Mass mortality events associated with cetacean morbillivirus (Ce MV) infection have been reported since 1988 (Van Bressem et al. 2001). In Australia six species have been recorded from Tasmania (Van Bressem et al. 2001), Western Australia (Holyoake et al. 2010), Queensland and New South Wales (Stone et al. 2012). During 2013, an Unusual Mortality Event (UME) of dolphins occurred in South Australia (SA).
Records of SA dolphin mortalities from 2012 and 2013 were summarized for geographic trends, life history, stomach contents and species identity. For 2013 dolphins (32 Tursiops aduncus, 2 T. truncatus and 7 Delphinus delphis) the following information was collected: gross pathology, histopathology, parasitology, bacteriology, mycology and virology [PCR and immunohistochemistry (IHC)]. IHC was performed on lung, lymph nodes, thymus, spleen and/or brain from 31 dolphins. Viral nucleic acid (RT-PCR) techniques were conducted on lung, brain, kidney and/or liver from 38 dolphins. Of the 18 IHC-positive dolphins, all but one were Tursiops aduncus, only one was T. truncatus. All were also from 2013 and from Gulf St Vincent. DNA from dolphin morbillivirus (DMV) 2013 SA strain was identified in 34 dolphins from several regions of SA and during both 2012 and 2013. In the first part of the event, dolphins were predominantly young, but later those that died were mostly adults. Many were emaciated. Common gross pathology findings were 1) severe local subdermal haemorrhaging, 2) enlarged and swollen lymph nodes and spleen, 3) pneumonia associated with tracheal luminal and intrabronchial lung nematodes, 4) severe meningeal congestion, and 5) stomachs with few or no contents. Subdermal hemorrhaging was most frequent on the lower jaw, sometimes extending to the deep muscle layer of the head/neck region. Histological examination of the lungs identified necrosuppurative and necrogranulomatous pneumonia associated with lung nematodes and fungal hyphae (Aspergillus fumigatus). In a subset of dolphins, multinucleated syncytial cells were found in the bronchiolar epithelium and alveolar septae. Additional findings included embolic necrosuppurative encephalitis and myocarditis associated with intralesional fungal hyphae. Bacteriology conducted on 26 animals isolated pathogenic bacteria: Escherichia coli (n = 1) or Vibrio sp. (n = 6) from the lungs of six dolphins. Aspergillus fumigatus was isolated from the lungs of two dolphins. Parasites identified were: Toxoplasma gondii in the brain of one T. aduncus, Halocercus lagenorhynchi in the lungs of three T. aduncus and one Delphinus delphis. Trematodes were found in soft tissue adjacent to the bulla and periotic of five T. aduncus and from liver of two T. aduncus.
The 2013 UME SA is the largest mortality event associated with CeMV that has recorded in Australia. This is also the first record of DMV infection in SA cetaceans. The underlying causes for this event are not clear. In March and April 2013 a large fish die-off occurred in the region and there may be a connection between these events.
The cause of death of the dolphins appeared to be multifactorial, and it is hypothesized that primary morbillivirus infection may have precipitated subsequent secondary infection. Although the pathology findings did not indicate brucellosis, future studies may test for this disease.
This study would not have been possible without the enormous efforts of many people who assisted in many ways. Tony Flaherty was especially supportive of this study. Special thanks to David Stemmer and volunteers at the South Australian Museum; Department of Environment, Water and Natural Resource (DEWNR); Primary Industries and Resources SA (PIRSA); Adelaide Dolphin Sanctuary; Mike Bossley (WDCS) and Aaron Machado (AMWRRO). Funding assistance was provided by DEWNR, Adelaide Mt Lofty NRM and Biosecurity SA.
1. Duignan PJ, Geraci JR, Raga JA, Calzada N. Pathology of morbillivirus infection in striped dolphins (Stenella coeruleoalba) from Valencia and Murcia, Spain. Canadian Journal of Veterinary Research. 1992;56:242–248.
2. Holyoake C, Finn H, Stephens N, Duignan P, Salgado C, Smith H, Bejder L, Linke T, Daniel C, Lo HN, Ham GS, Moiler K, Allen S, Bryant K, McElligott D. 2010. Technical report on the Bottlenose dolphin (Tursiops aduncus) unusual mortality event within the Swan Canning Riverpark, June–October 2009, Murdoch University.
3. Stone BM, Blyde DJ, Saliki JT, Blas-Machado U, Bingham J, Hyatt A, Wang J, Payne J, Crameri S. Fatal cetacean morbillivirus infection in an Australian offshore bottlenose dolphin (Tursiops truncatus). Australian Veterinary Journal. 2011;89:452–457.
4. Stone BM, Blyde DJ, Saliki JT, Morton JM. Morbillivirus infection in live stranded, injured, trapped and captive cetaceans in south eastern Queensland and northern New South Wales, Australia. Journal of Wildlife Diseases. 2012;48(1):47–55.
5. Van Bressem MF, Van Waerebeek K, Jepson PD, Raga JA, Duignan PJ, Neilsen O, Di Beneditto AP, Siciliano S, Ramos R, Kant W, Peddemors V, Kinoshita R, Ross PS, López-Fernandez A, Evans K, Crespo E, Barrett T. An insight into the epidemiology of dolphin morbillivirus worldwide. Veterinary Microbiology. 2001;81:287–304.