An infestation is the development of a pathogenic organism on, rather than in, the body. The term is also used to describe the presence of a population of arthropods (including insects, ticks, and other mites) that cause damage to, or disease of, the host. The most common infestations affecting pediatric patients will be discussed, with an emphasis on scabies, ticks, lice, bedbugs, and fleas.
Mites are a diverse group of tiny, 8-legged arthropods that possess the ability to live freely in the environment or to parasitize plants and animals. Ticks are closely related to mites and, like mites, are members of the class Arachnida. Both ticks and mites possess a head and nonsegmented abdomen and are covered by an exoskeleton. Certain mites and ticks can attach to or burrow into the skin of human hosts, causing pruritus and/or localized bite reactions. Scabies and chiggers are the mites of greatest importance in the pediatric population.
Scabies is a common, intensely pruritic skin infestation caused by the Sarcoptes scabiei var hominis mite. As an obligate human parasite, scabies is primarily transmitted by human-to-human contact, although the ability to live away from human skin for up to 36 hours allows for limited transmission via fomites. All developmental stages of the scabies mite may burrow into the stratum corneum where the life cycle is completed. Female mites lay eggs into the burrow and the eggs hatch after a 3- to 4-day incubation. Resulting larvae mature into adults over 10 to 13 days. The chronology of the scabies life cycle has important implications on the timing of treatment. Two treatments, spaced 1 week apart, are recommended to target nymphs hatched from eggs that survived the initial treatment.
Scabies has 4 basic clinical presentations: classic (most common), incognito, nodular, and crusted. The signs and symptoms of scabies generally appear about 3 weeks after a primary-exposure and are thought to represent a delayed type IV hypersensitivity response to the mite, its eggs, or its feces; however, an immediate hypersensitivity reaction can occur within 24 hours upon re-exposure. Severe pruritus is often the first symptom. Burrows consist of gray-white, serpiginous lines several millimeters in length and are pathognomonic for scabies but often limited in number or absent. Burrows are most commonly located in the web spaces of the fingers, near the flexural surface of the wrists and elbows, along the waist, or on the armpits, breasts, genitals, and lateral aspect of the feet (Fig. 363-1A). A black dot at one end of the burrow may indicate the location of the mite (Fig. 363-1B). Papules and excoriations are more common clinical features of classic scabies and are generally located on the shoulders, back, axillae, flexor aspect of the elbows, ...