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

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.

Phocine distemper virus in northern sea otters in the Pacific Ocean, Alaska, USA.

Phocine distemper virus (PDV) has caused 2 epidemics in harbor seals in the Atlantic Ocean but had never been identified in any Pacific Ocean species. We found that northern sea otters in Alaska are infected with PDV, which has created a disease threat to several sympatric and decreasing Pacific marine mammals.

Genetic diversity and phylogenetic analysis of the attachment glycoprotein of phocine distemper viruses of the 2002 and 1988 epizootics.

To investigate the possible origin and spread of the dramatic re-emergent 2002 distemper epizootic observed among seals in Danish Waters, we have sequenced wild-type genes of the attachment (H) glycoproteins of viruses from both the 2002 and 1988 epizootics. Phylogenetic analysis of the H genes of phocine distemper virus (PDV) together with other morbilliviruses, suggests that the re-emergent 2002 PDV is more closely related to a putative recent ancestral PDV than the 1988 PDV isolates. Moreover, upsurges of distemper disease in land-living carnivores linked in time and locality to the 2002 seal epizootic in Danish Waters was investigated and determined to be caused by canine distemper virus, the closest relative of PDV, revealing no direct epidemiological link to the seal epizootics.

Antigenic characterization of phocine distemper virus causing mass mortality in 2002 and its relationship to other morbilliviruses.

The antigenic relationship between the phocine distemper virus (PDV) strain causing the epidemic in 2002 and the PDV strain of 1988, canine distemper virus from two dogs and one marten, and one measles virus strain was investigated in vivo and in vitro using monospecific polyclonal and monoclonal antibodies directed against five different proteins of canine or phocine distemper virus (N, P, M, F, H). Epitopic mapping revealed no difference between the PDV strains causing the epidemics in 1988 or 2002. However, the use of these antibodies allowed discrimination between different morbilliviruses including a vaccine strain of canine distemper virus. The major differences among the investigated morbilliviruses were found in the H protein.

Identification and real-time PCR quantification of Phocine distemper virus from two colonies of Scottish grey seals in 2002.

The North Sea European harbour seal (Phoca vitulina) population has endured two phocine distemper virus (PDV) epidemics in 1988 and 2002. The grey seal (Halichoerus grypus) is a sympatric seal species that shows little or no mortality from PDV. Two Scottish grey seal breeding colonies were sampled for evidence of PDV infection approximately 2 months after the peak of the 2002 epidemic. In both colonies, a proportion of mothers (13/109) and pups (6/84) tested positive for PDV in their leukocytes. All infected animals were asymptomatic and completed the breeding season successfully. These results illustrate that grey seals come into contact with infectious seals and can become infected themselves without experiencing acute effects. In some seals the virus is able to replicate from the primary site of infection. This study provides evidence that grey seals may have an active role in the spread of PDV during an epidemic.

Phocine distemper in German seals, 2002.

Approximately 21,700 seals died during a morbillivirus epidemic in northwestern Europe in 2002. Phocine distemper virus 1 was isolated from seals in German waters. The sequence of the P gene showed 97% identity with the Dutch virus isolated in 1988. There was 100% identity with the Dutch isolate from 2002 and a single nucleotide mismatch with the Danish isolate.

Retrospective differentiation of canine distemper virus and phocine distemper virus in phocids.

Formalin-fixed paraffin-embedded tissues from one Caspian seal (Phoca caspica), one harp seal (Phoca groenlandica), one hooded seal (Cystophora cristata), and one harbor seal (Phoca vitulina vitulina) were used to compare the utility of immunohistochemistry (IHC) versus that of a novel seminested reverse transcriptase polymerase chain reaction (RT-PCR) to detect and differentiate canine distemper virus (CDV) and phocine distemper virus (PDV). Four antibodies made against PDV were able to detect both viruses. Two antibodies made against cetacean morbillivirus (CMV) did not label antigens from either CDV or PDV. A third anti-CMV antibody inconsistently stained CDV antigens but did not label PDV antigens. The seminested RT-PCR was able to detect RNA of the phosphoprotein gene in all positive cases. Nucleotide sequence analyses of seminested RT-PCR products were used to differentiate CDV RNA from PDV RNA. From these data, it was determined that IHC using antibodies generated against PDV provided a rapid means of detection for both CDV and PDV antigens; however, differentiation between CDV and PDV was achieved only with the RT-PCR assay.

Biological properties of phocine distemper virus and canine distemper virus.

Morbilliviruses constitute a major threat to the health of animal and man. To date the Morbillivirus genus in the Paramyxoviridae family comprises five established members, namely canine distemper virus (CDV), phocine distemper virus (PDV), measles virus (MV), rinderpest virus (RPV), and peste-des-petits-ruminants virus (PPRV). In addition, morbillivirus candidates infecting aquatic mammals were recently discovered. The present review on the biology of morbilliviruses focuses on knowledge gained by our group in studies on PDV and CDV. The aims of these studies were: i) to investigate the biological properties of the recently recognized PDV, which was found to be the primary etiology of epidemics with high mortality in seals in Western Europe, ii) to extend our knowledge of the biological properties of CDV. The morbillivirus particle is enveloped. The helical nucleocapsid core contains a single-stranded, non-segmented RNA genome of negative sense of 15 to 16 kilobases in length. The genome is organized in six transcriptional units or genes. Overall, the studies of the genome of PDV revealed a genetic map principally fitting with that determined for other morbilliviruses. The nucleotide and deduced amino acid sequences have been determined for five PDV genes named in analogy with the encoded structural proteins of other morbilliviruses in the order: 3'N(1683)-P(1644)-M(1443)-F(2206)-H(1952)-L5' (The figures in brackets denote nucleotide lengths of the genes of the Danish PDV isolate). The L gene (covering approximately 8900 nucleotides) remains to be sequenced. The six genes are likely to code for at least eight distinct proteins. The nucleocapsid (N) protein was found to consist of 523 amino acids in PDV. The following gene of the transcription map encoded the P protein of 507 amino acid residues. Similar to other morbilliviruses, the P gene of PDV was shown to have additional coding capacity for two distinct proteins V (299 amino acids) and C (174 amino acids). The results presented provide evidence for editing at transcript of the PDV P gene by insertion of nontemplated G residues at a specific site. The edited version of the mRNA was found to encode the cystein-rich V protein. The three envelope-associated proteins of PDV were predicted to consist of 335 (M), 537 (F0) and 607 (H) amino acid residues. The nucleotide and deduced amino acid sequences of the N, P, M, F, and H genes of PDV were aligned with corresponding sequences of other established members of the genus Morbillivirus.(ABSTRACT TRUNCATED AT 250 WORDS)