Passalurus ambiguus, a pinworm nematode parasite, infects domestic and wild rabbits, hares, and rodents worldwide.

The current parasitological study was performed during January–December 2016, to investigate helminth parasites infecting the domestic rabbit species Oryctolagus cuniculus at the Department of Animal Production, Faculty of Agriculture, Cairo University, Cairo, Egypt.

Of the twenty rabbit specimens examined for gastrointestinal nematodes, 75% were infected with adult oxyurid species, which were morphologically characterized using light and scanning electron microscopy studies. The oxyurid species had a triangular mouth opening surrounded by simple lips with four cephalic papillae and a pair of lateral amphidial pores with three teeth-like structures, an esophagus divided into a cylindrical corpus and globular bulb supported internally with tri-radiate valvular apparatus, and four caudal papillae distributed on the posterior end of males with a single short protruding spicule and ovijector apparatus opening ventrally by the vulva, surrounded by protruded lips in female worms. The species were compared morphometrically with other Passalurus species described previously; light differences were found in different body part sizes. Molecular characterization based on 18 small subunit (SSU) rDNA sequences showed ~ 85% similarity with other Chromadorea species. A preliminary genetic comparison between the 18S rDNA sequences of the isolated parasite and those of other oxyurid species suggested that it belonged to Passalurus ambiguus. The 18S rDNA sequence of the parasite was deposited in GenBank (accession no., MG310151.1).

The 18S rDNA gene of P. ambiguus was shown to yield a unique genetic sequence that confirms its taxonomic position within the Oxyuridae family.