Follow-up histopathology showed that 23 had infectious disease as a major cause of death. 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. Keywords: unusual mortality event, cetacean morbillivirus, Australia, Indo-Pacific bottlenose dolphin, environmental perturbation == 1 . 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. UMEs caused by biotoxins appear to be increasing during the last 40 NSC5844 years, although changing mammal abundance and inconsistent effort to report and investigate all events may make it more difficult to document true frequency and causal factors [4]. The first documented UME dates to the early 1900s and most have occurred since about 1980 [2, 5]. Some events have been linked to biotoxins produced by harmful algal blooms [5, 6] and others to morbillivirus [7] and naval activities [8], but for many the cause was not NSC5844 determined [2]. In 2009, two UMEs were documented in Australia: a small event involving Indo-Pacific bottlenose dolphins, Tursiops aduncus, linked to dolphin morbillivirus (DMV) and presumed poxvirus infections in the Swan River, Western Australia [9, 10], and an abnormally high number of humpback whale, Megaptera novaeangliae, mortalities along the Western Australian coast [11]. A third, suspected, UME was observed in Western Australian Indo-Pacific bottlenose dolphins during 20082009 [12]. In a review of emerging infectious diseases of cetaceans worldwide, Van Bressemet al.[13] discussed four categories of pathogens: viruses (including cetacean morbillivirus (CeMV), papillomavirus and poxvirus), Brucellaspp., Toxoplasmaspp. andLacazia loboi(lobomycosis). Pathogens that infect cetaceans may be host-specific (e. g. viruses) or host-opportunistic (e. g. bacteria, fungi and protozoa). Van Bressemet al.[13] concluded that environmental degradation may have disturbed the evolutionary equilibrium between cetaceans and their pathogens, thus making some populations more susceptible to disease and mortality. The causes NSC5844 of UMEs are likely to be complex and involve a broad spectrum of factors in synergy. Van Bressemet al.[13] noted that there is mounting Rabbit Polyclonal to RBM34 circumstantial evidence that chemical pollution has increased the frequency and severity of some diseases in cetaceans and pinnipeds. Evidence for morbillivirus has been found in cetaceans from all ocean basins but sizable mortality events have not been documented for the Southern Hemisphere [3, 5]. Morbillivirus has been identified in six cetacean species from Australian waters [3, 14]. Van Bressemet al. [7] reported that one of five common bottlenose dolphins, Tursiops truncatus, collected in Tasmania during 1997 tested positive for DMV-specific antibodies. Stoneet al. [14] identified antibodies to CeMV in four species of delphinid and one baleen whale, all from southern Queensland and northern New South Wales and dating back to 1985. Stoneet al. [15] also reported a fatal case of a common bottlenose dolphin from the same region. Viral genome and antigen of CeMV have NSC5844 been identified in Indo-Pacific bottlenose dolphins collected during the Swan River UME in Western Australia during 2009 [10]. Toxoplasmosis has been identified in two Australian cetaceans: the Australian humpback dolphin, Sousa sahulensis(Sousa chinensisin Bowateret al. [16]) and Indo-Pacific bottlenose dolphins [17]. At present, it is not considered a significant cause of cetacean mortality in Australia. However , there are no targeted surveys to identify its presence, therefore , its true prevalence and impact is not known. To detect a UME, it is essential to have consistent, long-term monitoring of mortalities [4] so that variations from the usual pattern can be identified. In Australia, stranding networks are usually run by state and territory wildlife agencies but there is rarely a comprehensive post-mortem programme of mortalities. In South Australia (SA) a stranding network began in 1990 and is coordinated by South Australian Museum (SAM), with input from other government and non-government agencies. Trends in stranding patterns have been summarized by Segawa & Kemper [18] and circumstance of death (including a review of diseases) by Kemperet al. [19]. Post-mortems have been conducted since the beginning of the stranding programme, with the most detailed results from 2005. The aim of this study was to document an unprecedented.