SCABIES

Defination

Scabies is a common ectoparasitic infection of humans, caused by the mite (arthropod-acarina) Sarcoptes scabiei var homninis

Transmission

Spread of disease occurs through direct contact, prolonged hand holding or sharing of bed. Spread by fomites is uncommon as the mite cannot survive for more than two hours at room temperature. In some cases, it may be sexually transmitted. After an incubation period of a month, symptoms arise as a result of hypersensitivity to mite and its products. Scabies is more commonly seen in poor socioeconomic group. This can be attributed to overcrowding and poor hygiene.

Clinical features

Intense itching that is worse at night or when the patient is warm is the most common presentation of scabies. Usually other members of the family are also affected.
In the early stages, lesions are classically distributed over the finger webs, flexor aspect of the wrist elbow, anterior axillary fold, umbilicus, periumbilical region, genitalia, upper thighs and nipples and areolae in females. But as the disease progresses the patient may complain of generalized itching.
On examination, lesions consist of burrows and papules Burrow is the pathognomonic lesion of scabies. It is a raised, gray-brown tortuous lesion about 5 mm in length seen commonly in the web spaces, sides of fingers, borders of hands, wrists, instep of feet and genitalia. Burrow may be a dot, dotted line, curve or curved line with mite as white dot at the blind end.

Complications

Secondary infection (folliculitis or impetigo) and eczematization may occur.

Diagnosis

Presence of itching which is worse at night, burrows, characteristic distribution pattern of lesions and itching in household members or other contacts points towards diagnosis of scabies. Differentiall diagnosis like atopic dermatitis, papular urticaria, dermatitis herpetiformis and lichen planus should bei ruled out. Senile eczema, neurotic excoriations and HIV associated pruritus must also be excluded with careful history and examination.

Treatment

Topical Treatment

Permethrin 5% cream is most commonly used scabicide. Repeat application after 1 week is avdised as it is not effective against eggs of scabiesi mite. These eggs may hatch in a week’s time from first application and the hatchlings may then be killedi bv repeat permethrin application. Other topical agents used for treatment of scabies include 0.5% malathion, 10% topical crotamiton ointment, 10% sulfur in yellow soft paraffin (2.5% in infants), 6% precipitated suulfur (safe in infants) and topical 1% ivermectin.
Scabicides must be applied throughout the body except head, i.e. neck downwards as scalp and head are not involved except in infants and immunocom promised patients. Hands, web spaces, flexures, anogenital region, feet, under the nails (subungual area serves as a reservoir of infestation) , umbilicus and behind the ears should be covered properly. Since 30 g is the quantity of cream that is required to cover the entire body, patients should be instructed to apply entire 30 g of scabicide cream in order to cover the entire body. All intimates of the affected individual (i.e. family members and contacts) should be treated at about the same time irrespective of whether they are apparently affected or not. Clothes and bedding (bed sheets, pillow covers, quilt) used over past 2 days should be washed in hot water, sun dried and ironed.

Systemic Treatment
Ivernectin is the systemic drug of choice for scabies, given in a single dose of 200 ug/kg (adult dose of 12 mg), two doses separated by an interval of one week. Repeat dosing after 7 days is required as it is not effective against ova. Oral ivermectin is however not more effective than permethrin application. It finds its utility in cases where topical scabicide application is not practical such as in a non-compliant patient, in case of severe eczematization where it can lead to irritation and as a part of treatment for norwegian scabies. It is a relatively safe drug with occasional side effects like fever, dizziness, edema,i postural hypotension, somnolence, tremor or ataxia. It is avoided in children below 5 years, elderly and pregnant patients.
Patient should be counseled that itching and papules will take around 15 days after successful treatment with scabicides to subside as they are caused by hypersensitivity reaction. This can be tackled with oral antihistamines, emollients and application of mild topical corticosteroid like hydrocortisone. Topical or oral antibiotics are indicated in cases with secondary infection. Nodular scabies however may be resistant to conventional therapy and potent topical corticosteroids, topical tacrolimus or intralesional steroids may be required for complete resolution. Oral ivermectin is the treatment of choice for norwegian scabies along with prolonged therapy with several applications of scabicides.