Indian Journal of Sexually Transmitted Diseases and AIDS
REVIEW ARTICLE
Year
: 2020  |  Volume : 41  |  Issue : 1  |  Page : 10--16

Genital scabies: Haven of an unwelcome guest


Hima Gopinath1, Kaliaperumal Karthikeyan2,  
1 Department of Dermatology, All India Institute of Medical Sciences, Mangalagiri, Andhra Pradesh, India
2 Department of Dermatology, Venereology and Leprosy, Sri Manakula Vinayagar Medical College and Hospital, Puducherry, India

Correspondence Address:
Dr. Hima Gopinath
All India Institute of Medical Sciences, Mangalagiri, Guntur - 522 503, Andhra Pradesh
India

Abstract

The itch mite Sarcoptes scabiei var. hominis has been a menace to humanity for ages. Diagnosing scabies can be a challenge in view of the varied presentations of the disease. The male genitalia are an important area of predilection of the mite. Examination of this often overlooked area is essential as it may reveal both characteristic and atypical manifestations of scabies. Genital involvement also attains special relevance in view of the possible sexual transmission of the mite. In addition to the morbidity caused by itching, patients may have to deal with myths, stigma, and embarrassment.



How to cite this article:
Gopinath H, Karthikeyan K. Genital scabies: Haven of an unwelcome guest.Indian J Sex Transm Dis 2020;41:10-16


How to cite this URL:
Gopinath H, Karthikeyan K. Genital scabies: Haven of an unwelcome guest. Indian J Sex Transm Dis [serial online] 2020 [cited 2020 Aug 5 ];41:10-16
Available from: http://www.ijstd.org/text.asp?2020/41/1/10/287013


Full Text

 Introduction



Scabies caused by Sarcoptes scabiei var. hominis is a common health problem with a worldwide prevalence of around 300 million/year.[1] The link between the mite and the disease was described in 1687 by Giovani Cosimo Bonomo.[2] Scabies affects humanity irrespective of sex, age, socioeconomic class, or ethnicity and can cause debilitating and depressing itch. It can present with typical or atypical presentations and mimic a wide range of diseases. The male genitalia are a classical site of infestation.[3],[4] Scabies can be sexually transmitted and lesions limited to the genitalia or genital itch may be among the presenting features of the disease causing diagnostic dilemmas.[2],[5],[6]

 Etiology



The causative agent of scabies is the burrowing obligate ectoparasite, S. scabiei var. hominis.[7] The life cycle involves eggs, larvae, protonymphs, and tritonymphs prior to emergence of the adult mite.[8],[9]

 Genital Involvement in Scabies



Genital lesions are commonly reported (16.8%–60%) in clinical studies on human scabies.[10],[11],[12],[13] However, the genitalia are usually spared in animal scabies.[14] In a case series of 886 men with scabies, Mellenby isolated 8.4% of the total mites from the penis and scrotum and 4% from the buttocks.[15] The different structures, varying epithelium, moisture, higher temperature, and mechanical friction in the genital area may modify the presentation of dermatoses.[16]

The exact mechanisms of host seeking and reasons for localization in specific sites are not known. Scabies mites respond to thermal, chemical, light, and odor stimuli.[17] The mites are lesser in areas with increased density of pilosebaceous glands.[18] Soft folded skin may be preferred by the mite.[19] The mites, especially adult females, are attracted to 17 lipids present in or on the epidermis. These included both saturated (pentanoic, hexanoic, octanoic, lauric, pentadecanoic, and stearic acid) and unsaturated fatty acids (oleic, linoleic, and arachidonic), fatty acid methyl esters, cholesterol, squalene, and tripalmitin.[20] Mites are also attracted to nitrogenous waste and phenolic compounds that may act like pheromones and cause aggregation of mites.[21] Scabies mite proteases assist digestion of host proteins and enable penetration and migration through skin. Ease of availability of nutrients and chemical, physical, and immunological attributes of skin in different areas may be responsible for distribution of the mite in specific areas.[20],[22]

 Clinical Features



Classical scabies usually presents with pruritus that is worse at night. Symptoms usually begin 3–4 weeks after infestation. However, pruritus may manifest immediately in previously sensitized individuals.[23],[24]

The pruritus is of two types: a generalized type and the localized type. The localized pruritus is of a burning type caused by activity of the mite. Rarely, patients may not have itch.[25] Pruritus of the penis may be an early clue of scabies infestation.[26] Pruritus occurring exclusively on the scrotum has also been reported.[6]

Two main types of cutaneous lesions are seen: a generalized pruritic papular eruption and papules and vesicles associated with burrows. The latter is associated with the presence of the mite. The tiny papules (”larval papules”) and vesicles associated with the burrows may be single or grouped and are due to reaction to larvae or immature stages of the mite. Papular lesions on the penis and scrotum are of diagnostic value in scabies. The generalized eruption is profuse, severely itchy, and is mainly seen in the axilla, periareolar region, abdomen, buttocks, and thighs.[9],[23],[25]

A burrow is classical sign of the disease. They are grayish, reddish, or brownish, 2–15 mm long serpiginous tunnels, wherein copulation, ovulation, and birth of larvae occur.[2],[27] Burrows are common in areas where there are no or few hair follicles and where the stratum corneum is thin and soft making the genital area an ideal site for infestation. The color of the burrow may vary with the site affected, color of skin, and cleanliness. Burrows on the penis, buttocks, elbows, and knees appear pale [Figure 1].[25],[26] Burrows can be obliterated by bathing, scratching, crust formation, or secondary infection.[28] Many typical burrows and papules may be seen on the glans penis, penile shaft, and scrotum.[29] The crease in the lower part of the buttocks where it joins the upper thigh is affected in scabies. Natal cleft involvement and extension onto the buttocks may occur [Figure 2].[30] Pustules may develop on the buttocks in those who are seated for long time.[25] Knowles reported marked involvement of the penis with many burrows and pustules in military personnel during World War I.[31] Burrows limited to the penis have also been reported in Japanese prisoner of war camps.[25]{Figure 1}{Figure 2}

Scabies usually affects thighs and buttocks and spares vulva in females.[32] However, scabies may cause pruritus vulvae, and vulvar nodules have been reported.[33],[34]

Secondary lesions such as excoriations, crusts, eczematization, and secondary infections may be seen [Figure 3]a and [Figure 3]b.[35] Chronic scratching and irritation may cause hyperpigmentation.[26]{Figure 3}

 Atypical Scabies



Nodular scabies

Nodular or granulomatous scabies presents with firm, dull-red, brownish-red, or violaceous pruritic nodules measuring up to 2 cm that persist for months despite treatment. Nodules are seen on covered areas or soft skin such as may be seen over the elbows, axilla, thighs, penis, and scrotum [Figure 4]a, [Figure 4]b, [Figure 4]c. Secondary infection or eczematization may alter the clinical appearance. The nodules do not indicate the presence of the mite. It represents a hypersensitivity response to the mite antigens.[35],[36],[37],[38] It has been proposed that antigenic components of the mite enter the dermis and produce nodular lesions.[39] The histopathology of nodular scabies is similar to persistent bite reactions with dense superficial and deep infiltrate of lymphocytes, macrophages, plasma cells, eosinophils, Langerhans cells, and atypical mononuclear cells. Lymphoid follicles may be present.[40]{Figure 4}

Nonpersistent nodules may be seen in infants. Nonpersistent hemorrhagic nodules that ulcerated and mimicked chancres have been reported on the penis.[25]

Vesiculobullous scabies

Vesiculobullous scabies is a rare subtype predominantly affecting elderly individuals.[36] It may mimic bullous pemphigoid or can present with true bullous pemphigoid triggered by scabies. Bullous scabies may also be seen in very young children due to thin stratum corneum and loosely attached epithelial layers.[38] Bullous lesions may involve the genitalia. Penile bullae that showed poor response to topical steroids but responded to topical sulfur have been reported.[41]

Crusted scabies

Crusted scabies or Norwegian scabies presents with massive infestation of mites in immunocompromised patients and those with reduced sensations or inability to scratch. It presents with thick crusts and warty hyperkeratotic lesions. Lesions are usually extensive, atypical, and can involve atypical sites.[38] Burrows, vesicles, and papules may be masked by the keratotic plaques. Margins of the plaques or non-keratotic areas such a penis may reveal burrows.[25] Crusted scabies may have generalized or localized presentations. Lesions may be limited to the genitalia in both males and females. Crusted scabies presenting as a single, asymptomatic, thick crusted plaque on the shaft of the penis has been reported in an AIDS patient.[5] Crusted scabies of the vulva presenting with an ill-defined yellowish and beige psoriasiform plaque on the labia majora and clitoris has been reported in an HIV patient. It was proposed the weight loss, thinning, and protrusion of labia minora, and increased keratinization due to loss of moisture might have led to the unusual involvement of the vulva. Crusted scabies is a differential for scaly plaques that appear “like heaps of beige sand” in any location or of any size.[42]

Scabies incognito

Topical and oral steroids may alter the presentation of scabies. There is cutaneous atrophy, reduced inflammation, increased vascularity, and increased secondary infection. There may be vesicles, pustules, and nodules along with manifestations of steroid use.[38]

 Complications



Secondary infections

Scabies can disrupt the skin barrier, and predispose to staphylococcal and streptococcal infections. There may be impetigo, ecthyma, furuncles, lymphangitis, and cellulitis. Streptococcal infections may lead to poststreptococcal glomerulonephritis.[23]

Sepsis and death may occur in immunocompromised patients. Infections in the genital region can cause inguinal lymphadenopathy and bubo formation.[37],[43]

Psychological effects

Genital scabies has deleterious effect on the psychosexual well-being of patients. Patients may have disbelief, shame, guilt, and persistent delusions of parasitosis. Counseling on the nature of the disease and its transmission of the disease is needed.[37]

Others

Genital scabies has also been associated with male genital edema [Figure 5].[44]{Figure 5}

Post-scabetic pruritus

Post-scabetic pruritus may be present for days to weeks after treatment due to hypersensitivity to the mite antigens.[37]

 Scabies as a Sexually Transmitted Disease



Scabies is recognized as a sexually transmitted disease.[8] The localization of lesions over the genital area may cause diagnostic difficulties with other sexually transmitted infections.[16] The distribution of the mite is not related to the site of infection.[45] Scabies is transmitted by close physical contact. The fertilized female mite is implicated in transmission, but numerous immature mites on the skin surface may have a more significant role.[43] Sexual transmission is not the common route, and the association with other sexually transmitted diseases is controversial.[25] It does not have the classical pattern of sexually transmitted diseases, and the incidence trends do not parallel other sexually transmitted infections.[43] Nonsexual transmission may occur among family members. Fomite transmission can occur.[2] This is rare in classical scabies, but fomites may be important in crusted scabies. Men who have sex with men and sporadic sexual contact are risk factors for scabies.[3]

Singh et al. reported scabies as the most common venereal disease among juvenile inmates in a prison in India. This was attributed to common bedding and homosexual abuse by senior criminals.[46] Otero et al. studied 9751 patients in a sexually transmitted infection clinic over a period of 15 years and found that the annual infestation percentage varied from 0.6% to 2.7%. A range of 0.3%–2.4% was reported by other authors. Cases were more frequent in autumn and winter. Scabies was most common in men who have sex and more common in heterosexual men compared to women.[47]

 Scabies and Other Sexually Transmitted Infections



Scabies is common in venereal disease clinics and has been reported to coexist with other sexually transmitted infections such as syphilis, gonorrhea, and pediculosis pubis. David et al. reported higher prior sexually transmitted diseases without significant coexisting sexually transmitted diseases.[48] Evaluation of patients for other sexually transmitted disease is often recommended.[8],[49]

 Scabies and Syphilis



“Chancre galeuse” is the syphilitic chancre occurring on the cutaneous lesions of scabies.[25],[49] Infiltrated papules found on the penis and scrotum may be confused with early syphilis.[50]

 Scabies and Hiv



The prevalence of scabies in HIV is around 2%–4%.[29] The mite does not transmit HIV.[3] Typical scabies may be seen in HIV patients with minimal immunosuppression. As immunosuppression advances, two highly contagious and severe types of scabies are seen: papular or atypical or exaggerated scabies and crusted or hyperkeratotic or Norwegian scabies. Exaggerated scabies is intensely pruritic and characterized by generalized papules that may be topped by scaly burrows. Scabies must be suspected when there are atypical or itchy lesions in HIV and HIV should be ruled out in atypical manifestations of scabies particularly in patients with risk factors for HIV.[51]

 Diagnosis



Demonstration of scabies mite, eggs, or feces in skin scrapings is the standard test for diagnosis. Web spaces, hands, feet, wrist, and penis are among the good sites to examine for the mite. Burrows and nearby vesicles and papules are scraped and examined under the microscope with mineral oil, potassium hydroxide, or saline.[2],[37] Repeated scrapings from different sites may be needed as sensitivity is low. It is cumbersome to do and may be uncomfortable for the patient. Other tests include burrow ink test, adhesive plaster test, and polymerase chain reaction-based test for identifying the mite DNA in skin scrapings.[52]

“Jetliner with a trail” appearance on dermoscopy can be used in the diagnosis of scabies. This may be difficult to appreciate in dark skin and hairy areas. Proximity of the examiner's head to the genital area with handheld dermoscope may be embarrassing to the patient. Videodermoscopy can offer fast and clear demonstration of burrows, scabies mite, larvae, eggs, and feces.[52]

Confocal reflectance microscopy and optical coherence tomography can demonstrate the burrows, scabies mite, larvae, and feces. However, both these diagnostic tests are expensive, have a long learning curve and low sensitivity, and are available only at specialized centers.[52]

Skin biopsy may be done but is usually nonspecific.[3] “Pink pigtail” structures connected to the stratum corneum are suggestive of scabies.[28]

Detection of antibodies by ELISA which are present prior to onset of symptoms is a promising test.[52]

Differential diagnosis

Scabies has been described as the easiest and yet the most difficult to diagnose.[43] The differential diagnosis includes almost all pruritic dermatoses and includes urticarial, atopic dermatitis, lupus erythematosus, animal scabies, eczema, lichen planus, pityriasis rosea, dermatitis herpetiformis, necrotizing vasculitis, papular urticaria, delusion of parasitosis, and pruritic dermatoses of pregnancy. Sexually transmitted diseases mimicked by scabies include syphilis, pediculosis pubis, and phthiriasis pubis. The differential diagnosis of atypical manifestations of scabies is summarized in [Table 1].[23],[25],[36],[37],[38],[53],[54]{Table 1}

 Management



Topical agents

Topical agents are the mainstay of therapy for genital scabies. Isolated genital involvement does not preclude from whole-body application of the agent. Genital skin is sensitive with increased systemic absorption of topical agents.[16] Increased local absorption may occur from erosions of bullous scabies.[38] Permethrin is the most effective agent against scabies. It is synthetic pyrethroid that acts on sodium channels causing delayed repolarization, paralysis, and death. It can cause burning, stinging, and itchy, especially in sensitive eroded areas. The preservative formaldehyde may also cause allergic contact dermatitis.[36],[55] It is recommended, especially for infants, young children, and pregnant and lactating women.

Lindane is a second-line agent for scabies in view of its neurotoxicity. It is not recommended in children below 10 years. Increased absorption may occur immediately after bath or in patients with extensive dermatitis causing seizures. It may cause ulcerative irritant contact dermatitis, aplastic anemia, thrombocytopenia, and pancytopenia. Sulfur is among the oldest agents used for scabies. It can be used in pregnancy, infants, and in children but is irritant, messy, smelly, and stains clothes.[36],[56] Other agents include benzyl benzoate, malathion, esdepallethrine, monosulfiram, and crotamiton.[57]

Compliance to topical therapy may be poor in situ ations where there are inadequate privacy and facilities. It may be difficult to apply in certain special situations such in aged care institutions in mentally and physically disabled individuals.[55]

Ivermectin

Ivermectin is a synthetic macrocyclic lactone that blocks gamma-aminobutyric acid-gated chloride channels and causes paralytic death of the mite. It is a well-tolerated efficacious drug that ensures better compliance and avoids irritation of topical scabicides and convenient for bedridden patients.[22],[36] It is not recommended in pregnant and breastfeeding women and children weighing <15 kg. Moxidectin is a promising second-generation macrocyclic lactone that may be effective in a single dose. Other modalities being investigated include immunotherapy, vaccination, and direct targeting scabies mite molecules.[55]

Special situations

Nodular scabies can be managed with topical or intralesional corticosteroids, topical pimecrolimus, and methotrexate in recalcitrant cases.

Postscabetic pruritus may require treatment with oral antihistaminics and emollients; topical and oral corticosteroids may be required in severe cases.[36],[37] The pruritus may last for several weeks, particularly in individuals with atopy. Test for cure by examination for living mite may be done, especially in crusted scabies.[58]

Management of outbreaks, especially in institutions and epidemics, requires treatment of cases as well as at-risk population. Ivermectin along with topical scabicides is useful in such situations.[56]

Scabies with HIV

Uncomplicated scabies in HIV-affected individuals are treated with the same regimens as HIV-negative individuals.[56]

Crusted scabies

Combination therapy with 5% topical benzyl benzoate or 5% permethrin (daily for 1 week followed by twice-weekly till discharge or cure) along with oral ivermectin 200 μg/kg on 1, 2, 8, 9, and 15 has been recommended for crusted scabies. Severe cases can be administered additional doses on days 22 and 29. Lindane is not recommended as systemic absorption from the eroded areas can cause neurotoxicity.[56]

The entire skin including the head should be treated. Isolation till cure is needed, along with epidemiological measures to treat contacts. Clothing and bedding may be washed at temperatures above 50°C, dry-cleaned or kept in a plastic bag for 7 days.[58]

 Management of Contacts



Treatment of contacts at the same time as the case will reduce the chances of re-infestation.[4] However, the Centers for Disease Control and Prevention recommends that close personal, household, and sexual contacts in the previous 1 month should be examined and treated if found to be infested.[56] European guidelines recommend that sexual contacts in the previous two months are evaluated and treated. Sexual contact is to be avoided until both partners are treated condoms do not prevent transmission.[58]

 Conclusion



Genital involvement in scabies is often neglected. Awareness of the diverse manifestations of genital scabies is needed to diagnose and manage the deceptive itch mite and its debilitating impact on humanity.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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