Onchocerca flexuosa

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 : 276-277

3.1.1. Onchocerca flexuosa

Adult worms are white-brownish, opalescent. The intestinal tract of some specimens is brown coloured, in other specimens, all internal organs are brown ( Figs. 4 and 9 ). Mouth opening minute in both sexes, smaller than 2 μm in diameter. Oesophagus clearly divided into anterior muscular and wider and longer posterior glandular part.

3.1.1.1. Male. Body length 85.7 mm (44.7 mm). Oesophagus very long with 8.5 mm (7.65 mm); muscular part of oesophagus 1.2 mm (0.8 mm). Nerve ring at 350 μm (300 μm) from anterior end. Body slowly tapering

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Surface of front and back end with fine rounded transversal annulations over a clear, transparent deeper cuticular layer. Surface of cuticle close to cloaca of one female forming Onchocerca-typical ridges with striae in deeper layer with ratio 1: 4 respectively. Adjacent to midbody ridges of upper cuticle transformed to transversal rounded cushions, with striae underneath still visible ( Fig. 7A ). At midbody cuticle with rudimentary ridges on smooth surface, but basis of cuticle forming transversal ridges ( Fig. 7B ), changing over to undulation of entire cuticle ( Fig. 7C ). In some posterior parts cuticle transformed to transversally repeated pattern of one bigger swelling followed by two smaller swellings ( Figs. 3G and 7D ). Oesophagus 8.5 mm (6.9 mm) long, with slightly thicker and much longer glandular part. Nerve ring at 220 μm (200 μm), vulva at 370 μm (350 μm) from anterior end. The anterior 2 mm of body tapering slowly, then more rapidly from just behind the vulva to the blunt head end. Width at nerve ring 130 μm (120 μm), at vulva 180 μm (150 μm), at posterior end of oesophagus and midbody 200 μm (220 μm) ( Fig. 3D ). Ovejector enlarged to more than half of diameter of body ( Fig. 3E ). Intestine and uteri forming loops inside spacious female body ( Fig. 8 ). Tail 310 μm (550 μm) long, conical, end rounded, with two prominent phasmids and two protuberances at tip ( Fig. 3F ). In other, degenerating females, the uterine tubes appeared very stretched inside a tightly undulated body, which becomes very fragile ( Fig. 9 ).

3.1.1.3. Microfilaria. Microfilaria (measured inside distal unpaired uterus) unsheathed, very thin, 3–4 μm in diameter, 200 μm (195–200 μm) long ( Fig. 3H and I ).

Figures

Fig. 9. Detail of Onchocerca flexuosa female: Uterine tubes (arrow) straightened inside curly body.

Fig. 7. Onchocerca flexuosa: Heteromorphous cuticle of female: A. Onchocerca-similar cuticle in two layers, with fine striae in medulla, but lacking ridges on surface. B. Medullar waves without cuticular ridges. C. Entire cuticle forming transversal rings. D. Cuticle with repeated pattern of one bigger, followed by two smaller transversal rings.

Fig. 3. Onchocerca flexuosa: A. Head end of male. B. Spicules in situ with thorn like hook of right spicule protruded and tip of left spicule at proximal entrance of ventral groove of right spicule. C. Tail of male showing alae and distribution of papillae. D. Head end of female showing vulva with unpaired uterus, oesophagus-intestinal junction depicted and marked with dots at posterior end. Note loose course of uterus with loop. E. Head end of female with oesophagus and expansion of ovejector before vulva. F. Round tail end of female with spiky phasmid at base of flaps. G. Longitudinal section in posterior half of female body showing peculiar repetition of one bigger transversal cuticular ring (marked with dot at left), followed by two smaller rings. H, I. Microfilaria, in I in same scale as microfilaria in Fig. 10J as comparison.

Fig. 8. Onchocerca flexuosa: Relation between vast internal space in body and thin intestine (i) and unpaired uterus forming loops (u).