Antigenic and nucleotide characterization of a herpesvirus isolated from Pacific harbor seals (Phoca vitulina richardsii)

Novel herpesvirus discovered in walrus liver

A walrus (Odobenus rosmarus) born in an aquarium and hand-reared in Japan died at the age of 11 months. The affected animal showed fever and anorexia and had high levels of AST and ALT. Necropsy showed multiple necroses in the liver and adrenal glands and histological examination revealed necrotic lesions of the liver and adrenal cortex, both of which contained intranuclear inclusions. Electron microscopic analysis of the liver sample showed herpesvirus-like particles. High-throughput sequencing analysis of the liver sample and phylogenetic analysis of herpesvirus polymerase genes identified a new virus, Walrus alphaherpesvirus 1 (WaHV-1), which belonged to the subfamily Alphaherpesvirinae and had high homology with Phocid alphaherpesvirus 1. Phylogenetic analysis of the UL30 gene encoding glycoprotein B revealed that WaHV-1 was closely related to a cluster of phocid herpesviruses, including one that caused high mortality rates in harbor seals during past outbreaks. The mother walrus of the dead animal showed evidence of herpesvirus infection in the past and potentially harbored WaHV-1. As a result of hand-rearing, the dead animal might have acquired WaHV-1 from its infected mother and succumbed to WaHV-1 due to lack of maternal IgG, including those that could neutralize WaHV-1.

HERPESVIRUSES INCLUDING NOVEL GAMMAHERPESVIRUSES ARE WIDESPREAD AMONG PHOCID SEAL SPECIES IN CANADA

Little is known about herpesviruses in Canadian pinnipeds. We measured prevalence of antibodies to herpesviruses in the sera from Canadian phocid seals by an indirect enzyme-linked immunosorbent assay. Wild harbor seals (Phoca vitulina) and captive harbor seals were positive for antibodies to Phocid herpesvirus 1 (PhoHV-1) at prevalences of 91% and 100%, respectively. Sera from wild hooded seals (Cystophora cristata), harp seals (Pagophilus groenlandica), and grey seals (Halichoerus grypus) were positive for antibodies to PhoHV-1 antigenically related herpesvirus antigens at 73%, 79%, and 96%, respectively. We isolated new herpesviruses in cell culture from two hunter-harvested ringed seals (Pusa hispida) in poor body condition from Ulukhaktok, Northwest Territories, Canada; one lethargic hooded seal from the St. Lawrence Estuary, Québec, Canada; and one captive, asymptomatic harp seal from the Magdalen Islands, Québec. Partial sequencing of the herpesvirus DNA polymerase gene revealed that all four virus isolates were closely related to PhoHV-2, a member of the Gammaherpesvirinae subfamily, with nucleotide similarity ranging between 92.8% and 95.3%. The new seal herpesviruses were genetically related to other known pinniped herpesviruses, such as PhoHV-1, Otariid herpesvirus 3, Hawaiian monk (Monachus schauinslandi) seal herpesvirus, and Phocid herpesvirus 5 with 47-48%, 55%, 77%, and 70-77% nucleotide similarities, respectively. The harp seal herpesvirus and both ringed seal herpesviruses were almost identical to each other, whereas the hooded seal herpesvirus was genetically different from the three others (92.8% nucleotide similarity), indicating detection of at least two novel seal herpesviruses. These findings are the first isolation, partial genome sequencing, and identification of seal gammaherpesviruses in three species of Canadian phocid seals; two species of which were suspected of exposure to one or more antigenically related herpesviruses based on serologic analyses.

First molecular detection and characterization of herpesvirus and poxvirus in a Pacific walrus (Odobenus rosmarus divergens)

Background

Herpesvirus and poxvirus can infect a wide range of species: herpesvirus genetic material has been detected and amplified in five species of the superfamily Pinnipedia; poxvirus genetic material, in eight species of Pinnipedia. To date, however, genetic material of these viruses has not been detected in walrus (Odobenus rosmarus), another marine mammal of the Pinnipedia clade, even though anti-herpesvirus antibodies have been detected in these animals.

Case presentation

In February 2013, a 9-year-old healthy captive female Pacific walrus died unexpectedly at L’Oceanografic (Valencia, Spain). Herpesvirus was detected in pharyngeal tonsil tissue by PCR. Phylogenetic analysis revealed that the virus belongs to the subfamily Gammaherpesvirinae. Poxvirus was also detected by PCR in skin, pre-scapular and tracheobronchial lymph nodes and tonsils. Gross lesions were not detected in any tissue, but histopathological analyses of pharyngeal tonsils and lymph nodes revealed remarkable lymphoid depletion and lymphocytolysis. Similar histopathological lesions have been previously described in bovine calves infected with an alphaherpesvirus, and in northern elephant seals infected with a gammaherpesvirus that is closely related to the herpesvirus found in this case. Intracytoplasmic eosinophilic inclusion bodies, consistent with poxviral infection, were also observed in the epithelium of the tonsilar mucosa.

Conclusion

To our knowledge, this is the first molecular identification of herpesvirus and poxvirus in a walrus. Neither virus was likely to have contributed directly to the death of our animal.

Molecular identification of novel alpha- and gammaherpesviruses from cetaceans stranded on Japanese coasts

Herpesviral infections have been documented in some cetaceans; however, they have not yet been identified in species in the western North Pacific. In the present study, 178 tissue samples from 76 stranded cetacean individuals were tested for the presence of herpesviruses. Herpesvirus genomic DNA fragments surrounding the DNA polymerase gene were amplified in samples from four individuals. TA cloning and direct sequencing of these DNA fragments revealed the presence of two novel alphaherpesviruses, and two novel gammaherpesviruses in the four cetacean individuals. The alphaherpesviruses were associated with the lung tissue of a false killer whale (Pseudorca crassidens), and with the mucus of a melon-headed whale (Peponocephala electra). The gammaherpesviruses were found in the lymph tissues of a Stejneger's beaked whale (Mesoplodon stejnegeri) and a sperm whale (Physeter macrocephalus). The phylogenetic tree using amino acid sequences of the DNA polymerase gene supported the inclusion of the novel viruses identified here in a single monophyletic group containing alphaherpesviruses from other Atlantic cetacean species. Conversely, the novel gammaherpesviruses formed an independent clade distant from other known cetacean gammaherpesviruses.

Phylogenetic analysis of marine mammal herpesviruses

Five novel DNA-dependent DNA polymerase (Dpol) herpesviral sequences were generated using nested consensus polymerase chain reaction (PCR) in clinical samples from a harbor seal (Phoca vitulina), bottlenose dolphin (Tursiops truncatus), orca (Orcinus orca), California sea lion (Zalophus californianus), and a Phocid herpesvirus 2 (PhHV-2) isolate from a harbor seal (used as positive control). These novel sequences and other representative herpesvirus sequences were included in Bayesian and Maximum Likelihood analyses to illustrate the phylogeny of herpesviruses amongst the marine mammal host species and in comparison to those of other animals. All 19 novel and known marine mammal herpesviruses included in the analyses aligned with members of the Alphaherpesvirinae or Gammaherpesvirinae subfamilies. The novel harbor seal herpesvirus clustered with members of the Macavirus genus, subfamily Gammaherpesvirinae. The novel bottlenose dolphin herpesvirus clustered together in a monophyletic group with another delphinid alphaherpesvirus but could not be associated with an established genus. The orca herpesvirus also clustered with a delphinid alphaherpesvirus and formed a separate clade. The sea lion herpesvirus clustered with PhHV-2. PhHV-1 clustered with varicelloviruses and PhHV-2 clustered strongly in the Gammaherpesvirinae genus Percavirus. All cetacean gammaherpesviruses formed a monophyletic clade and could not be associated with an established gammaherpesviral genus.

Proliferative dermatitis associated with a novel alphaherpesvirus in an Atlantic bottlenose dolphin (Tursiops truncatus)

Herpesviruses and herpes-like viruses have been reported in only a small number of species of cetaceans, and, to date, clinical manifestations have been either as a life-threatening, disseminated infection or as a non-life-threatening dermatitis. A stranded juvenile Atlantic bottlenose dolphin, Tursiops truncatus, was admitted to the Dolphin and Whale Hospital for rehabilitation. On initial physical examination, the rostral skin had multifocal regions of hyperplasia, and the skin of the dorsum contained a large number of small papules. Histologically, epithelial hyperplasia was evident, and clusters of epithelial cells contained 5-15-microm intranuclear inclusion bodies. Transmission electron microscopic investigation revealed numerous 170-190-nm enveloped virions in both the intracellular spaces and the cytoplasm of epithelial cells, with numerous nucleocapsids noted in epithelial cell nuclei. Consensus primer polymerase chain reaction identified the presence of a novel herpesvirus associated with the lesions. Phylogenetic analysis of the deduced amino acid sequences of the herpesvirus DNA polymerase gene fragment showed it to align with alphaherpesvirus sequences from humans and domestic animals. Although clearly distinct, it was most closely related to two previously described alphaherpesviruses of dolphins. This case represents the first documentation of herpesvirus dermatitis in the Atlantic bottlenose dolphin.

Identification of novel alpha- and gammaherpesviruses from cutaneous and mucosal lesions of dolphins and whales

Total DNA extracted from mucosal and skin lesions of captive and stranded cetaceans was analyzed for herpesvirus DNA by nested and direct polymerase chain reactions (PCR). The targeted sequences corresponded to a region of the DNA polymerase gene containing multiple conserved amino acid motifs. Herpesvirus genomic DNA fragments (222-244 bp) were amplified from 11 lesions by nested PCR and from eight lesions ( approximately 730 bp) using direct PCR from US cetaceans. Fragments of various sizes were also amplified from skin, spleen and blood of a German dolphin. Sequencing and BLAST analysis of these DNA fragments indicated that alpha- or gammaherpesviruses were present in the cetacean lesions. Alphaherpesviruses were associated with skin lesions of three Atlantic bottlenose dolphins (Tursiops truncatus), while gammaherpesviruses were present in genital lesions of five Atlantic bottlenose dolphins, one Risso's dolphin (Grampus griseus), one dwarf sperm whale (Kogia sima) and one Blainville's beaked whale (Mesoplodon densirostris), as well as in one oral lesion from an Atlantic bottlenose dolphin. Phylogenetic analysis of deduced amino acid sequences showed that the cetacean alphaherpesviruses were most closely related to human alphaherpesviruses, namely, herpes simplex-1 and -2. On the other hand, cetacean gammaherpesviruses were most closely related to Rhadinoviruses. These novel cetacean herpesviruses appeared to be distinct from known herpesviruses of marine and terrestrial vertebrates. The sequencing data strongly suggest that these viruses are most likely cetacean specific and possibly have coevolved with their cetacean hosts.

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. The corresponding antibody and T cell proliferative responses were higher against PhHV-1 than against FHV. These data favour further testing of these candidate vaccines based on gB and gD in the FHV-cat model.

Tissue distribution of phocine herpesvirus-1 (PhHV-1) in infected harbour seals (Phoca vitulina) from the central Californian coast and a comparison of diagnostic methods

The polymerase chain reaction (PCR) was used to determine the tissue distribution of phocine herpesvirus-1 (PhHV-1) DNA in 20 stranded Pacific harbour seals (17 pups and three seals older than one year) that died during rehabilitation. The aim was to begin to define stages of infection and to investigate the relation between the presence of PhHV-1 in tissues, histological lesions and serology. PhHV-1 DNA was detected in a wide range of tissues from 10/17 pups and 3/3 subadults or adults. Different clinical patterns emerged from the examination of ante- and post-mortem samples. These patterns probably represented pups with active PhHV-1 infection, pups recovering from infection, and older harbour seals with chronic, reactivated infection. As PhHV-1 DNA was detected in tissues in the absence of typical histological lesions in seven seals and in the absence of PhHV-1 specific antibodies in four seals, it is clear that both histological examination and serology underestimate the presence of infection. These results showed that infection can occur in the absence of obvious disease and that seroconversion may be associated with clinical recovery.

The development of methods for immunophenotypic and lymphocyte function analyzes for assessment of Southern sea otter (Enhydra lutris nereis) health

The Southern sea otter (Enhydra lutris nereis) is listed as threatened under the Endangered Species Act. The population began a pattern of slow decline in 1995. The decline was attributed to high adult mortality rates with infectious disease being the major cause of death. Multiple pathogens were implicated in these deaths including opportunistic pathogens such as Coccidiodes immitis and Toxoplasma sp. These findings suggested that the immunological health of mature animals in this population might be compromised. The primary goal of this study was to establish techniques for assessing phenotypic and functional baseline data for peripheral blood mononuclear cells (PBMC) in free-ranging sea otters. Standard total and differential white blood cell counts were augmented by emumeration of T and B lymphocyte subsets. Lymphocyte function was determined by both mitogen-induced proliferation and expression of IL-2 receptors. In addition to establishing normal ranges for adult animals, age-related changes were identified in B lymphocyte numbers and cell-surface density of major histocompatability complex class II (MHC II) proteins. The predominant lymphocyte subpopulation in Southern sea otters is the T lymphocyte. Substantial variation among individual animals was observed within the B lymphocyte population both in cell number and density of MHC II expression. Pups had greater numbers of T and B lymphocyte, as well as, greater MHC II expression on B lymphocytes than adults. Mitogen-induced proliferation of peripheral blood mononuclear cells (PBMC) was variable among individual animals with no significant difference in cell response between age class and gender. Concanavalin (ConA) was a more effective mitogen in stimulating proliferation and interleukin (IL)-2 receptor expression than pokeweed. This data can be used to augment routine hematology profiles and aid in the identification of animals with immunologic perturbations.

The Effect of Paralogous Lineages on the Application of Reconciliation Analysis by Cophylogeny Mapping

Paralogy defines similarity caused by duplication rather than common descent and is well known in the case of paralogous gene copies within a single genome. The term is here extended to paralogous lineages of associates within a single host. The phylogenies of four genera within the Herpesviridae were reconciled with host phylogenies using cophylogenetic mapping. The observed correspondence for each pair of phylogenies was evaluated through randomization of the viral phylogeny and demonstrated to be greater than expected by chance. A simulation study was then carried out to assess the influence of paralogous lineages on the efficacy of reconciliation analysis. Combining viral taxa from different genera that infected common hosts introduced incongruence into the cophylogenies and reduced both the minimum and maximum observed number of codivergence events relative to the initial analysis of orthologous clades. However, at an average sample size this did not alter the fundamental significance of observed correspondence. With smaller sample sizes, the number of orthologous taxa selected at random from the pool of taxa was reduced. False-negative results then increased in proportion from 0.02 to 0.33. These results demonstrated that reconciliation analysis is robust under conditions of paralogy at "normal" sample sizes but is adversely affected by a combination of paralogy and low sample size. Consideration of phylogenies for Papillomavirus, Atadenovirus, and Mastadenovirus suggest that paralogous lineages may be a widespread phenomenon among DNA viruses and that duplication irrespective of host speciation is an important cause of viral diversification.

The transmission of phocine herpesvirus-1 in rehabilitating and free-ranging Pacific harbor seals (Phoca vitulina) in California

Phocine herpesvirus-1 (PhHV-1) causes regular outbreaks of disease in neonatal harbor seals (Phoca vitulina) at rehabilitation centers in Europe and in the U.S. To investigate transmission of this virus samples were collected from harbor seal pups during exposure studies at a Californian rehabilitation center from 1999 to 2002 and from free-ranging harbor seals off central California during the same period. The exposure studies provided evidence that PhHV-1 can be transmitted horizontally between animals most likely through direct contact with oro-nasal secretions. However vertical transmission may also occur, as adult female harbor seals were found to be shedding the virus in vaginal and nasal secretions, and premature newborn pups had evidence of early infection. Results also indicated that PhHV-1 infections were common in both free-ranging (40%, 49/121) and rehabilitating (54%, 46/85) young harbor seals, during the spring and early summer. This timing, which correlated with pupping and weaning, suggested that the majority of animals were infected and infective with PhHV-1 between pupping and breeding.

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 8.5 and Us 9 proteins of HSV were identified. Comparative analysis of the ORF encoding the gD equivalent of PhHV-1 identified the corresponding proteins of the alphaherpesviruses canine herpesvirus and, to lesser degree, feline herpesvirus as the closest relatives.

Partial characterization of a novel gammaherpesvirus isolated from a European badger (Meles meles)

A herpesvirus causing a cytopathic effect was isolated from pulmonary fibroblast cultures established from a European badger (Meles meles). A study was undertaken to classify and to assess some in-vitro growth characteristics of this virus. From a panel of 27 mammalian cell lines, in-vitro replication of the badger herpesvirus (BadHV) was only demonstrated with a mink lung cell line, suggesting a high degree of host specificity. Using PCR with degenerate primers, three independent fragments of the BadHV genome were sequenced. The largest of these fragments comprised a 6.2 kb segment including the DNA polymerase and glycoprotein B genes. Phylogenetic analysis of these sequences demonstrated that the BadHV is novel and clearly grouped with members of the Gammaherpesvirinae. In view of the oncogenic and immunosuppressive potential of many related herpesviruses, it is possible that BadHV can impact on existing acute or chronic disease in badgers.

Otarine herpesvirus-1: a novel gammaherpesvirus associated with urogenital carcinoma in California sea lions (Zalophus californianus)

The incidence of neoplasia in California sea lions (CSLs) is considered to be unusually high. Electron microscopic examination of some of these urogenital tumours revealed the presence of virions with typical herpes-like structure. While current attempts to cultivate this virus have not been successful, molecular studies employing DNA extracted from tumour tissues allowed both the classification of the agent and its identification in tumours and archived tissue samples. Two genome fragments generated using degenerate primers in PCR demonstrated highest identities with other mammalian gammaherpesviruses. Phylogenetic analysis showed that this novel virus, tentatively designated Otarine herpesvirus-1 (OtHV-1), grouped with members of the gammaherpesvirus subfamily and was distinct from PHV-2, a previously described pinniped gammaherpesvirus. An OtHV-1 specific PCR was established and used to investigate the presence of this virus in CSL tissues. PCR of DNA isolated from animals with these tumours, demonstrated that this virus was present in 100% (16/16) of tumours. Furthermore, DNA extracted from archived brain and muscle tissues was also positive in 29% (4/14) and 50% (7/14) of cases examined. This preliminary study provides evidence to support the hypothesis that the presence of this novel gammaherpesvirus is a factor in the development of urogenital carcinoma in CSLs.

Humoral immune responses to phocine herpesvirus-1 in Pacific harbor seals (Phoca vitulina richardsii) during an outbreak of clinical disease

Infection with phocine herpesvirus type-1 (PHV-1) has been associated with morbidity and high mortality in neonatal harbor seals (Phoca vitulina). A PHV-1 specific indirect enzyme linked immunosorbent assay (ELISA) was developed to sequentially measure the serological status of 106 harbor seal neonates admitted to a Pacific coast rehabilitation center (total number of sera tested was 371). Early in the season (February-April), the majority of pups had low serum levels of PHV-1 specific antibody. A dramatic increase in PHV-1 specific antibody, involving the majority of hospitalized pups, was observed during a 4-week period in May. This coincided with a high incidence of PHV-1 associated adrenal lesions and mortality. Although there was overall agreement between the timing of seroconversion to PHV-1 and histological evidence of PHV-1 infection, 82.4% of individual pups with adrenalitis had no evidence of a humoral response to PHV-1 at the time of their death. This suggests either a rapid disease course, or an inability to develop a humoral response in some neonatal seals.