Subcutaneous merocercoids of Clistobothrium sp. in two Cape fur seals (Arctocephalus pusillus pusillus)

Molecular investigation of endoparasites of marine mammals (Cetacea: Mysticeti, Odontoceti) in the Western Mediterranean

Introduction

Whales, dolphins, and porpoises are susceptible to infections by protozoan and metazoan parasites.

Methods

In this study, tissue samples, as well as flatworms and roundworms, were collected from a common bottlenose dolphin (Tursiops truncatus), three short-beaked common dolphins (Delphinus delphis), two striped dolphins (Stenella coeruleoalba), a harbor porpoise (Phocoena phocoena), a long-finned pilot whale (Globicephala melas), and a fin whale (Balaenoptera physalus). These samples were molecularly analyzed.

Results

In one D. delphis, Toxoplasma gondii was detected in multiple organs, including the cerebellum. The cysts of the tapeworms Clistobothrium delphini and Clistobothrium grimaldii were identified in G. melas. Flukes collected from D. delphis belong to Brachycladium atlanticum, while those removed from S. coeruleoalba probably represent a new species. Four species of lungworms were also identified: Halocercus delphini in S. coeruleoalba, Halocercus sp. in T. truncatus, Stenurus globicephalae in G. melas, and a potentially new Pharurus sp. in P. phocoena.

Conclusion

These findings show, to the best of our knowledge, for the first time, the presence of T. gondii DNA in D. delphis. The cerebellum of the animal was Toxoplasma-infected, which might be relevant to inadvertent stranding. In this study, new genetic markers were sequenced for several helminth parasites of marine mammals, possibly including undescribed species.

Larvae of Clistobothrium grimaldii (Cestoda: Phyllobothriidea) from a Cape fur seal (Arctocephalus pusillus pusillus) kept in a zoo in Japan

The larval form of the Phyllobothriidea cestode was found in the blubber of a Cape fur seal (Arctocephalus pusillus pusillus) from a zoo in Japan. Bladder-bearing larval cestodes with a scolex have been occasionally reported from blubbers of pinnipeds and morphologically identified as Clistobothrium delphini (formerly known as Phyllobothrium delphini) or rarely Clistobothrium grimaldii (Monorygma grimaldii). Although the larvae here morphologically resembled C. delphini, the 28S rDNA sequence was 100% (1,430/1,430 bp) homologous to the registered sequence of C. grimaldii (GenBank Accession No. KU724058). This discrepancy between morphological and molecular analyses confirms the difficulty of identifying C. delphini and C. grimaldii larvae based solely on morphology, and the need for molecular data to elucidate the morphological variations in Clistobothrium parasites.

First report of a severe nasopulmonary acariasis caused by Orthohalarachne diminuata Doetschmann, 1944 (Acari: Halarachnidae) in a captive South American sea lion (Otaria flavescens Shaw, 1800)

Obligatory endoparasitic mites of the genera Halarachne Allman, 1847 and Orthohalarachne Newell, 1947 (Acari: Halarachnidae) parasitize different segments of the respiratory tract of marine mammals, including pinnipeds and sea otters, and infestations can cause asymptomatic to serious respiratory diseases. However, knowledge on biology, pathogenic potential and occurrence of halarachnid mites infesting pinnipeds, especially in captivity, is scarce. A two-year-old South American sea lion (Otaria flavescens Shaw, 1800) male, born and held at the Vienna Zoo, was anesthesized for routine pre-transport examinations, including computed tomography, bronchoalveolar lavage, and blood sampling. During the final phase of general anesthesia, the individual abruptly became apneic and died despite all attempts at resuscitation. At necropsy, 45 highly motile whitish millimeter-sized structures were macroscopically detected in the trachea, bifurcatio tracheae and main bronchi and were identified as adult stages of Orthohalarachne diminuata Doetschman, 1944 following morphological descriptions. After trepanation of the nasal cavity and sinus paranasalis, a total of 407 larval and 3 nymphal specimens distributed in clusters were detected. Macroscopically, sinus mucosa showed hyperemia and multiple petechial hemorrhages. Histopathological analyses of paranasal sinuses revealed mite cross-sections surrounded by sanioserous exudate and epithelial exfoliation. For the first time, O. diminuata was molecularly characterized and phylogenetically analyzed based on its 16S rDNA. Our study constitutes the first record of a severe O. diminuata infestation in captive O. flavescens and one of the few host-parasite records in general. We present clinical data and pathological results, the first scanning electron microscopic images of a O. diminuata larval stage and discuss the etiology of this autochthonous infestation, possible transmission pathways and detrimental effects. Further studies on biology and pathogenic effects of halarachnid mites, as well as on the development of non-invasive sampling techniques are essentially required for a better understanding of (ortho-)halarachnosis in pinnipeds held in zoological gardens.

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First record of Orthohalarachne diminuata in a captive South American sea lion.

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One of the few host-parasite records.

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Autochthonous infestation, since infested animal was born in captivity.

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First scanning electron microscopic images of a O. diminuata larva.

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First molecular characterization and phylogenetic analysis of O. diminuata.

Clistobothrium sp. (Cestoda: Tetraphyllidea) in oarfish (Regalecus russelii) stranded on the coast of Akita Prefecture, Japan

Oarfish (Regalecus russelii Cuvier) are mesopelagic fish with little known about their life history. Oarfish live in deep water, making it difficult for researchers to collect specimens; thus, records of their parasitic helminths are limited. Two plerocercoids were found for the first time in an oarfish stranded on the coast of Akita Prefecture, Japan. These plerocercoids were identified as Clistobothrium sp. RR-1 using morphological and molecular analyses. It was revealed that oarfish represent one of the intermediate hosts of the genus Clistobothrium, and large sharks are the definitive hosts for these parasites.

Causes of cetacean stranding and death on the Catalonian coast (western Mediterranean Sea), 2012-2019

The causes of cetacean stranding and death along the Catalan coast between 2012 and 2019 were systematically investigated. Necropsies and detailed pathological investigations were performed on 89 well-preserved stranded cetaceans, including 72 striped dolphins Stenella coeruleoalba, 9 Risso's dolphins Grampus griseus, 5 bottlenose dolphins Tursiops truncatus, 1 common dolphin Delphinus delphis, 1 Cuvier's beaked whale Ziphius cavirostris and 1 fin whale Balaenoptera physalus. The cause of death was determined for 89.9% of the stranded cetaceans. Fisheries interaction was the most frequent cause of death in striped dolphins (27.8%) and bottlenose dolphins (60%). Cetacean morbillivirus (CeMV) was detected on the Catalan coast from 2016 to 2017, causing systemic disease and death in 8 of the 72 (11.1%) striped dolphins. Chronic CeMV infection of the central nervous system was observed from 2018-2019 in a further 5 striped dolphins. Thus, acute and chronic CeMV disease caused mortality in 18% of striped dolphins and 14.6% of all 89 cetaceans. Brucella ceti was isolated in 6 striped dolphins and 1 bottlenose dolphin with typical brucellosis lesions and in 1 striped dolphin with systemic CeMV. Sinusitis due to severe infestation by the nematode parasite Crassicauda grampicola caused the death of 4 out of 6 adult Risso's dolphins. Maternal separation, in some cases complicated with septicemia, was a frequent cause of death in 13 of 14 calves. Other less common causes of death were encephalomalacia of unknown origin, septicemia, peritonitis due to gastric perforation by parasites and hepatitis caused by Sarcocystis spp.

Intrigue surrounding the life-cycles of species of Clistobothrium (Cestoda: Phyllobothriidea) parasitising large pelagic sharks

This study aimed to locate the adults, and thus also the definitive hosts, of three species of marine mammal-parasitising larval cestodes that have molecular affinities with Clistobothrium. New collections led to the discovery of adults of two new species of Clistobothrium, one from the longfin mako shark and one from the salmon shark. New material of Clistobothrium tumidum was collected from the great white shark and new material of a previously reported undescribed species of Clistobothrium was collected from the porbeagle shark. Larvae of Clistobothrium were opportunistically collected from sockeye salmon and four species of small squaliform sharks. Sequence data for the D1-D3 region of the 28S rDNA gene were generated for all but one of these taxa. The tree resulting from maximum likelihood analysis of those data, in combination with comparable data from GenBank, indicates that squaliform sharks can serve as intermediate hosts for the species from the porbeagle shark. The larvae from salmon exhibit a unique molecular signature and, based on diet data, may be conspecific with adults from the salmon shark. Informed by sequence data for new material of Monorygma and existing data for Phyllobothrium, the larvae provisionally identified as Monorygma grimaldii and Phyllobothrium delphini were formally transferred to Clistobothrium. Especially puzzling was that the molecular signatures of none of the eight species of Clistobothrium match those of the three marine mammal-parasitising larval forms. We are at a loss as to where else to look for the three corresponding adult forms. The great white shark remains the most likely candidate given it consumes marine mammals with some regularity, but seems unlikely to host five species of Clistobothrium. Alternatively, we are left wondering if the large marine mammal predator Carcharocles megalodon may not be extinct after all.

Molecular Characterization of Clistobothrium sp. Viable Plerocercoids in Fresh Longfin Inshore Squid (Doryteuthis pealeii) and Implications for Cephalopod Inspection

Cephalopods, an appreciated seafood product, are common hosts of marine cestodes. The aim of this work is to report visible alive plerocercoids in longfin inshore squid (Doryteuthis pealeii), a cephalopod species commercialized as fresh and whole in Italy. Seventy D. pealeii from the Northwest Atlantic (FAO area 21) were collected and visually inspected. In total, 18 plerocercoid larvae were found in the viscera of 10 host specimens (P: 14.3% 95% CI 7.1–24.7; MI: 1.8, MA: 0.26; range 1–4) and molecularly analyzed targeting the variable D2 region of the large subunit (LSU) rRNA gene and the cytochrome c oxidase subunit I (COI) gene. The molecular characterization allowed to identify all the plerocercoids as Clistobothrium sp., a cestode of the Phyllobothriidae family with Lamnidae sharks as definitive hosts, and cephalopods as second intermediate hosts. These findings represent the first molecular record of Clistobothrium sp. in D. pealeii, thus contributing to elucidate its poorly known life cycle. Even if not affecting consumer’s health, these visible parasites may represent a reason for disgust for consumers. Therefore, the results suggest that Food Business Operators should also check for the presence of these visible parasites during inspection and underline the importance of a correct consumers’ education.

A Perspective Around Cephalopods and Their Parasites, and Suggestions on How to Increase Knowledge in the Field

Although interest in several areas of cephalopod research has emerged over the last decades (e.g., neurobiology, aquaculture, genetics, and welfare), especially following their 2010 inclusion in the EU Directive on the use of animals for experimental purposes, knowledge regarding the parasites of cephalopods is lacking. Cephalopods can be intermediate, paratenic, or definitive hosts to a range of parasites with a wide variety of life cycle strategies. Here, we briefly review the current knowledge in cephalopod parasitological research, summarizing the main parasite groups that affect these animals. We also emphasize some topics that, in our view, should be addressed in future research, including: (i) better understanding of life cycles and transmission pathways of common cephalopod parasites; (ii) improve knowledge of all phases of the life cycle (i.e., paralarvae, juveniles, adults and senescent animals) and on species from polar deep sea regions; (iii) exploration of the potential of using cephalopod-parasite specificity to assess population boundaries of both, hosts and parasites; (iv) risk evaluation of the potential of standard aquacultural practices to result in parasite outbreaks; (v) evaluation and description of the physiological and behavioral effects of parasites on their cephalopod hosts; (vi) standardization of the methods for accurate parasite sampling and identification; (vii) implementation of the latest molecular methods to facilitate and enable research in above mentioned areas; (viii) sharing of information and samples among researchers and aquaculturists. In our view, addressing these topics would allow us to better understand complex host-parasite interactions, yield insights into cephalopod life history, and help improve the rearing and welfare of these animals in captivity.