Parasitic gastroenteritis (PGE) caused by infection of the gut with parasitic nematodes is one of the most important diseases of livestock animals from both financial and welfare perspectives. Parascaris equorum and Habronema microstoma are of the most endemic nematodes of the world which are currently the major cause of PGE of the domestic horses in Egypt. The present investigation introduced the first morphological description of these nematodes recovered from the domestic horse, Equus ferus caballus (Equidae), in Egypt by light and scanning electron microscopy. Seven P. equorum (fifth stage) and 18 adults of H. microstoma were recovered from the gastrointestinal tracts of four young domestic horses collected during the year of 2015. Microscopic examination of the isolated fifth stage P. equorum revealed that it possessed a long body with a broad anterior end equipped by large shamrock-like lips with deep transverse groove on medial surface set off from the rest of the body by a deep post-labial constriction giving the body a shouldered appearance. The total body length was 12-15 (14 ± 2) cm for males and 13-18 (16 ± 2) cm for females. Lips were three in number in the form of one dorsal and two sub-ventral surrounding the central stoma. The isolated adult worms of H. microstoma were whitish in color narrowed slightly at the anterior end. Single lateral ala in the cephalic region in both sexes was observed. The buccal vestibule was markedly thickened and equipped by two tridentate teeth. The adult worms had two bilobed lateral lips surrounding the mouth with four sub-median cephalic papillae and two amphids. The males were 14.5-18.0 (17.2 ± 0.3) mm long and 1.23-1.57 (1.42 ± 0.3) mm wide. The posterior end was spirally coiled and had wide caudal alae. The spicules were unequal. The females were 13.5-21.0 (16.2 ± 0.3) mm long and 1.55-1.75 (1.69 ± 0.3) mm wide. The anal pore had a thin upper rim and was located 177.0 μm from the posterior end.
Keywords: Equus ferus caballus; Habronema microstoma; Light and scanning electron microscopy; Nematoda; Parascaris equorum.