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Parasitic infection caused by mite Sarcoptes scabies var hominis, an arthropod of the Acarina order.
The mite Sarcoptes scabies var hominis, lives its entire approximately 14 day lifecycle in the human epidermis.
Female adult mites lay eggs in the uppermost layer of the skin that hatch in 3 to 4 days before developing into adult mites over one to two weeks.
Skin hypersensitivity results in reactions that occur 4 to 6 weeks later with cutaneous manifestations.
The transmission of mites typically requires at least 15 to 20 minutes of direct skin to skin contact occurs with overcrowding, shared living spaces, shared bed, sexual contact, and caregiving in shelters and long-term facilities.
Transmission between hosts via fomites that include linens and clothing is infrequent in common scabies, it can occur in crested scabies, condition in which thousands to millions of mites are present on skin and shed scale.
Scabies also sometimes known as the seven-year itch, is a contagious human skin infestation by the tiny (0.2–0.45 mm) mite Sarcoptes scabiei, variety hominis.
World prevalence about 300 million cases per year.
In 2021 approximately 622 million cases of scabies occurred globally.
Prevalence of disease is highest in low to middle income tropical countries, and among children in these regions.
In high income, countries, sporadic scabies cases and outbreaks may occur in shelters, nursing facilities, childcare centers, and other institutional settings.
An extremely contagious skin infestation.
May be endemic in impoverished communities.
Often affects children, with varying presentations in different age groups.
Transmitted primarily through person to person contact.
In resource poor settings, especially in tropical regions, it is a major underlying cause of high rates of bacterial skin infection.
Prevalence varies by season, state of war, population movements and crowding.
Causes rash and itching and may also be associated with a superinfection.
Risk of severe outbreaks increased in hospitals and nursing homes as well as among socially disadvantaged and immunocompromised patients.
Associated with an obligate parasite that completes its entire life cycle in humans.
Transmission requires close contact among individuals.
Infection secondary to direct skin-skin contact.
Transmitted through close personal contact with an infected individual or his or her personal items, including clothing, bedding, towels, and gloves.
Symptoms develop within 2-6 weeks after infection.
Fomite transmission via mite attachment to clothing, bedding and towels is not common (Mellanby K).
Live mites can be found in the environs of patients, where they survive for 2-3 days.
Only the female mites can burrow into the skin.
The female burrows tunnels into the skin and lays her eggs which hatch in about 1 week.
About 5-15 female mites live on a host with scabies infection, but hundreds to millions can be present in crusted scabies.
Maturation process lasts about 15 days with larval emergence 2-3 days after the eggs are laid.
Skin eruption a result of infestation and hypersensitivity reaction to the mite.
Incubation period prior to symptoms occur 3-6 weeks for primary infestation, but may be as short as 1-3 days in cases of reinfestation.
Classically lesions are most often present on the interdigital finger webs and flexor surfaces of the wrist.
The pathognomic findings of scabies is a burrow, a curvilinear thread like lesion, ending in an erosion or vesicle where the mite is located.
Common scabies lesions range from pappules and eczematous plaques to chronic scratching manifestations including excoriations, prurigo nodularis and lichenification.
Frequently elbows, axillae, buttocks and genitalia may be involved.
The scalp may be involved in infants and the elderly.
Priritudbassociated with scabies occurs about 4-6weeks after infestation due to the delayed antigen sensation.
With reinfestation, pruritus can present as early as 24 hours after infestation.
Pruritus is often severe and worse at night: infants, older adults, and individuals using topical or systemic anti-inflammatory treatments they have minimal and no pruritus.
Studies in residential care facilities show that more than 50% of residents are asymptomatic.
Neonates with scabies are ineffective scratchers and fussiness, irritability, and restlessness at night, rather than scratching with secondary excoriations are common in neonatal scabies
Chronic hypersensitivity reactions lead to nodular scabies, and pruritic nodules can be seen in axilla, groin and genitalia.
Crusted scabies occurs when mite replication is not controlled by the patients immune system and a hyper infection develops.
Crusted scabies occurs mainly in immunocompromised individuals such as patients with AIDS patients on immunosuppressive treatments.
Crusted scabies are highly infectious lesions and can be responsible for community outbreaks, and secondary bacterial septic lesions with high death rates.
Crusted scabies is a severe form of scabies occurring when immunity fails to controls mite proliferation and results in
Large quantity of mites trigger an inflammatory and hyperkeratotic reaction to the epidermis in crusted scabies.
Typical clinical findings in crusted scabies include erythematous patches that evolve into 3-15 mm thick gray or tan crusts.
Crusted scabies are most prominent over the palms, soles, extensor surfaces, and under the fingernails.
Crusted scabies classically presents without pruritus due to the hosts impaired immune response.
50% of patients with hcrusted scabies have some degree of itch, particularly in those with HIV.
Crusted scabies risk factors include AIDS, T-cell leukemia, lymphoma, systemic steroids, transplantation, diabetes, other immunocompromised states, severe mental or physical disabilities or neurologic disorders.
Associated with generalized itching, which is particularly more intense at night.
May lead to secondary infections with Streptococcus pyogenes or Sytaphylococcus aureus.
Acute post streptococcal glomerularnephritis can occur as a complication of secondary skin scabies infection.
Diagnosis is generally made by looking for burrows, or rash, on a person’s skin.
Diagnostic confirmation can be made with visualization of mites, eggs, or feces on light microscopy, or a high powered imaging device.
A clinical diagnosis can be made, if burrows, typical of lesions affecting genitalia in men, or typical lesions in a typical distribution or present.
A suspected diagnosis can be made if typical lesions and typical distribution are present with one historical feature or atypical lesions or atypical distribution are present with two historical features.
Scraping are made with mineral oil and placed on a slide and visualized with microscopy.
Dermocopy can be used to identify sites of burrows.
Laboratory testing may confirm the presence of eosinophilia.
Diagnosis can be done by removing the mite from the end of its burrow using the tip of a needle or by obtaining a skin scraping to examine under a microscope for mites, eggs, or mite fecal matter.
By scraping burrows from multiple sites, microscopic evidence of mites and ova can confirm the diagnosis, which are easily detected with or without smears or stains such as Tzanck and KOH preparation.
Patients can be infested even if mites, eggs, or fecal matter cannot be found
Fewer then 10-15 mites may be present on an infested person who is otherwise healthy.
Three topical treatments are approved for the treatment of scabies in adults. Permethrin 5% cream, Crotamiton 10% cream or lotion and spinosad 0.9% topical suspension.
Permethrin is a synthetic pyrethroid agent used as a topical 5% cream that disrupts the function of voltage gated sodium channels of arthropods prolonging depolarization of nerve cell membranes and disrupt neurotransmission (Zlotkin E).
Permethrin is most commonly used due to its efficacy and limited adverse effects: high cure rate greater than 80% at 3 to 6 weeks post treatment.
Permethrin mnnay be associated with irritation itching and contact dermatitis.
Ivermectin is an oral semisynthetic macrolytic lactone antibiotic that disrupts ligand chloride ion channels, causing persistent opening of the channels (Geary TG).
Invermectin does not sterilize scabies eggs.
In a trial of topical permethrin compared to ivermectin in 85 patients, the former drug was associated with a 98% cure rate compared to 70% for ivermectin., however, a second dose of ivermectin increased the cure rate to 95%.
Ivermectin is an effective therapy in crusted scabies in patients who do not have a response to topical treatment.
Ivermectin may be favored in situations where it would be difficult to administer topical medications, lack of privacy, lack of access to shower or bath to wash off the medication or for whom topical therapy may exacerbate baseline skin disorders.
Permethrin 5% topical is the preferred treatment for classical scabies.
Evaluating treatment to ensure resolution is important, and weekly skin scraping is recommended to ensure eradication of all mites.
It is essential in the management of crusted scabies to address the risk of transmission to healthcare workers and patient contacts.
Recommended are outbreak management teams to oversee infection control.
Decontamination measures arebrecommended because transmission of scabies to others through fomites is possible.
Clothing and linens should be exposed to temperatures of 122°F in hot water and high heat drying and if this is not possible, they should be enclosed in plastic bag for 72 hours.
All close contacts of patients with scabies, or with known skin to skin contact should be treated empirically either with oral or topical treatments, even if asymptomatic.