A new brachycladiid species (Digenea) from Gervais' beaked whale Mesoplodon europaeus in north-western Atlantic waters

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.

Pathological, morphological, and molecular characterization of the infection by Brachycladium goliath in humpback whale Megaptera novaeangliae

The humpback whale (Megaptera novaeangliae) is a cosmopolitan migratory, seasonal mysticete that frequents the Brazilian coast. Strands of specimens may occur during the migratory stay in the country. In 2021 and 2022, three live humpback whales stranded on the coast of Rio Grande do Sul and Santa Catarina states in southern Brazil. After euthanasia, specimens were necropsied, and organs were thoroughly examined for lesions. Grossly, in all three cases, the liver exhibited multifocal, irregular, firm, white areas on the hepatic capsule, which extended into the parenchyma. On the cut surface, the livers were yellow to pale brown with orangish to greenish areas, the bile ducts were prominent, thickened, and severely dilated, and leaf-shaped flukes were found inside of them. Additionally, one case showed moderate atrophy of the right hepatic lobe. The histological findings included dilation of bile ducts, hyperplasia of the bile duct epithelium, marked inflammatory infiltration of lymphocytes, plasma cells, and eosinophils, and portal fibrosis. The parasite Brachycladium goliath was both morphologically and molecularly identified based on diagnostic key for trematodes and the original description of the species, and the amplification and sequencing of the ITS-2 region, respectively. Even though hepatic injury was not the primary cause of stranding, it may have contributed to the debilitation of the whales. To the authors' knowledge, this is the first study that reports M. novaeangliae as a definitive host of B. goliath and that describes the lesions caused by the parasite in cetaceans.

A first record of digenean parasites of the dwarf sperm whale Kogia sima with morphological and molecular information

Two species of digenean trematodes of the family Brachycladiidae were obtained from two male dwarf sperm whales Kogia sima that stranded along the island of Kyushu, southern Japan in 2017. From the liver of the first animal, a single, large gravid specimen of a digenean species was collected. The morphological features were consistent with those of the genus Brachycladium. The worm had a large body and was characterized by anterior caeca without lateral diverticula, the shape of testes, ovary, and eggs. Molecular analyses using gene sequences of the 28S rRNA and the mitochondrial NADH dehydrogenase subunit 3 also supported the inclusion of this specimen into the genus Brachycladium. The identity of this worm is undetermined due to the lack of information on the genus and is reported as Brachycladium sp. From the cranial sinuses of the second animal, 33 specimens of digeneans were collected that were morphologically identified as Nasitrema gondo. This report documents a new host record for N. gondo, and the sequence information is provided for this digenean for the first time. This is the second record of digenean parasites for the family Kogiidae, and the first record with morphological and molecular information. The possibility of digenean infection in the liver and cranial sinus should be kept in mind during the necropsy of stranded kogiids.

Cerebral nasitremiasis in a Blainville's beaked whale (Mesoplodon densirostris) stranded in the Canary Islands

Ten species within the genus Nasitrema (subfamily Nasitrematinae, family Brachycladiidae) have been reported infecting a wide variety of odontocetes worldwide, although there is still a lack of information about their presence in beaked whales (BWs). Nasitrema spp. are commonly described inhabiting the pterygoid sinus, the tympanic cavities, and the middle and inner ear; although aberrant migrations through the brain have been also reported. This trematode may cause different type of lesions, ranging from mild to severe saculitis, neuritis, otitis, and/or meningoencephalitis that may impede cetaceans to survive in the wild, resulting in incoordination, loss of equilibrium, and echolocation dysfunction ending in a stranding event. The presence of Nasitrema sp. was found in an adult female Blainville beaked whale stranded death in Fuerteventura, Canary Islands, on November 2016. The most relevant gross finding was a severe chronic-active multifocal pyogranulomatous and necrotizing encephalitis. Histologically, multiple areas of necrosis, pyogranulomatous and eosinophilic inflammation, haemorrhages and occasional cholesterol crystals were found associated with parasitic structures compatible with an adult trematode and its eggs. Molecular analysis, based on a quantitative polymerase chain reaction (qPCR) of the brain tissue sample detected 99% homology with a partial sequence of the NADH dehydrogenase subunit 3 (ND3) gene of Nasitrema delphini. In addition, liver, kidney, prescapular lymph node and brain samples were positive to herpesvirus (conventional nested PCR). Evidence of the presence of this parasite was not found in any of the 54 beaked whales (n = 54) stranded on the Canary Islands between 1999 and 2017, specifically 35 Cuvier's BWs and 19 specimens belonging to the Mesoplodon genus. To our knowledge, the current study represents the first description of a nasitremiasis in a member of the Ziphiidae family.

The mitochondrial genome and ribosomal operon of Brachycladium goliath (Digenea: Brachycladiidae) recovered from a stranded minke whale

Members of the Brachycladiidae are known to cause pathologies implicated in cetacean strandings and it is important to develop accurate diagnostic markers to differentiate these and other helminths found in cetaceans. Brachycladium goliath (van Beneden, 1858) is a large trematode found, as adults, usually in the hepatic (bile) and pancreatic ducts of various cetaceans. Complete sequences were determined for the entire mitochondrial genome, and phylogenetically informative nuclear genes contained within the ribosomal operon, from a small piece of an individual worm taken from a common minke whale Balaenoptera acutorostrata Lacépède, 1804. Genomic DNA was sequenced using an Illumina MiSeq platform. The mtDNA is 15,229 bp in length consisting of 12 protein-coding genes, 22 tRNA genes, 2 rRNA genes and 2 non-coding regions of which the larger is comprised of 4 tandemly repeated units (260 bp each). The ribosomal RNA operon is 9297 bp long. These data provide a rich resource of molecular markers for diagnostics, phylogenetics and population genetics in order to better understand the role, and associated pathology of helminth infections in cetaceans.