Environmental Dermatology

What’s Eating You? Human Body Lice (Pediculus humanus corporis)

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Diagnosis can be reached by visualizing adult lice, nymphs, or viable nits on the body or more commonly within inner clothing seams; nits also fluoresce under Wood light.15 Although dermoscopy has proven useful for increased sensitivity and differentiation between viable and hatched nits, the insects also can be viewed with the unaided eye.16

Treatment: New Concerns and Strategies

The mainstay of treatment for body lice has long consisted of thorough washing and drying of all clothing and linens in a hot dryer. Treatment can be augmented with the addition of pharmacotherapy, plus antibiotics as warranted for louse-borne disease. Pharmacologic intervention often is used in cases of mass infestation and is similar to head lice.

Options for head lice include topical permethrin, malathion, lindane, spinosad, benzyl alcohol, and ivermectin. Pyrethroids, derived from the chrysanthemum, generally are considered safe for human use with a side-effect profile limited to irritation and allergy17; however, neurotoxicity and leukemia are clinical concerns, with an association more recently shown between large-volume use of pyrethroids and acute lymphoblastic leukemia.18,19 Use of lindane is not recommended due to a greater potential for central nervous system neurotoxicity, manifested by seizures, with repeated large surface application. Malathion is problematic due to the risk for mucosal irritation, flammability of some formulations, and theoretical organophosphate poisoning, as its mechanism of action involves inhibition of acetylcholinesterase.15 However, in the context of head lice treatment, a randomized controlled trial reported no incidence of acetylcholinesterase inhibition.20 Spinosad, manufactured from the soil bacterium Saccharopolyspora spinosa, functions similarly by interfering with the nicotinic acetylcholine receptor and also carries a risk for skin irritation.21 Among all the treatment options, we prefer benzyl alcohol, particularly in the context of resistance, as it is effective via a physical mechanism of action and lacks notable neurotoxic effects to the host. Use of benzyl alcohol is approved for patients as young as 6 months; it functions by asphyxiating the lice via paralysis of the respiratory spiracle with occlusion by inert ingredients. Itching, episodic numbness, and scalp or mucosal irritation are possible complications of treatment.22

Treatment resistance of body lice has increased in recent years, warranting exploration of additional management strategies. Moreover, developing resistance to lindane and malathion has been reported.23 Resistance to pyrethroids has been attributed to mutations in a voltage-gated sodium channel, one of which was universally present in the sampling of a single population.24 A randomized controlled trial showed that off-label oral ivermectin 400 μg/kg was superior to malathion lotion 0.5% in difficult-to-treat cases of head lice25; utility of oral ivermectin also has been reported in body lice.26 In vitro studies also have shown promise for pursuing synergistic treatment of body lice with both ivermectin and antibiotics.27

A novel primary prophylaxis approach for at-risk homeless individuals recently utilized permethrin-impregnated underwear. Although the intervention provided short-term infestation improvement, longer-term use did not show improvement from placebo and also increased prevalence of permethrin-resistant haplotypes.2

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