Abstract
Cetacean Morbillivirus (CMV) has caused several epizootics in cetaceans globally. An unusual mortality event among Tursiops aduncus in Perth, Western Australia (WA) coincided with increased strandings statewide in 2009. Necropsy of two dolphins identified mycotic encephalitis and pneumonia as the cause of death, respectively. Morbilliviral antigen was detected in multiple tissues using immunohistochemistry and confirmed by reverse transcriptase polymerase chain reaction (RT-PCR) using primers for morbilliviral N and P genes. Sequencing of amplified RT-PCR products (approximately 238 bp in length from the N gene & 425 bp from the P gene) confirmed the presence of CMV in both dolphins and facilitated phylogenetic analysis. The N and P genes from the WA dolphins had respectively, 79% - 83% and 75% - 79% nucleotide identity to the highly conserved N and P genes of various strains of CMV. There was only 79% - 83% identity between the N and P nucleotide sequences from the WA dolphins and a variant from a Tursiops truncatus that stranded in Queensland (QLD), Australia in 2010. This is the first report of CMV-related mortality for T. aduncus in Australian waters and for the Indian Ocean. Preliminary phylogenetic data suggest that the WA variant is distinct from all other morbilliviruses, and is closely related to, but divergent from, other cetacean morbilliviruses. It is distinct from the QLD CMV variant, which is more closely related to the CMV isolates from the Northern Hemisphere. Furthermore, the WA variant appears to be the most closely related marine mammal morbillivirus to the terrestrial genus members identified to date. Evidence of a divergent CMV has implications for understanding the evolutionary history of CMV and supports ongoing surveillance and archival sampling to elucidate the role of CMV and other pathogens in future mortalities.