Abstract
The Dolphin Morbillivirus (DMV) genome from the first Mediterranean epidemic (1990-’92) is the only cetacean Morbillivirus that has been completely sequenced. Here, we report the first application of next generation sequencing (NGS) to morbillivirus infection of aquatic mammals. A viral isolate, representative of the 2006-’08 Mediterranean epidemic (DMV_IZSPLV_2008), efficiently grew on Vero.DogSLAMtag cells and was submitted to whole genome characterization by NGS. The final genome length was 15,673 nucleotides, covering 99.82% of the DMV reference genome. Comparison of DMV_IZSPLV_2008 and 1990-’92 DMV strain sequences revealed 157 nucleotide mutations and 47 amino acid changes. The sequence similarity was 98.7% at the full genome level. Whole-genome phylogeny suggested that the DMV strain circulating during the 2006-’08 epidemics emerged from the 1990-’92 DMV strain. Viral isolation is considered the “gold standard” for morbillivirus diagnostics but efficient propagation of infectious virus is difficult to achieve. The successful cell replication of this strain allowed performing NGS directly from the viral RNA, without prior PCR amplification. We therefore provide to the scientific community a second DMV genome, representative of another major outbreak. Interestingly, genome comparison revealed that the neglected L gene encompasses 74% of the genetic diversity and might serve as “hypervariable” target for strain characterization.
Highlights
Three strains of CeMV, namely dolphin morbillivirus (DMV), porpoise morbillivirus (PMV) and the pilot whale morbillivirus (PWMV), previously considered as distinct viruses, are classified as one species and constitute the “old” CeMV lineage, which includes the recently discovered beaked whale morbillivirus (BWMV)[3]
Successful viral isolation on Vero.DogSLAMtag cell line was demonstrated by cytopathic effect (CPE) observed after five days, consisting in syncitia formation and rounding-up of cells
This result seems to confirm the high sensitivity of this cell line for isolating cetacean morbillivirus; importantly, extensive CPE was evident after only 48 h of incubation
Summary
Three strains of CeMV, namely dolphin morbillivirus (DMV), porpoise morbillivirus (PMV) and the pilot whale morbillivirus (PWMV), previously considered as distinct viruses, are classified as one species and constitute the “old” CeMV lineage, which includes the recently discovered beaked whale morbillivirus (BWMV)[3]. In 1990-’92, a DMV outbreak in the Mediterranean Sea involved thousands of striped dolphins (Stenella coeruleoalba) with high mortality[7]. Another major epidemic event was the DMV outbreak in 2006–2008 affecting three cetacean species along the Mediterranean coast: the striped dolphin S. coeruleoalba, the bottlenose dolphin T. truncatus and the long-finned pilot whale Globicephala melas[8,9,10,11]. We report the first retrospective isolation of DMV from a striped dolphin (Stenella coeruleoalba) stranded along the Ligurian coast of Italy in 2008, within the Pelagos Sanctuary We provide the second genome sequence of a cetacean morbillivirus; the sequence of the DMV is near complete and a genome comparison with the 1990-’92 DMV strain was carried out
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