Scabies: What's That Itch!

The clinical presentation of scabies varies extensively, with the body’s immune response to the mite being the key determinant in presentation. As a result, immediate and delayed (Type 1 & 4) hypersensitivity reactions are implicated in the cutaneous reaction.
On primary exposure, it may take 2-3 weeks from infestation to the onset of symptoms, however after initial exposure to the mite; symptoms may appear within 1-4 days of re-infestation .

Itch:

The itch is the predominant indicator of a scabies infestation with a generalized pruritis which is often exacerbated throughout the night and after hot showers, coinciding with sensitization to the mite. This itch is caused by a combination of immunological events and non-specific factors as hypersensitivity to the mite and by-products increases. Often, secondary dermatitis spreads to the affected areas with scratching, immunological reactions, and symptomatic pharmacological treatment (such as topical corticosteroids) applied without reference to the causative agent.

Burrows:

An infested individual may present with papules, vesicles and / or linear burrows containing mites and eggs commonly in the inter-web space of fingers and toes, along with lesions on the wrists, elbows, axillary folds, thighs, abdomen, buttocks, areolas of female breasts and male genitals . These intraepidermal tracks are made by the egg-laying female as she burrows through the dermis and are usually <10mm in length. The opening to the burrow often presents with mild scaling and erythema which is sometimes masked by scratching or good hygiene.

Other Presentations:

Whilst uncommon, scabies may also cause urticarial or blistering rashes in very hypersensitive and immunocompromised patients . For comprehensive list of clinical presentations of scabies see attached Appendix 1 - Clinical Presentation of Scabies (Wines & Shumack, 2000)

Are there any complications?

Complications that often present in Aboriginal communities include infection with Group A Streptococcus (GAS) Streptococcus pyogenes bacteria and Staphylococcus aureus (in more southerly parts of Australia). This leads to pyoderma (impetigo or skin sores) which has been noted in 50-70% of all scabetic individuals. Treatment of GAS infections may simultaneously occur with treatment of scabies, with the recommended treatment regimen still a single dose of Benzathine penicillin.

Group A Streptococcus (as above) is also the main cause of ‘post-streptococcal glomerulonephritis’ (ASPGN) and ‘acute rheumatic fever’ (AFR) which often leads to chronic renal disease in patients repeatedly exposed to the causative agents (exacerbated by scabetic infestations) .