Scabies | Medical Science Optional Notes for UPSC PDF Download

Scabies

• Transmission method
• Clinical signs and symptoms
• Crusted (Norwegian) scabies
• Nodular scabies
• Potential complications
• Treatment options
• Preventive measures
• The female scabies mite, one of the five types that infect humans, is large enough (0.3-0.4 mm) to be visible without magnification, while the male is approximately half this size. The mite, with four pairs of legs, moves at a speed of 2.5 cm per minute and lacks the ability to fly or jump.
• Despite completing its life cycle on the host, the mite can survive on bedding, clothing, or other surfaces at room temperature for 2-3 days, maintaining its ability to infest and burrow.

Scabies-Modes of Transmission

• Scabies primarily spreads through direct skin-to-skin contact.
• The mite's penetration is limited to the superficial layer of the skin, specifically the stratum corneum.
• Individuals carrying the mites can transmit scabies even if they show no symptoms.
• There could be a significant time gap (up to 10 weeks) between the initial infection, during which the person becomes contagious, and the appearance of clinical signs.
• Although scabies is less commonly transmitted indirectly via items like infested bedding or clothing, the risk increases with a higher number of parasites on a person, as seen in crusted scabies.

Scabies-Life cycle

• Mature female mites, carrying eggs, create shallow burrows in the outer layer of the skin known as the stratum corneum, laying three or fewer eggs each day.
• Larvae with six legs undergo development, transforming into eight-legged nymphs and eventually reaching adulthood.
• About eight days later, matured gravid adult females emerge onto the skin's surface before (re)invading the skin of the same individual or another host.
• Transfer of newly fertilized female mites occurs primarily through direct skin-to-skin contact between individuals and is facilitated by factors like crowded conditions, poor hygiene, and engaging in sexual activity with multiple partners.

Scabies-Pathophysiology

• The fertilized female mite burrows into the superficial layer of the skin (stratum corneum), creating tunnels where she lays eggs and deposits feces known as scybala.
• Two months later, the female parasite perishes at the burrowing site.
• After a three-week period, the larvae develop into adult mites, perpetuating the infestation cycle.
• The antigens present in the excretions and decomposing bodies of the mites trigger an immunological response, characterized by a severe itching sensation and skin abrasions in the form of a type IV hypersensitivity reaction.

Circle of Hebra

The characteristic indication of Scabies is the presence of burrows, which are intraepidermal tunnels formed by the female mite as it moves.
These burrows manifest as serpiginous, grayish, threadlike elevations in the top layer of the skin, measuring between 2-10 mm in length.
Typically, affected areas include the finger webs, wrists, axillae, areola, umbilicus, lower abdomen, genitalia, and buttocks.
Infants, however, tend to exhibit involvement on the face, scalp, neck, palms, and soles. These designated areas collectively create an imaginary circle referred to as the Circle of Hebra.

Scabies-classical

• In the case of a typical scabies infection, there are usually 10-15 mites present on the host, with a range of 3-50.
• A delayed type IV hypersensitivity reaction is triggered by the mites, eggs, and scybala (feces).
• The 4-week asymptomatic latent period in primary infestations is likely due to the time required for the development of immunity.
• Upon reinfestation, individuals sensitized to the mites may experience a rapid reaction occurring within hours.
• The distinctive skin eruption and the accompanying intense itching are characteristic features of classic scabies.

Scabies-complication

• Norwegian or Crusted scabies
• Subsequent infections
• Secondary lesions include pustules, eczematized lesions, and nodules (nodular scabies)

Scabies-crusted/norwegian

• This is a unique and highly transmissible variation of the disease.
• In this form, the host individual, often immunocompromised, elderly, or physically or mentally disabled, becomes infested with hundreds to millions of mites.
• Impairments in motor nerves lead to an inability to scratch in response to itching, preventing the effective removal of mites and the destruction of burrows.
• Crusted scabies can be mistaken for severe dermatitis or psoriasis because it presents with widespread lesions covered in thick, hyperkeratotic scales over the elbows, knees, palms, and soles.
• When suspected dermatitis or presumed psoriasis does not respond to standard treatments, the possibility of crusted scabies should be considered in the diagnosis.
• Patients with crusted scabies exhibit significantly elevated levels of serum immunoglobulin E (IgE) and IgG.
• In classic scabies, cell-mediated immunity shows a predominance of T4 cells in the dermal infiltrate, while a study suggests that crusted scabies may have a predominance of T8 cells.

Scabies-nodular scabies

• Nodular scabies is a recognized clinical variation of scabies, marked by persistent pruritic nodules even after specific scabies treatment.
• Approximately 7% of scabies patients experience this variant.
• The nodules indicate a hypersensitivity reaction to residual mite parts or antigens on the body.
• It predominantly occurs in the genitalia and scrotum, with these areas being more susceptible to induration and nodule formation due to the absence of a fatty layer beneath the skin.
• The standard treatment approach involves scabicidal treatment followed by addressing the nodules symptomatically.
• Despite attempts to treat nodular lesions with topical or intralesional steroids, the response is often unsatisfactory, and relapses are frequent.

Scabies-diagnosis

• The clinical diagnosis of scabies is often possible in individuals presenting with an itchy rash and identifiable linear burrows.
• The confirmation of the diagnosis involves the microscopic identification of mites, larvae, eggs, or scybala (feces) in skin scrapings.
• Clinically asymptomatic infections can be identified by amplifying Sarcoptes DNA in epidermal scales using a polymerase chain reaction (PCR) assay.
• Additionally, some patients with scabies may show increased IgE titers and eosinophilia.

Locating Mite Burrows

• Burrow Tracing Test: To locate a burrow, rub a washable felt-tip marker over the suspected area and wipe away the ink with alcohol. If a burrow is present, the ink will penetrate the stratum corneum, outlining the site. This method is particularly effective for children and individuals with few burrows.
• Tetracycline Application: An alternative to the burrow tracing test involves applying topical tetracycline solution. After applying and removing excess tetracycline with alcohol, examine the burrow under a Wood light. The remaining tetracycline within the burrow will emit a greenish fluorescence. This approach is favored because tetracycline is a colorless solution, allowing for the examination of large skin areas.

Scabies-management

1. Topical Scabicides

• Permethrin 5% (Preferred treatment)
• Crotamiton 10%
• Benzyl benzoate 25%

Topical agents are applied from the neck down, typically before bedtime, and left on for approximately eight to 14 hours, followed by washing off in the morning.
It is crucial to cover the entire skin surface, not just affected areas, as any untreated patch can serve as a refuge for mites.
While one application is generally effective since permethrin eliminates eggs, larvae, and adult mites, some practitioners recommend a second application as a precaution three to seven days later.

2. Oral Treatment

• Ivermectin (Single oral dose)
• Pruritus can be partially relieved with an oral antihistamine like hydroxyzine hydrochloride, diphenhydramine hydrochloride, or cyproheptadine hydrochloride.

3. Antibiotics may be necessary to address secondary infections.

Special Considerations for Crusted Scabies:

• Due to a substantial mite burden, repeated applications of topical agents may be needed.
• Supplemental treatment with oral ivermectin may be required.
• Patients or caregivers dealing with crusted scabies should be instructed to remove excess scales, enhancing the penetration of topical scabicidal agents and reducing the infestation burden. This can be achieved through warm water soaks followed by the application of a keratolytic agent, such as 5% salicylic acid in petrolatum or Lac-Hydrin cream.

Scabies-Prevention

• People afflicted with scabies should refrain from direct skin-to-skin contact with others. Individuals with regular scabies can resume normal activities, including school or work, 24 hours after the initial treatment.
• Mass-treatment initiatives utilizing topical permethrin or oral ivermectin have proven successful in diminishing the prevalence of scabies in various populations. There is currently no vaccine for scabies.
• It is advisable to treat all close contacts simultaneously, irrespective of whether they display symptoms (asymptomatic), to minimize the chances of recurrence.

Cleansing

• Items such as bedding, clothing, and towels utilized by individuals with scabies or their close contacts within the 3 days preceding treatment should undergo decontamination. This can be achieved through washing in hot water and drying in a hot dryer, dry-cleaning, or sealing in a plastic bag for at least 72 hours. Scabies mites typically cannot survive beyond 2-3 days when away from human skin.
• Given that mites have a limited lifespan without a host, there is minimal risk of transmission from other objects in the environment, except in the instance of crusted scabies. For rooms used by individuals with crusted scabies, thorough cleaning is essential.
• The use of insecticide sprays and fumigants is not advisable.

Scabies-Repeats

Q1: Scabies (2000) 

Q2: Describe the clinical manifestations and treatment of scabies (2004). 

Q3: Write briefly on: Scabies, Ichthyoids (2007) 

Q4: Enumerate the various anti-scabetic drugs and the precautions to be taken to prevent the spread of scabies in healthy contacts. (2011)

Q5: How is scabies transmitted? Mention the complications of scabies. Discuss the clinical features of crusted scabies and its management. (2012) 

Q6: A child in 2nd class of a public school had an itchy skin lesion. Within next 1 month, this lesion spread to 10 other students in the same class. Examination revealed multiple excoriated papulovesicular itchy lesions in finger-webs and flexural aspects of wrists. What is the most likely diagnosis? Outline the prophylactic measures to be undertaken to prevent the spread to other children. Outline the management of individual children in this class. (2013) 

Q7: A 5-year-old male child presents with generalized itchy excoriated papules over trunk, limbs and genitals of two weeks duration. There were few papulovesicular on palms and soles. His other sibling had similar skin problem. (2017)
(i) What is the likely diagnosis?
(ii) What is the cause for his condition?
(iii) Enumerate the various topical preparations available to treat this condition. Describe the method of application of one preparation. 

Q8: How does Classical scabies differ from Crusted" scabies infection? How do you treat "Crusted" scabies infection in an institution? (2018)