They can also be found on the heads of infants particularly post auricular folds. 

• The typical burrow is a serpiginous tract that measures 1cm in length. It may be obscured by excoriation marks or by vesiculation in infants. 

• The reddish-brown nodules of scabies are seen in axillary and inguinal regions, wrists and male genitalia and these may persist for several months.  These nodules are caused by delayed hypersensitivity reaction to the female mite, its eggs and faeces (scybala) deposited in the epidermis, rather than by an active infection. 

• Some of the lesions may be altered by excoriations, eczematisation and secondary bacterial infection.

Scabies management

Getting rid of mites 

The most commonly used treatment for scabies is a topical (cream) medication such permethrin 5% cream (Elimite). Permethrin is applied to all areas of the skin from the neck to the feet and is washed off in a shower or bath after 8 to 14 hours. This should be repeated after one week. An oral medication (ivermectin) is available but cannot be used in pregnant or lactating women or small children. Permethrin is safer than oral ivermectin or other creams and is usually the preferred treatment.

Other drugs

• Benzyl Benzoate 10 – 25% lotion

• Precipitated sulphur6 to 10% Petroleum base

• Crotamiton 10%Ointment

• Lindane 1% Lotion/cream (Gamma benzene hexachloride)

In order for any treatment to be successful, it must be used correctly. Creams or lotions must be applied carefully to cover all skin from the neck down, and rinsed off according to instructions. 

Treat Household Members

In some cases, household members (family, roommates or housemates) and close contacts of a person with symptoms need treatment for scabies, even if there are no symptoms, to avoid a repeating cycle of infection. 

Although scabies is less frequently spread by touching the clothing or bedsheets of an infected person, it is still a good idea to wash or isolate any clothing, bedding, towels, pajamas, or underwear that the person has touched within three days before treatment. It is not usually necessary to wash other items. Reasonable options for eliminating mites from these items include placing them in plastic bags for at least five days, machine washing and then ironing or drying in an electric dryer on the hot setting, or dry cleaning.

Crusted scabies is more likely to be spread through shared clothing or objects than typical scabies.

Relieving itching 

Antihistamines may help to control itching. Non-sedating antihistamines, such as (loratadine/Claritin)  (cetirizine/Zyrtec), fexofenadine/Allegra are generally recommended during the day while sedating antihistamines (eg, diphenhydramine/Benadryl) can help to control itching and improve sleep at night. Avoiding long, hot showers or baths is recommended as they tend to strip the skin of natural oils.  Applying moisturizers after showering lessens dry skin and helps lessen itching. 

Itching may persist for several weeks after mites are eliminated; a steroid cream or a course of oral glucocorticoids may be recommended if itching is severe. If symptoms persist or become worse, the person may have become re-infected.

Treating secondary bacterial infection 

The skin usually heals without difficulty after mites are treated. Keeping the skin clean and dry and avoiding scratching can help to prevent infection. However, if signs of a skin infection develop (eg, redness, swelling, pus, pain), oral antibiotics are generally recommended.

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