The value of external morphology in the identification of larval anisakid nematodes: a scanning electron microscope study

Abstract

We studied larval nematodes of four genera of the Anisakidae using a scanning electron microscope (SEM). The anterior and posterior extremities and cuticular structures of the 3rd-stage larvae (L3) of Anisakis type I, Pseudoterranova decipiens, Contracaecum type B and Hysterothylacium were examined. The 4th-stage larvae (L4) of Anisakis type I, P. decipiens, recovered after infection into laboratory rats, and the L3 and L4 of Anisakis type I larvae from human were also examined in the same way. There were generic differences in the shape and size of the lip bulges, external papillary structures, the appearance of the boring tooth, the width and depth of the grooves and ridges of the cuticle and the caudal structures of the L3. In Anisakis type I and P. decipiens L3, changes were seen in the anterior extremity, cuticle and posterior extremity after molting to the L4. Similar changes can be expected in larvae infecting man. The L4 of Anisakis type I from rat and man were similar, while the L4 of Anisakis type I and P. decipiens showed differences. These ultrastructural differences might be of value in the identification of fragments recovered during endoscopy in man.

Acute intestinal anisakiasis in Spain: a fourth-stage Anisakis simplex larva

“…That the L3 of Anisakis spp. can pass to the fourth stage in humans, parasitizing the gastrointestinal tract has been confirmed elsewhere (Kagei et al 1978, Weerasooriya et al 1986, Clavel et al 1993. In experimental animals, it has been demonstrated that the parasite can pass from the L3 to the L4 stage in three days (Weerasooriya et al 1986).…”

“…can pass to the fourth stage in humans, parasitizing the gastrointestinal tract has been confirmed elsewhere (Kagei et al 1978, Weerasooriya et al 1986, Clavel et al 1993. In experimental animals, it has been demonstrated that the parasite can pass from the L3 to the L4 stage in three days (Weerasooriya et al 1986). In humans, according to Fujino et al (1984), the first moult occurs three to four days after ingestion of the larva, as has been reported for a number of experimental mammalian hosts (Weerasooriya et al 1986).…”

“…The end of this structure had a tiny hook. On the basis of its morphological features and according to the description (Weerasooriya et al 1986, Ishii et al 1989, the parasite was identified as a fourth-stage larva of A. simplex.…”

“…The larvae was identified by its morphology (Weerasooriya et al 1986, Ishii et al 1989, as the fourth larval stage of A. simplex, by the absence of a cuticular tooth, as seen by optical and electron microscopy ( Fig. 2), and by the presence of a rugose protuberance in the place of the mucron (Fig.…”

“…In experimental animals, it has been demonstrated that the parasite can pass from the L3 to the L4 stage in three days (Weerasooriya et al 1986). In humans, according to Fujino et al (1984), the first moult occurs three to four days after ingestion of the larva, as has been reported for a number of experimental mammalian hosts (Weerasooriya et al 1986). This is the ninth report of human anisakiasis in Spain, the second caused by M. enchasicholus and also the first case of anisakiasis in which the fourth-stage A. simplex larva has been isolated in Spain.…”