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 7-1 may be guessed with reasonable correctness to be mosquito “bites,” and Fig. 7-2 to be flea bites. We use quotation marks to suggest that the proboscis of a mosquito is not a true biting part. Fleas may nip.
The mark of mosquito feeding is usually recognized easily because the season is right; the actual event is frequently seen as well as felt; often it is interrupted by a slap, which, when successful, results in a dead assailant; and the clinical and symptomatic consequences are familiar. Figure 7-1 shows the type of pruritic, urticarial, or edematous lesion caused by mosquitoes. Figure 7-2 and Figs. 7-3 and 7-5 are characteristic of “bites” of insects that feed, browse, and feed again. Bedbugs and fleas are such insects. The marks tend to be aligned in rows of two or three. In the case of the bedbug, Cimex lectularis (Fig. 7-4), the number of lesions will depend on the number harbored and the immobility or restlessness and ineffable attractiveness of sleepers (Fig. 7-3). Commonly, only one of two or more contiguous bedfellows is afflicted.
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. The lesions in Fig. 7-5 may well have been caused by mosquitoes, bedbugs, or fleas, but instead of the usual central punctum and surrounding erythema and edema, vesiculation has developed, probably signifying more-than-average host response as a result of previous sensitization. Figure 7-6 shows a more intense vesicular reaction before scratching.