Ectoparasiticides

CHAPTER 100


Ectoparasiticides


Ectoparasites are parasites that live on the surface of the host. Most ectoparasites that infest humans live on the skin and hair. Some live on clothing and bedding, moving to the host only to feed. The principal ectoparasites that infest humans are mites and lice. Infestation with lice is known as pediculosis. Infestation with mites is known as scabies. Both conditions are characterized by intense pruritus (itching). With the exception of ivermectin, all of the drugs used for treatment are topical.




Ectoparasitic infestations


Pediculosis (infestation with lice)


Pediculosis is a general term referring to infestation with any of several kinds of lice. The types of lice encountered most frequently are Pediculus humanus capitis (head louse), Pediculus humanus corporis (body louse), and Phthirus pubis (pubic or crab louse). Infestation with any of these insects causes pruritus. Infestations with head, body, and pubic lice differ with regard to mode of acquisition and method of treatment.



Head lice

Head lice are common parasites, infesting 6 to 12 million people annually in the United States, and over 100 million people worldwide. Infestation is most common in children 3 to 11 years old. Head lice reside on the scalp and lay their nits (eggs) on the hair. Adult lice may be difficult to observe. Nits, however, are usually visible. Infestation may be associated with hives, boils, impetigo, and other skin disorders. The head louse is more democratic than the pubic or body louse and can be found infesting people from all socioeconomic groups. Head lice, which neither jump nor fly, are usually transmitted by head-to-head contact. Transmission by contact with combs, hairbrushes, and hats may also occur, but has not been proven. Because humans are the only host for these obligate parasites, infestation cannot be acquired through contact with pets or any other animals.


According to recommendations from the American Academy of Pediatrics (AAP), released in 2010, the treatments of choice are 1% permethrin and pyrethrins with piperonyl butoxide, provided resistance is not suspected. If resistance is suspected, either malathion, benzyl alcohol, or spinosad should be used. Oral ivermectin can be tried if these other drugs fail, although ivermectin is not approved for killing lice. A few days after drug treatment, dead lice (and remaining live lice) should be removed from the hair with a fine-toothed comb. Eradication of head lice does not require shaving or cutting the hair.



Body lice

Despite their name, body lice reside not on the body but on clothing. These lice move to the body only to feed. Consequently, body lice are rarely seen on the skin. Rather, they can be found in bed linens and the seams of garments. Transmission of body lice is by contact with infested clothing or bedding. Body lice are relatively uncommon in the United States, where regular laundering precludes infestation. Infestation is most likely among vagrants and other people whose clothes may not be frequently washed. The majority of body lice can be removed from the host simply by removing his or her clothing. Those lice that remain on the body can be killed by applying a pesticide; permethrin and malathion are drugs of choice. Clothing and bedding should be disinfected by washing and drying at high temperature. Oral ivermectin may be tried if topical treatments fail, although ivermectin is not approved for this use.




Scabies (infestation with mites)


Scabies is caused by infestation with Sarcoptes scabiei, an organism known commonly as the itch mite. Irritation results from the female mite burrowing beneath the skin to lay eggs. Burrows may be visible as small ridges or dotted lines. In adults, the most common sites of infestation are the wrists, elbows, nipples, navel, genital region, and webs of the fingers. In children, infestation is most likely on the head, neck, and buttocks. The primary symptom of scabies is pruritus. Itching is most intense just after going to bed. Scratching may result in abrasion and secondary infection. Transmission is usually by direct contact, either sexual or of a less intimate nature. Scabies may also be transmitted through contact with infested linen, towels, or clothing.


Scabies is usually treated with a pesticide-containing lotion or cream. To eradicate mites, the entire body surface must be treated (excluding the face and scalp in adults). To prevent reinfestation, bedding and intimate clothing should be machine washed and dried.


Several drugs can kill mites. Permethrin (5% cream formulation) is the drug of choice. This preparation is effective in just one application. Crotamiton is a preferred alternative. In addition, there is evidence that a single oral dose (200 mcg/kg) of ivermectin [Stromectol] can cure scabies, although the drug is not approved for this use.



Pharmacology of ectoparasiticides


As a rule, ectoparasitic infestations are treated with topical drugs. These agents are available in the form of creams, gels, lotions, liquids, and shampoos. Only one ectoparasiticide—ivermectin—is administered orally. Properties of the major ectoparasiticides are summarized in Table 100–1.

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Jul 24, 2016 | Posted by in NURSING | Comments Off on Ectoparasiticides

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