Causes of mortality and morbidity in wild juvenile and adult grey seals (Halichoerus grypus)

Mechanical properties of the California sea lion (Zalophus californianus) and northern elephant seal (Mirounga angustirostris) lower jaws explain trophic plasticity

The fossil record of pinnipeds documents a suite of morphological changes that facilitate their ecological transition from a terrestrial to an aquatic lifestyle. Among these is the loss of the tribosphenic molar and the behavior typically associated with it in mammals: mastication. Instead, modern pinnipeds exhibit a broad range of feeding strategies that facilitate their distinct aquatic ecologies. Here, we examine the feeding morphology of two species of pinnipeds with disparate feeding ecologies: Zalophus californianus, a specialized raptorial biter, and Mirounga angustirostris, a suction specialist. Specifically, we test whether the morphology of the lower jaws facilitates trophic plasticity in feeding for either of these species. We used finite element analysis (FEA) to simulate the stresses during the opening and closing of the lower jaws in these species to explore the mechanical limits of their feeding ecology. Our simulations demonstrate that both jaws are highly resistant to the tensile stresses experienced during feeding. The lower jaws of Z. californianus experienced the maximum stress at the articular condyle and the base of the coronoid process. The lower jaws of M. angustirostris experienced the maximum stress at the angular process and were more evenly distributed throughout the body of the mandible. Surprisingly, the lower jaws of M. angustirostris were even more resistant to the stresses experienced during feeding than those of Z. californianus. Thus, we conclude that the superlative trophic plasticity of Z. californianus is driven by other factors unrelated to the mandible's tensile resistance to stress during feeding.

Nasopulmonary mites (Acari: Halarachnidae) as potential vectors of bacterial pathogens, including Streptococcus phocae, in marine mammals

Nasopulmonary mites (NPMs) of the family Halarachnidae are obligate endoparasites that colonize the respiratory tracts of mammals. NPMs damage surface epithelium resulting in mucosal irritation, respiratory illness, and secondary infection, yet the role of NPMs in facilitating pathogen invasion or dissemination between hosts remains unclear. Using 16S rRNA massively parallel amplicon sequencing of six hypervariable regions (or "16S profiling"), we characterized the bacterial community of NPMs from 4 southern sea otters (Enhydra lutris nereis). This data was paired with detection of a priority pathogen, Streptococcus phocae, from NPMs infesting 16 southern sea otters and 9 California sea lions (Zalophus californianus) using nested conventional polymerase chain reaction (nPCR). The bacteriome of assessed NPMs was dominated by Mycoplasmataceae and Vibrionaceae, but at least 16 organisms with pathogenic potential were detected as well. Importantly, S. phocae was detected in 37% of NPM by nPCR and was also detected by 16S profiling. Detection of multiple organisms with pathogenic potential in or on NPMs suggests they may act as mechanical vectors of bacterial infection for marine mammals.

Nasopulmonary mites (Halarachnidae) of coastal Californian pinnipeds: Identity, prevalence, and molecular characterization

Mites from the family Halarachnidae Oudemans 1906 are obligate endoparasites that colonize the respiratory tracts of free-living and captive marine mammals. Infestations can range from mild to severe and result in respiratory tract irritation or impairment. Nasopulmonary acariasis was determined to be a contributing cause of death among several southern sea otters Enhydra lutris nereis Merriam 1904 in a longitudinal study of otter mortality, and proximity to Pacific harbor seals Phoca vitulina richardii Gray 1864 was a significant risk factor for sea otter infestation. Beyond scattered opportunistic reports, each halarachnid mite species' affinity for particular hosts and the extent of mite transmission between host species is poorly understood. We investigated the identity and prevalence of nasopulmonary mites from Pacific harbor seals, California sea lions Zalophus californianus Lesson 1828, northern elephant seals Mirounga angustirostris Gill 1866, northern fur seals Callorhinus ursinus Linnaeus 1758, and Guadalupe fur seals Arctocephalus philippii townsendi Merriam 1897 to complement published nasopulmonary mite findings from sympatric southern sea otters during a comparable timeframe. Halarachnid mite infestation was common among California sea lions (74.1%), northern fur seals (73.3%), and northern elephant seals (46.6%), but was less common among harbor seals (18.7%) and Guadalupe fur seals (8.8%). Observed host-mite relationships suggest a distinct host specificity, with genus Orthohalarachne infesting otariids, and genus Halarachne infesting phocids and lutrinids along the California coast. Harbor seals and southern sea otters were the primary hosts of H. halichoeri, but one nothern elephant seal was infested with both H. miroungae and a single H. halichoeri. We also present the first high-resolution SEM images for H. miroungae and O. attenuata and possible evidence for a new host record for H. halichoeri.

Novel Pulmonary Vasculitis with Splendore-Hoeppli Reaction in Grey Seals (Halichoerus grypus) Associated with Otostrongylus circumlitus Infection

Lungworm infection in seals is an important cause of morbidity and mortality, inducing bronchopneumonia and affecting population dynamics in some areas of the world. We present a series of cases of lungworm infection in grey seals (Halichoerus grypus) associated with novel, significant and unusual pulmonary vascular changes. Grey seals (n = 180) that were stranded, in rehabilitation or in long-term captivity in the UK were subjected to post-mortem examination between 2012 and 2018. Lung tissue was collected from 47 individuals for histopathological examination. Polymerase chain reaction (PCR) on formalin-fixed and paraffin wax-embedded (FFPE) material was attempted for parasite identification on selected sections using lungworm-specific primers, and nematode morphology within sections was evaluated histologically. Fourteen of 47 (30%) of these grey seals showed evidence of segmental granulomatous and eosinophilic vasculitis with an intramural Splendore-Hoeppli reaction in medium to large pulmonary arteries. Intravascular nematodes suggestive of Otostrongylus circumlitus were seen in two cases. PCR on FFPE material was unable to detect a signal on selected tissue sections. Of the 14 affected seals, nine had concurrent bronchopneumonia and four had intra-alveolar/bronchiolar Parafilaroides spp. Thirteen of 14 animals with vasculitis lesions were weaned pups with only one adult affected. Previous pathological descriptions of lungworm infection in grey seals have dealt mainly with the bronchopneumonia. This case series has identified previously unrecorded vascular changes characterized by an intramural Splendore-Hoeppli reaction. Such change would impact on vascular integrity, increasing the likelihood of vascular rupture with pulmonary haemorrhage and increased risk of intravascular coagulation. A host-parasite relationship with the persistence of antigenic material following close contact with, or migration through, the blood vessel wall is suspected.

There and back again - The return of the nasal mite Halarachne halichoeri to seals in German waters

The nasal mite Halarachne halichoeri (Acari; Halarachnidae) is adapted to live in the marine environment with pinnipeds as its primary host and can cause different levels of upper respiratory disease in both harbour seals (Phoca vitulina) and grey seals (Halichoerus grypus). Historical reports of H. halichoeri occurring in seals from German waters date back to the end of the 19th century. However, with the disappearance of the grey seal from German waters as a consequence of human over-exploitation, the mite vanished from the records and the fauna found in Germany for more than a century. Although a stranding network has been monitoring marine mammal health along the German coasts since the mid 1980s with extensive post-mortem investigations, this study reports the first and subsequent findings of H. halichoeri in grey and harbour seals from the North and Baltic Sea from 2014 onwards. The re-emergence of this endoparasitic mite in North and Baltic Sea habitats seems to have occurred simultaneously with the recolonisation of its primary host, the grey seal. During the course of its recolonisation, it was probably transmitted to harbour seals sharing the same haul-out sites. Molecular analyses showed a high similarity of rDNA sequences with H. halichoeri collected from sea otters (Enhydra lutris) in the USA. However, more thorough analyses of additional gene loci are required to fully assess the exchange and diversity of this parasite between geographically isolated regions and species.

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First finding of endoparasitic seal mite H. halichoeri in Germany after >100 years.

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Recolonisation of North and Baltic Sea in unison with primary host grey seal.

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Morphological comparison with century-old museum specimens.

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Minor histopathological alterations in upper respiratory tract associated.

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High genetic similarity of ITS-2 with H. halichoeri from sea otters in the USA.

Pathology and epidemiology of nasopulmonary acariasis (Halarachne sp.) in southern sea otters (Enhydra lutris nereis)

Halarachne sp. nasal mites infest harbor seals (Phoca vitulina) and southern sea otters (Enhydra lutris nereis) in California, but little is known about the pathophysiology of these infestations, or risk factors for exposure. To investigate these questions, a retrospective case-control study was performed using necropsy data from 70 mite-infested sea otters, and 144 non-infested controls. Case records for sea otters examined by pathologists from February 1999 through May 2015 were examined to assess risk factors for infestation, and lesions associated with nasopulmonary acariasis. Animals with a history of captive care within 10 days of death or carcass recovery were 3.2 times more likely to be infested with nasopulmonary mites than those with no history of recent rehabilitation. Sea otters stranding within 1 km of Elkhorn Slough in Monterey Bay were 4.9 times more likely to be infested with nasal mites than other areas; this site is characterized by high sea otter contact with sympatric harbor seals (a common host for Halarachne sp.), and a comparatively large population of rehabilitated and released sea otters. Aged adult otters were 9.4 times more likely to be infested than younger animals, and sea otters with nasopulmonary acariasis were 14.2 times more likely to have upper respiratory inflammation than un-infested animals. Additional findings in otters with nasopulmonary acariasis included lower respiratory tract bacterial infections, presence of medium-sized and/or fresh nose wounds at necropsy (indicators of recent face-to-face interaction between otters during copulation or fighting), and turbinate bone erosion. Our findings, although preliminary, suggest that captive rehabilitation and close contact with harbor seals could facilitate nasopulmonary mite transmission to sea otters. We also identified a high-risk zone for nasopulmonary acariasis in sea otters. We also provide preliminary data to suggest that nasopulmonary mite infestations can cause significant respiratory pathology in sea otters.

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Our data illustrates that nasopulmonary mites can be pathogenic for sea otters.

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High mite loads were associated with captive care, fresh nose wounds, and females.

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Mite-infested otters were 14 times more likely to have nasopharyngeal inflammation.

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Aged adult otters were 9 times more likely to be infested than other age groups.

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Otters hospitalized within 10 days of death were 3 times more likely to be infested.

Molecular characterization and prevalence of Halarachne halichoeri in threatened southern sea otters (Enhydra lutris nereis)

Parasitism, particularly in concert with other sublethal stressors, may play an important, yet underappreciated role in morbidity and mortality of threatened species. During necropsy of southern sea otters (Enhydra lutra nereis) from California submitted to the Marine Wildlife Veterinary Care and Research Center's Sea Otter Necropsy Program between 1999 and 2017, pathologists occasionally observed nasopulmonary mites infesting the respiratory tracts. Infestation was sometimes accompanied by lesions reflective of mite-associated host tissue damage and respiratory illness. Our objectives were to estimate prevalence of nasopulmonary mites, determine the taxonomic identity of the observed mites, and create a DNA reference for these organisms in southern sea otters as an aid in population management. Using unique morphological characteristics discerned via light and scanning electron microscopy (SEM), we identified the mites as Halarachne halichoeri, a species typically associated with harbor seals (Phoca vitiluna). The 18S, 16S, 28S and ITS1-2 genetic regions were sequenced and submitted to GenBank. We observed H. halichoeri mites in 25.6% (95% CI 19.9-33.4%). of southern sea otters from a subset of necropsies performed between 2012 and 2017. This is the first documentation of H. halichoeri in southern sea otters and is suggestive of parasite exchange between sea otters and harbor seals.

Patterns of stranding and mortality in common seals (Phoca vitulina) and grey seals (Halichoerus grypus) in The Netherlands between 1979 and 2008

Pathological examination of stranded marine mammals provides information on the causes of mortality in their populations. Patterns of stranding and causes of death of dead-stranded seals on the Dutch coast were analyzed over a 30-year period (1979-2008). Stranding data (n=1,286) and post-mortem data (n=379) from common seals (Phoca vitulina) and grey seals (Halichoerus grypus) found dead, or that died before admission to rehabilitation, were obtained from the Seal Rehabilitation and Research Centre database. Data for the years 1988 and 2002, when mass mortality occurred due to phocine distemper virus epidemics, were excluded. Common seal stranding increased from one to nearly 100 per year over this period. This coincides with the increase in the number of common seals in Dutch waters over recent decades. Grey seal stranding increased gradually from one to about 40 per year over the period, reflecting recolonization of Dutch waters by this species. For both species, the trend in stranding of dead seals was found to be in line with that of seals observed in Dutch waters during aerial surveys and did not provide any indications of a relative change in the stranding rate of dead seals. The total monthly stranding rates peaked at more than 120 in June and July for common seals and at nearly 60 in January for grey seals. This coincides with the pupping periods of the two species. Besides phocine distemper, the most common causes of death in investigated common seals (n=286) were by-catch (confirmed and inferred) (19%), pup starvation (7%), intestinal volvulus (7%) and parasitic bronchopneumonia (6%). The most common causes of death in investigated grey seals (n=93) were by-catch (confirmed and inferred) (15%), pup starvation (11%) and trauma (5%). The relative occurrence of by-catch significantly decreased over time for grey seals, but not for common seals. Common seals were affected by infectious disease significantly more often than grey seals, mainly because of a higher occurrence of parasitic pneumonia. Phocine distemper caused mass mortalities among common seals, but not among grey seals. These findings in dead-stranded seals differ in part from those reported elsewhere in live-stranded seals, for which pup starvation and parasitic bronchopneumonia were the main causes of stranding. A substantial proportion of seals in Dutch waters die from causes related to human activity. Continued monitoring of stranding patterns and causes of death is warranted for early detection of changes and the possibility of taking timely management actions.

Naso-pharyngeal mites Halarachne halichoeri (Allman, 1847) in Grey seals stranded on the NW Spanish Atlantic Coast

In North Atlantic European waters, the nasal mite Halarachne halichoeri has been described affecting Grey seals (Halichoerus grypus) producing different levels of respiratory disease. This study provides data on the prevalence, clinical signs and produced macro-pathology of this parasite mite infecting juvenile wild Grey seals stranded in North-Western Spanish coast. Among the 25 seals examined during the study, a total of 19 had nasal mites in their respiratory upper ways, including adult and larval stages. This represented a percentage of prevalence of 76 ± 8.37. All the live positive seals presented a typical clinical symptomatology associated to upper respiratory tract infections. In dead positive seals, a light to intense sinusitis could be diagnosed macroscopically. The presence of the parasite in the nasal sinuses appears as the primary cause of the high respiratory tract symptomatology presented in most of the juvenile seals stranded in the north coast of Spain. Ultrastructural characterization by scanning electronic microscopy (SEM) has confirmed the taxonomic status of the mite. This identification of H. halichoeri represents the first description of the occurrence of this parasite in Southern Europe.

Conditions in grey seal pups (Halichoerus grypus) presented for rehabilitation

A survey was carried out on the condition of 188 live grey seal (Halichoerus grypus) pups presented for rehabilitation from the coasts of south-west England between 1992 and 1998. The survey was carried out to assess the incidence of malnutrition, hyperthermia, respiratory and gastrointestinal conditions, and also the incidence of traumatic, skin, oral and ocular lesions. Malnutrition was a common finding in pups approaching weaning (mid-moult pups) and those at the point of weaning or postweaning (moulted pups) (62 per cent and 82 per cent, respectively). Separation from the dam, believed to be the main cause of malnutrition in grey seals, was encountered frequently in unweaned pups (91 per cent). Thirty-nine per cent of pups presented with a respiratory condition, 38 per cent with hyperthermia and 9 per cent with diarrhoea. Seven per cent and 14 per cent of pups had confirmed respiratory and gastrointestinal parasitic infestations respectively, although these were probably underestimates. Clinically significant traumatic lesions were seen in 41 per cent, oral ulceration in 26 per cent, ocular conditions in 13 per cent, nail bed infections in 13 per cent and oiling in 10 per cent of pups. Umbilical infections and other skin and oral conditions were also encountered. The incidence of these conditions is compared with data from dead grey seals, and clinical conditions in other pinniped species presented for rehabilitation.

Health condition of the Baltic grey seal (Halichoerus grypus) during two decades. Gynaecological health improvement but increased prevalence of colonic ulcers

Results obtained at postmortem examinations of 159 Baltic grey seals during the 20-year period 1977-1996 are presented. The investigation was initiated due to a serious reduction of the Baltic grey and ringed seal populations. Earlier, reduced reproductive ability with occlusions and stenoses of the uterus, as well as a disease complex in adult individuals of both sexes, was reported. The disease complex comprised lesions of claws, skull bone, intestine (colonic ulcers), kidneys (glomerulopathy, tubular cell proliferations), arteries (sclerosis) and adrenals (cortical hyperplasia, cortical adenomas). Besides occlusions and stenoses, tumours (leiomyomas) were common in the uterus. This report focuses on the results of a time-trend study covering the two decades 1977-1986 and 1987-1996. The prevalences (%) in the two decades of moderate to severe lesions of claws, intestine, arteries and adrenals are compared, as well as the prevalences of lesions of the female reproductive organs and rate of pregnancy. A similar comparison was made of animals born before 1980 and those born after 1979, in order to investigate a possible relation between the evident decrease in PCB and DDT pollution of the Baltic which occurred in the 1970s and seal health. A positive time trend respecting gynaecological health was confirmed, with a decreased prevalence of uterine obstructions, from 42 to 11%, and an increased prevalence of pregnancies, from 9 to 60%. The high incidence of uterine tumours (leiomyomas) seems to have decreased slowly (from 53 to 43%). Of special interest is the increased prevalence of colonic ulcers in young animals. The findings indicate that the food consumed by the Baltic seals may contain "new" or increased amounts of hitherto unidentified toxic factors which affect their immune system.

Causes of mortality and non-fatal conditions among grey seals (Halichoerus grypus) found dead on the coasts of England, Wales and the Isle of Man

A survey of the diseases detectable in 141 grey seals stranded on the coasts of England and Wales away from breeding colonies was carried out between mid-1989 and early 1997. The most common fatal conditions in pups less than three weeks of age were trauma (24 per cent of deaths) and dystocia (12 per cent); in pups more than three weeks of age thy were starvation (22 per cent) and pneumonia (22 per cent); in juveniles they were drowning in fishing gear (30 per cent) and starvation (19 per cent), and in adults a variety of respiratory diseases were the most common causes of death (45 per cent). Many other diseases, both fatal and non-fatal, were recorded.

Experimental transmission of Otostrongylus circumlitus (Railliet, 1899) (Metastrongyloidea: Crenosomatidae), a lungworm of seals in eastern arctic Canada

The transmission of few metastrongyloids infesting marine mammals is known. The results of experimental infections using Otostrongylus circumlitus (Crenosomatidae), a lungworm of pinnipeds, suggested that this metastrongyloid uses fish as intermediate hosts. Various marine organisms (crustaceans, molluscs, and fish) were exposed to first-stage larvae from naturally infected young-of-the-year ringed seals (Phoca hispida) from northern Quebec (Salluit). The first and second moults occurred 3 and 56 days post exposure in the mucosa and muscularis of the intestine of American plaice (Hippoglossoides platessoides) kept at 4 °C. Third-stage larvae were found under the intestinal serosa. Attempts to infect invertebrates were unsuccessful. Transmission to seals may occur from mid-June through the autumn as young seals start feeding intensively on invertebrates and fish. First-stage larvae leave the lungs via the bronchial escalator and are swallowed and released into the sea with the faeces of seals, where they would be available to benthic or pelagic fish. The morphology of the first three larval stages is described.

Pathology and bacteriology of adult male Antarctic fur seals, Arctocephalus gazella, dying at Bird Island, South Georgia

A high mortality rate occurs in Antarctic fur seal males on the breeding breaches of Bird Island, South Georgia. The main causes of death were infections of fighting wounds and pneumonias. The bacteria involved appear to be opportunistic pathogens, predominantly various strains of streptococci.

Histopathologic and immunocytochemical studies of distemper in seals

Thousands of harbor seals (Phoca vitulina) died in European seas during 1988. Respiratory distress and oculonasal discharge were common clinical signs. We necropsied 76 affected seals. The main necropsy finding was severe pneumonia. Microscopic lung changes were characterized by proliferation of type II pneumocytes, filling of alveolar lumina with serofibrinous exudate, leukocytes, and macrophages, and necrosis of bronchial and bronchiolar epithelium. Intracytoplasmic and intranuclear acidophilic inclusion bodies characteristic of morbillivirus infection were seen in bronchial and bronchiolar epithelial cells. Microscopic lesions of non-suppurative demyelinating encephalitis were seen in the brain. There was degeneration and necrosis of neurons, focal gliosis, perivascular cuffing, and patchy demyelination. Many neurons and astrocytes contained intracytoplasmic and intranuclear inclusions. Using an immunoperoxidase technique, we detected morbillivirus antigen in many tissues including lung, brain, spleen, and urinary bladder. The origin of the seal morbillivirus is unknown.