The organism was first identified in 1758 by Karl Linnaeus, who named it Oxyuris vermicularis. There are two species recognised currently: E. vermicularis and a more recently identified
E. gregorii (Ashford et al., 1988; Chittenden and Ashford, 1987), although some authors have cast doubt on the validity of this species (Hasegawa et al., 1998). The male measures 2-5 mm in length x 0.1-0.2 mm in diameter and has a single conspicuous copulatory spicule. The female measures 8-15mm in lengthx 0.3-0.5mm in diameter. The tail is sharply pointed and the vulva opens mid-ventrally just in front of the middle third of the body. In gravid females the uteri are distended and the entire body is packed with eggs. The eggs are ovoid, 5054 ^ x 20-27 ^ in size, and almost colourless. The shell is thick with an outer albuminous layer that assists in adherence to skin and other objects (see Figure 21.4).
Fig. 21.4 Typical D-shaped egg of Enterobius vermicularis
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