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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.
The most common symptoms are severe itchiness and a pimple-like rash.
Occasionally, tiny burrows may appear on the skin.
In a first-ever infection, the infected person usually develops symptoms within two to six weeks.
During a second infection, symptoms may begin within 24 hours.
These symptoms can be present across most of the body or just certain areas such as the wrists, between fingers, or along the waistline.
The head may be affected, but this is typically only in young children.
The itch is often worse at night.
Scratching may cause skin breakdown and an additional bacterial infection in the skin.
Seven-year itch.
itchiness, pimple-like rash.
Usual onset is 2–6 weeks for first infection), ~and 1 day In subsequent infections.
Sarcoptes scabiei mite spread by close contact.
Risk factors:
Crowded living conditions-child care facilities, group homes, prisons, lack of access to water, wearing second hand clothing.
Differential diagnosis: seborrheic dermatitis, dermatitis herpetiformis, pediculosis, atopic dermatitis.
Rates of scabies are negatively related to temperature and positively related to humidity.
204 million / 2.8%
Scabies is caused by infection with the female mite Sarcoptes scabiei var. hominis, an ectoparasite.
The mites burrow into the skin to live and deposit eggs.
The symptoms of scabies are due to an allergic reaction to the mites.
Scabies is most often spread during a relatively long period of direct skin contact with an infected person, for at least 10 minutes, such as that which may occur during sexual activity or living together.
Spread of the disease may occur even if the person has not developed symptoms yet.
Crowded living conditions, such as those found in child-care facilities, group homes, and prisons, increase the risk of spread.
Areas with a lack of access to water also have higher rates of disease.
Crusted scabies is a more severe form of the disease, that typically only affects those with a poor immune system; the number of mites also makes them much more contagious.
With crusted scabies,spread of infection may occur during brief contact or by contaminated objects.
The mite is very small and isat the limit of detection with the human eye.
Mite detection is improved with good lighting, magnification, and knowing what to look for.
Diagnosis is based either on detecting the mite, detecting typical lesions in a typical distribution with typical historical features,or detecting atypical lesions or atypical distribution of lesions with only some historical features present.
Several medications are available to treat those infected, including oral and topical ivermectin, and permethrin, crotamiton, and lindane creams.
Sexual contacts within the last month and people who live in the same house should also be treated at the same time.
Bedding and clothing used in the last three days should be washed in hot water and dried in a hot dryer: the mite does not live for more than three days away from human skin.
Symptoms may continue for two to four weeks following treatment.
Scabies is one of the three most common skin disorders in children, along with ringworm and bacterial skin infections.
It affects about 2.8% of the world population.
It is equally common in both sexes.
The young and the old are more commonly affected, and It also occurs more commonly in the developing world and tropical climates.
Other animals do not spread human scabies.
The characteristic symptoms of a scabies infection include intense itching and superficial burrows.
Because the host develops the symptoms as a reaction to the mites’ presence over time, typically a delay of four to six weeks occurs between the onset of infestation and the onset of itching.
Similarly, symptoms often persist for one to several weeks after successful eradication of the mites.
Those re-exposed to scabies after successful treatment may exhibit symptoms of the new infestation in a much shorter period—as little as one to four days.
In the classic scenario, the itch is made worse by warmth, and is usually worse at night, possibly because distractions are fewer.
Itch related to scabies is less common in the elderly.
The superficial skin burrows of scabies usually occur in the area of the finger webs, feet, ventral wrists, elbows, back, buttocks, and external genitals.
Except in infants and the immunosuppressed, infection generally does not occur in the skin of the face or scalp.
The burrows are created by excavation of the adult mite in the epidermis.
Acropustulosis, refers to blisters and pustules on the palms and soles of the feet, are characteristic symptoms of scabies in infants.
The trails of the burrowing mites are linear or S-shaped tracks in the skin.
The burrows are often accompanied by rows of small, pimple-like mosquito or insect bites.
Lesions are symmetrical, and mainly affect the hands, wrists, axillae, thighs, buttocks, waist, soles of the feet, areola and vulva in females, and penis and scrotum in males.
The neck and above are usually not affected, except in cases of crusted scabies and in infestations of infants, the elderly, and the immunocompromised.
Symptoms typically appear two to six weeks after infestation for individuals never before exposed to scabies.
For those previously exposed, the symptoms can appear within several days after infestation.
Symptoms may appear after several months or years.
The elderly, disabled, and people with impaired immune systems are susceptible to crusted scabies (also called Norwegian scabies.
The mites in crusted scabies are not more virulent than in noncrusted scabies but are much more numerous, sometimes up to two million.
With crusted scabies exhibit scaly rashes, slight itching, and thick crusts of skin that contain large numbers of scabies mites.
For this reason, persons with crusted scabies are more contagious to others than those with typical scabies.
Crusted scabies areas make eradication of mites particularly difficult, as the crusts protect the mites from topical miticides/scabicides, necessitating prolonged treatment of these areas.
Sarcoptes scabiei, variety hominis, is the cause of scabies.
Sarcoptes is a genus of skin parasites and part of the larger family of mites collectively known as scab mites.
These organisms have eight legs as adults, and are placed in the same phylogenetic class (Arachnida) as spiders and ticks.
S. scabiei mites are under 0.5 mm in size; they are sometimes visible as pinpoints of white.
Gravid females tunnel into the dead, outermost layer of a host’s skin and deposit eggs in the shallow burrows.
The eggs hatch into larvae in three to ten days, and the young mites move about on the skin and molt into a “nymphal” stage, before maturing as adults, which live three to four weeks in the host’s skin.
Male mites roam on top of the skin, occasionally burrowing into the skin.
In general, the total number of adult mites infesting a healthy hygienic person with non-crusted scabies is small.
It is the movement of mites within and on the skin that produces an intense itch.
The itch has the characteristics of a delayed cell-mediated inflammatory response to allergens.
IgE antibodies are present in the serum and the site of infection, and react to multiple protein allergens in the body of the mite.
Some of these cross-react to allergens from house dust mites.
Immediate antibody-mediated allergic reactions,wheals, have been elicited in infected persons, but not in those not infected; immediate hypersensitivity of this type is thought to explain the observed far more rapid allergic skin response to reinfection seen in persons who have been infected previously, especially within the previous year or two.
Scabies is contagious and can be contracted through prolonged physical contact with an infested person.
This includes sexual intercourse, although a majority of cases are acquired through other forms of skin-to-skin contact.
Scabies infestation can happen through the sharing of clothes, towels, and bedding, but this is not a major mode of transmission; individual mites can survive for only two to three days, at most, away from human skin at room temperature.
As with lice, a latex condom is ineffective against scabies transmission during intercourse, because mites typically migrate from one individual to the next at sites other than the sex organs.
Healthcare workers are at risk of contracting scabies from patients, because they may be in extended contact with them.
The symptoms are caused by an allergic reaction of the host’s body to mite proteins, though exactly which proteins remains a topic of study.
The mite proteins in feces, which are deposited under the skin.
The allergic reaction is both of the delayed cell-mediated and immediate antibody-mediated type, and involves IgE antibodies to mediate the very rapid symptoms on reinfection.
The allergy-type symptoms of itching continue for some days, and even several weeks, after all mites are killed: Nodular lesions from scabies may continue to be symptomatic for weeks after the mites have been killed.
New lesions may even appear for a few days after mites are eradicated.
Nodular lesions from scabies may continue to be symptomatic for weeks after the mites have been killed.
Diagnosis:
Scabies may be diagnosed clinically in geographical areas where it is common when diffuse itching presents along with either lesions in two typical spots or itchiness is present in another household member.
Scabies classical sign is the burrow made by a mite within the skin.
The burrow suspected area is rubbed with ink which glows under a special light, providing its evidence.
A definitive diagnosis is made by finding either the scabies mites or their eggs and fecal pellets.
Scraping a suspected area, mounting the sample in potassium hydroxide and examining it under a microscope, or using dermoscopy to examine the skin directly for evidence of mites.
Symptoms of early scabies mirror other skin diseases, including dermatitis, syphilis, erythema multiforme, various urticaria-related syndromes, allergic reactions, ringworm-related diseases, and other ectoparasites such as lice and fleas.
Mass-treatment programs that use topical permethrin or oral ivermectin have been effective in reducing the prevalence of scabies in a number of populations.
No vaccine is available for scabies.
The simultaneous treatment of all close contacts is recommended, even if they show no symptoms of infection (asymptomatic), to reduce rates of recurrence.
Mites can survive for only two to three days without a host, other objects in the environment pose little risk of transmission except in the case of crusted scabies.
Cleaning is of little importance.
Treatment: Several medications are effective in treating scabies.
Treatment should involve the entire household, and any others who have had recent, prolonged contact with the infested individual.
In addition to treating the infestation, options to control itchiness include antihistamines and prescription anti-inflammatory agents.
Bedding, clothing and towels used during the previous three days should be washed in hot water and dried in a hot dryer.
Permethrin, a pyrethroid insecticide, is the most effective treatment for scabies.
Permethrin is the treatment of choice.
Permethrin is applied from the neck down, and left on for about eight to 14 hours, then washed off in the morning.
The entire skin surface, should be treated, not just symptomatic areas as any patch of skin left untreated can provide a haven for one or more mites to survive.
One application is normally sufficient, as permethrin kills eggs and hatchlings, as well as adult mites.
Many physicians recommend a second application three to seven days later as a precaution.
Crusted scabies may require multiple applications, or supplemental treatment with oral ivermectin (below).
Permethrin may cause slight irritation of the skin.
Oral ivermectin is effective in eradicating scabies, often in a single dose, and It is the treatment of choice for crusted scabies, and is sometimes prescribed in combination with a topical agent.
It is not recommended for children under six years of age.
Oral ivermectin is usually effective for treatment of scabies, it does have a higher treatment failure rate than topical permethrin.
Scabies is markedly reduced in populations taking ivermectin regularly.
Ivermectin drug is widely used for treating scabies and other parasitic diseases particularly among the poor and disadvantaged in the tropics.
Other treatments include lindane, benzyl benzoate, crotamiton, malathion, and sulfur preparations.
Lindane is effective, but has concerns over potential neurotoxicity.
Some 10% sulfur solutions are effective.
Scabies is endemic in many developing countries.
Scabies is one of the three most common skin disorders in children, along with tinea and pyoderma.
It affects about 100 million people,1.5% of the population, and its frequency is not related to gender.
Mites are distributed around the world and equally infect all ages, races, and socioeconomic classes in different climates.
Scabies is more often seen in crowded areas with unhygienic living conditions.
About 1–10% of the global population is estimated to be infected with scabies, but in certain populations, the infection rate may be as high as 50–80%.
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.