Surface ultrastructures of the third-stage larvae of Gnathostoma hispidum.

A scanning electron microscopic study was performed to observe the surface ultrastructures of the third-stage larvae of Gnathostoma hispidum. The early third-stage larvae (EL3) were collected from the viscera of Chinese loaches by the artificial digestion method. The advanced third-stage larvae (ADL3) were recovered from mice experimentally infected with EL3. Both larval worms were fixed with 2.5% glutaraldehyde, dehydrated in graded alcohol, dryed in critical point dryer, and coated with gold. The specimens were observed with a SEM (DS-130C). On the head bulb of both larval stage, the mouth had a pair of lateral lips of equal size and of half moon shape. Each lip had a couple of labial papillae and a small amphid located between the two papillae. The hooklets on the head bulb had single-pointed tips and curved posteriorly. The cuticular spines of EL3 were larger and more densely distributed in the anterior area (about 1.8 micron in length) and gradually decreased in size and number posteriorly. The cuticular spines in the anterior area of ADL3 were sharp-pointed and about 4.5 micron in length, and those in the middle area were about 1.75 micron. The velvety cuticular folds and dot-like cuticular spines were distributed in the posterior area. A cervical papilla was located between the 7th and 8th transverse striations. A dome-like body papilla was located at the posterior 1/4 of body. An ellipsoidal excretory pore was located between the 17th and 18th striations. From the above results, it is suggested that the characteristic SEM findings obtained from this study may be helpful on the species identification of larval Gnathostoma.