PARASITES

Charles Sheard, M.D.
Rhett Drugge, M.D.
Stamford, Connecticut

Scabies Sarcoptes scabiei
This is probably one of the most common parasitic infections, usually spread by bodily contact, though other contaminated objects can also infect. There is severe itching, usually worse at night, with lesions (mostly excoriated burrows) on the fingerwebs, volar wrists, buttocks, penis, axillary folds and around the nipples in women.
Diagnosis
Diagnosis is confirmed by curettage of a burrow followed by KOH microscopy of the arthropod, its scat or eggs. This technique is often unyielding leaving clinical judgement to rule in half of cases. Inquiry as to the source of infection can be an important clinical correlate. Such personal contacts should be evaluated and treated for scabies to avoid reinfection.
Treatment
Treatments such as Kwell lotion given twice daily for 3 days, then repeated weekly for 3 weeks, Eurax cream or lotion (Geigy) twice a day, and the old-fashioned remedy of 10% sulfur ointment applied at night for four nights in a row and washing it off in the morning are effective. The best treatment is benzyl benzoate. Benzyl benzoate 25% emulsion applied from the neck down after a hot bath while the skin is still damp, and then left on, is effective if repeated nightly for three nights when the bedding is changed and fresh clothing is worn in the morning. Treatment should be repeated once, a week later. Particular attention should be paid to body folds. If hands are washed, the emulsion should be reapplied for 24-hour contact. Permethrin, a crysanthenum derivative applied neck down, left overnight and repeated in a week is sufficient when combined with hot water laundry of linen. Permethrins have not the neurotoxicity which characterizes lindane, especially in infants with a high surface to mass ratio and highly permeable skin. Norwegian scabies is a crusted variant featuring thousands of organisms in neurologically impaired or immunologically suppressed individuals, whereas a normal scabies infestation is by fewer than 20 organisms. A single dose of methotrexate is curative in Norwegian scabies.

Fleas (Siphonoptera)
Plague, rickettsiae and murine typhus are probably transmitted by rodent fleas. Most flea bites seen in this country are from dog and cat fleas, who lay their eggs in floor cracks, rugs or in dust or other debris. Fleas can go without seeking food for long periods of time, and larvae in a rug can take up to a year to reach the adult stage, so infestations can be stubborn (life cycle). Diagnosis is made by seeing three or four bites in a straight line, evenly spaced, or wheals with a pinpoint central hemorrhagic puncta on the ankles, or legs. Another way to detect the presence of fleas in a house is to wear white socks, sit in the dark, then turn on the light suddenly and see the fleas on the socks.
Treatment
Flea powers dusted on the animal or a flea collar, plus spraying the rugs and animals' sleeping places with Raid are necessary. Occasionally naphtha crystals are needed to deinfest a rug. Better yet, all the rugs should be sent out to be cleaned, and repellants should be worn on the ankles. Shuffling across a floor with flypaper leggings will catch many leaping fleas. Black Flag is a good killer spray.

Sand Fleas (Tunga penetrans)
Sand fleas are burrowing insects indigenous to South America, the West Indies and Africa producing shallow lesions usually around the great toenail but in general on the lower extremities. The fleas gradually engorge themselves with blood as they burrow and should be removed carefully with a flat needle. The lesions are referred to as chigo itch (no relation to chiggers). Good solid shoes usually prevent this.

Pediculosis (Lice, Anoplura)

Pediculosis Corporis
The lice live in clothing; the nits hatch in 9 days and must feed within 24 hours. The adult lives about 30 days and is a vector for relapsing fever and typhus. Diagnosis is made by seeing parallel linear scratch marks on the shoulders, back, buttocks and thighs, sparing the face and hands, with small red puncta and an urticarial eruption. In long-standing cases (vagabonds' disease), enlarged regional lymph nodes and a peculiar melanoderma not unlike Addison's disease are features.
Treatment
Historically in large populations, 10% DDT in talc blown into the clothing was used to deinfest; otherwise hot soap-and-water baths and sterilization of the clothing, including bedding, in an autoclave or oven (hotter than 160 F) is satisfactory.

Pediculosis Capitis
Blacks are immune to this infestation of the scalp hair. Characteristically the nape of the neck is excoriated, itchy and may be impetiginized and crusted with a bad odor. The nits can be seen attached to the hair, firmly. They have a characteristic fluorescence when tested with Wood's light (white). This pediculosis is more common in children than in adults.
Treatment
Benzyl benzoate emulsion, lindane or permethrin are effective. A steel fine comb facilitates the cure. It is advisable to repeat the treatment several times and ensure cure. Sources of infestation must be removed, and family, school mates and other acquaintances should be checked. Soaking the combs in ammonia water for 2 hours allows the nits to be easily removed. Hats are best discarded. Nits hatch in a week, so weekly examination must be done. Vinegar has some dissolving effect on the nit cement as does derosene (used 50% in mineral oil). Benzyl benzoate is most reliable.

Pediculosis Pubis
Ordinarily the crab louse is confined to the pubic and anal hair, but in hirsute or heavily infested patients, the chest hair, arm and leg hair, as well as the axilla, beard and eyelashes can be infested. These areas should be examined thoroughly on each visit. The nits attach themselves to the hair and probably are nourished by apocrine secretion. This disease is seen in all classes of society, as opposed to other varieties of lice which favor the poorer sections of the population. One hairy patient who periodically has to make a 6-week swing through some small towns with inferior hotels, shaves himself from head to foot before and during his trip. Once bitten, twice shy. Undoubtedly some people are more susceptible than others. Crab lice are considered a sexually transmitted disease although this is not always the case.
Treatment
Often these lice can be exasperatingly difficult to eradicate in a clean person; treatment should be for three weeks as a rule and threat the marital partner at the same time. Treatment with Kwell shampoo daily and Kwell lotion, or benzyl benzoate applied twice a week from navel to knees and elsewhere as needed, with occasional steel combing, has been necessary despite optimistic one-shot treatments recommended elsewhere. For eyelid infestation, yellow oxide of mercury ophthalmic ointment 1% is very helpful, pulling the nits off with forceps. Maculae caeruleae (taches bleuatres), slate-gray bluish macules 4-10 mm in diameter, are occasionally encountered on the chest, thighs or abdomen of heavily infested patients, and they can in general be disregarded as a vasomotor phenomenon secondary to the material injected into the skin while the louse is dining.

Bedbugs (Cimicidae)
This cosmopolitan disease is caused by a flat, hard 4-mm-long and 3-mm-wide insect that could survive a year in a test tube with no food, generally lives in cracks and wooden beds or furniture or under baseboards, wallpaper or mattress tufts, lays eggs over a long period and has three or four generations per year. It comes out at night to attack the sleeper and takes 10-15 minutes to gorge. For diagnosis, the occurrence of two to five grouped and evenly spaced lesions, usually urticarial papules at the exposed areas, e.g., the wrist, ankle, waist and neck, with new lesions occurring nightly either in a segment of a circle or in a straight line, is strongly suggestive. Often others in the room will be affected, too.
Treatment
The beds should be taken apart and all the joints sprayed with an effective spray, as well as baseboards, mattress tufts, floors and walls. The sprays linger for 3 to 4 months, so perhaps spraying every few months for a year is the best way to deal with this problem. Heating the house to 130 F with the windows closed will also destroy the bedbugs.

Larva Migrans (Creeping Eruption)
This disease consists of irregular wandering tunnels because of the invasion of the skin by a larval form of certain roundworms (usually cat and dog hookworms) in the sands of the southern United States. Cases have been contracted on New England beaches too. Larva currens (cutaneous Strongyloides) can mimic larva migrans, though the invasion usually is on the buttocks.
Treatment
Thiabendazole, 50 mg/kg body weight, given either all in one dose or over 2 days, is curative. Ethyl chloride spray refrigeration at the "head" for more than 60 seconds used to be the treatment. The thiabendazole suspension (10%) rubbed in locally either with or without occlusion is effective.

Pinworms (Oxyuriasis)
This usually involves children, though parents can also be infested. The disease manifests itself by anal itching. A flashlight at night will occasionally demonstrate the worms, and anal smears, if done first thing in the morning will catch ova. A small piece of Scotch tape can be used for this purpose, stuck on a glass slide and mailed to the provincial or state laboratory.
Treatment
Any good antibiotic will slow up the worm either internally or externally, since it hatches its eggs outside the anus. Pyrinium pamoate, 5-10 mg/kg body weight, given once and repeated in a week, gives excellent results. The tablets are superior to the liquid, which has an unpleasant oily clinging flavor. Mebendazole, is a second choice with a single dose of 100 mg; repeat after 2 weeks. A single dose of 100 mg for children >2 years; repeat after 2 weeks.Piperazine adipate, one teaspoon given three times a day for a week, and Antepar, given according to weight, are alternative treatments. Since the infestation is continued by the fingernails transmitting eggs from anus to mouth, obvious precautions include a nail brush, tight shorts worn in bed at night and frequent changes of bed linen.

This document is a resource from the
Internet Dermatology Society
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Rhett Drugge, M.D.
Last Update: February 17,1997