Findings

Non-human primates might act as aberrant hosts for a number of cestode species after peroral infection and larval development in extra-intestinal locations can have potentially severe clinical consequences [1–6]. In most cases the circumstances of infection of captive monkeys remains unclear [3]. Tonkean macaques (Macaca tonkeana, Cercopithecidae) are housed in social groups in large enclosures, and are often used for ethological research [7]. Taenia martis (Zeder, 1803) is a tapeworm that develops in the small intestine of wild carnivores (Mustelidae). In Europe it is commonly found in Martes foina, the stone marten, and in M. martes, the pine marten. Other mustelids, and more rarely canids, might also act as definitive hosts [8]. The stone marten is established in the Northern Hemisphere and is widely found in France with the highest population densities reported in eastern regions [9]. T. martis has been observed in martens in Italy, Germany and Switzerland [10, 11] but there is a lack of information concerning its distributional range in France. However, cestodes found in Martes foina near Nancy and Paris, which were originally described as T. intermedia (Rudolphi, 1809), were later classified as T. m. martis[12, 13]. T. martis is maintained in a wild-animal cycle between carnivores and small rodents which act as intermediate hosts, mainly Myodes voles and Apodemus field mice. In Europe, prevalences of T. martis larvae in different rodents have been reported to vary between 0.95% in bank voles (Clethrionomys [currently Myodes] glareolus) in the French Pyrenees, 2% in Apodemus flavicollis in Switzerland, and 22% in musk rats (Ondatra zibethicus) in Belgium [11, 14, 15]. Recently, a first case of cysticercosis due to T. martis was observed in a human patient in Germany that shows the zoonotic potential of this cestode species [16]. The susceptibility of primates to T. martis infection is also supported by the present case of a peritoneal cysticercosis due to T. martis in a Tonkean macaque that, to the best of our knowledge, had never been reported before in a non-human primate.

The animal was a subadult 3-year-old male Tonkean macaque with a weight of 5.2 kg, born and raised at the Strasbourg University Centre of Primatology, located near the Niederhausbergen forest (Alsace, northeastern France). The monkey was kept in a social group of 16 Tonkean macaques dedicated to ethological studies and housed in a semi free-range parkland closed by wire fencing. The animals feed on fruits and seeds provided by the Centre and on natural vegetation foraged in the park. Inside indoor-cages they have access to water and banana-flavoured monkey chunks ad libitum. A preventive anthelmintic treatment is administered twice a year (ivermectin 1 mg/3 kg subcutaneously, then fenbendazole 48 mg/kg orally, 6 months later). No abnormalities were reported for the infected animal until March 2009 when an abdominal mass (±10 cm × 5 cm) was detected at palpation during a routine check-up. No other clinical signs such as fever, diarrhea, anorexia or weight loss were observed. Blood tests revealed an increased alkaline phosphatase level (1610 UI/l) and a mild anaemia: haemoglobin 9.1 g/dl (reference range: 12.2 ± 0.8 g/dl), haematocrit 32.2% (40.3 ± 3.7%), erythrocytes 5.53 M/mm3 (6.5 ± 0.71 M/mm3). Other values were within normal range. Abdominal echography was performed and the lesion was visualized in the upper left part of the abdomen, obviously between the liver and the left kidney. After celiotomy, the mass appeared embedded in the mesentery (Figure 1). It contained hundreds of ellipsoidal to spherical transparent vesicles ranging from 5 to 30 mm in length. The vesicles had a white, opaque area at one pole and a tapering end at the opposite, some with an elongated extremity. No budding of daughter cysts was observed. They were identified as cysticerci at microscopic examination. Each cysticercus contained a single invaginated scolex (1 mm in diameter), with 4 suckers and 28 to 30 rostellar hooks arranged in two rows (Figure 2). The hooks had the same morphological aspect (upper edge nearly straight; handle thin, longer and in the same axis than the blade; blade short, rather abruptly curved; guard very prominent) and measured 140 to 160 μm and 180 to 212 μm in length for small and large hooks, respectively (Figure 3).

Figure 1
figure 1

Aspect of the lesion after celiotomy. A vesicular mass embedded in the mesentery is shown. Some isolated cysticerci (5 to 30 mm long) are located at the right bottom.

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Figure 2
figure 2

Close-up appearance of the invaginated scolex inside a cysticercus. Scale bar 250 μm.

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Figure 3
figure 3

Morphology of small and large rostellar hooks of Taenia martis from the present case (left: scale bar 100 μm; right: scale bar 50 μm).

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Morphology of the cysticerci and rostellar hooks, and comparison with the closely related species T. crassiceps, led to the identification of T. martis[8, 17, 18]. Molecular tools confirmed the morphological identification. Sequences of the mitochondrial cytochrome c oxidase subunit 1 (cox1) and NADH dehydrogenase subunit 1 (nad1) genes were amplified by PCR with primer pairs JB3/JB4.5 and JB11/JB12 [19, 20]. The sequences showed identities of 99.8% (438/439 bp, nad1, GenBank accession number EU544606) and 99.7% (382/383 bp, cox1, AB731758) with sequences published for T. martis. Sequence homologies with the closely related species T. twitchelli and T. crassiceps were 94.0% (346/368 bp, EU544598) and 90.6% (347/383 bp, AF216699) for cox1 and 86.8% (381/439 bp, EU544650) and 82.7% (363/439 bp, EU544600) for nad1, respectively. Phylogenetic tree was drawn by using the sequences obtained in this study as well as sequences available for representative Taenia species in GenBank (Figure 4). Diagnosis of peritoneal cysticercosis due to T. martis was therefore established. Surgical exeresis of the parasitic mass was not possible because of its localization and structure. Praziquantel (5.7 mg/kg, intramuscularly) was given twice at an interval of 3 days. Two months later, the abdominal mass was no longer palpable and the ultrasonography confirmed its dramatic decrease. No signs of recurrence were noticed during the 4-year follow-up period. The monkey exhibited normal growth and is presently healthy, and socializes perfectly within the group.

Figure 4
figure 4

Phylogenetic tree based on Cox1 sequences showing the phylogenetic relationships between the Taenia martis isolate from Macaca tonkeana and other Taenia species. Shaded triangle refers to the sequence generated by this study and the Genbank accession numbers of each strain are given into parenthesis. Bootstrap values >70% are included to indicate branch support.

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The case of peritoneal cysticercosis caused by T. martis described herein in a Tonkean macaque, constitutes a first record of a metacestodosis in this mammalian host. Diagnosis of T. martis cysticercosis is difficult because clinical signs are not specific. Different etiologies were suspected for the abdominal mass detected in the macaque. Abdominal tumor and other metacestodoses, including alveolar echinococcosis (AE) were initially considered. AE has been described in captive monkeys including other Macaca spp., and Echinococcus multilocularis is endemic in the Alsace region where the animal lives [3, 6, 21]. The parasites sampled from the lesion were diagnostic for cysticercosis but identification of Taenia species is challenging due to the similarities of their morphological characteristics [22]. Cysticerci of T. crassiceps, T. hydatigena and T. solium have been described in non-human primates. In the current case, some larvae showed a strobila-like structure, which is commonly seen in T. polyacantha[23]. However, the size of the small hooks and, most importantly, the total number of hooks in the present case clearly distinguished it from T. polyacantha (112–148 μm and 62 hooks). Due to the size of the cysticerci and their high number, T. crassiceps infection was also suspected, but comparison of scolices and hooks with those of T. crassiceps collected from a fox and a dog, and the absence of budding cysticerci in our case, ruled out this hypothesis (Figure 5) [8, 17, 18].

Figure 5
figure 5

Morphology of small and large rostellar hooks of T. crassiceps from a fox (left: scale bar 100 μm; right: scale bar 50 μm).

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In the present case, the completion of the cestode life-cycle is highly probable in the environment of the park as small rodents and carnivores including martens were regularly observed in the close vicinity. The infection of the monkey was likely through ingestion of taeniid eggs during foraging activities, which are quite developed in Tonkean macaques [7]. Taeniid eggs might contaminate soil and grass when scattered by rain from faeces of wild carnivores, which are often found near the fences or possibly inside the enclosure as access of martens to this wooded park is not excluded. Direct infection by picking the potentially contaminated faeces, especially when they contain fruit stones or during grooming from the fur of monkeys from the ground, are other hypotheses. In our case, clinical evolution was quite favourable. Although praziquantel had demonstrated a variable efficacy in the treatment of metacestodoses [17, 24], this cestodicidal drug was chosen because its injectable administration to the macaque was easier and more reliable than fenbendazole or albendazole, which would have required daily oral administration for several weeks. The localized infection observed in this macaque and the complete cure without surgical resection could be explained by a high sensitivity of T. martis larvae to praziquantel, by adequate host defenses (as no sign of immunosuppression was observed in the animal), and also by the absence of proliferation of the parasites. Indeed, the fully-developed cysticerci of T. martis are non-multiplying larvae contrary to those of T. crassiceps which proliferate by budding [8, 17, 25]. In the case of T. martis metacestodosis reported recently in an immunocompetent woman in southeastern Germany, the lesion was due to a single cyst localized in the eye and the cure was obtained by surgical removal of the parasite [16]. The present report shows the susceptibility of macaque to T. martis larvae and indicates the occurrence of an environmental contamination with T. martis eggs. It highlights the potential risk of infection for captive monkeys and also for humans with this taeniid species, which should be considered in the etiology of atypical cysticercosis cases.