Cetacean morbillivirus in coastal Indo-Pacific bottlenose dolphins, Western Australia

Abstract

Cetacean morbillivirus (CeMV) has caused several epizootics in multiple species of cetaceans globally and is an emerging disease among cetaceans in Australia. We detected CeMV in 2 stranded coastal Indo-Pacific bottlenose dolphins (Tursiops aduncus) in Western Australia. Preliminary phylogenetic data suggest that this virus variant is divergent from known strains.

Keywords: Australia; IHC; Indian Ocean; Indo-Pacific bottlenose dolphin; PCR; Paramyxoviridae; Tursiops aduncus; Tursiops truncatus; Western Australia; cetacean; common bottlenose dolphin; dolphin; epizootic; gene amplification; immunohistochemical testing; morbillivirus; pathology; phylogeny; viruses.

Figure 1

Images of tissue samples from 2 stranded coastal Indo-Pacific bottlenose dolphins (Tursiops aduncus) from Western Australia, Australia. A) Brain of dolphin 2 showing cerebral hemisphere with focally extensive suppurative and necrotizing encephalitis surrounding an arteriole. There are intramural and perivascular septate branching hyphae. Hematoxylin and eosin stain. Scale bar = 50 μm. B) Lung of dolphin 3 showing a transected lobar surface exhibiting multifocal pyogranulomas (white arrows). C) Lung of dolphin 3 showing bronchointerstitial pneumonia with branching septate hyphae within a bronchiolar lumen and surrounding the bronchiolar cartilage. Grocott hexamine silver. Scale bar = 50 μm. D) Lung of dolphin 3 showing alveolar lumens filled with desquamated pneumocytes, macrophages, and neutrophils. Enlarged macrophages are occasionally binucleate (white arrows) and rarely exhibit eosinophilic intracytoplasmic inclusions or margination of chromatin and eosinophilic intranuclear inclusions (black arrows). Hematoxylin and eosin stain. Scale bar = 20 μm. E) Mesenteric lymph node of dolphin 2 showing intense staining of morbilliviral antigen in lymphocytes within the cortex. Thick-walled structures (arrow) are trematode eggs. DAB and hematoxylin stain. Scale bar = 200 μm. F) Liver of dolphin 3 showing morbillivirus antigen in Kupffer cells and sinusoidal endothelial cells. DAB and hematoxylin stain. Scale bar = 100 μm.

Figure 2

Phylogenetic trees showing partial sequences of morbillivirus nucleoprotein (A) and phosphoprotein (B) genes of cetacean morbillivirus (CeMV) isolates found in 2 stranded coastal Indo-Pacific bottlenose dolphins (Tursiops aduncus) from Western Australia, Australia (boldface), and those of other known morbilliviruses. Trees were generated by the neighbor-joining method; bootstrap (1,000 replicates) values of >50 are indicated at the internal nodes. The length of each pair of branches represents the distance between the sequence pairs. Scale bars indicate percentage of nucleotide differences. DMV, dolphin morbillivirus; QLD, Queensland (Australia); PMV, porpoise morbillivirus; PWMV, pilot whale morbillivirus; CDV, canine distemper virus; OND vacc, Onderstepoort strain (used for vaccination); PDV, phocine distemper virus; MV, measles virus; RPV, rinderpest virus; PPRV, peste des petits ruminants virus.