Novel cetacean morbillivirus in a rare Fraser's dolphin (Lagenodelphis hosei) stranding from Maui, Hawai'i

Abstract

Cetacean morbillivirus (CeMV) is a global threat to cetaceans. We report a novel morbillivirus from a Fraser's dolphin (Lagenodelphis hosei) that stranded in Maui, Hawaii in 2018 that is dissimilar to the beaked whale morbillivirus previously identified from Hawaii and to other CeMV strains. Histopathological findings included intranuclear inclusions in bile duct epithelium, lymphoid depletion, rare syncytial cells and non-suppurative meningitis. Cerebellum and lung tissue homogenates were inoculated onto Vero.DogSLAMtag cells for virus isolation and cytopathic effects were observed, resulting in the formation of multinucleated giant cells (i.e., syncytia). Transmission electron microscopy of infected cell cultures also revealed syncytial cells with intracytoplasmic and intranuclear inclusions of viral nucleocapsids, consistent with the ultrastructure of a morbillivirus. Samples of the cerebellum, lung, liver, spleen and lymph nodes were positive for morbillivirus using a reverse transcription-polymerase chain reaction. The resulting 559 bp L gene sequence had the highest nucleotide identity (77.3%) to porpoise morbillivirus from Northern Ireland and the Netherlands. The resulting 248 bp P gene had the highest nucleotide identity to porpoise morbillivirus in Northern Ireland and the Netherlands and to a stranded Guiana dolphin (Sotalia guianensis) in Brazil (66.9%). As Fraser's dolphins are a pelagic species that infrequently strand, a novel strain of CeMV may be circulating in the central Pacific that could have additional population impacts through transmission to other small island-associated cetacean species.

Figure 1

The sub-adult male Fraser’s dolphin (Lagenodelphis hosei) that stranded at Olowalu, Maui, Hawaii. Photo courtesy of Cindy Kern.

Figure 2

(A) Left lung. There are firm nodules present throughout the pulmonary parenchyma. The nodules may also be related to parasitism; (B) Meninges. H&E stain: Lymphocytic infiltrates within the meninges (arrow). Bar = 100 µm; (C) Cerebrum. H&E stain: Perivascular lymphocytic cuffing. Bar = 2 mm; (D) Lung. H&E stain: Alveolar spaces contain sloughed Type II pneumocytes, erythrocytes and rare syncytial cells (arrow). Vessels are congested. Bar = 500 µm; (E) Lymph node. H& E stain: Lymphoid follicle depletion. Bar = 2 mm; (F) Lymph node. H&E stain: Germinal center necrosis. Syncytium (arrow). Bar = 500 µm; (G) Bile duct. H&E stain: Portal hepatitis with biliary hyperplasia and viral nuclear inclusions in biliary epithelial cells (arrow head) Bar = 500 µm; (H) Lymph node. Morbillivirus immunohistochemical stain. Bar = 20 µm; (I) Brain. Morbillivirus immunohistochemical stain: Immunoreactivity within neuronal perikarya. Bar = 500 µm;

Figure 3

(A) Vero.DogSLAMtag control cells. Bar = 200 µm; (B) Vero.DogSLAMtag infected with Fraser’s dolphin cerebellum 8 days post infection showing large syncytium. Bar = 200 µm.

Figure 4

(A) A portion of a syncytium with multiple nuclei and a morbillivirus nucleocapsid cytosolic inclusion (upper left corner, asterisk). The surface of the monolayer (bottom) looks “foamy” due to multiple projections of plasmalemma forming multiple “vacuoles’. Bar = 2 µm; (B) A fragment of intracytosolic nucleocapsid inclusion with multiple (spiral) strands ~ 20 nm in diameter. A portion of the nucleus is in the left lower corner. Bar = 200 nm; (C) Large intranuclear inclusion of morbillivirus nucleocapsid (asterisk) in an attached cell in the monolayer 7 days post-infection (dpi). Bar = 200 nm; (D) Intranuclear inclusion of nucleocapsid in a syncytium (asterisk). Portions of two other nuclei at the top of an infected one. Attached cells 7 dpi. Bar = 500 nm.

Figure 5

Genetic analysis of 23 partial nucleotide sequences of the L gene. The final data set contained 559 characters including gaps. Values are expressed as a percentage of identity. BWMV beaked whale morbillivirus; FDMV Fraser’s dolphin morbillivirus, PWMV pilot whale morbillivirus; PMV porpoise morbillivirus; GDMV Guiana dolphin morbillivirus; DMV dolphin morbillivirus; MeV measles virus; RPV rinderpest virus; PPRV peste-des-petits-ruminants virus; PDV phocine distemper virus; CDV canine distemper virus; FeMV feline morbillivirus.

Figure 6

Genetic analysis of 30 partial nucleotide sequences of the P gene. The final data set contained 248 characters including gaps. Values are expressed as a percentage of identity. BWMV beaked whale morbillivirus; FDMV Fraser’s dolphin morbillivirus; PWMV pilot whale morbillivirus; PMV porpoise morbillivirus; GDMV Guiana dolphin morbillivirus; DMV dolphin morbillivirus; MeV measles virus; RPV rinderpest virus; PPRV peste-des-petits-ruminants virus; PDV phocine distemper virus; CDV canine distemper virus; FeMV feline morbillivirus.

Figure 7

Maximum Likelihood (ML) phylogenetic analysis based on the partial nucleotide (nt) sequences of the P gene. Each sequence is denoted by its strain/isolate name, geographic area of stranding (where available), and GenBank accession number (where available). The phylogeny includes 30 nucleotide sequences with a total of 248 characters (including gaps) in the final dataset. IQ-TREE software (http://iqtree.cibiv.univie.ac.at/) was used to determine best-fit models and perform ML phylogenetic analysis with 1000 non-parametric bootstraps. The best-fit model for the alignment was TPM2 + G4TPM2u + G4, chosen based on Bayesian Information Criterion. BWMV beaked whale morbillivirus; FDMV Fraser’s dolphin morbillivirus; PWMV pilot whale morbillivirus; PMV porpoise morbillivirus; GDMV Guiana dolphin morbillivirus; DMV dolphin morbillivirus; MeV measles virus; RPV rinderpest virus; PPRV peste-des-petits-ruminants virus; PDV phocine distemper virus; CDV canine distemper virus; FeMV feline morbillivirus.