The 1988 and 2002 phocine distemper virus epidemics in European harbour seals

Echoes from the past: Regional variations in recovery within a harbour seal population

Terrestrial and marine wildlife populations have been severely reduced by hunting, fishing and habitat destruction, especially in the last centuries. Although management regulations have led to the recovery of some populations, the underlying processes are not always well understood. This study uses a 40-year time series of counts of harbour seals (Phoca vitulina) in the Wadden Sea to study these processes, and demonstrates the influence of historical regional differences in management regimes on the recovery of this population. While the Wadden Sea is considered one ecologically coupled zone, with a distinct harbour seal population, the area is divided into four geo-political regions i.e. the Netherlands, Lower Saxony including Hamburg, Schleswig-Holstein and Denmark. Gradually, seal hunting was banned between 1962 and 1977 in the different regions. Counts of moulting harbour seals and pup counts, obtained during aerial surveys between 1974 and 2014, show a population growth from approximately 4500 to 39,000 individuals. Population growth models were developed to assess if population growth differed between regions, taking into account two Phocine Distemper Virus (PDV) epizootics, in 1988 and 2002 which seriously affected the population. After a slow start prior to the first epizootic, the overall population grew exponentially at rates close to assumed maximum rates of increase in a harbour seal population. Recently, growth slowed down, potentially indicative of approaching carrying capacity. Regional differences in growth rates were demonstrated, with the highest recovery in Netherlands after the first PDV epizootic (i.e. 17.9%), suggesting that growth was fuelled by migration from the other regions, where growth remained at or below the intrinsic growth rate (13%). The seals' distribution changed, and although the proportion of seals counted in the German regions declined, they remained by far the most important pupping region, with approximately 70% of all pups being born there. It is hypothesised that differences in hunting regime, preceding the protection in the 1960's and 1970's, created unbalance in the distribution of breeding females throughout the Wadden Sea, which prevailed for decades. Breeding site fidelity promoted the growth in pup numbers at less affected breeding sites, while recolonisation of new breeding areas would be suppressed by the philopatry displayed by the animals born there. This study shows that for long-lived species, variable management regimes in this case hunting regulations, across a species' range can drive population dynamics for several generations.

Pinnipediae

This chapter reviews common diseases of pinnipeds, including species in the Otariidae (fur seals and sea lions), Phocidae (true seals), and Odobenidae (walrus) families. Much of the knowledge on pathologic conditions of pinnipeds comes from necropsies of stranded animals and those housed in captivity. As such, disease knowledge is biased toward species frequently housed in zoos and aquaria, those that strand more commonly, or those in which free-ranging populations are more easily accessible. Though historically systematic evaluations of wild populations have rarely been accomplished, in the past 10 years, with advances in marine mammal medicine and anesthesia, biologists and veterinarians more frequently completed live animal health field investigations to evaluate health and disease in free-ranging pinniped populations.

Partially observed epidemics in wildlife hosts: modelling an outbreak of dolphin morbillivirus in the northwestern Atlantic, June 2013-2014

Morbilliviruses cause major mortality in marine mammals, but the dynamics of transmission and persistence are ill understood compared to terrestrial counterparts such as measles; this is especially true for epidemics in cetaceans. However, the recent outbreak of dolphin morbillivirus in the northwestern Atlantic Ocean can provide new insights into the epidemiology and spatio-temporal spread of this pathogen. To deal with uncertainties surrounding the ecology of this system (only stranded animals were observed), we develop a statistical framework that can extract key information about the underlying transmission process given only sparse data. Our self-exciting Poisson process model suggests that individuals are infectious for at most 24 days and can transfer infection up to two latitude degrees (220 km) within this time. In addition, the effective reproduction number is generally below one, but reaches 2.6 during a period of heightened stranding numbers near Virginia Beach, Virginia, in summer 2013. Network analysis suggests local movements dominate spatial spread, with seasonal migration facilitating wider dissemination along the coast. Finally, a low virus transmission rate or high levels of pre-existing immunity can explain the lack of viral spread into the Gulf of Mexico. More generally, our approach illustrates novel methodologies for analysing very indirectly observed epidemics.

Prevalence of influenza A virus in live-captured North Atlantic gray seals: a possible wild reservoir

Influenza A virus (IAV) has been associated with multiple unusual mortality events (UMEs) in North Atlantic pinnipeds, frequently attributed to spillover of virus from wild-bird reservoirs. To determine if endemic infection persists outside of UMEs, we undertook a multiyear investigation of IAV in healthy, live-captured Northwest Atlantic gray seals (Halichoerus grypus). From 2013 to 2015, we sampled 345 pups and 57 adults from Cape Cod, MA, USA and Nova Scotia, Canada consistently detecting IAV infection across all groups. There was an overall viral prevalence of 9.0% (95% confidence interval (CI): 6.4%-12.5%) in weaned pups and 5.3% (CI: 1.2%-14.6%) in adults, with seroprevalences of 19.3% (CI: 15.0%-24.5%) and 50% (CI: 33.7%-66.4%), respectively. Positive sera showed a broad reactivity to diverse influenza subtypes. IAV status did not correlate with measures of animal health nor impact animal movement or foraging. This study demonstrated that Northwest Atlantic gray seals are both permissive to and tolerant of diverse IAV, possibly representing an endemically infected wild reservoir population.

Host-parasite coevolution: why changing population size matters

Host-parasite coevolution is widely assumed to have a major influence on biological evolution, especially as these interactions impose high selective pressure on the reciprocally interacting antagonists. The exact nature of the underlying dynamics is yet under debate and may be determined by recurrent selective sweeps (i.e., arms race dynamics), negative frequency-dependent selection (i.e., Red Queen dynamics), or a combination thereof. These interactions are often associated with reciprocally induced changes in population size, which, in turn, should have a strong impact on co-adaptation processes, yet are neglected in most current work on the topic. Here, we discuss potential consequences of temporal variations in population size on host-parasite coevolution. The limited empirical data available and the current theoretical literature in this field highlight that the consideration of such interaction-dependent population size changes is likely key for the full understanding of the coevolutionary dynamics, and, thus, a more realistic view on the complex nature of species interactions.

Population structure of two rabies hosts relative to the known distribution of rabies virus variants in Alaska

For pathogens that infect multiple species, the distinction between reservoir hosts and spillover hosts is often difficult. In Alaska, three variants of the arctic rabies virus exist with distinct spatial distributions. We tested the hypothesis that rabies virus variant distribution corresponds to the population structure of the primary rabies hosts in Alaska, arctic foxes (Vulpes lagopus) and red foxes (Vulpes vulpes) to possibly distinguish reservoir and spillover hosts. We used mitochondrial DNA (mtDNA) sequence and nine microsatellites to assess population structure in those two species. mtDNA structure did not correspond to rabies virus variant structure in either species. Microsatellite analyses gave varying results. Bayesian clustering found two groups of arctic foxes in the coastal tundra region, but for red foxes it identified tundra and boreal types. Spatial Bayesian clustering and spatial principal components analysis identified 3 and 4 groups of arctic foxes, respectively, closely matching the distribution of rabies virus variants in the state. Red foxes, conversely, showed eight clusters comprising two regions (boreal and tundra) with much admixture. These results run contrary to previous beliefs that arctic fox show no fine-scale spatial population structure. While we cannot rule out that the red fox is part of the maintenance host community for rabies in Alaska, the distribution of virus variants appears to be driven primarily by the arctic fox. Therefore, we show that host population genetics can be utilized to distinguish between maintenance and spillover hosts when used in conjunction with other approaches.

Effects of Methylmercury on Harbour Seal Peripheral Blood Leucocytes In Vitro Studied by Electron Microscopy

Methylmercury (MeHg) is highly immunotoxic and can alter the health status of the harbour seal, Phoca vitulina, from the North Sea. To investigate the mechanism of MeHg-induced toxicity in harbour seal lymphocytes, Concanavalin A (ConA)-stimulated peripheral blood leucocytes were exposed in vitro to sublethal concentrations of MeHgCl (0.2, 1, and 2 µM) for 72 h and then analysed for their viability and ultrastructure. After 72 h of incubation, cells were counted with a propidium iodide staining technique, a metabolic MTS assay was performed, and cells exposed to 1 µM of MeHgCl were observed by transmission electron microscopy (TEM). Alive cell numbers decreased with increased MeHgCl concentrations. In presence of ConA and 1 µM of MeHgCl, TEM images revealed a higher frequency of apoptotic cells. Exposed cells displayed condensation of the chromatin at the nuclear membrane and mitochondrial damages. The results suggest that in vitro MeHgCl-induced apoptosis in harbour seal lymphocytes through a mitochondrial pathway.

Essential and Toxic Elements in Blood Samples of Harbor Seals (Phoca vitulina) from the Islands Helgoland (North Sea) and Anholt (Baltic Sea): A Comparison Study with Urbanized Areas

The harbor seals (Phoca vitulina) from Helgoland (North Sea) and Anholt (Kattegat, Baltic Sea) are top predators within the marine food web and an indicator species of the environmental contamination. Furthermore, they are a main tourist attraction. Despite these important roles, little is known about the health and pollutant contamination of these seals. The objective of this study was therefore to investigate 18 essential and nonessential/toxic elements (Al, As, Be, Ca, Cr, Cu, Fe, K, Mn, Mo, Ni, P, Pb, Rb, S, Se, Sr, and Zn) in blood samples using inductively coupled plasma mass spectrometry and total X-ray-fluorescence spectrometry. Blood concentrations of mineral nutrients, such as Ca, K, P, and S, were within the reference ranges described for harbor seals. Likewise, for the trace elements, As, Be, Rb, Se, and Sr, no significant differences were observed compared with previous studies. Interestingly, blood concentrations of nine nonessential as well as essential trace metals (Al, Cr, Cu, Fe, Mn, Mo, Ni, Pb, Zn) measured significantly lower in the offshore living seals from Helgoland and Anholt compared with results obtained from animals living close to urbanized areas, such as the Wadden Sea and Elbe estuary. This suggests that industrial emissions, sewage deposition, shipping traffic and dredging tasks might be the cause of increased metal concentrations of inshore harbor seals.

Cross-species transmission of canine distemper virus-an update

Canine distemper virus (CDV) is a pantropic morbillivirus with a worldwide distribution, which causes fatal disease in dogs. Affected animals develop dyspnea, diarrhea, neurological signs and profound immunosuppression. Systemic CDV infection, resembling distemper in domestic dogs, can be found also in wild canids (e.g. wolves, foxes), procyonids (e.g. raccoons, kinkajous), ailurids (e.g. red pandas), ursids (e.g. black bears, giant pandas), mustelids (e.g. ferrets, minks), viverrids (e.g. civets, genets), hyaenids (e.g. spotted hyenas), and large felids (e.g. lions, tigers). Furthermore, besides infection with the closely related phocine distemper virus, seals can become infected by CDV. In some CDV outbreaks including the mass mortalities among Baikal and Caspian seals and large felids in the Serengeti Park, terrestrial carnivores including dogs and wolves have been suspected as vectors for the infectious agent. In addition, lethal infections have been described in non-carnivore species such as peccaries and non-human primates demonstrating the remarkable ability of the pathogen to cross species barriers. Mutations affecting the CDV H protein required for virus attachment to host-cell receptors are associated with virulence and disease emergence in novel host species. The broad and expanding host range of CDV and its maintenance within wildlife reservoir hosts considerably hampers disease eradication.

SURVEY FOR INFECTIOUS DISEASE IN THE SOUTH AMERICAN FUR SEAL (ARCTOCEPHALUS AUSTRALIS) POPULATION AT PUNTA SAN JUAN, PERU

The Peruvian population of the South American fur seal ( Arctocephalus australis ) is a distinct evolutionarily significant unit that is endangered. One of the largest rookeries for this species in Peru is located within the Punta San Juan marine protected area (15°22'S, 75°12'W). To better understand the current health status of this population, exposure to 10 pinniped pathogens was evaluated in adult female fur seals (n=29) via serology and polymerase chain reaction (PCR) techniques in November 2010. The results suggest this population is naïve to canine and phocine distemper viruses (serum neutralization test), five Leptospira interrogans serovars (microscopic agglutination test), and Brucella canis (card test). Indirect fluorescent antibody testing for Toxoplasma gondii , Neospora caninum , and Sarcocystis neurona was also uniformly negative. PCR testing of nasal swabs using previously described Mycoplasma spp. primers was positive in 37.9% (11/29) of samples. One animal was positive via card test for Brucella abortus , whereas 53.7% (15/28) were positive or suspect using a marine Brucella competitive enzyme-linked immunosorbent assay. Antibody to phocine herpesvirus-1 (PHV-1) was identified in 85.7% (24/28) of the sampled population by serum neutralization testing. Overall, exposure to Mycoplasma spp., Brucella spp., and PHV-1 was observed, but results demonstrated low to no exposure to many key pinniped pathogens. The expansion of human populations, agriculture, and industry along the Peruvian coast may lead to increased pathogen exposure from human, domestic, and wild animal sources. The naïve nature of this key population of South American fur seals raises concerns about potential risk for disease outbreaks.

MOLECULAR DETECTION OF ANTIBIOTIC-RESISTANCE DETERMINANTS IN ESCHERICHIA COLI ISOLATED FROM THE ENDANGERED AUSTRALIAN SEA LION (NEOPHOCA CINEREA)

Greater interaction between humans and wildlife populations poses significant risks of anthropogenic impact to natural ecosystems, especially in the marine environment. Understanding the spread of microorganisms at the marine interface is therefore important if we are to mitigate adverse effects on marine wildlife. We investigated the establishment of Escherichia coli in the endangered Australian sea lion (Neophoca cinerea) by comparing fecal isolation from wild and captive sea lion populations. Fecal samples were collected from wild colonies March 2009-September 2010 and from captive individuals March 2011-May 2013. Using molecular screening, we assigned a phylotype to E. coli isolates and determined the presence of integrons, mobile genetic elements that capture gene cassettes conferring resistance to antimicrobial agents common in fecal coliforms. Group B2 was the most abundant phylotype in all E. coli isolates (n = 37), with groups A, B1, and D also identified. Integrons were not observed in E. coli (n = 21) isolated from wild sea lions, but were identified in E. coli from captive animals (n = 16), from which class I integrases were detected in eight isolates. Sequencing of gene cassette arrays identified genes conferring resistance to streptomycin-spectinomycin (aadA1) and trimethoprim (dfrA17, dfrB4). Class II integrases were not detected in the E. coli isolates. The frequent detection in captive sea lions of E. coli with resistance genes commonly identified in human clinical cases suggests that conditions experienced in captivity may contribute to establishment. Identification of antibiotic resistance in the microbiota of Australian sea lions provides crucial information for disease management. Our data will inform conservation management strategies and provide a mechanism to monitor microorganism dissemination to sensitive pinniped populations.

Dental and Temporomandibular Joint Pathology of the Eastern Pacific Harbour Seal (Phoca vitulina richardii)

Skulls from 214 Eastern Pacific harbour seals (Phoca vitulina richardii) were examined macroscopically according to predefined criteria. The museum specimens were acquired from strandings along the west coast of the USA between 1909 and 2014. Ninety-eight skulls (45.8%) were from male animals, 108 (50.5%) from female animals and eight (3.7%) from animals of unknown sex. Their age varied from neonate to adult, with 101 adult animals (47.2%), 93 juvenile animals (43.5%) and 20 neonatal animals (9.3%). The majority of teeth were available for examination (90.0%); 7.5% of teeth were absent artefactually, 2.3% were deemed absent due to acquired tooth loss and 0.2% were absent congenitally. Males were no more likely than females to have either acquired tooth loss (P = 0.492) or congenitally absent teeth (P = 0.494). Adults had significantly more acquired tooth loss than juveniles (P <0.0001). All teeth were normal in morphology, except for four teeth from one skull that exhibited macrodontia. An unusual number of roots were found in most maxillary molar teeth; three roots were counted on six maxillary molar teeth and almost all other maxillary molar teeth available for examination had a fused root. Only 26 maxillary molar teeth exhibited two roots. Supernumerary teeth were associated with 13 normal teeth in nine specimens. The most common sites associated with supernumerary teeth were the left and right mandibular first premolar teeth (53.9% of all supernumerary teeth). No persistent deciduous teeth were found in any of the juvenile or adult specimens. Of the total number of teeth available for examination, 22.1% were abraded; six adult specimens showed attrition/abrasion on all of their teeth present. Adults were found to have a greater prevalence of abraded teeth than juveniles (P <0.0001). No significant difference was found in the appearance of attrition/abrasion between males and females (P = 0.518). Tooth fractures were uncommon, affecting 11 teeth (0.2%) in seven animals. Periapical lesions were found in four skulls (2.1% of the total number of specimens). None of the specimens showed signs of enamel hypoplasia. More than half (55.6%) of alveoli, either with or without teeth, showed signs of alveolar bony changes consistent with periodontitis. A total of 178 specimens (91.8%) had at least one tooth associated with mild periodontitis. Lesions consistent with temporomandibular joint osteoarthritis (TMJ-OA) were found in 67 specimens (34.5%). The most common articular surface to be affected was the left mandibular fossa of the temporal bone, with lesions in 44 cases (32.8% of all lesions). In 13 specimens (6.7%) all articular surfaces were affected. Both periodontal disease and TMJ-OA were significantly more common in adults than in juveniles (P <0.0001). Although the significance of the high incidence of periodontitis and TMJ-OA in the Eastern Pacific harbor seal remains unknown, the occurrence and severity of these diseases as found in this study may play an important role in the morbidity and mortality of this species.

Dental and Temporomandibular Joint Pathology of the Northern Fur Seal (Callorhinus ursinus)

Skulls from 145 northern fur seals (Callorhinus ursinus) were examined macroscopically according to predefined criteria. The museum specimens were acquired from strandings along the west coast of the USA between 1896 and 2008. Seventy-one skulls (49.0%) were from male animals, 56 (38.6%) from female animals and 18 (12.4%) from animals of unknown sex. Their age varied from juvenile to adult, with 58 adult animals (40.0%) and 87 juvenile animals (60.0%). The majority of teeth were available for examination (95.1%); 3.4% of teeth were artefactually absent, 0.8% were deemed absent due to acquired tooth loss and 0.6% were deemed congenitally absent. Males were no more likely than females to have either acquired tooth loss (P = 0.054) or congenitally absent teeth (P = 0.919). Adults had significantly more acquired tooth loss than juveniles (P = 0.0099). Malformations were seen in 11 teeth (0.2% of all 4,699 teeth available for examination). Two roots, instead of the typical one root, were found on 14 teeth (0.3%). Supernumerary teeth were associated with 14 normal teeth (0.3%) in eight specimens (5.5% of the total number of specimens). A total of 22 persistent deciduous teeth were found, 19 of which were associated with the maxillary canine teeth. Attrition/abrasion was seen on 194 teeth (3.9%); the canine teeth were most often affected, accounting for 39.7% of all abraded teeth. Adults were found to have a greater prevalence of abraded teeth than juveniles (P <0.0001). No significant difference was found in the appearance of attrition/abrasion between males and females (P = 0.072). Tooth fractures were found in 24 specimens (16.6%), affecting a total of 54 teeth (1.1%). Periapical lesions were found in two skulls (1.4%). None of the specimens showed signs of enamel hypoplasia. About a fifth (18.6%) of alveoli, either with or without teeth, showed signs of alveolar bony changes consistent with periodontitis. A total of 108 specimens (74.5%) had at least one tooth associated with mild periodontitis. Lesions consistent with temporomandibular joint osteoarthritis (TMJ-OA) were found in 29 specimens (20.0%). Both periodontal disease and TMJ-OA were significantly more common in adults than in juveniles (P <0.0001). Periodontitis was found to be more common in males than in females (P <0.012). Although the significance of the high incidence of periodontitis and TMJ-OA in the northern fur seal remains unknown, the occurrence and severity of these diseases found in this study may play an important role in this species morbidity and mortality.

Phocine distemper virus: current knowledge and future directions

Phocine distemper virus (PDV) was first recognized in 1988 following a massive epidemic in harbor and grey seals in north-western Europe. Since then, the epidemiology of infection in North Atlantic and Arctic pinnipeds has been investigated. In the western North Atlantic endemic infection in harp and grey seals predates the European epidemic, with relatively small, localized mortality events occurring primarily in harbor seals. By contrast, PDV seems not to have become established in European harbor seals following the 1988 epidemic and a second event of similar magnitude and extent occurred in 2002. PDV is a distinct species within the Morbillivirus genus with minor sequence variation between outbreaks over time. There is now mounting evidence of PDV-like viruses in the North Pacific/Western Arctic with serological and molecular evidence of infection in pinnipeds and sea otters. However, despite the absence of associated mortality in the region, there is concern that the virus may infect the large Pacific harbor seal and northern elephant seal populations or the endangered Hawaiian monk seals. Here, we review the current state of knowledge on PDV with particular focus on developments in diagnostics, pathogenesis, immune response, vaccine development, phylogenetics and modeling over the past 20 years.

Surveillance for zoonotic and selected pathogens in harbor seals Phoca vitulina from central California

The infection status of harbor seals Phoca vitulina in central California, USA, was evaluated through broad surveillance for pathogens in stranded and wild-caught animals from 2001 to 2008, with most samples collected in 2007 and 2008. Stranded animals from Mendocino County to San Luis Obispo County were sampled at a rehabilitation facility: The Marine Mammal Center (TMMC, n = 175); wild-caught animals were sampled at 2 locations: San Francisco Bay (SF, n = 78) and Tomales Bay (TB, n = 97), that differed in degree of urbanization. Low prevalences of Salmonella, Campylobacter, Giardia, and Cryptosporidium were detected in the feces of stranded and wild-caught seals. Clostridium perfringens and Escherichia coli were more prevalent in the feces of stranded (58% [78 out of 135] and 76% [102 out of 135]) than wild-caught (42% [45 out of 106] and 66% [68 out of 106]) seals, whereas Vibrio spp. were 16 times more likely to be cultured from the feces of seals from SF than TB or TMMC (p < 0.005). Brucella DNA was detected in 3.4% of dead stranded harbor seals (2 out of 58). Type A influenza was isolated from feces of 1 out of 96 wild-caught seals. Exposure to Toxoplasma gondii, Sarcocystis neurona, and type A influenza was only detected in the wild-caught harbor seals (post-weaning age classes), whereas antibody titers to Leptospira spp. were detected in stranded and wild-caught seals. No stranded (n = 109) or wild-caught (n = 217) harbor seals had antibodies to phocine distemper virus, although a single low titer to canine distemper virus was detected. These results highlight the role of harbor seals as sentinel species for zoonotic and terrestrial pathogens in the marine environment.

Modelling exposure of oceanic higher trophic-level consumers to polychlorinated biphenyls: pollution 'hotspots' in relation to mass mortality events of marine mammals

Marine mammals in the past mass mortality events may have been susceptible to infection because their immune systems were suppressed through the bioaccumulation of environmental pollutants such as polychlorinated biphenyls (PCBs). We compiled mortality event data sets of 33 marine mammal species, and employed a Finely-Advanced Transboundary Environmental model (FATE) to model the exposure of the global fish community to PCB congeners, in order to define critical exposure levels (CELs) of PCBs above which mass mortality events are likely to occur. Our modelling approach enabled us to describe the mass mortality events in the context of exposure of higher-trophic consumers to PCBs and to identify marine pollution 'hotspots' such as the Mediterranean Sea and north-western European coasts. We demonstrated that the CELs can be applied to quantify a chemical pollution Planetary Boundary, under which a safe operating space for marine mammals and humanity can exist.

The role of canine distemper virus and persistent organic pollutants in mortality patterns of Caspian seals (Pusa caspica)

Persistent organic pollutants are a concern for species occupying high trophic levels since they can cause immunosuppression and impair reproduction. Mass mortalities due to canine distemper virus (CDV) occurred in Caspian seals (Pusa caspica), in spring of 1997, 2000 and 2001, but the potential role of organochlorine exposure in these epizootics remains undetermined. Here we integrate Caspian seal mortality data spanning 1971–2008, with data on age, body condition, pathology and blubber organochlorine concentration for carcases stranded between 1997 and 2002. We test the hypothesis that summed PCB and DDT concentrations contributed to CDV associated mortality during epizootics. We show that age is the primary factor explaining variation in blubber organochlorine concentrations, and that organochlorine burden, age, sex, and body condition do not account for CDV infection status (positive/negative) of animals dying in epizootics. Most animals (57%, n = 67) had PCB concentrations below proposed thresholds for toxic effects in marine mammals (17 µg/g lipid weight), and only 3 of 67 animals had predicted TEQ values exceeding levels seen to be associated with immune suppression in harbour seals (200 pg/g lipid weight). Mean organonchlorine levels were higher in CDV-negative animals indicating that organochlorines did not contribute significantly to CDV mortality in epizootics. Mortality monitoring in Azerbaijan 1971–2008 revealed bi-annual stranding peaks in late spring, following the annual moult and during autumn migrations northwards. Mortality peaks comparable to epizootic years were also recorded in the 1970s–1980s, consistent with previous undocumented CDV outbreaks. Gompertz growth curves show that Caspian seals achieve an asymptotic standard body length of 126–129 cm (n = 111). Males may continue to grow slowly throughout life. Mortality during epizootics may exceed the potential biological removal level (PBR) for the population, but the low frequency of epizootics suggest they are of secondary importance compared to anthropogenic sources of mortality such as fishing by-catch.

No serological evidence that harbour porpoises are additional hosts of influenza B viruses

Influenza A and B viruses circulate among humans causing epidemics almost annually. While various hosts for influenza A viruses exist, influenza B viruses have been detected only in humans and seals. However, recurrent infections of seals in Dutch coastal waters with influenza B viruses that are antigenetically distinct from influenza B viruses circulating among humans suggest that influenza B viruses have been introduced into this seal population by another, non-human, host. Harbour porpoises (Phocoena phocoena) are sympatric with seals in these waters and are also occasionally in close contact with humans after stranding and subsequent rehabilitation. In addition, virus attachment studies demonstrated that influenza B viruses can bind to cells of the respiratory tract of these animals. Therefore, we hypothesized that harbour porpoises might be a reservoir of influenza B viruses. In the present study, an unique set of serum samples from 79 harbour porpoises, stranded alive on the Dutch coast between 2003 and 2013, was tested for the presence of antibodies against influenza B viruses by use of the hemagglutination inhibition test and for antibodies against influenza A viruses by use of a competitive influenza A nucleoprotein ELISA. No antibodies were detected against either virus, suggesting that influenza A and B virus infections of harbour porpoises in Dutch coastal waters are not common, which was supported by statistical analysis of the dataset.

Length of intervals between epidemics: evaluating the influence of maternal transfer of immunity

The length of intervals between epidemic outbreaks of infectious diseases is critical in epidemiology. In several species of marine mammals and birds, it is pivotal to also consider the life history of the species of concern, as the contact rate between individuals can have a seasonal flux, for example, due to aggregations during the breeding season. Recently, particular interest has been given to the role of the dynamics of immunity in determining the intervals between epidemics in wild animal populations. One potentially powerful, but often neglected, process in this context is the maternal transfer of immunity. Here, we explore theoretically how the transfer of maternal antibodies can delay the recurrence of epidemics using Phocine Distemper in harbor seals as an example of a system in which epidemic outbreaks are followed by pathogen extinction. We show that the presence of temporarily protected newborns can significantly increase the predicted interval between epidemics, and this effect is strongly dependent on the degree of synchrony in the breeding season. Furthermore, we found that stochasticity in the onset of epidemics in combination with maternally acquired immunity increases the predicted intervals between epidemics even more. These effects arise because newborns with maternal antibodies temporarily boost population level immunity above the threshold of herd immunity, particularly when breeding is synchronous. Overall, our results show that maternal antibodies can have a profound influence on the dynamics of wildlife epidemics, notably in gregarious species such as many marine mammals and seabirds.

Immune-relevant and new xenobiotic molecular biomarkers to assess anthropogenic stress in seals

Harbour seals as top predators and indicators for ecosystem health are exposed to increasing pressure caused by anthropogenic activities in their marine environment. After their lactation period of about 24 days pups are weaned and left to hunt on their own. Little is known about the development of their immune system and a better understanding of anthropogenic impacts on the general health and immune system of harbour seal pups is needed. mRNA transcription of six immuno-relevant biomarkers was analysed in 13 abandoned harbour seal pups from the North Sea, fostered at the Seal Centre Friedrichskoog, Germany. RNAlater blood samples were taken at admission, day 22 and before release and analysed using RT-qPCR. Significant differences in HSP70, cytokine IL-2 and xenobiotic biomarkers AHR, ARNT and PPARα transcription were found between admission, during rehabilitation and before release. Highest levels at admission may result from dehydration, handling, transport and contaminant exposure via lactation. The significant decrease is linked to health improvement, feeding and adaptation. The increase before release is suspected to be due to infection pressure and contaminant exposure from feeding on fish. Molecular biomarkers are a sensitive tool to evaluate health and pollutant exposure and useful to serve as early warning indicators, monitoring and case-by-case tool for marine mammals in human care and the wild.

Pup mortality in a rapidly declining harbour seal (Phoca vitulina) population

The harbour seal population in Orkney, off the north coast of Scotland, has reduced by 65% between 2001 and 2010. The cause(s) of this decline are unknown but must affect the demographic parameters of the population. Here, satellite telemetry data were used to test the hypothesis that increased pup mortality could be a primary driver of the decline in Orkney. Pup mortality and tag failure parameters were estimated from the duration of operation of satellite tags deployed on harbour seal pups from the Orkney population (n = 24) and from another population on the west coast of Scotland (n = 24) where abundance was stable. Survival probabilities from both populations were best represented by a common gamma distribution and were not different from one another, suggesting that increased pup mortality is unlikely to be the primary agent in the Orkney population decline. The estimated probability of surviving to 6 months was 0.390 (95% CI 0.297 – 0.648) and tag failure was represented by a Gaussian distribution, with estimated mean 270 (95% CI = 198 – 288) and s.d. 21 (95% CI = 1 – 66) days. These results suggest that adult survival is the most likely proximate cause of the decline. They also demonstrate a novel technique for attaining age-specific mortality rates from telemetry data.

PFAS profiles in three North Sea top predators: metabolic differences among species?

Profiles of seven compounds of perfluoro-alkyl substances (PFASs) were compared among three species of top predators from the Danish North Sea: the white-beaked dolphin (Lagenorhynchus albirostris), the harbor porpoise (Phocoena phocoena), and the harbor seal (Phoca vitulina). The seals had higher total burdens (757.8 ng g(-1) ww) than the dolphins (439.9 ng g(-1) ww) and the porpoises (355.8 ng g(-1) ww), probably a reflection of feeding closer to the shore and thus contamination sources. The most striking difference among the species was the relative contribution of perfluorooctanesulfonamide (PFOSA) to the profiles; the seals (0.1%) had much lower levels than porpoises (8.3%) and dolphins (26.0%). In combination with the values obtained from the literature, this result indicates that Carnivora species including Pinnipedia have a much higher capacity of transforming PFOSA to perfluorooctane sulfonic acid (PFOS) than cetacean species. Another notable difference among the species was that the two smaller species (seals and porpoises) with supposedly higher metabolic rates had lower concentrations of the perfluorinated carboxylic acids, which are generally more easily excreted than perfluorinated sulfonamides. Species-specific characteristics should be recognized when PFAS contamination in marine mammals is investigated, for example, several previous studies of PFASs in cetaceans have not quantified PFOSA.

Relationships between in vitro lymphoproliferative responses and levels of contaminants in blood of free-ranging adult harbour seals (Phoca vitulina) from the North Sea

In vitro culture of peripheral blood leucocytes (PBLs) is currently used in toxicological studies of marine mammals. However, blood cells of wild individuals are exposed in vivo to environmental contaminants before being isolated and exposed to contaminants in vitro. The aim of this study was to highlight potential relationships between blood contaminant levels and in vitro peripheral blood lymphocyte proliferation in free-ranging adult harbour seals (Phoca vitulina) from the North Sea. Blood samples of 18 individuals were analyzed for trace elements (Fe, Zn, Se, Cu, Hg, Pb, Cd) and persistent organic contaminants and metabolites (ΣPCBs, ΣHO-PCBs, ΣPBDEs, 2-MeO-BDE68 and 6-MeO-BDE47, ΣDDXs, hexachlorobenzene, oxychlordane, trans-nonachlor, pentachlorophenol and tribromoanisole). The same samples were used to determine the haematology profiles, cell numbers and viability, as well as the in vitro ConA-induced lymphocyte proliferation expressed as a stimulation index (SI). Correlation tests (Bravais-Pearson) and Principal Component Analysis with multiple regression revealed no statistically significant relationship between the lymphocyte SI and the contaminants studied. However, the number of lymphocytes per millilitre of whole blood appeared to be negatively correlated to pentachlorophenol (r=-0.63, p=0.005). In adult harbour seals, the interindividual variations of in vitro lymphocyte proliferation did not appear to be directly linked to pollutant levels present in the blood, and it is likely that other factors such as age, life history, or physiological parameters have an influence. In a general manner, experiments with in vitro immune cell cultures of wild marine mammals should be designed so as to minimize confounding factors in which case they remain a valuable tool to study pollutant effects in vitro.

Molecular characterization of poxviruses associated with tattoo skin lesions in UK cetaceans

There is increasing concern for the well-being of cetacean populations around the UK. Tattoo skin disease (characterised by irregular, grey, black or yellowish, stippled cutaneous lesions) caused by poxvirus infection is a potential health indicatora potential health indicator for cetaceans. Limited sequence data indicates that cetacean poxviruses (CPVs) belong to an unassigned genus of the Chordopoxvirinae. To obtain further insight into the phylogenetic relationships between CPV and other Chordopoxvirinae members we partially characterized viral DNA originating from tattoo lesions collected in Delphinidae and Phocoenidae stranded along the UK coastline in 1998-2008. We also evaluated the presence of CPV in skin lesions other than tattoos to examine specificity and sensitivity of visual diagnosis. After DNA extraction, regions of the DNA polymerase and DNA topoisomerase I genes were amplified by PCR, sequenced and compared with other isolates. The presence of CPV DNA was demonstrated in tattoos from one striped dolphin (Stenella coeruleoalba), eight harbour porpoises (Phocoena phocoena) and one short-beaked common dolphin (Delphinus delphis) and in one 'dubious tattoo' lesion detected in one other porpoise. Seventeen of the 18 PCR positive skin lesions had been visually identified as tattoos and one as a dubious tattoo. None of the other skin lesions were PCR positive. Thus, visual identification had a 94.4% sensitivity and 100% specificity. The DNA polymerase PCR was most effective in detecting CPV DNA. Limited sequence phylogeny grouped the UK samples within the odontocete poxviruses (CPV group 1) and indicated that two different poxvirus lineages infect the Phocoenidae and the Delphinidae. The phylogenetic tree had three major branches: one with the UK Phocoenidae viruses, one with the Delphinidae isolates and one for the mysticete poxvirus (CPV group 2). This implies a radiation of poxviruses according to the host suborder and the families within these suborders.

Variation in breeding phenology provides insights into drivers of long-term population change in harbour seals

Phenological trends provide important indicators of environmental change and population dynamics. However, the use of untested population-level measures can lead to incorrect conclusions about phenological trends, particularly when changes in population structure or density are ignored. We used individual-based estimates of birth date and lactation duration of harbour seals (Phoca vitulina) to investigate energetic consequences of changes in pupping phenology. Using generalized linear mixed models, we first demonstrate annual variation in pupping phenology. Second, we show a negative relationship between lactation duration and the timing of pupping, indicating that females who pup early nurse their pups longer, thereby highlighting lactation duration as a useful proxy of female condition and resource availability. Third, individual-based data were used to derive a population-level proxy that demonstrated an advance in pupping date over the last 25 years, co-incident with a reduction in population abundance that resulted from fisheries-related shootings. These findings demonstrate that phenological studies examining the impacts of climate change on mammal populations must carefully control for changes in population density and highlight how joint investigations of phenological and demographic change provide insights into the drivers of population declines.

Dynamics of Vibrio with virulence genes detected in Pacific harbor seals (Phoca vitulina richardii) off California: implications for marine mammal health

Given their coastal site fidelity and opportunistic foraging behavior, harbor seals (Phoca vitulina) may serve as sentinels for coastal ecosystem health. Seals using urbanized coastal habitat can acquire enteric bacteria, including Vibrio that may affect their health. To understand Vibrio dynamics in seals, demographic and environmental factors were tested for predicting potentially virulent Vibrio in free-ranging and stranded Pacific harbor seals (Phoca vitulina richardii) off California. Vibrio prevalence did not vary with season and was greater in free-ranging seals (29 %, n = 319) compared with stranded seals (17 %, n = 189). Of the factors tested, location, turbidity, and/or salinity best predicted Vibrio prevalence in free-ranging seals. The relationship of environmental factors with Vibrio prevalence differed by location and may be related to oceanographic or terrestrial contributions to water quality. Vibrio parahaemolyticus, Vibrio alginolyticus, and Vibrio cholerae were observed in seals, with V. cholerae found almost exclusively in stranded pups and yearlings. Additionally, virulence genes (trh and tdh) were detected in V. parahaemolyticus isolates. Vibrio cholerae isolates lacked targeted virulence genes, but were hemolytic. Three out of four stranded pups with V. parahaemolyticus (trh+ and/or tdh+) died in rehabilitation, but the role of Vibrio in causing mortality is unclear, and Vibrio expression of virulence genes should be investigated. Considering that humans share the environment and food resources with seals, potentially virulent Vibrio observed in seals also may be of concern to human health.

Detection of canine distemper virus serum neutralizing antibodies in captive U.S. phocids

Antibodies to morbilliviruses have been documented in free-ranging pinnipeds throughout populations in the Atlantic and Arctic Oceans, but not from the Pacific Ocean. As a symbolic geographic barrier between the exposed Atlantic and naive Pacific populations, the captive phocid population in North America had undocumented serologic status. In this study, canine distemper virus (CDV) serum neutralization assays were used to assess the prevalence of antibodies in this population with participation of 25 U.S. institutions from grey seals (Halichoerus grypus, n = 6) and harbor seals (Phoca vitulina, n = 108). Historic and environmental risk factors associated with the epidemiology of distemper virus were collected by survey. Based on antibodies to canine distemper virus, the prevalence of exposure in this population was 25.5%, with 28 seals (grey, n = 2; harbor, n = 26) demonstrating antibody titers > or = 1:16, and positive titers ranged from 1:4 to 1:1,536. By survey analysis, strong associations with seropositive status were identified for captive origin (P = 0.013) and movement among institutions (P = 0.024). Size of population has positive correlation with likelihood of seropositive seals at an institution (P = 0.020). However, no major husbandry or enclosure-based risk factors were identified in institutions with seropositive seals, and no interaction between individual or institutional risk factors was identified. Previously undocumented prior to this study, CDV antibodies were measured in harbor seals (n = 2) recently stranded from the Pacific coast.

Anisakid larvae in the liver of cod (Gadus morhua) L. from the southern Baltic Sea

In the present investigation a sample of 490 cod (Gadus morhua) was examined from three regions in the southern Baltic Sea (the Polish Exclusive Economic Zone, EEZ). Three species of anisakid nematodes with zoonotic potential, namely species of Contracaecum, Anisakis and Pseudoterranova, were found in the liver of cod, with Contracaecum being the most dominant species. The prevalence of infection was highest in the Western Baltic (22.5%) compared to the Central Baltic (10.4%) and the Gulf of Gdansk (3.4%). Generalized linear models (GLMs) were applied to analyse the prevalence of infection with Anisakis sp. and Contracaecum sp. relative to biological and spatial parameters. The effect of the sampling region, age and body length of the fish were significant in both GLMs. The effect of region was higher in the Western Baltic than in other regions. The prevalence of infection was correlated with the length of the fish and was higher in adult compared with sub-adult fish. These results suggest that the prevalence of infection with anisakid nematodes (especially Contracaecum sp.) in cod sampled in Polish waters of the Baltic Sea has significantly increased compared with previous studies undertaken over the past few decades.

Plastic ingestion by harbour seals (Phoca vitulina) in The Netherlands

Abundance of ingested debris by seals has been mentioned as a potential indicator of marine litter in the European Marine Strategy Framework Directive (MSFD). A sample of 107 stomachs, 100 intestines and 125 scats of harbour seals from the Netherlands was analysed for the presence of plastics. Incidence of plastic was 11% for stomachs, 1% for intestines, and 0% for scats. Younger animals, up to 3 years of age, were most affected. This is the first quantitative study of plastic ingestion by phocid seals. The observed level of incidence is of environmental concern, but is low in the sense of suitability of seals for MSFD monitoring purposes.

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. Antibodies were detected in most seals in 2002 and 2003 while after 2003 antibodies were detected only in seals less than two month-old and adult seals that probably had survived the 2002 PDV-epizootic. We estimated the current proportion of seals with antibodies against PDV at 11%. These findings suggest that at present the vast majority of seals are not immune to PDV infection. PDV re-introduction in this area may cause a major epizootic with infection of >80% and mass-mortality of >50% of the population.

A virological investigation into declining woylie populations

The woylie (Bettongia penicillata ogilbyi) is a critically endangered small Australian marsupial that is in a state of accelerated population decline for reasons that are currently unknown. The aim of the present study was to elucidate the involvement of several viral pathogens through strategic serological testing of several wild woylie populations. Testing for antibodies against the Wallal and Warrego serogroup of orbiviruses, Macropod herpesvirus 1 and Encephalomyocarditis virus in woylie sera was undertaken through virus neutralisation tests. Moreover, testing for antibodies against the the alphaviruses Ross River virus and Barmah Forest virus and the flaviviruses Kunjin virus and Murray Valley encephalitis virus was undertaken through virus neutralisation tests and ELISA mainly because of the interest in the epidemiology of these important zoonoses as it was considered unlikely to be the cause of the decline. Between 15 and 86 samples were tested for each of the four sites in south-western Australia (Balban, Keninup, Warrup and Karakamia). Results indicated no exposure to any of the viral pathogens investigated, indicating that all populations are currently naïve and may be at risk if these pathogens were to be introduced.

Collapse of a marine mammal species driven by human impacts

Understanding historical roles of species in ecosystems can be crucial for assessing long term human impacts on environments, providing context for management or restoration objectives, and making conservation evaluations of species status. In most cases limited historical abundance data impedes quantitative investigations, but harvested species may have long-term data accessible from hunting records. Here we make use of annual hunting records for Caspian seals (Pusa caspica) dating back to the mid-19^th century, and current census data from aerial surveys, to reconstruct historical abundance using a hind-casting model. We estimate the minimum numbers of seals in 1867 to have been 1–1.6 million, but the population declined by at least 90% to around 100,000 individuals by 2005, primarily due to unsustainable hunting throughout the 20^th century. This collapse is part of a broader picture of catastrophic ecological change in the Caspian over the 20^th Century. Our results combined with fisheries data show that the current biomass of top predators in the Caspian is much reduced compared to historical conditions. The potential for the Caspian and other similar perturbed ecosystems to sustain natural resources of much greater biological and economic value than at present depends on the extent to which a number of anthropogenic impacts can be harnessed.

Natural selection on marine carnivores elaborated a diverse family of classical MHC class I genes exhibiting haplotypic gene content variation and allelic polymorphism

Pinnipeds, marine carnivores, diverged from terrestrial carnivores ~45 million years ago, before their adaptation to marine environments. This lifestyle change exposed pinnipeds to different microbiota and pathogens, with probable impact on their MHC class I genes. Investigating this question, genomic sequences were determined for 71 MHC class I variants: 27 from harbor seal and 44 from gray seal. These variants form three MHC class I gene lineages, one comprising a pseudogene. The second, a candidate nonclassical MHC class I gene, comprises a nonpolymorphic transcribed gene related to dog DLA-79 and giant panda Aime-1906. The third is the diversity lineage, which includes 62 of the 71 seal MHC class I variants. All are transcribed, and they minimally represent six harbor and 12 gray seal MHC class I genes. Besides species-specific differences in gene number, seal MHC class I haplotypes exhibit gene content variation and allelic polymorphism. Patterns of sequence variation, and of positions for positively selected sites, indicate the diversity lineage genes are the seals' classical MHC class I genes. Evidence that expansion of diversity lineage genes began before gray and harbor seals diverged is the presence in both species of two distinctive sublineages of diversity lineage genes. Pointing to further expansion following the divergence are the presence of species-specific genes and greater MHC class I diversity in gray seals than harbor seals. The elaboration of a complex variable family of classical MHC class I genes in pinnipeds contrasts with the single, highly polymorphic classical MHC class I gene of dog and giant panda, terrestrial carnivores.

Spatial trends of perfluorochemicals in harbor seals (Phoca vitulina) from Danish waters

Spatial trends of concentrations of perfluorinated chemicals (PFCs) were investigated in harbour seal liver tissue from seven locations in Denmark, ranging from the Wadden Sea in the southern North Sea to the Western Baltic. All samples were collected during the phocine distemper epizootic in 2002 which provided access to a large number of comparable samples over a short time period. PFOS was dominating (mean: 92% of ∑PFC) among the PFCs in the samples, followed by considerably lower concentrations of PFHxS (1.8%), PFDA (1.7%), PFNA (1.6%) PFUnA (1.5%), PFOA (0.9%) and PFOSA (0.5%). The concentrations of all the investigated compounds showed significant differences among the seven locations. PFOS showed the highest concentrations in the Wadden Sea, where high burdens have also been recorded in German seals. Most compounds showed a trend towards higher concentrations at one or both extremes of the geographic range. Two different patterns of relative PFC concentrations were detected; one in the inner Danish waters where PFOSA and PFUnA were more prevalent and another in the Wadden Sea and Limfjord where PFOA, PFHxS and PFNA were found in greater proportions. These patterns probably represent Baltic and North Sea contamination sources.

Increased migration in host-pathogen metapopulations can cause host extinction

There are at least two potentially counteracting effects of migration in host-pathogen metapopulations. On the one hand increased migration leads to increased colonization of empty habitats by healthy hosts; on the other hand migrants can carry infectious diseases to susceptible populations. Earlier metapopulation models have found that the beneficial effects of increasing migration (reduced infection) are likely to dominate, and a general recommendation for managers of endangered metapopulations has been to increase connectivity between habitat patches. We extend the model framework to simultaneously allow for (1) Allee effects in host colonization rate, (2) spillover of pathogens from a second host species, and (3) differential colonization success by infected and healthy hosts. We find that the dynamics of a host-pathogen system can be highly sensitive to increased migration rates. Allee effects make host populations vulnerable to spillover of pathogens from other hosts, and metapopulation extinction can emerge from seemingly stable situations of endemic coexistence. Increasing connectivity in endangered metapopulations can be a risky management action unless the details of the biology of the host-pathogen system are known.

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.

Variation in European harbour seal immune response genes and susceptibility to phocine distemper virus (PDV)

Phocine distemper virus (PDV) has caused two mass mortalities of European harbour seals (Phoca vitulina) in recent decades. Levels of mortality varied considerably among European populations in both the 1988 and 2002 epidemics, with higher mortality in continental European populations in comparison to UK populations. High levels of genetic differentiation at neutral makers among seal populations allow for the possibility that there could be potential genetic differences at functional loci that may account for some of the variation in mortality. Recent genome sequencing of carnivore species and development of genomic tools have now made it possible to explore the possible contribution of variation in candidate genes from harbour seals in relation to the differential mortality patterns. We assessed variation in eight genes (CD46, IFNG, IL4, IL8, IL10, RARa, SLAM and TLR2) encoding key proteins involved in host cellular interactions with Morbilliviruses and the relationship of variants to disease status. This work constitutes the first genetic association study for Morbillivirus disease susceptibility in a non-model organism, and for a natural mortality event. We found no variation in harbour seals from across Europe in the protein coding domains of the viral receptors SLAM and CD46, but SNPs were present in SLAM intron 2. SNPs were also present in IL8 p2 and RARa exon 1. There was no significant association of SLAM or RARa polymorphisms with disease status implying no role of these genes in determining resistance to PDV induced mortality, that could be detected with the available samples and the small number of polymorphisms indentified. However there was significant differentiation of allele frequencies among populations. PDV and other morbilliviruses are important models for wildlife epidemiology, host switches and viral evolution. Despite a negative result in this case, full sequencing of pinniped and other 'non-model' carnivore genomes will help in refining understanding the role of host genetics in disease susceptibility for these viruses.

Phocine distemper virus in seals, east coast, United States, 2006

: Phocine Distemper Virus in Seals

In 2006 and 2007, elevated numbers of deaths among seals, constituting an unusual mortality event, occurred off the coasts of Maine and Massachusetts, United States. We isolated a virus from seal tissue and confirmed it as phocine distemper virus (PDV). We compared the viral hemagglutinin, phosphoprotein, and fusion (F) and matrix (M) protein gene sequences with those of viruses from the 1988 and 2002 PDV epizootics. The virus showed highest similarity with a PDV 1988 Netherlands virus, which raises the possibility that the 2006 isolate from the United States might have emerged independently from 2002 PDVs and that multiple lineages of PDV might be circulating among enzootically infected North American seals. Evidence from comparison of sequences derived from different tissues suggested that mutations in the F and M genes occur in brain tissue that are not present in lung, liver, or blood, which suggests virus persistence in the central nervous system.