Pediatric Infectious Diseases: Open Access

Introduction

The mite Sarcoptes scabiei causes scabies, which is a parasitic skin infection. Scabies outbreaks are widespread in residential and nursing care homes in affluent countries, causing severe morbidity and misery. Diagnosis is difficult and often delayed, and outbreak control is costly. Over 200 million people are impacted globally, with a particularly high prevalence in resource-poor tropical areas. The Scabies Mite is a parasitic mite that causes scabies the pregnant female scabies mite burrows into the human epidermis and lays 2-3 eggs every day, beginning the life cycle of the scabies mite. After 48-72 hours, the larvae emerge and dig new tunnels. In 10-14 days, the larvae reach adulthood, mate, and the cycle begins again. Direct skin-to-skin contact is the mode of transmission. Human scabies mites may survive outside of the human body for 24-36 hours in normal room circumstances (21°C and 40%-80% relative humidity); they are still capable of infesting throughout this time. Indirect transmission (through clothing, bedding, and other fomites) has been hypothesised, but it has proven difficult to demonstrate in practise. Mellanby's early trials demonstrated that indirect transmission is unlikely to play a substantial role, with the exception of crusted scabies, where the host is extensively afflicted. In these studies, volunteers slept in bedding that had been used by scabies patients less than 24 hours previously. Only 1.3% of volunteers (4 out of 300) became affected when the parasite rates were 20-50. When the parasite rates were 200 or above, 30% of the volunteers (3 out of 10) became infected.

Infestation with the scabies mite causes a rash of papules, nodules, and vesicles that are extremely irritating. The majority of this is due to host hypersensitivity, however the direct action of mite invasion also plays a role. As a result, the incubation period before symptoms appear in cases of initial infestation is 3-6 weeks, but it can be as short as 1-2 days in situations of reinfestation. Sensitisation to mite antigens has been observed up to one month after original infection, and signs and symptoms of hypersensitivity can take up to six weeks to disappear. Symptoms that last longer than this should be investigated again. Burrows are generated as mature female mites consume the epidermis; even one burrow is pathognomonic; however, they are typically unrecognisable due to scratching, crusting, or secondary illness, and only appear in a small percentage of cases. In women, areas between the fingers, wrists, axillae, groynes, buttocks, genitals, and breasts are common places to find symptoms of infestation. The palms, soles, and head (facial, neck, and scalp) are more typically engaged in infants and young children. Mites appear to avoid regions where pilosebaceous follicles are abundant. Despite the existence of effective therapies, those who live in areas where the disease is endemic are vulnerable to reinfestation. Even when household contacts are addressed, this can happen quickly. Severe eczematous skin changes develop with chronic infestation, and so-called "scabies nodules" can be seen, particularly on the male genitalia and breasts. Scabies infection is characterised by intense, persistent itching, which can be extremely debilitating and stigmatising. Pruritus is commonly described as being most intense at night, and this is linked to sleep disruption and a decreased capacity to concentrate. Hyperinfestation can develop to crusted scabies in a rare number of cases, where the host is colonised by millions of mites. This is in contrast to traditional scabies, which causes the host to have 10 mites-15 mites on average. Crusted scabies is more common, but not always, in people who are immunosuppressed, such as those who have severe HIV infection or cancer. Pathogen variables such as the scabies mite's pathogenicity aren't thought to play a function. Clinically crusted scabies appears as a hyperkeratotic dermatosis on the palms and soles of the feet, often with deep skin fissures. Secondary bacterial infection is common and associated with a significant mortality rate. Generalized lymphadenopathy, peripheral blood eosinophilia, and raised serum IgE levels are frequently observed, and secondary bacterial infection is common and associated with a significant mortality rate. There is a crusted scabies clinical grading scale that can be used to assess disease severity and guide treatment. The score is determined by a clinical evaluation of four domains: illness distribution and extent (body surface area), severity/depth of skin crusting, number of previous episodes (hospitalizations) for crusted scabies, and degree of skin cracking and pyoderma. Each domain is given a score ranging from 1 (mild) to 3 (severe), which is then added together to provide an overall score: Grade 1 (scoring 4-6), grade 2 (scoring 7-9), and grade 3 (scoring 10-12).