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A parent brings in a 4-year-old boy suffering with anal itching. On examination, the physician finds several excoriations around the anus and suspects pinworms. The physician then applies Scotch tape to the perianal area and places the tape on a glass slide. Review of the slide demonstrates adult worms and ova of Enterobius vermicularis (pinworms) (Figure 223-1). The boy is treated with a single dose of chewable mebendazole and his symptoms resolve. The parent is told to repeat the mebendazole dose in 2 weeks to increase the long-term cure rate. If the Scotch tape test were negative, the physician could choose to treat empirically or have the parent apply the Scotch tape to the boy's perianal area first thing in the morning and bring that back to the office (the yield is higher in the morning).

FIGURE 223-1

Enterobius vermicularis (pinworms and ova) seen under the microscope from a Scotch tape specimen taken of the perianal region of a 4-year-old boy with anal itching. (Reproduced with permission from James L. Fishback, MD.)


Intestinal parasites are most common in places with warmer temperatures and high humidity, poor sanitation and unclean water, and a large number of individuals (especially children) living in close proximity. In general, the parasites are either asymptomatic or cause symptoms related to their presence in the GI tract. Several migrate through the lungs and can cause pulmonary symptoms during the migration. Diagnoses are made by history of worms being seen by the patient or parents or by laboratory examination for ova and parasites in the stool.


  • Nematoda is the phylum that contains pinworms, hookworms, Ascaris, Strongyloides, and whipworms.

    • E. vermicularis (pinworm) is the most prevalent nematode in the United States. Populations at risk include children under the age of 18, institutionalized persons, and household members of persons with pinworm infection1 (see Figure 223-1).

    • Necator americanus (Figures 223-2 and 223-3) and Ancylostoma duodenale (hookworms) are found worldwide in areas with warm, moist climates. An estimated 576–740 million people in the world are infected with hookworms.1

    • Ascaris lumbricoides, uncommonly seen in the United States, is the largest and most common roundworm worldwide, affecting 1000 million people. It is found in tropical and subtropical areas where sanitation and hygiene are poor (Figures 223-4 and 223-5).1

    • Strongyloides stercoralis is seen mostly in tropical, subtropical, and temperate areas and affects 30–100 million people worldwide (Figure 223-6). It is more commonly found in immigrants, rural areas, institutional settings, and lower socioeconomic groups.1

    • Trichuris trichiura (whipworm) is the third most common roundworm, affecting 604–795 million people worldwide. Infections are more frequent in areas with tropical weather and poor sanitation practices, and among children (Figure 223-7). ...

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