Molecular and serological studies on the recent seal virus epizootics in Europe and Siberia

Abstract

The virus epizootics which occurred in seals in both Europe and Siberia during 1987/1988 were caused by two different morbilliviruses, referred to as phocid distemper virus (PDV) 1 and 2, respectively. Molecular and serological studies have shown that the European virus is quite distinct from canine distemper virus (CDV), its closest relative in the morbillivirus group. Analysis of tissues obtained from infected seals from a wide geographical distribution over Northern Europe showed that the infectious agent (PDV 1) was identical in all cases. Nucleotide sequence analysis of one of the virus genes suggested that this virus has evolved away from CDV over a long time period and is most probably an enzootic virus of marine mammals. In contrast, the virus (PDV 2) which caused the deaths of many Siberian seals was indistinguishable, both serologically and at the molecular level, from CDV and must have originated from a land source.

In search of virus carriers of the 1988 and 2002 phocine distemper virus outbreaks in European harbour seals

“…Between 1988 and 1993, grey and harbour seals from the Dutch Wadden Sea were found to be seropositive for PDV [30]. Similar results were obtained for the grey seals from the British Farne Island in 1992 [1]. Whether these findings indicate a persistent infection or are residuals from the 1988 epidemic remained undetermined.…”

“…The length of the PCR product corresponded to a 364-bp band. For identification of morbillivirus RNA, a set of universal morbillivirus primers was used [1]. The expected amplicon length is 429 bp.…”

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

“…Samples taken from harbour seals in 1988 from Ireland, Denmark, and the Netherlands indicated that PDV was genetically identical among affected regions (Visser et al 1990, Barrett et al 1992. A comparison of the PDV isolates from 1988 and 2002 showed the strains to be almost identical (Jensen et al 2002).…”

“…It was concluded that PDV-2 was actually a strain of CDV, indicating that this event was unrelated to the north European outbreak in 1988 (Osterhaus et al 1989, Visser et al 1990, Barrett et al 1992). In the spring of 1997 and 2000, mass deaths of Caspian seals occurred and the cause was diagnosed as a different CDV strain (Mamaev et al 1995, Barrett 1999, Hall et al 1999, Kennedy et al 2000.…”

“…Hitherto unknown morbilliviruses with potentially important ecological consequences for marine mammals have been discovered over the past 15 yr; PDV in seals, porpoise morbillivirus (PMV), and dolphin morbillivirus (DMV) in dolphins, whales and porpoises. While PDV and CDV are believed to be the most closely related morbilliviruses, PMV and DMV constitute a separate branch in the phylogenetic tree and are more distant from the ancestral progenitor virus (McCollugh et al 1991, Rima et al 1992, Blixenkrone-Møller et al 1994, Barrett et al 1995, Barrett 1999.Samples taken from harbour seals in 1988 from Ireland, Denmark, and the Netherlands indicated that PDV was genetically identical among affected regions (Visser et al 1990, Barrett et al 1992. A comparison of the PDV isolates from 1988 and 2002 showed the strains to be almost identical (Jensen et al 2002).…”