After the mite burrows into the skin, it takes time to develop signs and symptoms. If patient had scabies before, the itching usually begins within 1 to 4 days. When a person has not had scabies, the body needs time to develop a reaction to the mite. It can take 2 to 6 weeks to develop symptoms.

Burrows are a pathognomonic sign and represent the intraepidermal tunnel created by the moving female mite. They appear as serpiginous, grayish, threadlike elevations in the superficial epidermis, ranging from 2-10 mm long. High-yield locations for burrows include the following:

• Webbed spaces of the fingers
• Flexor surfaces of the wrists
• Elbows
• Axillae
• Belt line
• Feet
• Scrotum (men)
• Areolae (women)

In geriatric patients, scabies demonstrates a propensity for the back, often appearing as excoriations. In infants and small children, burrows are commonly located on the palms and soles.

One- to 3-mm erythematous papules and vesicles are seen in typical distributions in adults. The vesicles are discrete lesions filled with clear fluid, although the fluid may appear cloudy if the vesicle is more than a few days old.

Nodular scabies

Nodules occur in 7-10% of patients with scabies, particularly young children. In neonates unable to scratch, pinkish brown nodules ranging in size from 2-20 mm in diameter may develop.

Crusted scabies

Also called Norwegian scabies, crusted scabies is a severe form of scabies. In crusted scabies, lesions are often hyperkeratotic and crusted and cover large areas. Marked scaling is common, and pruritus may be minimal or absent. Nail dystrophy and scalp lesions may be prominent. The hands and arms are the usual locations for lesions, but all sites are vulnerable.

Crusted scabies develops in people who have a weak immune system due to a medical condition, the elderly, and people who are living in institutions. Crusted scabies develops when the person’s body cannot develop any resistance to the mites. Without resistance, the mites quickly multiply.

Secondary lesions

These lesions result from scratching, secondary infection, and/or the host’s immune response against the scabies mites and their products. Characteristic findings include the following:

• Excoriations
• Widespread eczematous dermatitis
• Honey-colored crusting
• Postinflammatory hyperpigmentation
• Erythroderma
• Prurigo nodules
• Frank pyoderma

Signs and symptoms of scabies include:

• Itching, mainly at night: Itching is the most common symptom. The itch can be so intense that it keeps a person awake at night.
• Rash: Many people get the scabies rash. This rash causes little bumps that often form a line. The bumps can look like hives, tiny bites, knots under the skin, or pimples. Some people develop scaly patches that look like eczema.
• Sores: Scratching the itchy rash can cause sores. An infection can develop in the sores.
• Thick crusts on the skin: Crusts form when a person develops a severe type of scabies called crusted scabies. Another name for crusted scabies is Norwegian scabies. With so many mites burrowing in the skin, the rash and itch become severe. You’ll find more information about crusted scabies below.

Scabies is caused by the host-specific mite Sarcoptes scabiei hominis, an obligate human parasite. Adult mites are 0.3–0.4 mm long. It is a member of the family Sarcoptidae, which belongs to the order Astigmata, in the subclass Acari, class Arachnida.

Domestic and wild animals worldwide are susceptible to infestation with Sarcoptes scabiei, and the resultant disease is referred to as sarcoptic mange. Mange due to Sarcoptes scabiei varieties other than hominis has been reported in dogs, pigs, horses, camels, black bears, monkeys, dingoes, and wild foxes, among other animals.

It has limited cross-infectivity between different host species. Genotyping studies have revealed that the Sarcoptes mites segregate into separate host-associated populations, thus limiting the transmission across host species.

In the rare instance of transmission of nonhuman scabies from animals to humans, the clinical manifestations differ in many respects. The incubation period is shorter, the symptoms are transient, the infestation is self-limiting, no burrows are formed, and the distribution is atypical compared with infestation caused by Sarcoptes scabiei hominis.

Scabies is treated with 10% sulphur in yellow soft paraffin is traditional, effective, and safe. There are several more treatment options, including 25% benzyl benzoate emulsion, 0·5% malathion cream, 1% gamma benzene hexachloride lotion, and 1% permethrin. In children benzyl benzoate should be diluted to 10% and used with care as toxicity results from absorption. In infants over two months old permethrin or 2·5% sulphur ointment can be used. Gamma benzene hexachloride should not be given to children under 10 years or pregnant women in the first trimester. Important points are:

(1) The patient should wash properly: a hot bath was formerly advocated but it is now known that this may increase absorption through the skin.

(2) The lotion should be applied from the neck down, concentrating on affected areas and making sure that the axillae, wrists, ankles, and pubic areas are included. If there is any doubt about the thoroughness of application the process should be repeated in a few days.

(3) All contacts and members of the patient’s household should be treated at the same time.

(4) Residual papules may persist for many weeks. Topical steroids can be used to relieve the itching.

(5) Secondary infection as a result of scratching may need to be treated.

Consultation with a doctor is required for severe, refractory scabies or for disseminated scabies in patients who are immunocompromised.

• ABC Of Dermatology
• Clinical Dermatology
• Roxburgh’s common skin diseases
• Andrew’s Diseases of the skin