Go Back to the Top To Order, Visit the Purchasing Page for Details Chapter Skin Diseases Caused by Arthropods and Other Noxious Animals Various cutaneous symptoms, including blistering and contact dermatitis, allergic reaction and secondary infection, are caused by arthropods. Pathogens transmitted by insects or other noxious animals may cause systemic symptoms. Infestation by arthropods or insects may result in cutaneous symptoms, and various pathogens carried by arthropods and other noxious animals can infect humans. A. Diseases caused by insects and other noxious animals 1. Insect bite Insect bite is a general term for the dermatitis that is caused by the bite or sting of a mosquito, gnat, horsefly, bee or other insect. It is thought to be an allergic reaction to the salivary components that the insect discharges while sucking blood or to the venom of stings. The severity of the clinical symptoms depends largely on the age of the patient and the severity of allergic reaction. Immediately after an insect bite, itching wheals or erythema appears. There are two major clinical types of insect bites: those of immediate hypersensitivity, in which symptoms subside in 1 to 2 hours, and those of delayed hypersensitivity, in which erythema or blistering may occur 1 to 2 days after a bite (Figs..1-1 and.1-2). Treatments are topical steroid application for eruptions, and oral antihistamines for itching lesions. A bee sting may cause an anaphylactic reaction. a b c d e f g h 2. Hypersensitivity to mosquito bite After a mosquito bite, an allergic reaction occurs against the protein in the salivary components of the mosquito, sometimes leading to systemic symptoms such as high fever, liver dysfunction and lymph node enlargement, and cutaneous symptoms a including blistering. Later, swelling, induration, necrosis and ulceration occur. During the course of hypersensitivity to mosquito bite, the histopathological symptoms may resemble those of hydroa vacciniforme. Recent study has found the Epstein-Barr b c d e f g h i virus (EBV) to be associated with hypersensitivity to mosquito bite. Cases have proven the association between chronic EBV infection and NK/T cell lymphoma. Myiasis MEMO Flies lay eggs in necrotic tissue. Eggs and maggots are present at the site, requiring curettage. a b c d e f g h i j Fig..1-1 Insect bite. a: Itching erythema on the lower leg. b: A tense blister on the lower leg. c: Insect bite on the eyebrow. Severe edema occurred around the lesion. 499
500 Skin Diseases Caused by Arthropods and Other Noxious Animals Fig..1-2 Insect bite. Small, itching papules of about 5 mm in diameter occur, most frequently on the lower legs. 3. Caterpillar dermatitis The urticating hairs of larval moths and butterflies (caterpillars) including those of the tussock moth, tea tussock moth and browntail moth cause caterpillar dermatitis. The affected site has tingling pain. Punctate, itching erythema is followed by a red wheal (Fig..2) that progresses to vesicles and papules. 4. Dermatitis linearis The hemolymph of the beetle Paederus fuscipes Curtis comes into contact with the skin, causing dermatitis linearis (Fig..3). Two to three days after contact, characteristic linear skin lesions, reddening, vesicles, swelling, burning sensation and sharp pain occur. 5. Scabies Fig..2 Caterpillar dermatitis. Punctate, itching erythema occurs, accompanied by pruritus and blistering in some areas of the lesion. Outline It is an infestation caused by the mite Sarcoptes scabiei var. hominis. Multiple papules occur. Intense itching is present, worsening at night. The genitalia, trunk and interdigital areas are most frequently involved. It is characterized by tunnels (burrows) in the interdigital area. It may be transmitted by bedclothes or skin-to-skin contact. It often occurs as a STD or in-hospital epidemic. Benzyl benzoate, topical g -benzenehexachloride and oral ivermectin are the main treatments. Clinical images are available in hardcopy only. Fig..3 Dermatitis linearis. Fig..4-1 Scabies on the scrotum. Scabies is characterized by small multiple nodules.
A. Diseases caused by insects and other noxious animals 501 Small, multiple, light pink papules 2 mm to 5 mm in diameter occur on the trunk, genitalia, thighs, inner arms and interdigital areas (Figs..4-1 and.4-2). Small nodules may form in the genitalia and axillary fossae. Both the papules and nodules are accompanied by intense itching that worsens when the skin is warmed, such as at bedtime. Patients with scabies often complain of difficulty of sleeping from itching. Scratching of the skin lesions may lead to formation of eczematous plaques. When the interdigital areas and palms are involved, there may be slightly elevated, grayish-white linear lesions (mite burrows) several millimeters long where female insects lay eggs. Blistering occurs in some cases (Fig..4-2). Scabies is an infestation in the epidermal horny cell layer by the mite Sarcoptes (S.) scabiei var. hominis. This mite is ovoid and has body dimensions of 0.40.3 mm for males and 0.20.15 mm for females, with 4 pairs of legs at the adult stage (Fig..5). A mated female forms a mite burrow in the horny cell layer and lays 1 or 2 eggs daily there, dying in 4 to 5 weeks. Eggs incubate for 3 to 5 days. S. scabiei var. hominis inhabits creases of the skin or the hair follicles and grows to adult stage in 14 to 17 days. Scabies infestation is caused by direct skin-to-skin contact or indirect contact through bedclothes or clothing. The incubation period is about 1 month. Scabies often occurs within a family and at hospitals and eldercare homes. Infection may be direct, from sexual transmission. Norwegian (crusted) scabies is caused by a large number of S. scabiei var. hominis in persons with poor nutrition, poor hygiene or immunosuppression. Under such conditions, scabies is highly contagious and may cause severe symptoms including generalized hyperkeratosis and crusts. Fig..4-2 Scabies on the hand and foot of an elderly person. Distinct blistering is present. a b c d e f g h Diagnosis When disseminated small papules accompanied by intense itching are found on the trunk, mite burrows should be carefully searched for in the interdigital areas. Multiple papules on the genitalia, particularly on the scrotum or labia majora, should be carefully examined. To confirm the diagnosis, a specimen including the horny cell layer is removed from the skin by pinching with tweezers, scraping the skin with a scalpel, pricking with a b c d e f g h i needle, or exfoliating with adhesive tape for direct identification of the mite body or eggs by light microscopy. Inquiry on symptoms of scabies among the patient s family members and partners, and history-taking on sexual activity are helpful. Fig..5 Sarcoptes scabiei var. hominis. a: S. scabiei var. hominis has four pairs of legs. b: Eggs of S. scabiei var. hominis. Differential diagnosis Insect bite, eczema and urticaria are differentiated from scabies. Mite burrows and the nodules on the genitalia are useful for differentiation.
502 Skin Diseases Caused by Arthropods and Other Noxious Animals Fig..6 Eggs of the louse Phithilus pubis on pubic hair. Treatment Topical application of ointments containing sulfur, crotamiton and benzyl benzoate is helpful. Previously, g -BHC (benzene hexachloride) was most commonly used in the U.S. and Europe. It is important to apply the ointment to the entire body skin below the neck of all family members and partners, regardless of whether they are symptomatic. In recent years, oral ivermectin has become available for use. It is extremely effective, requiring only one administration a day. Antihistamines may be used, if necessary. Thorough laundering and sun drying of bedclothes is recommended. 6. Pediculosis Fig..7 Pediculosis. Definition, Classification Allergic reaction is induced by a louse that parasitizes human skin to suck blood, causing intense itching. Lice are host-specific and spend their entire life on the host. The three main causative lice of pediculosis are Pediculus capitis (head lice, 2 mm to 4 mm long, inhabiting head hair), Pediculus humanus (clothing or body lice, 2 mm to 4 mm long, inhabiting clothing), and Pthirus pubis (pubic or crab lice, 1 mm long, inhabiting pubic hair; Figs..6 and.7). It is impossible to distinguish between Pediculus capitis and Pediculus humanus by appearance. A louse parasitizes a hair shaft and lays eggs on the hair. The eggs incubate for about 1 week. The lice mature and suck human blood. In most cases, intense itching begins 1 to 2 months after infection. Eruptions do not usually occur. a b c d e f g Pediculus capitis infestation may become epidemic among schoolchildren h i j during k group activities l m at schools n or o p q daycare centers. Pthirus pubis infestation is caused most frequently by sexual intercourse. The eyebrows are involved in rare cases. Pediculus humanus infestation is epidemic among individuals under environments with poor hygiene, such as in the homeless. r Diagnosis, Treatment Itching on the head or genitalia is the main complaint of a a b c d e f g h patient, i jwhen pediculosis k l is msuspected. n It is o important p to q searchr Fig..8-1 A tick bite. a: Shoulder 2 hours after the bite. The legs of the for lice and eggs attached to the hair. Phenothrin shampoos and tick are still moving (the patient is Hiroshi Shimizu, the author of this textbook). b: A tick Skin diseases caused by jellyfish, MEMO bite on the eyelid. coral and sea anemones An eruption may be caused by the sting of jellyfish, coral or sea anemones in the ocean. Some marine organisms sting humans with the nematocysts on their tentacles or otherwise injure human skin by contact. Systemic symptoms may be severe.
B. Skin diseases transmitted by insects and other animals 503 powders are helpful treatments. The family members and sexual partners are also treated to avoid ping-pong infestation, in which the disease repeatedly rebounds from untreated to treated persons. 7. Tick bite Tick bite is caused by ixodid (hard) ticks. Because ticks of the family Ixodidae tend not to be felt when crawling on human skin, they are able to attach insidiously to the face, arms or even the trunk or genitals of humans (Figs..8-1 and.8-2). The bite tends to be painless. The main symptoms are inflammation around the bite, erythema, edematous swelling, bleeding and blistering. The mouthpart is firmly fixed in the skin while sucking blood; a tick bite is often found when the complaint has been a wart or skin tumor. A tick that has sucked its fill of blood falls naturally from the skin. Borrelia spirochetes may be transmitted by a tick bite, leading to Lyme disease (described later). a b c d e f g h i j Fig..8 A tick bite. c: A tick on the neck. Ixodidae are 2 mm to 8 mm long (Fig..9) and tend to inhabit grasslands or woods. They burrow into the skin of humans and animals to suck blood. Fig..9 An ixodid tick removed from human skin. It is generally 5 mm to 8 mm long. Treatment If a tick is forcefully pulled while sucking blood, it may tear, leaving the mouthpart in the skin. This can lead to foreign-body granuloma. The whole tick, including the mouthpart, should be removed by either inserting scissors into the bite spot or punching the site out with the tick attached. Oral administration of tetracycline 1 week after removal is advised as a prophylactic against Lyme disease. B. Skin diseases transmitted by insects and other animals 1. Lyme disease Outline It is an infection caused by the spirochete bacteria Borrelia burgdorferi sensu lato, transmitted by ticks of the family Ixodidae. It occurs most frequently in USA, Scandinavia and central Europe, during spring and summer. It begins as erythema chronicum migrans (first stage) and progresses to arthritis and cerebral meningitis (second stage) and then to dysfunction of the joints and central Table.1 Classification of Borrelia species. Borrelia " "! B. burgdorferi sensu lato Other Borrelia species B. burgdorferi B. garinii!b. afzelii Go Back to the Top To Order, Visit the Purchasing Page for Details