Insect “bites” Many effects of metazoal parasitism are attributed to bites. Some metazoa (insects in a loose sense) do indeed bite, and others sting, but what we frequently designate as insect bite is attachment for feeding. The result of such attachment looks like a bite and is sooner or later attended by pain, itching, or stinging. True bites and stings, however, are instantly painful; many have immediate or late, more baleful effects; and most are generally inflicted in self-defense or seemingly wanton offense, not for feeding.

Attachment for feeding is parasitism that may be silent for a while and then variably symptomatic. In a given region, common indigenous metazoa that cause cutaneous effects by a bite, sting, or attachment for feeding may be recognized or guessed from signs and symptoms. These two illustrations are representative. Figure 8-1 may be guessed with reasonable correctness to be mosquito “bites,” and Fig. 8-2, clustered on the lower leg and ankle, to be flea bites. Because different family members may have different degrees of sensitivity, it is possible that only one or several in the household will develop these lesions, and others will be spared.

Insect “bites” The location of bites gives important clues to the causative insects. Those pictured in Figs. 8-3 and 8-4 are unlikely to be from mosquitoes (which tend to bite on exposed areas of skin) or fleas (which tend to bite the ankles and lower legs). A variety of crawling insects and mites can cause lesions of this sort, including chiggers.

Chigger bites are caused by trombiculid mites. These mites live in tall grasses and weeds and are most active in summer and fall. They attach to the skin as one walks by and brushes up against the vegetation. Lesions tend to occur in areas that are warmer, moister, or covered by tight clothing. The intense itching may last for several days.

Insect “bites” Certain insects creep under clothes and bite when they reach a point of restriction such as a sock or belt. Figure 8-5 shows bite marks and vast edema on the penis. The assaulting insect may have been an ordinary one that merely took advantage of a child left undressed and unguarded.

When a subject has been bitten, stung, or fed upon, the consequent lesion may be typical at the time and in its course to resolution or may be modified by scratching, secondary infection, or idiosyncratic host response. In the case of the mosquito, the lesions may be one, few, or many, depending on the insensitivity, foolhardiness, or defenselessness of the subject assailed.

Insect “bites” The vesicular lesions in Fig. 8-6 and the bullous lesions in Fig. 8-7 are evidence of a strong hypersensitivity reaction to the offending insect.

Dermatitis caused by the common carpet beetle The common carpet beetle is not common in modern well-sanitized homes, and even where it is abundant, effects from it are not common. Nevertheless, on occasion, the crawl of the insect on an unwary individual leaves its marks as wheals, papulovesicles, or bullae. Figure 8-8 shows just such an event in the form of large, flaccid blisters. The three lesions in a line record the walk of a creature and the deposition of its irritant principle.

Spider bites Spiders, timid creatures for all their fierce looks, would rather entertain insects in their parlors than attack humans. The tarantula is more dangerous in fable than in fact. Two spiders can deliver painful bites and serious veneration if frightened or cornered: the black widow spider (Latrodectus mactans) and the brown recluse spider (Loxosceles reclusa). The bite of the latter is illustrated in Fig. 8-9. It is a hemorrhagic bleb; in time it will become a necrotic ulcer. The patient will be severely sickened.

Papular urticaria This is a pruritic dermatosis that is causally related to bites by mosquitoes, fleas, or other insects. Children with this common disorder tend to have recurrent episodes during the spring and summer months. The lesions consist of firm erythematous papules, sometimes with surrounding wheals. They favor exposed areas, especially the anterior lower extremities and lower arms. The individual papules are often excoriated and are sometimes impetiginized.

The lesions tend to last for several days to weeks but will persist longer if chronically scratched or rubbed. Papular urticaria is more common among children with atopic diathesis and represents a hypersensitivity reaction to the assaulting arthropod. Treatment consists of lotions, topical steroids, and antihistamines. The elimination of the offending insect from the household environment is helpful but will not prevent encounters during outdoor play.

Ticks Figure 8-12 shows an engorged deer tick attached to its human host. Ticks of the Ixodes species are vectors of Lyme disease as well as hemorrhagic fevers and viral encephalitis. Most tick bites are not painful and therefore may go unnoticed by patients for variable periods of time. A tick bite may appear as a red papule or may progress to erythema with local swelling, blistering, or ecchymosis. Chronic tick bite granulomas can develop and last for months to years.

Tick “bite” Tick infestation occurs when the female soft or hard tick inserts her proboscis into the skin in order to withdraw blood. The site of attachment may develop into an erythematous nodule, and persistent pruritus may result if tick parts are left within the skin. Although most tick bites are insignificant, these insects are the vectors of tick bite fever, Rocky Mountain spotted fever (Figs. 4-34 and 4-35) and erythema chronicum migrans (Lyme disease) (Figs. 4-8, 4-9, 4-10, 4-11).

Tick bite granuloma Sometimes at the site of a tick bite, a persistent firm papulonodular lesion may develop. A common site for this reaction to develop is in the scalp. This area may be very pruritic and with excoriation may result in secondary infection.

Scabies Infection of the skin by the human scabies mite (Sarcoptes scabiei var. hominis) is an extremely common skin disease of childhood. Figure 8-15 shows a child with multiple intensely pruritic lesions on the trunk. Examination of adult family members for lesions in the finger webs, waist line, and wrists provide a clue to the diagnosis in the child.

Figure 8-16 shows another severe case of scabies. The infant with scabies illustrated here has numerous excoriated papules and a diffuse eczematous dermatitis. In infants, scabies frequently involves the entire cutaneous surface including the face and scalp. Young infants without apparent pruritus may manifest extreme irritability.