INFECTIOUS DISEASES UPDATE THE DIAGNOSIS AND TREATMENT OF SCABIES AND PUBIC LICE Barbara M. Faber MD ELSEVIER Scabies and pediculosis pubis (infestation with pubic lice) are examples of infections caused by human parasites. The most common mode of transmission for both infections is through sexual contact. Scabies may affect multiple sites of the body and usually presents with severe pruritus accompanied by dirty-appearing burrows beneath the skin. The diagnosis is confirmed by demonstrating the presence of the parasite or its byproducts. Pediculosis pubis also presents with severe pruritus, but most commonly involves the pubic region. The diagnosis of pediculosis pubis is confirmed by the presence of nits or eggs attached to pubic hair. Several effective therapies are available for scabies and pediculosis pubis. A therapy useful for both infections is Lint/one 1% (KweII) applied to the affected region and removed after 12 hours. (Prim Care Update Ob/ Gyns 1996;3:20-24) Scabies PATHOPHYSIOLOGY Scabies infection is caused by the human itch mite, Sarcoptes scabiei var hominis. The adult female mite has a rounded body with four pairs of legs and measures only 0.35 to 0.40 mm in length. Its color is pearly white, with brownish legs and mouth parts. The organism can From the Division of Reproductive Endocrinology and Infertility, Department of Obstetrics and Gynecology, University of Florida College of Medicine, Gainesville, Florida. barely be seen without the aid of a magnifying lens. The adult male mite is approximately half the size of the female mite. The life cycle of the female mite lasts approximately 30 days and requires constant contact with human skin. The male impregnates the female on the skin surface or in a superficial burrow created by the female mite. The male mite dies shortly thereafter, in 1-2 days. After impregnation, the female mite begins to dig a deeper burrow into the stratum comeum of the skin. Into this burrow, she will deposit her eggs that will eventually hatch and continue the life cycle of the organism. The female mite lays two to three eggs per day. However, less than 10% of her eggs will develop into adult mites.1 The presence of the mite and its byproducts initiates an immunological response in the host. This sensitization results in the typical presentation of scabies. T cell lymphocytes, macrophages, IgM, IgA, and IgE antibodies, as well as complement (3) are involved in this process.2 EPIDEMIOLOGY For reasons that continue to be unknown, outbreaks of scabies occur in 30-year cycles, with a 15-year interval between the end of one outbreak and beginning of another.3 Conditions that promote close proximity of individuals such as poverty, overcrowding, war, sexual promiscuity, and the increased mobility af the population have been implicated in the pathogenesis of outbreaks. Close personal contact with an infected individual is necessary for the spread of scabies. However, this infection is not limited to those populations living in poverty or with poor hygiene. All socioeconomic groups are at risk. The most common mode of spread is through sexual contact, and therefore, scabies occurs more frequently in sexually active young adults. Nonsexual transmission is also common, involving any skin-to-skin contact such as occurs when children share beds.1 Though all groups are at risk, the frequency of scabies infection is less in African-Americans compared with other races.4 Scabies infection is more common in adult men than in women, but in children, it is more common in girls than boys.5 CLINICAL PRESENTATION Infection with the mite causes severe itching, which occurs predominantly at night and is exacerbated by bathing in hot water. The hands are more frequently involved, particularly the finger webs and the sides of the digits. The pathognomonic burrow is a short wavy dirtyappearing line (Figure 1). Other areas of the body that commonly are affected include the flexor surface of the wrist, extensor surface of the elbow, and the anterior axillary folds. Eczematous lesions caused by scratching may develop on the above areas as well as on the breasts (Figure 2). Erythematous, nodular papules that progress to crusts may 20 (C) 1996 Elsevier Science Inc. 1068-607X/96/$15.00 SSDI 1068-607X(95)00054-2 Prim Care Update Ob/Gynb
SCABIES & LICE Figure 1. Typical burrow of human itch mite. (Photograph courtesy of the Department of Dermatology, University of Florida, Gainesville, Florida.) appear on the abdomen, especially around the umbilicus, and on the penis and buttocks (Figure 3). In adults, the region above the neck is usually spared, as are the palms and soles. In children and infants, however, the palms, soles, and head are commonly affected.1 The body s reaction to infection with the itch mite is immunemediated. In a primary infection, sensitivity to the organism must develop, which accounts for the 3-4 week delay from infection to the presentation of symptoms. The clinician also needs to be aware that a secondary bacterial infection with group A streptococci or Staphylococcus aureus may coexist with the primary lesion. This situation, along with excoriations around the lesion, can make the diagnosis of scabies difficult to make.6 DIAGNOSIS The definitive diagnosis of scabies is made by demonstrating the presence of S. scabiei or its byproducts. Figure 2. Eczematous lesion on elbow of patient infected with scabies. (Photograph courtesy of the Department of Dermatology, University of Florida, Gainesville, Florida.) Commonly, an undisturbed burrow or papula can be identified. Mineral oil should then be applied to the lesion or placed on a small, sterile scalpel. The lesion should then be scraped vigorously, and the specimen should be examined under a low-power light microscope. The addition of 10% potassium hydroxide may eliminate debris and facilitate the visualization of the organism. Adult mites, ova, or fecal material may be observed (Figure 4).3 Alternatively, an epidermal shave biopsy may be performed. This is slightly more invasive but is well tolerated by cooperative patients without local anesthesia. In this procedure, a suspicious lesion is identified and immobilized between the examiner s fingers. The top of the lesion is cut off with a number 15 sterile scalpel in a direction parallel to the skin surface. Only a very superficial specimen is needed, which is then placed on a glass slide, covered with emersion oil, and examined with a low-power light microscope.1 For small children or uncooperative patients who may not tolerate the above procedures, the "burrow ink test" may be sufficient. In this Figure 4. Sarcoptes scabiei var horn nis, the human itch mite. (Photograp courtesy of the Department of Domic tology. University of Florida, Gaines ville, Florida.) Volume 3, Number 1, 1996
test, the burrow can be visualized by placing pen ink on a suspicious lesion or papule followed by wiping the surface with an alcohol pad. A dark zigzag line is characteristic of infection and marks the path of the itch mite. TREATMENT Many agents currently are used to treat scabies. Lindane lotion 1% (Kwell [Reed & Camick, Jersey City, NJ]) is the most popular scabicide in thq United States and is also used as a pesticide. A single application applied as a thin layer over the trunk and extremities and removed after 8-12 hours is all that is necessary to eradicate the mite and ova. Lindane is a moderately toxic pesticide, and its adverse effects include nausea, vomiting, seizures, respiratory failure, blood dyscrasias, and even death from neurotoxicity.7 Seizure activity has been the most commonly reported CNS side effect. However, in the majority of these reports, toxicity was associated with inappropriate use of the drug.8 Nevertheless, because of lindane s potential toxicity, several authors recommend alternative therapies for use in infants, children, pregnant or lactating women, or patients with severe excoriations or a seizure disorder. Crotamiton 10% cream or lotion is an alternative treatment. Precipitated sulfur 5% to 10% in petrolatum is also available. However, both of these therapies require multiple nights of treatment. Crotamiton 10% must be applied nightly for at least 2 nights, and it has been sug^ gested that five daily applications may be better than the current recommendation of two applications. Precipitated sulfiir in petrolatum must be applied nightly for three nights. In addition, sulmr preparations have a foul odor and may stain clothing and bed linens. A newer drug, permethrin 5%, is now available in the United States. One application, which is left on for 8-14 hours, is recommended. Permethrin is as effective as lindane and is more effective than crotamiton for the treatment of scabies. No systemic reactions have been noted, and the drug has not been shown to be teratogenic.9 ^ Whichever therapy is employed, the clinician should only prescribe enough medication to treat the individual as recommended by the manufacturer. Affected patients must be cautioned against excessive use of scabicides to avoid toxicity. In addition to treating the primary infection, antipruritic medications such as the antihistamine, diphenhydramine (Benadryl, Parke-Davis, Morris Plains, NJ), 25-50 mg every 6 hours may be required to control itching. Topical hydrocortisone preparations may also provide symptomatic relief. Patients should be instructed that pruritus may persist for 2-4 weeks after adequate treatment and does not indicate treatment failure. Rarely, an oral antibiotic is needed to treat a secondary infection. Group A streptococci and 5. aureus are the most common organisms involved, and therefore, dicloxacillin (250-500 mg qid) or erythromycin (250-500 mg qid) are appropriate antibiotic choices. The role of fomites in scabies is unclear and is not thought to be a major factor in transmission. However, the laundering of all contaminated clothing, bed linens, and towels in hot water will kill all forms of the mite.1 Affected individuals should also be screened for other sexually transmitted diseases when it appears that the individual was infected with scabies through sexual contact. Pubic Lice PATHOPHYSIOLOGY Pubic lice infection, pediculosis pubis, is caused by the crab louse, Figure.5. Phthirus pubis, the crab louse. (Photograph courtesy of the Department of Dermatology, University of Florida, Gainesville, Florida.) Phthirus pubis. Other well known species in this family are Pediculus human us capitis, the head louse, and Pediculus humanus corporis, the body louse. Pubic lice are about 1 mm long and have enlarged hind legs, middle legs, and claws. The abdomen is wider than it is long; therefore, the organism looks like a crab (Figure 5). The crab louse hind legs are equipped to hold firmly to pubic and axillary hair. The life cycle of the louse is approximately 25 days. The louse feeds by inserting its mouth portion into the host s skin and periodically sucking the host s blood. While feeding, the crab louse releases saliva into the wound to prevent clotting. The host then develops an immunological reaction to the saliva, resulting in the development of symptoms approximately 30 days after the initial exposure.5 EPIDEMIOLOGY Pediculosis pubis most commonly is transmitted through sexual con- 22 Prim Care Update Ob/Gyns
tact; fomites such as linens and towels may also be involved. As with most STDs, pediculosis pubis ;s prevalent in patients between 15 and 40 years of age. It is more common in women between 15 and 19 years of age than men. After 20 years of age, the disease in more common in men.5 Approximately one third of patients with pediculosis pubis will also have another sexually transmitted disease at the time of diagnosis.10 CLINICAL PRESENTATION Pruritus in the pubic area is the most common presenting symptom. Other areas that may be involved include the thighs, trunk, and occasionally the beard, the mustache, and eyelashes. Constant itching may produce erythema, small skin ulcerations, and secondary bacterial infections. Small blue macular lesions may also be seen and are caused by the anticoagulant released by the louse while feeding.5 DIAGNOSIS Once pediculosis pubis is suspected, the clinician should use a magnifying glass to look for adult lice in the patient s pubic hair. Sometimes, the actual organism may look like crusted skin or debris. More commonly, the diagnosis is made by identifying nits or eggs attached by a cementing substance to pubic hair (Figure 6). The diagnosis should be confirmed by plucking a hair and observing the nits under a low-power light microscope. TREATMENT Several prescription and nonprescription treatments are available for pubic lice. Lindane 1% is often prescribed and should be applied to the affected area for 12 hours. It is then thoroughly washed away and the remaining nits should be removed with a fine toothed comb. A Volume 3, Number 1, 1996 Multiple lice nits in pubic hair. (Photograph courtesy of the Department Figure 6. of Dermatology, University of Florida, Gainesville, Florida.) second application should be repeated in one week if viable nits persist or if new nits appear at the pubic hair bases. Lindane shampoo is also effective. The patient should shampoo the affected site for 4 minutes and then follow with a thorough rinsing. As discussed in the treatment of scabies, lindane is not recommended by some physicians for infants, small children, pregnant women, or individuals with severe excoriations. Other prescription medications include crotamiton 10%, sulfur 10% ointment, and benzyl benzoate 20%. These therapies require several applications and therefore are less desirable. Over the counter medications such as Rid (Pfizer Consumer Health Care, Parsippany, NJ), and A-200 Pediculicide Shampoo (SmithKline Beecham Pharmaceuticals, Philadelphia) are products that contain pyrethrins and piperonyl butoxide. The medication is applied to dry hair for ten minutes and then rinsed away thoroughly. Dead lice and nits are then removed with a special comb provided with the medication, A second application is repeated in one week to 10 days. Permethrin 1% (Nix [Burroughs Wellcome Co., Research Triangle Park, NC]) is an effective treatment for head lice, and although it is not specifically indicated for the treatment of pubic lice, it may also be effective if other medications are not available. The recommended regimen is to apply permethriri 1% to dry hair and allow the solution to remain for 10 minutes before rinsing with water. If live lice or new nits are observed seven days or more after the first application, a second treatment should be given. Patients should be counseled that pruritus may persist after adequate treatment and does not indicate treatment failure. An antipruritic medication or topical corticosteroid cream may be added to the pediculicide for symptomatic relief. The patient should be evaluated in 1 week to be certain that the chosen therapy has been successful. Furthermore, a diagnosis of pediculosis pubis should prompt a search for coexisting sexually transmitted diseases. All sexual contacts should be treated simultaneously to avoid re- 23
infestation. Clothing and bed linens should be washed in hot water or dry cleaned after treatment. Articles that cannot be cleaned should be treated with an insecticide that is intended for home use such as Black Flag (Boyle/Midway, Wayne, NJ) or Raid (S.C. Johnson Wax, Racine, WI).11 Special Considerations in Pregnancy and Lactation The safety of treating scabies or pediculosis pubis during pregnancy with lindane 1% (Kwell) has been questioned. In animals, very high doses of lindane cause an increase in stillbirths, but not teratogenic effects. Controlled studies of the use of lindane in pregnancy are not available. Consequently, the manufacturer warns that only the recommended dosage should be used to treat pregnant women and nursing mothers. Others recommend that until appropriate toxicologic data are available, lindane should not be used to treat pregnant or nursing mothers.5 The safety of other available antiparasitic drugs in human pregnancy and lactation has not been assessed, but to date no adverse effects have been reported. References 1. Gurevitch AW. Scabies and lice. Pediatr Clin North Am 1985;32: 987-1016. 2. Van Nest DJ. Human scabies in perspective. Int J Dermatol 1988;27: 10-5. 3. Levine GI. Sexually transmitted parasitic diseases. Prim Care 1991; 18:101-28. 4. Alexander AM. Role of race in scabies infestation. Arch Dermatol 1978;114:627. 5. Orkin M, Maibach H. Current views of scabies and pediculosis pubis. Cutis 1984;33:85-116. 6. Orkin M, Maibach H, Parrish L, Schwartzman R. Scabies and pediculosis. Philadelphia: JB Lippincott, 1977. 7. Shacter B. Treatment of scabies and pediculosis with lindane preparations: an evaluation. Am Acad Dermatol 1981;5:517-27. 8. Kramer MS, Hutchinson TA, Rudnick SA. Operational criteria for adverse drug reactions in evaluating suspected toxicity of a popular scabicide. Clin Pharmacol Ther _1980;27:149-55. 9. The medical letter: Permethrin for scabies. 1990;32:21-2. 10. Chapel TA, Katta T, Kuszmar T, DeGiusti D. Pediculosis pubis in a clinic for treatment of sexually transmitted diseases. Sex Transm Dis 1979;6:257-60. 11. Billstein SA, Mattaliano VJ. Thf nuisance sexually transmitted diseases: Molluscum contagiosum, scabies, and crab lice. Clin North Am 1990;74:1487-505. Address correspondence and reprint requests to Barbara M. Faber, MD, University of Florida, 1600 SW Archer Rd., P. 0. Box 100294, Ob/Gyn, Gamesville. FL 32610-0294. \ 24 Prim Care Update Ob/Gyns