Syphacia obvelata (Nematode, Oxyuridae) infecting laboratory mice Mus musculus (Rodentia, Muridae): phylogeny and host-parasite relationship.

Syphacia obvelata is a pinworm nematode parasite infecting man and laboratory animals in high abundance. This parasitological study was carried out during the period of March 2014-February 2015 to investigate the helminth parasites infecting the laboratory mice Mus musculus in the Animal House at Cairo University, Egypt. The prevalence of S. obvelata in M. musculus was 75.0 %. The extent of infection with S. obvelata is analyzed according to the sex of the host mice. It was shown that the prevalence of male infection was greater than female worms. Morphological characterization revealed that the present Oxyurid species possesses a rounded cephalic end with less developed lips, esophagus divided into cylindrical corpus, and globular bulb supported internally with valvular apparatus; three mamelons are located at the ventral surface with a single chitinized spicule and a gubernaculum provided with an accessory hook in males, and ovijector apparatus opens ventrally by the vulva surrounded by protruded lips in female worms. Body of the male was 0.623-1.130 (0.830 ± 0.11) mm long and 0.092-0.130 (0.110 ± 0.01) mm wide; the esophagus was 0.164-0.280 (0.210 ± 0.01) mm long; the nerve ring and excretory pore are located at 0.035-0.132 (0.073 ± 0.01) and 0.087-0.191 (0.145 ± 0.01) mm from the anterior end, respectively, while the female measured 2.930-4.650 (3.540 ± 0.1) mm long and 0.120-0.232 (0.156 ± 0.001) mm wide; the esophagus was 0.213-0.410 (0.342 ± 0.01) mm long; the nerve ring, excretory pore, and vulval opening are located at 0.026-0.157 (0.121 ± 0.01), 0.134-0.243 (0.195 ± 0.01), and 0.323-0.632 (0.546 ± 0.11) mm from the anterior end, respectively; eggs measured 0.120-0.139 (0.129 ± 0.001) mm long and 0.030-0.052 (0.045 ± 0.001) mm wide. It compared morphometrically with other Syphacia species described previously and showed little differences in measurements. Molecular characterization based on small subunit ribosomal DNA (rDNA) was done to confirm the obtained morphological and morphometric results. A preliminary genetic comparison between SSU rDNA of the present parasite and other species of Oxyuridae places it as a putative sister taxon to other S. obvelata.