Enterobius vermicularis
المؤلف:
Patricia M. Tille, PhD, MLS(ASCP)
المصدر:
Bailey & Scotts Diagnostic Microbiology
الجزء والصفحة:
13th Edition , p657-660
2025-10-21
91
GENERAL CHARACTERISTICS
Enterobius vermicularis (pinworm) is distributed worldwide and commonly identified in group settings of children ages 5 to 10 years. The life cycle is considered direct; transmission occurs from an infected host to another individual (Figure 1). During the night, the mature female worm migrates out of the anus of the infected host and lays eggs in the perianal region. The embryonated eggs will mature and a third-stage larva stage develops, resulting in infectivity within hours. Transmission occurs by ingestion or inhalation of eggs. Reinfection may also occur when the eggs hatch and larvae return to the intestine where they mature.
Fig1. Life cycles of Enterobius vermicularis and Trichuris trichiura (direct life cycle).
EPIDEMIOLOGY
Pinworm is more prevalent in school-age children up to about 14 years of age. Infections are associated with institutional crowding and are familial. Transmission is also associated with an increased rate of reinfection within a group or autoinfection from hatched larvae.
PATHOGENESIS AND SPECTRUM OF DISEASE
Infections with E. vermicularis are typically asymptomatic. The most common complaint is perianal pruritus (itching) and resultant restless sleep. Occasionally, the parasite may migrate to other nearby tissues, causing pelvic, cervical, or peritoneal granulomas. See Table 1 for a summarized detail of associated diseases.
Table1. Pathogenesis and Spectrum of Associated Diseases
Table1. Pathogenesis and Spectrum of Disease—cont’d
LABORATORY DIAGNOSIS
Diagnosis is typically by microscopic identification of the characteristic flat-sided ovum (Figure 2). The eggs are collected using a sticky paddle or cellophane tape pressed against the perianal region. Eggs are not typically identified in feces, although they may occasionally be found in a stool specimen. Although adult pinworms may be visible, they can be easily confused with small pieces of thread. The female worm measures 8 to 13 mm long with a pointed “pin” shaped tail. In gravid females, almost the entire body will be filled with eggs (Figure 3). The males measure only 2 to 5 mm in length, die following fertilization, and may be passed in feces.
Fig2. Enterobius vermicularis eggs (cellophane [Scotch] tape preparation).
Fig3. Enterobius vermicularis gravid female. (Courtesy Dr. Henry Travers, Sioux Falls, S.D.)
THERAPY
Anthelmintic therapy is generally effective with one of the following agents: albendazole, mebendazole, pyrantel pamoate, or ivermectin.
PREVENTION
Regular good personal hygiene is the major factor for prevention of continued reinfection and autoinfection.
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