Onchocerca skrjabini

Manzanell, Ralph, Stocker, Anna-Sophia, Deplazes, Peter & Mathis, Alexander, 2022, Morphological description and multilocus genotyping of Onchocerca spp. in red deer (Cervus elaphus) in Switzerland, International Journal for Parasitology: Parasites and Wildlife 19, pp. 273-284 : 277-279

3.1.2. Onchocerca skrjabini

Adult worms are whitish, opalescent very thin and difficult to detect by the naked eye in situ ( Fig. 1 ). Mouth opening minute in both sexes, smaller than 2 μm in diameter. Oesophagus of one male and of two female specimens with well distinguished muscular and glandular part. In all other specimens the transition from the muscular to the glandular

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μm (110 μm, 105 μm) long, both with well-developed heads. Left spicule with distal half flattened with margins bend ventrad to form a closed tube with clearly visible proximal and distal opening. Right spicule forming a ventral groove in distal half, the distal end enlarged dorsally with a subterminal rounded knob ( Fig. 10D and E ). Papillae in a pericloacal and a distal group. An unpaired precloacal papilla, 4 pairs of papillae laterally to cloaca and one small pair medially behind the cloacal opening. Posterior group with 3 pairs of papillae: One terminal pair close to tip of tail and 2 subterminal pairs. Distribution slightly varying between specimens ( Fig. 10B and C ). Pair of phasmids opening in a spine between the terminal and subterminal pair of papillae.

part was not clearly distinguished, whether by an increase in diameter nor by a sudden onset of glandular cells. The glandular cells only gradually increased in number towards the posterior end.

3.1.2.1. Male. Body length 35 mm (27 mm, 36 mm), with a diameter at midbody of 75 μm (80 μm, 80 μm), with slight dilatation of body diameter at level of nerve ring. Cuticle with thin transverse annulations, getting finer towards both ends. Oesophagus length 1300 μm (1090 μm, 1150 μm), the 1090 μm long oesophagus with 400 μm muscular part. Nerve ring at 270 μm (250 μm, 260 μm) from anterior ( Fig. 10A ). Tail 100 μm (85 μm, 100 μm) long, with alae ( Fig. 10C ). Spicules unequal and dissimilar. Left spicule 228 μm (257 μm, 245 μm), right spicule 95

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smaller and narrower ( Fig. 10H ).

Body diameter tapers rapidly towards anus. Tail with slight clubshape 170 μm (140 μm, 150 μm) in length, with diameter of 70 μm in all three specimens. Two pointed subterminal phasmids and a fine terminal knob at tail tip ( Fig. 10H and I ).

3.1.2.3. Microfilaria. Microfilariae measured in the distal part of unpaired uterus 410–430 μm long and 10–11 μm wide. Head of microfilaria with subapical oval mark with protruding rim ( Figs. 10J and 12 ).

3.1.2.2. Female. Body length not determined, the longest single piece 180 mm long. Body sectioned in two different diameters: thin head end extending over 120 mm with diameter of 80 μm–100 μm, posteriad expanding 2.5 times to 225 μm–270 μm ( Fig. 1 and 11 ). Unpaired uterus in front end filling most of lumen of body, giving typical tight aspect in this species ( Figs. 10G and 12 ). Slight dilatation at level of nerve ring, as in male. Diameter at nerve ring 100 μm (80 μm, 100 μm). Oesophagus length 1380 μm (1500 μm, 1220 μm). The muscular part extending over 670 μm in the 1380 μm long oesophagus and 450 μm in the 1220 μm long oesophagus ( Fig. 10F ). Nerve ring at 300 μm (260 μm, 260 μm) from anterior end. Vulva just posterior to end of oesophagus, at 1430 μm (or just anterior, at 1300 μm, 950 μm) from anterior end. Ovejector connects to vulvar opening with a small duct ( Fig. 10F ).

Cuticle with Onchocerca-typical two layers: Outer cuticle with marked transversal annulation, which fade out over the lateral line without touching each other, without or with only rudimental bifurcations ( Fig. 13 ). The internal medullar part of cuticle transversely striated, ratio of annular ridges: striae is mostly 1: 4 ( Figs. 10G and 11 ). Towards head and tail end the annulation is smoothing out, becoming

Figures

Fig. 1. Onchocerca skrjabini in situ in carpal skin. A. Freshly cut piece of skin shown from inside (note turned around piece of fur on top). Added methylene blue stains the O. skrjabini specimens and makes them visible for the naked eye. B. Parasitic burden in the same piece of skin in process of digestion. Hair follicles seen as dark dots. Fragments of O. skrjabini show different body width. Note very thin anterior headends (arrows). (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)

Fig. 10. Onchocerca skrjabini: A. Head end of male, with undifferentiated oesophagus. B, C. Distribution of papillae on male tail of two different individuals. D. Lateral view of male tail with spicules in situ. E. Longer left and smaller right spicule. Right spicule in two views to show ventral groove in distal part: on right hand side in lateral view, on left hand side in ventral view, showing dorsolateral knob on tip. F. Female head end, with differentiated oesophagus, vulva in distal forth of oesophagus. G. Longitudinal section in small anterior part of female, showing unpaired part of uterus filling out anterior body with relatively large microfilaria in it. Cuticular ridges over striae in ratio 1: 4. H. Tail end of female, with two phasmids spaced apart. Fine cuticular transversal annulation is indicated. I. Tail end of a second female, lateral view (in smaller scale). Note slight club shape of both. J. Microfilaria (intrauterine) with fine striation hinted at the neck, subapical oval marking with ridges.

Fig. 12. Onchocerca skrjabini: two microfilariae protrude from broken frontal part of a female, showing very tight setting in small anterior body part in this species. Note subapical oval mark with protruding rim on head of microfilaria.

Fig. 11. Different body width of one specimen of Onchocerca skrjabini in comparison. Midbody at left, tapering part in the middle, thin anterior body at right. Note Onchocerca typical structure of cuticle with ridges on the surface and striae in medulla in ratio 1: 4.

Fig. 13. Onchocerca skrjabini female: cuticular ridges do not meet over the lateral line, they taper and disappear distant from each other.