Spermatozoa of tapeworms (Platyhelminthes, Eucestoda): advances in ultrastructural and phylogenetic studies

New data on spermiogenesis and the ultrastructure of spermatozoa of 'true' tapeworms (Eucestoda) are summarized. Since 2001, more than 50 species belonging to most orders of the Eucestoda have been studied or reinvestigated, particularly members of the Caryophyllidea, Spathebothriidea, Diphyllobothriidea, Bothriocephalidea, Trypanorhyncha, Tetraphyllidea, Proteocephalidea, and Cyclophyllidea. A new classification of spermatozoa of eucestodes into seven basic types is proposed and a key to their identification is given. For the first time, a phylogenetic tree inferred from spermatological characters is provided. New information obtained in the last decade has made it possible to fill numerous gaps in the character data matrix, enabling us to carry out a more reliable analysis of the evolution of ultrastructural characters of sperm and spermiogenesis in eucestodes. The tree is broadly congruent with those based on morphological and molecular data, indicating that convergent evolution of sperm characters in cestodes may not be as common as in other invertebrate taxa. The main gaps in the current knowledge of spermatological characters are mapped and topics for future research are outlined, with special emphasis on those characters that might provide additional information about the evolution of tapeworms and their spermatozoa. Future studies should be focused on representatives of those major groups (families and orders) in which molecular data indicate paraphyly or polyphyly (e.g. 'Tetraphyllidea' and Trypanorhyncha) and on those that have a key phylogenetic position among eucestodes (e.g. Diphyllidea, 'Tetraphyllidea', Lecanicephalidea, Nippotaeniidea).

Finding of Parastrongylus cantonensis (Chen, 1935) in Rattus rattus in Tenerife, Canary Islands (Spain)

Parastrongylus cantonensis is a parasite of murid rodents that can infect humans and cause health problems as eosinophilic meningitis. Although it is endemic in south Asia, the Pacific islands, Australia, USA, and a few Caribbean islands, it has been extended to new geographical regions. In the Canary Islands (Spain) a survey of helminths of Rattus rattus, Rattus norvegicus and Mus musculus domesticus was carried out. Furthermore, five species of molluscs were examined for nematode larvae to determine whether they are potential intermediate hosts of P. cantonensis. Nematodes were found in the lungs of 15% of 67 R. rattus examined in Tenerife, one of the four studied islands, with a prevalence of 20% in the highest focus of infection. Based on morphological and molecular analysis, with the complete internal transcribed spacer 2 (ITS-2) and a fragment of the small subunit ribosomal RNA (SSU rRNA) nucleotide sequences, nematodes were identified as P. cantonensis. Larval nematodes found from snails and slugs were identified as third-stage (L(3)) Metastrongyloidea, but the molecular study showed that they did not belong to P. cantonensis. This is the first finding of angiostrongyliasis in rats in the Canary Islands (Spain). New molecular data for this species and Parastrongylus dujardini are reported. The presence of P. cantonensis in Tenerife could be of importance from the public health point of view. Further studies are required in order to look for other potential foci of infections in the Canary Islands.

Trace element concentrations in Raillietina micracantha in comparison to its definitive host, the feral pigeon Columba livia in Santa Cruz de Tenerife (Canary Archipelago, Spain)

The use of systems involving bird parasites as bioindicators of environmental pollution has been scarcely studied in comparison to other models involving fish and rodent parasites, which have been demonstrated as particularly adequate due to their bioaccumulation capacities. The present study evaluated the accumulation of nine trace elements in the cestode Raillietina micracantha and in its host Columba livia collected from the densely populated city of Santa Cruz de Tenerife (Canary Islands, Spain). Samples (kidney, liver, pectoral muscle, feathers, and R. micracantha) of 27 infected C. livia were selected for trace element analysis by inductively coupled plasma-mass spectrometry. Element levels in pigeon tissues revealed some degree of pollution in Santa Cruz de Tenerife, particularly by Pb and Zn. Pb and Mn mean concentrations were higher in R. micracantha than in the pigeon's soft tissues, with subsequent high bioaccumulation factors for Pb (kidney = 15.38, liver = 10.38, muscle = 79.83) and Mn (kidney = 6.81, liver = 7.52, muscle = 19.89, feathers = 6.11), among others. The negative relations detected for As concentrations between liver and R. micracantha emphasize a possible role of the cestode in As detoxification in host tissues. Considering the obtained bioaccumulation factors, the system R. micracantha/C. livia is proposed as another promising bioindicator system to evaluate environmental toxic element exposure, particularly Pb and Mn, in areas where pollution levels are still relatively low and where both common species are present.

Toxic element concentrations in the Razorbill Alca torda (Charadriiformes, Alcidae) in Portugal

The present study provides the first data on inorganic element levels (As, Cd, Co, Cr, Cu, Hg, Mn, Pb, Se, and Zn) in juvenile, immature, and adult razorbills (Alca torda) collected along the central coast of Portugal. Element concentrations were assessed by ICP-MS in kidney, liver, muscle, and feathers of 28 razorbills, including 4 juveniles, 17 subadults, and 7 adults. The effect of age and tissue on element accumulation was also assessed. The detected levels in razorbills may indicate a possible contamination risk by Hg and Cr. With respect to bird tissues, higher accumulation of Se and Cd was detected in kidney, Zn and Pb in feathers, and As and Mn in liver. Age was found to affect the accumulation of Cd, Cr, Cu, Hg, and Mn, juveniles presenting higher levels of Cu and Mn than older individuals. In razorbill kidney, Zn-Hg constituted the most significant relationship among metal concentrations. Liver presented the highest number of significant relationships (mostly involving Zn and Co). With regard to feathers, the most significant relationships involved Se, Zn, Cr and Cu concentrations. Positive linear relationships were detected among kidney, liver, and muscle, with emphasis on relationships involving Se and Hg, which may be indicative of similar accumulation/regulation mechanisms in those organs. Element concentrations are discussed in view of possible detoxification mechanisms in seabirds.

Trace element concentrations in Proteocephalus macrocephalus (Cestoda) and Anguillicola crassus (Nematoda) in comparison to their fish host, Anguilla anguilla in Ria de Aveiro, Portugal

The use of some fish parasites as bioindicators of heavy metal pollution has been demonstrated as particularly adequate due to their capacity of bioconcentration. This study evaluated the effect of Proteocephalus macrocephalus on the accumulation of trace elements in the edible fish, Anguilla anguilla, in a contaminated area in Portugal (Ria de Aveiro). Also, the model P. macrocephalus/A. anguilla was assessed as a bioindicator system in the presence of the highly prevalent nematode Anguillicola crassus. Samples (kidney, liver, muscle, A. crassus and P. macrocephalus) of 20 eels harbouring A. crassus and another 20 harbouring both A. crassus and P. macrocephalus were selected for element analysis by ICP-MS. The highest concentrations of Cr, Ni and Zn were detected in P. macrocephalus. However, there was a higher liver and muscle Cr concentration in eels not infected by P. macrocephalus. Also, the nematode A. crassus presented higher Cr concentrations in those eels harbouring P. macrocephalus. Results suggest that P. macrocephalus individuals accumulate Cr and Ni while levels of Cr in eel livers and Ni levels in eel kidney are reduced. The system P. macrocephalus/A. anguilla yielded bioaccumulation factors for Cr, Ni, Pb and Zn, whereas bioaccumulation of Cu, Cr and Pb in A. crassus varied according to eel co-infection with P. macrocephalus, thus emphasising the possible role of cestode infection in metal metabolization/storage processes in host tissues. Results suggest that heavy metal pollution in Ria de Aveiro has been decreasing although it is still higher than in other contaminated areas in Europe. Nevertheless, eel consumption in Ria de Aveiro represents no risk for humans although they may represent a real contamination risk for wildlife. The system P. macrocephalus/A. anguilla is proposed as another promising bioindicator system to evaluate environmental Cr, Ni, Pb and Zn exposure in estuarine areas where both species co-occur.

Ultrastructure of the spermatozoon of Parachristianella trygonis Dollfus, 1946 (Trypanorhyncha: Eutetrarhynchidae)

The ultrastructural organization of the mature spermatozoon of the trypanorhynch cestode Parachristianella trygonis is described by transmission electron microscopy. The spermatozoon is a long and filiform cell, tapered at both ends, lacking both mitochondrion and crested bodies. Its cytoplasm contains 2 axonemes of the 9+'1' pattern of the Trepaxonemata longitudinally displaced, parallel cortical microtubules, the nucleus and glycogen in form of both alpha-glycogen rosettes and beta-glycogen particles. The anterior extremity of the spermatozoon is characterized by the presence of an arclike row of up to 10 parallel cortical microtubules that partially surround the first axoneme. The present study emphasizes the ultrastructural similarity between mature spermatozoa of all 4 trypanorhynchs that have been studied to date. Nevertheless, several features, i.e., the characteristics of spermatozoa extremities, the absence of crested bodies, and the possible presence of an arclike layer of cortical microtubules, need a more thorough analysis or confirmation in some of these species.

Mesocestoides lineatus (Goeze, 1782) (Mesocestoididae): new data on sperm ultrastructure

Spermiogenesis and the ultrastructural characters of the spermatozoon of Mesocestoides lineatus are described by means of transmission electron microscopy, including cytochemical analysis for glycogen. Materials were obtained from a golden hamster (Mesocricetus auratus) after experimental infection with tetrathyridia metacestodes obtained from naturally infected lizards (Anolis carolinensis) from Louisiana. Spermiogenesis in M. lineatus is characterized by the orthogonal growth of a free flagellum, a flagellar rotation, and a proximodistal fusion. The zone of differentiation contains 2 centrioles associated with striated rootlets and a reduced intercentriolar body. The mature spermatozoon of M. lineatus lacks a mitochondrion, and it is characterized by the presence of (1) a single, spiraled, crested body 150 nm thick; (2) a single axoneme of the 9+'1' pattern of trepaxonematan Platyhelminthes; (3) a parallel and reduced row of submembranous cortical microtubules; (4) a spiraled cordon of glycogen granules; and (5) a spiraled nucleus encircling the axoneme.

The helminth parasites of the wild rabbit Oryctolagus cuniculus and their effect on host condition in Dunas de Mira, Portugal

The present study focuses on the helminth parasite community of the wild rabbit in a sand dune area in Portugal over a 5-year period. The influence of host sex and year on the composition of the helminth community is assessed, along with the potential effect of the detected helminths on host body condition. The basic structure of the helminth community comprises Mosgovoyia ctenoides, Graphidium strigosum, Trichostrongylus retortaeformis, Nematodiroides zembrae and Passalurus ambiguus. Mean intensities of G. strigosum varied between years. General G. strigosum intensities were also found to vary according to both year and host sex, but not according to the interaction of both factors. When assessing the effect of helminths on rabbit body condition (expressed by the kidney fat index), higher burdens of M. ctenoides, a cestode that presents a relatively large body mass, were found to induce a reduction in rabbit condition.

Helminth parasites of the Eurasian otter Lutra lutra in southwest Europe

The helminth fauna in 109 Eurasian otters (Lutra lutra L.) from France, Portugal and Spain was analysed, together with 56 faecal samples collected in Portugal and 23 fresh stools from otters included in a reintroduction programme. Seven helminth species were found in L. lutra in southwest Europe: Phagicola sp. (Trematoda), Aonchotheca putorii, Eucoleus schvalovoj, Strongyloides lutrae, Anisakis (third stage larvae) and Dirofilaria immitis (Nematoda), and Gigantorhynchus sp. (Acanthocephala). Eucoleus schvalovoj was the dominant species throughout southwest Europe. Strongyloides lutrae was significantly more prevalent in the Iberian Peninsula than in France. Apart from these two dominant nematodes and A. putorii, the other helminth species were incidental parasites of L. lutra in southwest Europe. The helminth fauna of L. lutra in southwest Europe is, in general, poorer than that reported in eastern Europe and in all other aquatic mustelids in southwest Europe. Phagicola specimens are reported for the first time in a non-marine wild carnivore in Europe. The prevalences of E. schvalovoj and S. lutrae obtained by necropsy were higher than those observed by coprological analysis using a formalin-ether concentration method (Ritchie). Nevertheless, the culture of fresh faeces appears to be the best method to study infection of L. lutra by Strongyloides.

CELLULAR ORGANIZATION OF THE ONCOSPHERE OF MOSGOVOYIA CTENOIDES (CESTODA: ANOPLOCEPHALIDAE)

The ultrastructure of the infective oncosphere of the cestode Mosgovoyia ctenoides (Anoplocephalidae) is described. The surface of the infective oncosphere is covered by a thin cytoplasmic layer of tegument connected by a narrow cytoplasmic process with the binucleate subtegumental cell, situated deeper in the body. Below the basal matrix of the cytoplasmic layer of the tegument are situated wide bands of the peripheral, somatic musculature responsible for body movements. The 3 pairs of hooks and their muscles form a complex hook muscle system, responsible for coordinated hook action. Five major types of cells have been distinguished: (1) a binucleate subtegumental cell, (2) a binucleate penetration gland, (3) 2 nerve cells, (4) numerous somatic cells, and (5) about 6 germinative cells. The approximate number of cells is 24 (26 nuclei, including 2 syncytial structures). The results of this study, when compared with other published reports from other cestode taxa, support previous hypotheses that the progressive reduction of oncosphere cells is an adaptive feature in cestode evolution.

Spermiogenesis and spermatozoon ultrastructure of the cestode Mosgovoyia ctenoides (Cyclophyllidea: Anoplocephalidae), an intestinal parasite of Oryctolagus cuniculus (Lagomorpha: Leporidae)

Ultrastructural characters in spermiogenesis and spermatozoa are considered important tools to elucidate the phylogenetic relationships within the Platyhelminthes. In the Anoplocephalidae, ultrastructural data refer to the spermatozoon of 14 species, whereas data on spermiogenesis refer to only 7 species. The present study focused on the spermiogenesis and spermatozoon of the anoplocephalid cestode Mosgovoyia ctenoides, as revealed by transmission electron microscopy. Type IV spermiogenesis was detected, beginning with the formation of a differentiation zone containing 2 centrioles, with a centriolar adjunct and vestigial striated rootlets. Different forms of the latter character have been described in other anoplocephalids. This study supports spermiogenesis of type IV as the most frequent in the Anoplocephalidae and confirms the presence of a centriolar adjunct in yet another type IV spermiogenesis species. The spermatozoon of M. ctenoides possesses 1 axoneme of the 9+ '1' trepaxonematan type, 2 crestlike bodies, dense plates, and granules of electron-dense cytoplasmic material, nucleus, and twisted cortical microtubules. It was again confirmed that the presence of granular material and the absence of both a periaxonemal sheath and intracytoplasmic walls are constant characters in the spermatozoa of all the Anoplocephalinae.

Spermiogenesis and spermatozoon ultrastructure of the cranial digenean Troglotrema acutum (Leuckart, 1842)

Ultrastructure of spermiogenesis and the main characters of the mature spermatozoon of Troglotrema acutum are described by means of transmission electron microscopy. Specimens were obtained from the nasolacrimal sinuses of an American mink (Mustela vison). Spermiogenesis in T. acutum follows the general pattern of digeneans. The zone of differentiation is a conical-shaped area bordered by cortical microtubules and delimited at its base by a ring of arched membranes. This area contains 2 centrioles associated with striated rootlets and an intercentriolar body between them. The centrioles develop 2 free flagella that grow ortogonally to the median cytoplasmic process. The posterior flagellar rotation and proximodistal fusion of the free flagella with the median cytoplasmic process originate the spermatozoon. The mature spermatozoon of T. acutum is characterized by the presence of 2 axonemes of different lengths presenting the 9+'1' trepaxonematan pattern, 2 bundles of parallel cortical microtubules, 2 mitochondria, a nucleus, and granules of glycogen. These ultrastructural characters are compared with other digenean species previously studied and the importance of different spermatological features is discussed.

Cranial helminths of Mustela vison Schreber, 1777 in Spain

A survey was carried out to investigate the presence of cranial helminths in 337 American minks (Mustela vison) from Spain. This information was obtained partly in order to evaluate potential conservation problems and sanitary risks to the congeneric European mink (Mustela lutreola), one of the most endangered carnivores in the world. Skulls and rectal faeces of each specimen were simultaneously analysed. Troglotrema acutum and Skrjabingylus nasicola were found in 5.6% of the M. vison analysed. No cranial lesions were seen in any of the examined skulls. The finding of both helminths in Spanish free-living M. vison specimens enlarges their natural definitive host spectrum in Western Europe. One relatively important focus of T. acutum in M. vison was detected (30.4%) in the Spanish Alava province while S. nasicola was found to be very infrequent. The suitability of both analytical methods was assessed in order to know to what degree coprological analysis reflects the real prevalence of cranial helminths in this host. It is possible to conclude that coprological analysis can be used instead of necropsies to analyse the possible incidence of pathogenic cranial helminths in mustelids. This aspect is very important and useful when trying to analyse the helminthological status of endangered species such as the native mink (M. lutreola) particularly in areas where both congeneric species are present and strict competition occurs.

Ultrastructure of the spermatozoon of Dollfusiella spinulifera (Beveridge and Jones, 2000) Beveridge, Neifar and Euzet, 2004 (Trypanorhyncha, Eutetrarhynchidae)

The ultrastructural organization of the mature spermatozoon of the trypanorhynch cestode Dollfusiella spinulifera is described. The spermatozoon is a long filiform cell, tapered at both ends, which lacks mitochondria. Its cytoplasm contains (1) two axonemes of different lengths of the 9+'1' pattern of trepaxonematan Platyhelminthes, (2) two rows of parallel cortical microtubules, each of which is adjacent to the opposite sides of the plasma membrane, (3) the nucleus, and (4) glycogen in the form of both alpha-glycogen rosettes and beta-glycogen particles. Unlike the majority of cestode spermatozoa, the spematozoon of D. spinulifera lacks crested bodies and periaxonemal sheath. In view of the present results, the postulated synapomorphic value of crested bodies for the Eucestoda is questioned.

Concentration of some toxic elements in Oryctolagus cuniculus and in its intestinal cestode Mosgovoyia ctenoides, in Dunas de Mira (Portugal)

The need for sentinel organisms reflecting small-scale changes in heavy metal pollution of different habitats has been previously stated and the role of terrestrial mammalian parasites has been pointed out as an important field of research aiming at the potential use of parasitic models as bioindicators. The scope of the present study was to assess the concentration of some toxic (Cd, Pb, As and Hg) elements in Dunas de Mira (Natura 2000 PTCON055) while testing the model constituted by the wild rabbit (Oryctolagus cuniculus Linnaeus, 1758) and its intestinal cestode parasite Mosgovoyia ctenoides Railliet, 1890 as potential bioindicators. Wild rabbits were harvested by hunters and analysed for intestinal cestodes. Samples of kidney, liver, intestinal mucosa, muscle of host and also M. ctenoides were taken and deep-frozen for posterior element analysis by ICP-MS. In general, levels of contamination in rabbit tissues were found to be low although some of the elements were detected in higher quantities when compared to other previous reports for wildlife in Europe. The highest quantity of Pb was found in rabbit muscle (3.81 ppm) while highest Cd and Hg values were found in kidney (1.02 and 0.08 ppm). Significant linear relationships were found between Pb concentration in the parasite and Pb concentration in kidney (P=0.0047), muscle (P=0.0002) and intestinal mucosa (P=0.0181) and between As concentration in the parasite and As concentration in liver (P=0.0024), kidney (P=0.0010), muscle (P=0.0003) and intestinal mucosa (P=0.0047). The most significant relationships for Pb and As were detected between element concentration in the cestode and in host muscle. However, maximum Pb and As concentrations in M. ctenoides were only twice as high as those found for rabbit kidney and therefore it is not possible to confirm the role of the model O. cuniculus/M. ctenoides as a promising bioindicator system unlike other mammalian host/cestode models tested in other studies. The contrasting results might be due to differences in the absorption processes in the tegument of different cestode families. Furthermore, the large size of the cestodes used in the present study might also explain the relatively low element concentration values obtained.

Dicrocoelium hospes Looss, 1907 (Digenea, Dicrocoeliidae): spermiogenesis, mature spermatozoon and ultrastructural comparative study

This work describes the first ultrastructural results on spermiogenesis and on the mature spermatozoon of Dicrocoelium hospes (Trematoda, Digenea) collected in Bos indicus from Senegal (Africa). Examination of this species was processed by TEM. Spermiogenesis follows the general pattern found in the digenean, but reveals a particularity consisting of the appearance of glycogen granules in the late spermatids within the testes. The mature spermatozoon possesses five distinct regions and presents all features found in Digenea gametes: two axonemes, mitochondria, nucleus and parallel cortical microtubules. However, several characters allow us to distinguish D. hospes from other digenetic trematodes within the Dicrocoeliidae family. In fact, we observed several structures that are absent in the other species of Dicrocoeliidae studied until now, such as: a cytoplasmic expansion, extramembranar ornamentation, spine-like bodies and two parallel mitochondria in the mature sperm. Moreover, additional particular characteristics were observed in this species in both extremities of the spermatozoon. This work produced new data on the ultrastructure of this trematode family which may be useful for phylogenetic purposes.

An ultrastructural study of embryonic envelope formation in the anoplocephalid cestode Mosgovoyia ctenoides (Railliet, 1890) Beveridge, 1978

In this study the ultrastructural aspects of egg envelope formation in the anoplocephalid cestode Mosgovoyia ctenoides are described. In the early stage of oncospheral morphogenesis, formation of three following primary embryonic envelopes takes place: (1) the capsule, (2) the outer envelope, and (3) the inner envelope. The capsule is formed from the vitellocyte material. Two macromeres contribute to the formation of the outer envelope and three mesomeres take part in the formation of the inner envelope. The three primary envelopes undergo further differentiation and transformation into the secondary envelopes, the so-called oncospheral or egg envelopes. In the advanced preoncospheral phase, the inner envelope undergoes differentiation into three sublayers: (1) a thick extra-embryophoral cytoplasmic layer; (2) an electron-dense embryophore, as a stiff pyriform apparatus; and (3) a thin intra-embryophoral cytoplasmic layer containing mesomere nuclei. The oncosphere is located in the extended cupule-like part of the pyriform apparatus. The two embryophoral horns elongate and fuse, thus forming a rigid cone. Four egg envelopes surround the mature infective oncosphere of M. ctenoides: (1) a thick capsule; (2) the outer envelope; (3) the inner envelope with a characteristic embryophore, in the form of the pyriform apparatus; and (4) the oncospheral membrane. The differentiation and ultrastructure of the egg envelopes of M. ctenoides are compared, in particular to those described in other anoplocephalids, and in general to the oncospheres of other cestode species.

Thiolic antioxidant supplementation of the diet reverses age-related behavioural dysfunction in prematurely ageing mice

We have studied in a model of premature ageing in mice based on their impaired behavioural response in a simple T-maze test the effect of the ingestion of thioproline (TP) plus N-acetylcysteine (NAC) (0.1% w/w of each antioxidant) by female and male mice of Swiss and BALB/c strains on performance in two behaviour tests. The antioxidant treatment (4 weeks in two different periods of life, i.e., adult and old age) protected all animals against early-age-associated behavioural impairment, but this improvement was more evident in the prematurely ageing mice (PAM) in comparison to the control group or non-prematurely ageing mice (NPAM). An improvement of the exploratory activity and neuromuscular coordination after the thiolic antioxidant treatment was found in the PAM, bringing the behavioural parameters to the NPAM levels. These effects could be due to the glutathione precursor role of NAC and TP that replenish the intracellular reduced glutathione (GSH) levels despite advancing age. In conclusion, diet supplementation with thiolic compounds appears to be an effective therapy for protection against early behavioural decline in prematurely ageing mice.