Abstract：
An unusual mass mortality event (MME) of harbour seals (Phoca vitulina) and harbour porpoises (Phocoena phocoena) occurred in Denmark and Sweden in June 2007. Prior to this incident, the region had experienced two MMEs in harbour seals caused by Phocine Distemper Virus (PDV) in 1988 and 2002. Although epidemiology and symptoms of the 2007 MME resembled PDV, none of the animals examined for PDV tested positive. Thus, it has been speculated that another - yet unknown - pathogen caused the June 2007 MME. To shed new light on the likely cause of death, we combine previously unpublished veterinary examinations of harbour seals with novel analyses of algal toxins and algal monitoring data. All harbour seals subject to pathological examination showed pneumonia, but were negative for PDV, influenza and coronavirus. Histological analyses revealed septicaemia in multiple animals, and six animals tested positive for Klebsiella pneumonia. Furthermore, we detected the algal Dinophysis toxin DTX-1b (1-115 ng g-1) in five seals subject to toxicology, representing the first time DTX-1b has been detected in marine vertebrates. However, no animals tested positive for both Klebsiella and toxins. Thus, while our relatively small sample size prevent firm conclusions on causative agents, we speculate that the unexplained MME may have been caused by a chance incidence of multiple pathogens acting in parallel in June 2007, including Dinophysis toxin and Klebsiella. Our study illustrates the complexity of wildlife MMEs and highlights the need for thorough sampling during and after MMEs, as well as additional research on and monitoring of DTX-1b and other algal toxins in the region.
摘要：
2007年6月，丹麦和瑞典发生了一次不寻常的海豹（Phocavitulina）和海豚（Phocoenaphocoena）大规模死亡事件（MME）。在这次事件之前,在1988年和2002年，该地区在海豹中经历了两次由Phocine犬瘟热病毒（PDV）引起的MME。尽管2007年MME的流行病学和症状类似于PDV，没有检测PDV的动物呈阳性。因此，据推测，另一种未知的病原体引起了2007年6月的MME。为了揭示可能的死因，我们将以前未发表的海豹兽医检查与藻类毒素和藻类监测数据的新分析相结合。所有接受病理检查的海豹均显示肺炎,但是PDV阴性，流感和冠状病毒。组织学分析显示多种动物败血症，六只动物肺炎克雷伯菌检测呈阳性。此外，我们在五只接受毒理学检查的海豹中检测到藻类Dinphysis毒素DTX-1b（1-115ngg-1），代表首次在海洋脊椎动物中检测到DTX-1b。然而,没有动物的克雷伯菌和毒素检测呈阳性。因此，虽然我们相对较小的样本量阻止了对致病因素的坚定结论，我们推测,原因不明的MME可能是由2007年6月同时作用的多种病原体的偶然发生率引起的,包括Dinphysis毒素和克雷伯菌.我们的研究说明了野生动物MME的复杂性，并强调了在MME期间和之后进行彻底采样的必要性，以及对该地区DTX-1b和其他藻类毒素的其他研究和监测。
