Abstract
A retrospective survey for detecting the cetacean morbillivirus (CeMV) was carried out in beaked whales (BWs) stranded in the Canary Islands (1999–2017). CeMV is responsible for causing worldwide epizootic events with the highest mass die-offs in cetaceans, although the epidemic status of the Canarian Archipelago seems to be that of an endemic situation. A total of 319 tissue samples from 55 BWs (35 Cuvier’s BWs and 20 specimens belonging to the Mesoplodon genus) were subjected to the amplification of a fragment of the fusion protein (F) and/or phosphoprotein (P) genes of CeMV by means of one or more of three polymerase chain reactions (PCR). RNA integrity could not be demonstrated in samples from 11 animals. Positivity (dolphin morbillivirus strain (DMV)) was detected in the skin sample of only a subadult male Cuvier’s BW stranded in 2002, being the earliest confirmed occurrence of DMV in the Cuvier’s BW species. The obtained P gene sequence showed the closest relationship with other DMVs detected in a striped dolphin stranded in the Canary Islands in the same year. A phylogenetic analysis supports a previous hypothesis of a cross-species infection and the existence of the circulation of endemic DMV strains in the Atlantic Ocean similar to those later detected in the North-East Atlantic, the Mediterranean Sea and the South-West Pacific.
Highlights
The cetacean morbillivirus (CeMV; genus Morbillivirus, Paramyxoviridae family, orderMononegavirales), consisting of a single linear molecule of negative-sense single-stranded RNA, has been responsible for major epizootic diseases in cetaceans, causing many of the biggest mass die-offs worldwide in these species [1]
Two lineages of CeMV have been proposed [1,6]: CeMV-1 for the “old” northern hemisphere lineage that includes dolphin morbillivirus (DMV) [7], porpoise morbillivirus (PMV) [7], pilot-whale morbillivirus (PWMV) [8] and beaked-whale morbillivirus (BWMV) [9] strains; and CeMV-2 for the “new” southern hemisphere lineage, consisting of virus strains detected in a Guiana dolphin (Sotalia guianensis) from Brazil [10] and in Indo-Pacific bottlenose dolphins (Tursiops aduncus) from Western Australia [11]
It has been recently reported that a novel morbillivirus was detected in a Fraser’s dolphin (Lagenodelphis hosei) stranded in Hawaii that is dissimilar to the BWMV previously identified from Hawaii and to other CeMV strains, showing an 83.9–88.7% nucleotide similarity depending on the P or N gens of these reported sequences [12]
Summary
The cetacean morbillivirus (CeMV; genus Morbillivirus, Paramyxoviridae family, orderMononegavirales), consisting of a single linear molecule of negative-sense single-stranded RNA, has been responsible for major epizootic diseases in cetaceans, causing many of the biggest mass die-offs worldwide in these species [1]. The main pathological findings described in infected cetaceans are broncho-interstitial pneumonia, lymphoid depletion and nonsuppurative meningoencephalitis, as well as an increased susceptibility to opportunistic infections [1–5]. It has been recently reported that a novel morbillivirus was detected in a Fraser’s dolphin (Lagenodelphis hosei) stranded in Hawaii that is dissimilar to the BWMV previously identified from Hawaii and to other CeMV strains, showing an 83.9–88.7% nucleotide similarity depending on the P or N gens of these reported sequences [12]. Few cases of CeMV infections have been previously reported in beaked whales (BWs). The infection (BWMV strain) was first documented in a Longman’s BW (Indopacetus pacificus) stranded in Hawaii in 2010 [9,13]. The infection (DMV strain) has been recognized in one of the seven Longman’s BWs that stranded together in Southern New Caledonia in 2013 [14], with no pathological descriptions; and in a Cuvier’s BW stranded in Italy in 2015 [15] with mild pathological findings in its lungs. More details (multifocal fibrinous bronco-pneumonia with mild, multifocal necrotizing bronchiolitis) were revealed upon a microscopic examination and associated with verocytotoxic (VT1) Escherichia coli
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