Mites are ubiquitous parasites that infest humans and domestic animals such as dogs and cats, as well as wild birds, chickens, bats, rodents, and even snakes. Humans encounter mites on pets or in their natural habitat while engaging in outdoor activities such as hiking and camping. The human itch mite, Sarcoptes scabiei, is transmitted by close personal contact and thus easily spread among children.

Although some mites are vectors for viral and rickettsial diseases, the most common clinical manifestation is local skin inflammation. The reaction, which typically occurs within minutes to hours of a bite occurring, may be the result of hypersensitivity to agents secreted during feeding. For example, chiggers, also known as harvest mites or red bugs, attach to the skin, inject proteolytic enzymes, and then feed on the degraded tissue. The chigger may remain attached for as long as 4 days, and then it drops off into the soil to mature into its adult form. The bite itself is painless, so hosts often do not know they have been bitten until pruritic macules appear 3 to 24 hours later. Sarcoptes scabie also is the cause of scabies. The female adult mite becomes pregnant and then burrows through the skin, leaving behind a trail of eggs, feces, and debris. Clinically, an intensely pruritic hypersensitivity reaction occurs in the form of erythematous papules, nodules, vesicles, or pustules. The clinical distribution varies depending on the age of the child. The feet, palms, axillae, and scalp are the usual sites of infestation in infants, whereas older children have burrows and lesions on the wrist, the genitalia, the waist or umbilicus, or in the finger webs. The diagnosis is confirmed by scraping the representative skin lesions and viewing the mites, eggs, and/or feces under the microscope.

Whereas most mite bites are treated symptomatically to reduce itching and to prevent secondary infections, the scabies mite completes its entire life cycle on the human host, and thus infestation may persist until an effective scabicide is used. Lindane was the recommended treatment of scabies; however, growing resistance and safety concerns over potential neurologic side effects in children have rendered other agents first-line therapy. Permethrin 5% cream is the treatment of choice for children older than 2 months of age and adults; precipitated sulfur (5% to 15%) in petrolatum is safe for infants (Table 227.1). A single dose of oral ivermectin [200 μg/kg (not for children < 15 kg)] also has been shown to be effective in treating scabies. Topical ivermectin and aqueous malathion (0.5%) are additional scabicides currently being investigated. To avoid reinfestation, all close contacts must be treated at the same time, and all
clothing, bedding, and other items in close contact with the patient must be washed and dried thoroughly.

Ticks are macroscopic arthropods that may cause a local reaction after a bite but, more importantly, also can transmit several potentially serious infectious diseases to their human hosts (Table 227.2). Tick bites most commonly occur in the spring and summer when their hosts (e.g., dogs and children) can be found playing outside, especially in wooded areas. Most ticks that feed on humans attach themselves using barbed mouth parts called chelicerae. They then secrete a strong, cement-like substance that secures the attachment for as long as 7 days. After engorging themselves with blood, they drop off their hosts. Because the bite is painless, ticks often are noted only when the child bathes or is undressed.

The local reaction, thought to be mediated by complement, may result from hypersensitivity, injected toxins, or irritation to the tick’s secretions. A pruritic red papule with or without swelling, blistering, and bruising usually occurs within days to weeks of being bitten. Most tick bites heal in 2 to 3 weeks, but the reaction may persist for months to years as a nodular tick-bite granuloma.

Some pregnant female ticks secrete a neurotoxin that causes tick paralysis, an acute neurologic syndrome characterized by an ascending lower motor neuron paralysis. The patient develops ataxia and areflexia 1 to 2 days after the tick attaches, and if the tick is not removed, the syndrome can progress to involve the trunk, upper extremities, pharynx, and tongue. Death may result from respiratory compromise. Tick paralysis can be diagnosed by clinical course only; the patient’s neurologic symptoms improve once the tick is removed. Therapy otherwise is supportive.

The best treatment is prompt removal of the tick (usually within 48 hours) to prevent transmission of infection. The recommended method for removal of a tick is to grasp it with curved forceps or protected fingers as close to the skin as possible and then exert a steady pulling force until the tick is withdrawn from the skin. Remaining mouth parts (chelicerae) also should be removed.

Prevention of tick bites includes practical avoidance measures as well as the use of chemical repellants. The American Academy of Pediatrics recommends removing potential tick habitats by clearing brush and leaf litter, removing woodpiles, and keeping grass lawns mowed in endemic residential areas. Endemic wooded areas should be avoided entirely, but if this is not possible, the Academy recommends using (and not straying from) wide trails and not sitting on the ground. Selection of clothing is also important. Hats, long-sleeved shirts tight at the wrists, and long pants tight at the waist and tucked into socks are preferred. All items should be light in color to help identify the ticks. Repellants with N, N-diethyl-3-methylbenzamide (DEET) should be applied and reapplied every 1 to 2 hours for additional protection (for further discussion of DEET, please see mosquito treatment and prevention section). Another protective agent against ticks is permethrin, an insecticide that kills ticks on contact and is applied to clothing and outdoor equipment rather than the skin. Permethrin also is effective against mosquitoes, biting flies, chiggers, and scabies mites.