Morbillivirus-associated unusual mortality event in South Australian bottlenose dolphins is largest reported for the Southern Hemisphere.

C M Kemper,S S Bastianello,J Wang,L Woolford,S E Gibbs,C Dickason,D Kelly,J Bingham,I Tomo

doi:10.1098/rsos.160838

Abstract

Cases of morbillivirus have been recorded in the Southern Hemisphere but have not been linked to significant marine mammal mortality. Post-mortems were conducted on 58 carcasses (44 Indo-Pacific bottlenose dolphins, two common bottlenose dolphins, 12 short-beaked common dolphins) from South Australia during 2005–2013, including an unusual mortality event (UME) in St Vincent Gulf Bioregion (SVG) during 2013. Diagnostic pathology, circumstance of death, body condition, age and stomach contents were documented for Indo-Pacific bottlenose dolphins. At least 50 dolphins died during the UME, 41 were Indo-Pacific bottlenose dolphins and most were young. The UME lasted about seven months and had two peaks, the first being the largest. Effect on the population is unknown. Diagnostic testing for morbillivirus was conducted on 57 carcasses, with evidence for infection in all species during 2011–2013. All tested UME bottlenose dolphins were positive for cetacean morbillivirus (CeMV), and the pathology included interstitial pneumonia, lymphoid depletion and syncytia. Concurrent pathologies, including lung parasite and fungal infections, and severe cutaneous bruising were observed in many dolphins. The event coincided with elevated water temperatures, a diatom bloom and significant fish die-offs. We conclude that the cause for the UME was multifactorial and that CeMV was a major contributor.

Highlights

An unusual mortality event (UME) of marine mammals is defined in the United States Marine Mammal Act as ‘a stranding that is unexpected; involves a significant die-off of any marine mammal population; and demands immediate response’ [1]
We demonstrate that the 2013 dolphin UME in South Australia (SA) was associated with morbillivirus infection
Other infectious conditions were present in affected animals, the UME clearly coincided with the appearance of severe morbillivirus bronchopneumonia, and we conclude that morbillivirus was a major causative agent for the event

Summary

Introduction

An unusual mortality event (UME) of marine mammals is defined in the United States Marine Mammal Act as ‘a stranding that is unexpected; involves a significant die-off of any marine mammal population; and demands immediate response’ [1]. These events have been documented in cetaceans, pinnipeds and sirenians [2,3] and can be multispecies in nature. A third, suspected, UME was observed in Western Australian Indo-Pacific bottlenose dolphins during 2008–2009 [12]

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