Taxonomic summary
Species: Passalurus ambiguus Rudolphi, 1819 (F: Oxyuridae)
Host: Domestic rabbits Oryctolagus cuniculus (F: Leporidae).
Locality: Qena Governorate, Upper Egypt.
Site of infection: Large intestine.
Prevalence: 45% (90 out of 200).
Intensity: 15–20 specimens of adult nematodes per infected rabbit.
A- Morphological analysis
The present study revealed the occurrence of Passalurus ambiguus that were seen by naked eye in the appendix and rectum of domestic rabbits (fig. 1 A). The enlarged appendix showing small white nodules (fig. 1 B). Worms attached in fecal pellets (fig. 1 C).
1- Light microscopy
Male (Based on 12adult worms)
The length of the body is 4.622 mm (2.838–7.172 mm), the width is 0.278 mm (0.139–0.558 mm). The club-shaped esophagus measures 0.710 mm (0.391–0.1238 mm) in length (Figs. 2A, 3A, and 3C), the corpus measures 0.538 mm (0.274–0.908 mm) in length (Figs. 2B, 2C, 3B, 6A, and 6B), and the subspherical bulb measures 0.165 mm (0.094–0.304 mm) in diameter (Figs. 2B, 3B, and 6A). Testis (3A, 3C, and 6A) opens into thin-walled vas deferens. Vas deferens opens into the cloaca containing a single short protruded spicule measuring 0.094 mm (0.068–0.153 mm) in length (Figs. 2A, 2D, 2E, 3A, 3D, 6A, and 6C).
The cloaca was shown anteriorly by two pairs of large papillae (Figs. 2D, 2E, and 6C) and posteriorly by one pair of small papillae (Figs. 2D, 2E, 3D, and 6C). Two caudal papillae (Figs. 2D, 3C, and 6C) are present in the region of the tail. The body ended with a small coiled tail and measured 0.298 mm (0.145–0.492 mm) long (Figs. 2A, 2D, 3A, 3C, 6A, and 6C, and table 2).
Female (Based on 12 adult worms)
The body length is 5.622 mm (2.347–9.532 mm), and the width is 0.314 mm (0.185–0.381 mm). The club-shaped esophagus measures 0.484 mm (0.435–0.571 mm) in length (Figs. 4A and 5A), the corpus measures 0.369 mm (0.325–0.451 mm) in length (Figs. 4B, 4C, 5B, 6B, and 6D), and the subspherical bulb measures 0.124 mm (0.100–0.146 mm) in diameter (Figs. 4C, 5B, and 6D). Two large thin-walled ovaries (Figs. 5A and 6D) lie near the body wall and open posteriorly into the much-convoluted oviducts (Fig. 6D) packed with eggs in mature females. Eggs were elliptical with one side flattened, containing a knob in the anterior end, double thin walled and a developing embryo, and measuring 0.080 mm (0.075–0.088 mm) in length, and 0.034 mm (0.034–0.035 mm) in width (Figs. 4A, 4D, 5D, and 6F).
Oviducts empty into the straight transparent uterus (Fig. 6D) with its characteristically pointed end. The uterus continues as a straight tube with the vagina (Fig. 6D), which opens at the genital opening (Fig. 6D). Parallel to the uterus is a long tubule that connects to the vagina and extends posteriorly, ending in a convoluted mass in the anus region. From its position and structure, this tubule appears to be a rudimentary uterus and oviduct. The tail exhibits fine striations over the entire length, even showing through the annular bands and measuring 0.828 mm (0.579–0.945 mm) in length (Figs. 4A, 5A, 5C, 6D, and 6E, and table 2).
2- Scanning electron microscopy
In both males and females, transverse cuticular striations were visible on the body. Four papillae were found on the dorsal and ventral surfaces of P. ambiguus, indicating its anterior termination. The mouth was triangular and surrounded by three teeth (Figs. 7B, 8A, and 8B). No lips were seen.
Males of Passalurus ambiguus with a coiled posterior end, one short spicule (Figs. 7A, 7C, 7D, and 7E) protruding from the body in the cloacal region, and two pairs of large papillae around the cloaca, the second pair usually sessile (Figs. 7C, 7D, and 7E). In contrast, one couple was seen post cloacal as small and vestigial (Fig. 7D). The male body ends with a small papillary-like structure (Fig. 7E). The caudal appendix starts on its dorsal surface; however there is no pronounced striation.
Females of P. ambiguus have lateral wings in the anterior part of the body and plugs on the ventral surface. The tail was long, with noticeable loops, and it terminated with an exposed, pin-like tip (Figs. 8C and 8D). Prominent bands or annular structures (Figs. 8C and 8D) characterize the tail of mature females. As the worm approaches maturity, these bands increase in number and prominence, beginning at the posterior end of the large portion of the tail toward the anus. No bands could be detected in young or medium-sized specimens. The tail exhibits fine striations over the entire length, even showing through the annular bands.
B- Molecular analysis
Partial domains D1 and D2 of the 28S rDNA gene were amplified and sequenced for Passalurus ambiguus belonging to the families of Taeniidae Ludwig, 1886. The PCR amplification ranged from 700 to 800 bp. The sequence data of Passalurus ambiguus (781 nucleotides) examined were deposited in GenBank with accession numbers MZ571165.
The obtained sequences were aligned with 12 reference sequences representing the Oxyuroidea available species (Table 3); three species of Thelandros (T. galloti, T. tinerfensis, and T. filiformis); two species of Pharyngodon (P. micipsae and P. echinatus) and Skrjabinema (S. ovis and S. longicaudatum); one species of Batracholandros (B. salamandrae), Passalurus (P. ambiguus), Oxyuris (O. equis), Heteroxynema (H. cucullatum), and Aspicularis (A. tetraptera) together with Ascaridia galli (Ascaridiidae) as an outgroup. Thus, all sequences (including outgroup) were aligned over 872 positions.
The phylogenetic analysis was done using ML and MP methods. The obtained phylogenetic trees are shown in Figs. 9 and 10.
Phylogenetic trees based on the partial 28S sequence data showed that the superfamily Oxyuroidea was divided into four monophyletic clades, representing three families. Family Pharyngodonidae included genera of Pharyngodon (P. micipsae and P. echinatus), Thelandros (T. galloti, T. tinerfensis, and T. filiformis) and Batracholandros (B. salamandrae). Family Oxyuridae included genera of Passalurus (P. ambiguus), Oxyuris (O. equis), and Skrjabinema (S. ovis and S. longicaudatum), and were divided into two monophyletic clades. Family Heteroxynematidae included Heteroxynema (H. cucullatum) and Aspicularis (A. tetraptera).
In the phylogenetic tree constructed by the ML method, representatives of the family Oxyuridae are distributed into two monophyletic clades. Clade 1 included Passalurus ambiguus, representing the subfamily Syphaciinae. Clade 2 included Oxyurisequis, Skrjabinemaovis, and S. longicaudatum, representing the subfamily Oxyurinae.
In the phylogenetic tree constructed by the MP method, Oxyurisequis separated from members of Skrjabinema, and it acts as a basal clade to the rest of included members of Oxyuroidea.
The present Passalurus ambiguus clustered together with the same species that having accession no. KY990018 with a strong bootstrap value (ML = 100, MP = 100). Skrjabinema ovis clustered together with Skrjabinema longicaudatum in a strong bootstrap value (ML = 100, MP = 100).
The genetic distance, estimated from 28S partial sequences, between the present Passalurus ambiguus and the previously recorded P. ambiguus was small (1.2%). The value between the Pharyngodonmicipsae, P. echinatus, and Thelandrosgalloti was small (1.7%). In contrast, high values between Thelandrosgalloti and T. tinerfensis and T. filiformis were observed (10.6% to 10.8%), as shown in Table 3. Therefore, the genetic distances support is consistent with the constructed phylogenetic trees (Figs. 9 and 10).
C- Pathological findings
The macroscopic appearance of the appendix was enlarged and filled with white nodules (Fig. 1A). The worms also appeared in the rectum pellets and were separated (Figs. 1B, C)
The histopathological examination revealed numerous nematode worms (Passalurus ambiguous) infested the appendiceal layers, particularly inside the germinal layer of the lymphoid follicle and appendiceal lumen (Figs. 11, 12). The worm detection mainly inside crypts deeply into the follicles, causing hyperplasia in the lymphoid tissues and the follicular epithelium cells (Fig. 13). The transverse section of Passalurus ambiguous with the anterior and posterior portions contained eggs, displayed beneath the hyperplastic cells, where lymphocyte and eosinophil cells aggregated and surrounded it (Fig. 14). Granulomatous reaction was induced due to cells injury and aggregation of chronic inflammatory cells against the worm infestation, with inflammatory edema surrounded it (Fig. 15). Appendicitis manifested with a heavy worm infestation accumulated inside the lumen, leading to hyperplasia in the epithelial lining of crypts and follicles projected to form papillary formation causing narrowing and obstruction with worm and cell debris, besides hypertrophy of their follicles with reactive lymphocytes (Figs. 16 A, B).