Taenia talicei Dollfus 1960

Taenia talicei Dollfus, 1960

(Figs. 1–14)

Type host: Ctenomys torquatus Lichtenstein, as established by the original description of the metacestode by Dollfus (1960).

Other hosts: C. talarum Thomas and C. australis Rusconi.

Microhabitat: Abdominal cavity.

Definitive host: Canis lupus familiaris Linnaeus (experimental infection); natural definitive host unknown.

Type locality: Uruguay.

Other localities: Mar de Cobo (Mar Chiquita, 37º58´S, 57º34´W) and Las Grutas (Necochea, 3833´S, 5845´W), Buenos Aires Province, Argentina.

Description: Adult forms (Figs. 1–8): Strobila 26.71 1.91 (22.80–30.50; N=10) cm in total length, with 120–150 proglottids each with single set of reproductive organs. Scolex 631 123 (450–860) long and 1.017 176 (710–1.210) wide bearing four rounded muscular suckers 273 31 (220–330) in diameter (Figs. 1–2). Rostellum armed with two rows of hooks; small hooks 168 26 (150–187), large hooks 237.50 7 (232–242). Total number of hooks 46 (44–50) (Figs. 1–4).

Male genitalia (meristic data and morphological description of male genitalia based on serial sections and whole specimens, measurements of male genital system corresponding to 5 proglottids from 3 worms): Testes oval, 124–138 in number, 65 (42–77) long, 54 (35–67) wide. Testicular field not extending laterally beyond osmoregulatory canals. In mature proglottid, cirrus pouch elongated and curved, reaching poral osmoregulatory canals, 157 18 (132–175) long and 121 6 (112–125) wide; coiled cirrus inside (Figs. 5–6). Vas deferens highly coiled; coiled region extends well into the medulla (Fig. 5). Male and female genital ducts pass between the ventral and dorsal longitudinal excretory canals (Fig. 7).

Female genitalia (meristic data and morphological description of female genitalia based on serial sections and whole specimens, measurements of female genital system corresponding to 5 proglotids from 3 worms): In mature segments, ovary bilobed; poral lobe 450 61 (360–480) by 350 28 (304–360) smaller than antiporal lobe 590 23 (48–60) by 580 76 (56–60). Vitelline gland postovarian. Vagina, thick-walled running parallel to cirrus sac, descending posteriorly forming a seminal receptacle at level of ootype region (Fig. 5). Vaginal sphincter absent. In gravid segments, number of uterine branches (unilateral) 10 to 12 which then subdivide (Fig. 8). Embryophore subspherical, 30 (29–30) by 25 (25– 27).

Metacestodes (Figs. 9–11, 12–14, Tables 1, 2): Both monocephalic and polycephalic metacestodes were found free in abdominal cavity. Cysticercus, small, transparent and globular with invaginated scolex. Fimbriocercus, elongated, milky-white form with invaginated scolex; polycephalic forms representing multiple fimbriocerci were also common (Figs. 11–12). Comparative morphometry of metacestodes is given in Table 1, number and measurements of rostellar hooks were similar among metacestodes. Comparative morphometry of monocephalic metacestodes from three Ctenomys species is given in Table 2.

Differential diagnosis: Based on our redescription, morphological characters of metacestodes observed in material from C. talarum and C. australis agree with the diagnostic characteristics of T. talicei described originally from C. torquatus by Dollfus (1960) (Table 2). The number and size of rostellar hooks of both larvae and adults, and the particular morphology of polycephalic and fimbriocercus metacestodes (see Hoberg et al. 2000) further agree with the original description of T. talicei. The structure, dimensions, and numbers of rostellar hooks serve to establish identity for adults and metacestodes, and are an additional basis for differentiating T. talicei from other related species in the genus.

Larval types of Cysticercus (n=5) Fimbriocercus (n=5) Polycephalic fimbriocercus (n=2) Taenia talicei Mean Range SD Mean Range SD Mean Range SD Total length (mm) 4.77 3.27–6.08 1.27 24.70 9.36–35.8 12.9 29.01 18.20–39.80 15.22 Number of hooks 46.4 44–48 0.75 46 40–50 2.12 44 44–46 0.70 Length of large hooks 237 225–244 7.21 242 241–244 1.14 242.3 241–243 1.94 Length of small hooks 157 150–161 4.16 161 158–162 1.54 156 155–156 0.77 Taenia talicei can be considered in the context of the phylogeny established for species of the genus (Hoberg et al. 2000; Hoberg 2006). Fimbriated metacestodes are limited to a few species of Taenia, and are most evident among those species that parasitize Mustelidae as definitive hosts (Korniushin & Sharpilo 1986) and have rodents as intermediate hosts (e.g. Taenia martis Zeder, 1803). Some polycephalic metacestodes are also limited to this group of host species (e.g. Taenia twitchelli Schwartz, 1924) although such metacestodes are also characteristic of Taenia endothoracicus Kirschenblatt, 1948, a parasite of Canidae.

Fimbriocercus and polycephalic metacestodes that develop by exogenous budding are proliferating metacestodes that usually occur in the pleural or pertitoneal cavity of a rodent intermediate host. Polycephalic metacestodes of T. talicei appear to develop by exogenous budding from a central bladder; in this case, fimbriated protoscolices eventually are arranged on elongate stalks following regression of the bladder. Fimbriocerci may subsequently break off of the original larval mass and thus can appear free in the peritoneal cavity. This ontogenetic pattern appears to be most similar to that described for Taenia twitchelli in porcupines (Erethizon dorsatum (L.)) (Rausch 1977). It is not clear, however, that the simple cysticerci of T. talicei that co-occur with polycephalic and fimbriocercus metacestodes in Ctenomys develop through a similar pattern, or represent an endpoint in ontogeny. Polymorphism in larval development is known among other species such as Taenia mustelae Gmelin, 1790 (e.g. Freeman 1956). Also in this regard, metacestodes of Taenia polyacantha arctica Rausch & Fay, 1988 are represented by cysticerci when mature, but ontogeny involves proliferation by exogenous budding (Rausch & Fay 1988).

Taenia talicei is clearly differentiated from those species with proliferating larvae (which develop through exogenous budding) based on structure, size and number of rostellar hooks (Verster 1969; Loos-Frank 2000). Proliferating metacestodes reported by Voge (1954) in C. peruanus, and the sigmodontids Phyllotis osilae Allen and Chinchilla sahamae Thomas from Peru, could be conspecific with T. talicei; these metacestodes were reported as having a 40–44 rostellar hooks with lengths of 120–140Μm for small and 190–220 for large.

Strobilate adults of T. talicei can be differentiated from other species in the global fauna. Serial sections of proglotids showed that the genital ducts pass between the longitudinal excretory canals when crossing from the medulla into the cortex. From a diagnostic standpoint (but not a phylogenetic one; see Hoberg et al. 2000), this feature is characteristic of Group 1 defined by Verster (1969); in Group 2 species such as T. taeniaeformis genital ducts pass ventrally to the longitudinal excretory canals.

Taenia talicei is distinguished from those species that occur naturally in Felidae from South America; no species are known in endemic Canidae. Taenia talicei is distinct from the following species based on the structure of the metacestode, dimensions and numbers of rostellar hooks and a suite of specific characters of the genital system in strobilate adults: (1) Taenia macrocystis Diesing, 1850 (in small felids and lagomorphs) by smaller and fewer rostellar hooks; in T. macrocystis - large hooks= 300–480 Μm, small hooks= 180–250, number = 52–74. (2) Taenia omissa Lühe, 1910 (large felids and deer) by smaller and a greater number of rostellar hooks; in T. omissa - large hooks= 230–300, small hooks= 160–225, number= 38–44. (3) Taenia pseudolaticollis Verster 1969 (small felids) by substantially smaller hooks of a different structure; in T. pseudolaticollis - large hooks= 350–420, small hooks= 220–240, number= 38–42. Non-proliferating cysticerci are typical metacestodes for T. omissa; a strobilocercus is described for T. macrocystis; the complete life cycle is unknown for T. pseudolaticollis (Loos-Frank 2000).

Taenia talicei is differentiated from those cosmopolitan species that circulate in synanthropic cycles with rodents (or lagomorphs) and domestic hosts such as cats and dogs in South America including Taenia pisiformis Bloch, 1780, Taenia serialis serialis Gervais, 1847, and T. taeniaeformis based on structure and number of the rostellar hooks and form of the metacestode. A simple cysticercus is typical for T. pisiformis, a coernurus is typical in T. serialis, whereas a strobilocercus is characteristic for T. taeniaeformis. Furthermore, T. taeniaeformis could be readily distinguished from T. talicei by having larger and a different number of rostellar hooks (number of rostellar hooks 34–36, large hooks 370–402, and small hooks 210–261).