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Scabies - The Itch that drives you mad

‘A small grey-coated gnat
Not half as big as a round little worm,
Prick’d from the lazy finger of a maid’

Romeo and Juliet, I, IV

William Shakespeare, an acute observer that he is, wrote about scabies and it’s causative agent in his play, Romeo and Juilet.

Scabies is an age old disease, it had been found in Indian manuscripts and even in the Bible. It was one of the 8 contagious diseases known to man in the middle ages.

 
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Sarcoptes scabiei var hominis is a microscopic mite, that transmits the disease. Though both male and female parasites are transferred between humans by intimate contact or though fomites, the females are known to act as the vector. The number of mites, or the duration of contact determine the severity of the disease. These mites are host specific to humans and complete their life cycle in the human being.

The female mites excavate small tunnels, called burrows in areas in the body where the skin are thin and moist, example, web spaces and the penile skin. They appear as grey thread like ridges that are 2-3mm long with a vesicle surrounded by an erythema around it. Though, burrows are the most important clinical lesion, they are present in only less than 25% of the patients.

 
Image Source  https://infograph.venngage.com/p/101167/scabies

Image Source https://infograph.venngage.com/p/101167/scabies

 

The burrow ink test, is rather a simple technique to demonstrate burrows in a patient. Use an ink or ball pen to draw on the suspected burrow and wipe it off immediately with a piece of cloth. If the burrow is present, the ink penetrates into the ridge and outlines the burrow. Another test to demonstrate the burrow is the Tetracycline Fluorescence test. Apply tetracycline generously on the suspected burrow and wipe it off after 10 minutes with an alcohol swab. Under a wood lamp examination, the burrows emit a green fluorescence.

The fundamental symptom of scabies is itching.  It is due to Type 4 hypersensitivity to the mites, thus will not be seen in immunocompromised individuals. It appears only after 4-6 weeks after the initial infection. After sensitisation, itching re-appears in less than 24 hours. It worsens at night due to increased cortisol levels and the warmth.

The chronic scratching leads to formation of linear, hyperpigmentory macules. Other form of lesions, scabies can produce include, papules, nodules, excoriations and weals. Because the lesions that present are so diverse, the distribution of these lesions is what helps us in the diagnosis of scabies.  Typically, it presents in the back of elbows, axillary pads, upper medial thighs and the buttocks.

The variants of the disease depend on the number of mites as we had discussed before. The Norwegian or crusted scabies develops in immunocompromised individual. The lesions are hyperkeratotic, crusted and present mostly in the extremities. Thousands of mites can be demonstrated in the burrows in their skin. The scabies incognito variant occurs in individuals who overuse or inappropriately use steroids. They are clinically clean and is very difficult to diagnose.

The diagnosis of scabies depends on a special criteria that divide the presentations into two.

  • The major criteria include, typical burrow associated with an itchy rash or positive skin scrapings showing mite eggs or faeces. Presence of one these presentations, confirms the disease.
  • The minor criteria include, typical rash which itches more at night or sudden onset of an itchy rash with characteristic distribution or contact with a scabetic patient. Presence of two of these minor criteria confirms the disease.

The treatment for scabies include, two important topical creams, Lindane 1%, which is an antiscabetic that works by destroying the CNS of the mite by inhibiting it’s inositol levels, and Permethrin 5%, which inhibits the sodium channels of the mites producing delayed polarisation causing paralysis and death of the mites. Overuse of the drugs should be avoided, as the itch remains even after the mites have been destroyed and patients shouldn’t regard this as a faulty treatment. Treatment should also be given to everyone that has been in contact with the scabetic patient.

Scabies, had incapicated thousands of men in the Napoleonic wars and is still seen in thousands of school going children in developing countries. But with the proper diagnosis and treatment, we can evade the disease once and for all.

Author: Madhumitha Ashokkumar