|Sarcoptes scabiei var canis|
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Synonyms and Keywords: Norwegian scabies
Scabies is a skin infection caused by Sarcoptes scabiei and the mite is transmitted mostly by direct skin-to-skin contact. Scabies can be classified into 2 major types depending on the resultant skin lesions into typical scabies infestation and crusted (or Norwegian scabies). Crusted scabies is usually associated with an immunocompromised status. The characteristic symptoms of scabies is that of intense itching, which is worse at night and erythema of the skin. Examination reveals skin lesions of various sizes in certain areas of predilection, which include the webs of fingers and toes and wrists. With appropriate antimicrobial therapy, scabies has an excellent prognosis. Treatment must be initiated for patients and individuals with close contact with the patient, even if they are asymptomatic.
- In 1687, Giovan Cosimo Bonomo, an Italian physician, described the relationship between mites infestation and the resultant skin lesions.
- Cases of scabies have been described in literature as early as 1853.
- In the early days, the use of sulfur-containing products, whether in the form of baths, vapors or ointments was believed to be the treatment of choice for scabies.
|Type of Scabies||Number of mites||Age Group||Associated Conditions||Characteristic Lesion||Areas of Predilection||Itching||Complications|
|Typical Infestation||Usually less than 100||Mostly children and adolescents||Patients are usually healthy||Papules, which can progress to vesicles and bullae||Intense||Secondary bacterial infection of the skin and soft tissues|
|Crusted Scabies (Scabies Crustosa, Norwegian Scabies, Keratotic Scabies)||Typically thousands||Mostly elderly||Exfoliating scales and crusts, which can become warty||Minimal or absent||Sepsis|
Mode of Transmission
- Sexual transmission, especially among men who have sex with men
- Fomites and shared clothing are a rare source of transmission of scabies; however, cases are more likely to occur with crusted scabies, due to the higher burden of mites
- Cross infectivity from other mammals: this is a rare mode of transmission, however, cases of cross infectivity of humans from companion dogs were reported.
Mite Lifecycle and Pathogenesis
- Away from the host, mites are viable for a period of 24-36 hours at a temperature of 21 C.
- Once the female mite comes in contact with human skin, it digs a small tunnel (i.e.: burrow) at a rate of 0.5-5.0 mm per day through the layers of the epidermis.
- A male mite searches for an unfertilized female, which lays 2-4 eggs per day and larvae hatches 2-4 days later. Larvae develop into adult mites 10-14 days later.
- The clinical presentation of intense itching, redness of the skin and the multiple skin lesions are due to a delayed type hypersensitivity reaction by the host immune system.
- Down Syndrome
- Underlying immunosuppression, such as patients with:
Differentiating Scabies from Other Diseases
|Disease||Skin Lesions||Areas of Predilection||Crusting||Itching||Age Group|
|Atopic dermatitis||—||✔||Usually children|
|Eczema||Depends on the type of eczema||✔||✔||No specific age group|
|Arthropod bites||—||—||✔||No specific age group|
|Tinea corporis||—||✔||No specific age group|
||Mostly sun-exposed areas||—||—||Usually middle-aged adults|
||Flexural areas:||✔||✔||Usually older adults|
|Langerhans cell histiocytosis||
||✔||—||Mostly children aged 1-3, but can occur at any age|
|Seborrheic dermatitis||Sebum-rich areas:||✔||✔||Can occur at any age, but most commonly in infancy and adults 30 to 60 years of age|
|Psoriasis||✔||✔||Bimodal age distribution: 20-30 and 50-60 years of age|
Epidemiology and Demographics
- The prevalence of scabies worldwide varies greatly; it ranges from 200 to 71,400 per 100,00 cases.
- All regions had a prevalence of more than 10,000 per 100,000 cases, except in Europe and the Middle East.
- It is estimated that there are 300 million cases of scabies worldwide.
- The Pacific and Latin America have the highest prevalence of scabies worldwide, while it is the lowest in Europe and the Middle East.
- Living in high-risk areas, such as Sub-Saharan Africa and indigenous communities in Australia and New Zealand
- Living in crowded areas
- Homeless or displaced children
- Poor hygiene: the role of poor hygiene in the development of scabies is uncertain, as mites burrowed under the skin remain alive even after daily hot baths and are usually resistant to water and soap
- Immunocompromised individuals, such as the elderly, malnourished and those with HIV, DM are at risk of developing Norwegian Scabies, which is the severe form
There are no screening recommendations for scabies.
Natural History, Complications and Prognosis
If left untreated, scabies infection can lead to secondary bacterial infection of the skin and underlying soft tissue. These can have severe complications, such as sepsis, post-streptococcal glomerulonephritis and rheumatic heart disease, especially in an immunocompromised host.
- Secondary bacterial infection of the skin and soft tissue, caused mainly by S. aureus and S. pyogenes, which include:
- Secondary bacterial infection of the skin and soft tissue can progress to life-threatening complications such as:
History and Symptoms
- In suspected cases of scabies, make sure to enquire about the following:
- History of exposure to a known case of scabies or coming in close contact with patients with a similar complaint (mainly itching)
- In the case of children, ask about daycare attendance
- History of hospitalization
- Recent travel history
- The main symptoms in patients with scabies include:
- Burrows: are the tunnels which the female mite penetrates into the skin. Initially, they are not clinically visible and can only be seen several days later, when the host immune system forms a local reaction around the tunnel. Burrows are characterized by short, wavy lines.
- Papules: they are usually small and erythematous. The distribution of the papules is variable; they can be sparse or very close to each other. Over the course of the infection, papules can transform into vesicles and/or bullae. Characteristic distribution of scabies usually involves the web spaces of fingers and toes, the wrists and areolae of breasts in females and penis in males. The back is usually spared, while face and neck involvement are usually only seen in infants and children.
- Excoriations: skin excoriations are commonly seen in patients with scabies, due to the intense itching associated with the infection.
Scabies (common location in ventral wrist) 
- Serologic testing for Sarcoptes scabiei has a very high sensitivity and specificity.
- Peripheral IgE levels are elevated in patients with Norwegian Scabies.
Other Diagnostic Studies
Medical therapy in patients with scabies consists of antimicrobial therapy, mainly either with topical permethrin or oral ivermectin. Patients may experience worsening pruritus and erythema early during the administration of antimicrobial therapy. However, the parasite is gradually eliminated during the body's natural shedding process. The following summarizes the preferred antimicrobial regimens in the treatment of scabies:
- Antimicrobial therapy
- 1. Adult
- Preferred regimen (1): Permethrin 5% cream applied to all areas of the body from the neck down and washed off after 8–14 hours
- Preferred regimen (2): Ivermectin 200 ug/kg given orally, 4 times daily and repeated in 2 weeks
- Alternative regimen: Lindane (1%) 1 oz of lotion or 30 g of cream applied in a thin layer to all areas of the body from the neck down and thoroughly washed off after 8 hours
- Note: Patients may experience worsening pruritus and erythema early during the administration of antimicrobial therapy
- 2. Infants and young children
- 3. Crusted Scabies
- Preferred regimen: (Topical scabicide 5% topical Benzyl benzoate 5% OR topical Permethrin 5% cream (full-body application to be repeated daily for 7 days then twice weekly until discharge or cure) AND treatment with Ivermectin 200 ug/kg PO on days 1,2,8,9, and 15. Additional Ivermectin treatment on days 22 and 29 might be required for severe cases
- 4.Pregnant or Lactating Women
One of the most important means of preventing scabies is to encourage good hygiene and advocate healthy living conditions away from crowded conditions.
Once a patient has been diagnosed with scabies, it is empirical to begin treatment with the appropriate antimicrobial therapy to eradicate the infection and prevent re-infection. However, the following measures must also be followed:
- Treatment of individuals who come in close contact with the patient, even if they are asymptomatic
- Fomites, such as clothes, towels and bed linens, must be machine washed and dried at a high temperature (60 C)
- Insecticide may be used for items that cannot be washed
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