Differentiation of Late Fourth and Early Fifth Stages of Ascaris suum Goeze, 1782 (Nematoda: Ascaridoidea) in Swine

Abstract

The morphology of late fourth and early fifth stages of Ascaris suum in swine was studied with light and scanning electron microscopy. Late fourth-stage larvae have dome-shaped lips, that are broadest at the base and incompletely separated laterally. The lips bear coarse, triangular denti- cles, irregularly spaced on the internomedial and internolateral walls. Large double papillae are lo- cated on the middle of the external lip surface. The cervical region gradually increases in width posteriorly. The late fourth-stage cuticle is marked by a coarse transverse striation and bears incom- plete longitudinal ridges, creating a brickwork pattern; longitudinal alae are present. Late fourth and early fifth stages have overlapping body lengths; late fourth-stage larvae at 21-24 DAI range from 13 to 27 mm long, and early fifth stages at 23-24 DAI range from 22 to 36 mm long. Early fifth-stage lips are truncate, broadest at the level of the prominent double papillae, constricted at the base and widely separated laterally. The lips bear a single row of fine, regularly spaced denticles on the internal margins. The prominent double papillae are located slightly anterior to the middle of the external lip surface. The cervical region sharply increases in width giving a shouldered appearance. The cuticle of early fifth stages is finely striated without markings; longitudinal alae are absent. Reliable anatomical characters and morphometrics for the late developmental stages of Ascaris suum are still lacking although the species has been studied by many investigators. Douvres et al. (1969) described the life cycle and the early development of A. suum in swine from the ingested infective egg through early fourth-stage larvae. The present report describes the structure of late fourth and early fifth stages of A. suum in swine.