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Virtually all organ systems are at risk for parasitic infestation, with symptoms depending on the system(s) involved. Some parasites only begin to produce symptoms months to years after the first exposure.
Ascaris lumbricoides is the largest and most prevalent human nematode, with an estimated one billion cases worldwide. Albendazole (400 mg orally as a single dose) or ivermectin (150–200 μg/kg orally as a single dose) is curative.
Enterobius vermicularis (pinworm) affects individuals of all ages and socioeconomic levels, with the most common presentation being that of a toddler or small child with anal itch. Scotch tape, placed sticky side to perianal skin when the child first awakens and viewed under low power may reveal the eggs, but may require repeated sampling.
Trichuris trichiura (whipworm) lives predominantly in the cecum and can cause malabsorptive symptoms, pain, bloody diarrhea, and fever but is usually asymptomatic. A heavy worm burden may cause a colitis-like picture with rectal prolapse and anemia.
The hookworms, Necator americanus and Ancylostoma duodenale, are one of the most prevalent infectious diseases of humans. The hallmark of hookworm infestation is the microcytic, hypochromic anemia of iron deficiency.
The avian schistosome Trichobilharzia ocellata is spread by migratory birds to the freshwater lakes of the northern United States. The cercariae cause dermatitis, known as swimmer's itch.
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Parasitic diseases are ubiquitous. Despite worldwide advances in sanitation, new medications, and the heightened awareness of health care providers, between one-fourth and one-half of the world's population has a parasitic infestation at any given time. Children's normal developmental oral exploratory behavior places them at particular risk for acquiring parasites. Travel, immigration, the importation of vectors via international trade, and the increased number of immunocompromised hosts have all led to an increase in disease. (see Chapter 59, Evaluation and Management of the Immunocompromised Patient and Chapter 66, Imported Diseases/Diseases in the Traveling Child). Parasitic diseases endemic to the United States are primarily described here.
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Three major groups of parasites cause human disease: helminths, protozoa, and arthropods (Anthropods discussed in Chapter XX in dermatology). Three important subgroups of helminths cause human disease: nematodes (roundworms), cestodes (flatworms), and trematodes (flukes).
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Important factors to be elicited in the history are included in Table 65-1. Virtually all organ systems are at risk for infestation, with symptoms depending on the system(s) involved. The varied and often nonspecific symptoms produced (Table 65-2) place parasitic infestation on the expanded differential diagnosis of most patients presenting to the emergency department (ED). Symptoms produced depend on the stage of the parasitic life cycle.
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