Surprisingly long body length of the lungworm Parafilaroides gymnurus from common seals of the Dutch North Sea.

Lungworms of the genera Parafilaroides and Otostrongylus are responsible for parasitic bronchopneumonia, the foremost disease of eastern Atlantic common seals (EACS, Phoca vitulina vitulina) in the Dutch North Sea. Recently, there have been increased reports of lungworm cases and observations of unusually long Parafilaroides sp. adults in this location.

Lungworm seroprevalence in free-ranging harbour seals and molecular characterisation of marine mammal MSP.

Harbour seals (Phoca vitulina) are frequently infected with the lungworms Otostrongylus circumlitus and Parafilaroides gymnurus. The infection is often accompanied by secondary bacterial infections and can cause severe bronchopneumonia and even death in affected animals. Hitherto, the detection of lungworm infections was based on post mortem investigations from animals collected within stranding networks and a valid detection method for live free-ranging harbour seals was not available.

Structural characterisation of Toll-like receptor 1 (TLR1) and Toll-like receptor 6 (TLR6) in elephant and harbor seals.

Pinnipeds are a diverse clade of semi-aquatic mammals, which act as key indicators of ecosystem health. Their transition from land to marine environments provides a complex microbial milieu, making them vulnerable to both aquatic and terrestrial pathogens, thereby contributing to pinniped population decline. Indeed, viral pathogens such as influenza A virus and phocine distemper virus (PDV) have been identified as the cause of several of these mass mortality events.

Seroprevalence of Antibodies against Seal Influenza A(H10N7) Virus in Harbor Seals and Gray Seals from the Netherlands.

In the spring and summer 2014, an outbreak of seal influenza A(H10N7) virus infection occurred among harbor seals (Phoca vitulina) off the coasts of Sweden and Denmark. This virus subsequently spread to harbor seals off the coasts of Germany and the Netherlands. While thousands of seals were reported dead in Sweden, Denmark and Germany, only a limited number of seals were found dead in the Netherlands.

Harbour seal (Phoca vitulina) PMN and monocytes release extracellular traps to capture the apicomplexan parasite Toxoplasma gondii.

Extracellular traps (ETs) are composed of nuclear DNA as backbone adorned with histones, cytoplasmic antimicrobial peptides/proteins which are released from a range of vertebrate and invertebrate host immune cells in response to several invading pathogens. Until now this ancient novel innate defence mechanism has not been demonstrated in any marine mammal. Interactions of harbour seal (Phoca vitulina)-PMN and -monocytes with viable tachyzoites of Toxoplasma gondii were investigated in this respect in vitro.

Identification of DNA sequences that imply a novel gammaherpesvirus in seals.

Various herpesviruses have been discovered in marine mammals and are associated with a wide spectrum of disease. In the present study we describe the detection and phylogenetic analysis of a novel gammaherpesvirus, tentatively called phocine herpesvirus 7 (PhHV-7), which was detected in samples collected during an outbreak of ulcerative gingivitis and glossitis from juvenile harbour seals (Phoca vitulina) at the Seal Rehabilitation and Research Centre, the Netherlands. The presence of this novel gammaherpesvirus was confirmed by viral metagenomics, while no other viruses other than four novel anelloviruses were detected.

Molecular epidemiology of seal parvovirus, 1988-2014.

A novel parvovirus was discovered recently in the brain of a harbor seal (Phoca vitulina) with chronic meningo-encephalitis. Phylogenetic analysis of this virus indicated that it belongs to the genus Erythroparvovirus, to which also human parvovirus B19 belongs. In the present study, the prevalence, genetic diversity and clinical relevance of seal parvovirus (SePV) infections was evaluated in both harbor and grey seals (Halichoerus grypus) that lived in Northwestern European coastal waters from 1988 to 2014.

Prevalence of phocine distemper virus specific antibodies: bracing for the next seal epizootic in north-western Europe.

In 1988 and 2002, two major phocine distemper virus (PDV) outbreaks occurred in harbour seals (Phoca vitulina) in north-western European coastal waters, causing the death of tens of thousands seals. Here we investigated whether PDV is still circulating among seals of the Dutch coastal waters and whether seals have protective serum-antibodies against PDV. Therefore seal serum samples, collected from 2002 to 2012, were tested for the presence of PDV-neutralizing antibodies.

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.

A dermal melanoma in a young common seal (Phoca vitulina).

A subcutaneous melanocytic tumor was diagnosed during the rehabilitation period of a stranded 7-mo-old common seal (Phoca vitulina) suffering from parasitic bronchopneumonia. The clinical signs of the seal as well as the histopathology of the tumor are described. This is the first time a melanocytic tumor has been diagnosed in a common seal.

Purification of phocid herpesvirus type 1 glycoproteins B and D and pilot studies of immunogenicity in mice.

In the process of developing a subunit vaccine against phocid herpesvirus type 1, we have cloned and expressed the glycoproteins B and D (gB and gD) of phicid herpesvirus type 1, using an eukaryotic baculovirus expression system. To establish the proof of concept, candidate iscom vaccines based on these affinity-purified proteins either alone or in combination, were tested for their immunogenicity in BALB/C mice. Mice immunised with a combination of gB and gD developed higher antibody and proliferative T cell responses against PhHV-1 than those immunised with gB or gD alone.

Cetacean morbilliviruses are phylogenetically divergent.

We performed a phylogenetic comparison of porpoise morbillivirus (PMV) and dolphin morbillivirus (DMV) isolates from porpoises and dolphins respectively according to criteria adopted by the World Health Organization for the phylogenetic comparison of measles viruses. PMV and DMV were more divergent than the most distantly related measles virus strains, thus challenging the classification of PMV and DMV as two strains of a single species, cetacean morbillivirus.

Seal gammaherpesviruses: identification, characterisation and epidemiology.

Phocid herpesvirus type 2 (PhHV-2), tentatively classified as a gammaherpesvirus, has been isolated from European and American harbour seals (Phoca vitulina). Here we describe the isolation and the molecular as well as biological characterisation of different PhHV-2 isolates from harbour seals and grey seals (Halichoerus grypus). Of 522 harbour seals and 231 grey seals that had been admitted to the seal research and rehabilitation centre in Pieterburen, The Netherlands, between 1992 and 2000, 38 and 18%, respectively, proved to have PhHV-2 neutralising antibodies.

Genetic characterization of the unique short segment of phocid herpesvirus type 1 reveals close relationships among alphaherpesviruses of hosts of the order Carnivora.

To further characterize phocid herpesvirus type 1 (PhHV-1) at the molecular level, a cluster of genes comprising the complete unique short (Us) region of PhHV-1 has been cloned and sequenced. Within this region, ORFs were detected that code for the equivalent of the Us 2- protein of herpes simplex virus (HSV), a putative protein kinase, and for the glycoprotein equivalents gG, gD, gI and gE. In addition, two small ORFs downstream of gE, homologous to the Us 8.

Immunogenicity and efficacy of recombinant subunit vaccines against phocid herpesvirus type 1.

Phocid herpesvirus type 1 (PhHV-1) is an alpha-herpesvirus that causes significant morbidity and mortality among young and immunocompromised harbour seals (Phoca vitulina) and therefore represents a major problem for seal rehabilitation centres. Consequently, there is a need for a safe and effective PhHV-1 vaccine. We tested an ISCOM-based recombinant PhHV-1 gB vaccine alone (gB) or with the addition of recombinant PhHV-1 gD (gBD) for (i).

Variations in the severity of phocid herpesvirus type 1 infections with age in grey seals and harbour seals.

The data recorded during an outbreak of phocid herpesvirus type 1 infection among 19 harbour seals and 29 grey seals being nursed in a seal rehabilitation centre in The Netherlands in 1998 were used, together with data from similar outbreaks in previous years, to compare the clinical signs observed in the two species at different ages. The severity of the disease was inversely correlated with age in the harbour seals, and the infected harbour seals generally developed more severe clinical signs than the infected grey seals.

Distemper outbreak and its effect on African wild dog conservation.

In December 2000, an infectious disease spread through a captive breeding group of African wild dogs (Lycaon pictus) in Tanzania, killing 49 of 52 animals within 2 months. The causative agent was identified as Canine distemper virus (CDV) by means of histologic examination, virus isolation, reverse transcriptase-polymerase chain reaction analysis, and nucleotide sequencing. This report emphasizes the importance of adequate protection against infectious diseases for the successful outcome of captive breeding programs of endangered species.

A candidate phocid herpesvirus vaccine that provides protection against feline herpesvirus infection.

Phocid herpesvirus type 1 (PhHV-1) causes significant morbidity and mortality among young and immunocompromised harbour seals. Therefore, the availability of an effective PhHV-1 vaccine would be of importance for orphanages and seal rehabilitation centres. Since possibilities to test PhHV-1 candidate vaccines in the target species are limited, a suitable animal model is needed.

Identification of morbilliviruses of probable cetacean origin in carcases of Mediterranean monk seals (Monachus monachus).

Two morbilliviruses were isolated from carcases of Mediterranean monk seals (Monachus monachus) which had died in coastal areas of Greece and Mauritania. They were characterised as being closely related to the previously identified dolphin and porpoise morbilliviruses on the basis of their serological cross-reactivities in immunofluorescence assays, and sequence homologies in their N and P genes. The results suggest that morbilliviruses of aquatic mammals may cross barriers between species of different orders.

Morbilliviruses in Mediterranean monk seals.

Two morbilliviruses were isolated from Mediterranean monk seals (Monachus monachus), one from a stranded animal in Greece and the other one from carcasses washed ashore during a mass die-off in Mauritania. From both viruses N and P gene fragments were sequenced and compared to those of other known morbilliviruses. The monk seal morbilliviruses most closely resembled previously identified cetacean morbilliviruses, indicating that interspecies transmission from cetaceans to pinnipeds has occurred.

Impaired cellular immune response in rats exposed perinatally to Baltic Sea herring oil or 2,3,7,8-TCDD.

While the immunotoxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) has been well established, the effects of complex environmental mixtures of polyhalogenated aromatic hydrocarbons (PHAHs) are poorly understood. Many PHAHs, including the polychlorinated-biphenyls (PCBs), -dibenzofurans (PCDFs), and dibenzo-p-dioxins (PCDDs), possess 'dioxin-like' activities, and accumulate in the aquatic food chain. Organisms occupying high trophic levels may therefore be exposed to concentrations which may present an immunotoxic risk.

Contaminant-induced immunotoxicity in harbour seals: wildlife at risk?

Persistent, lipophilic polyhalogenated aromatic hydrocarbons (PHAHs) accumulate readily in the aquatic food chain and are found in high concentrations in seals and other marine mammals. Recent mass mortalities among several marine mammal populations have been attributed to infection by morbilliviruses, but a contributing role for immunotoxic PHAHs, including the polychlorinated biphenyls (PCBs), polychlorinated dibenzo-p-dioxins (PCDDs), and polychlorinated dibenzofurans (PCDFs) was not ruled out. We addressed this issue by carrying out a semi-field study in which captive harbour seals were fed herring from either the relatively uncontaminated Atlantic Ocean or the contaminated Baltic Sea for 2 years.

Impaired immunity in harbour seals (Phoca vitulina) exposed to bioaccumulated environmental contaminants: review of a long-term feeding study.

Mass mortalities among seals and dolphins inhabiting contaminated marine regions have led to speculation about a possible involvement of immunosuppression associated with environmental pollution. To evaluate whether contaminants at ambient environmental levels can affect immune function of seals, we carried out an immunotoxicological study under semifield conditions. Two groups of 11 harbour seals (Phoca vitulina) originating from a relatively uncontaminated area were fed herring from either the highly polluted Baltic Sea or the relatively uncontaminated Atlantic Ocean.

Impaired immunity in harbour seals [Phoca vitulina] fed environmentally contaminated herring.

In recent years, mass mortalities among seals and dolphins have been attributed to infections with different morbilliviruses. In all cases, these marine top predators were exposed to high levels of persistent lipophilic environmental contaminants accumulated through the food chain. This observation led to the hypothesis that a contaminant-related suppression of the immune system might have contributed to the severity of the virus outbreaks.