Sudden elephant mortality in the Okavango delta: field investigation and effective monitoring of wildlife health under environmental change

博茨瓦纳奥卡万戈三角洲发生了一起大规模而重大的大象死亡事件，迄今已有359头大象被报告死亡。此类活动的罕见、偏远和难以进入的地形、当地缺乏病理和实验室诊断能力，以及由于新冠肺炎而难以获得国际支持，阻碍了调查。尽管进行了实验室检测，但原因仍不清楚。这一点以及其他有蹄类动物死亡事件的经验表明，可能涉及多种相互作用的因素，需要进行综合的多学科调查。迫切需要在野外仍可获得证据的情况下推动这项研究，并确定对这一大象和其他大象种群的影响。这一活动进一步提供了一个机会，让人们更好地了解野生动物的死亡事件，野生动物死亡事件似乎正在增加，并可能与环境变化有关。博茨瓦纳拥有世界上最大且不断扩大的非洲象种群，它们在周边国家面临着严重的狩猎压力。虽然特定的传染病以前曾导致非洲大象成群死亡，但大规模死于疾病的情况非常罕见，考虑到它们脆弱的保护地位和作为生态关键物种的作用，这一点令人担忧。大象是奥卡万戈三角洲生态系统的组成部分，对其生物多样性、稳定性和功能起着关键作用，因此大象数量的大幅减少可能会对博茨瓦纳的经济产生不利影响。此外，在其他地方较小的脆弱大象种群中类似的死亡可能会对种群生存产生更大的后果，找出灭绝的原因和环境因素的参与是重要的。鉴于病原体宿主转换在驱动人类疾病威胁方面的作用日益受到重视，在这一共享使用区域出现的疾病也是依赖牲畜的社区以及潜在的公共卫生的极大关切。在这个项目中，来自博茨瓦纳和英国的一个多学科科学家团队将在证据仍然存在的情况下共同开展紧急的现场和实验室调查，以确定死亡的原因。为了在这样一个具有挑战性的环境中帮助实现这一点，我们将使用先进的分子生物学方法对无脊椎动物(蚊子和扁虱)媒介进行采样，并使用生物分析来检测环境样本中的微量毒素。重要的是，包括死亡地点和时间在内的现有证据将由一个国际专家网络汇编和评估，以协助博茨瓦纳政府进行解释。空间模型将评估环境和感染因素及其相互作用的相对可能性。博茨瓦纳的合作实验室和现场工作人员在全球重要的奥卡万戈生态系统中调查未来类似事件的能力将通过这种合作和在那里建立新的分析而得到加强。博茨瓦纳和国际上的政府、保护组织、当地社区和其他感兴趣的各方将全程参与这项研究，并在项目结束时聚集在一个利益相关者论坛上，讨论结果并计划未来对野生动物灭绝的反应，以及使用One Health观点参与该地区野生动物健康的研究。

A large and significant mortality event in elephants (Loxodonta africana) has developed in the Okavango Delta in Botswana, with 359 elephants found reported dead to date. Investigations are hampered by the rarity of such an event, remote and inaccessible terrain, lack of local capacity for pathology and laboratory diagnosis, and difficulties accessing international support due to covid-19. Despite laboratory testing, the cause remains unknown. This, and experience from other mortality events in ungulates, suggests that multiple interacting factors might be involved, requiring integrated multidisciplinary investigation. There is an urgent need to instigate this research while evidence remains accessible in the field, and to determine implications for this and other elephant populations. The event further provides an opportunity to better understand die-off events in wildlife, which seem to be increasing in frequency and could be linked to environmental change.Botswana hosts the world's largest and expanding population of African elephants, which are under severe hunting pressure in surrounding countries. While specific infectious diseases have caused clusters of mortality in African elephants previously, large scale die-offs from disease are highly unusual, and are of concern given their vulnerable conservation status and role as a keystone species ecologically. Elephants are an integral part of the Okavango Delta ecosystem and play a pivotal role in its biodiversity, stability and functioning, such that a significant decrease in elephant numbers may have a detrimental effect on Botswana's economy. Moreover, similar mortality in smaller vulnerable elephant populations elsewhere could have larger consequences for population viability and it is important to work out the cause of the die-offs and the involvement of environmental factors. The emergence of disease in this shared use area is also of great concern for livestock-dependent communities and potentially for public health, given increasing appreciation of the role of pathogen host-switching in driving disease threats in people.In this project a multidisciplinary team of scientists from Botswana and the UK will work together to undertake urgent field and laboratory investigations while evidence is still available, to determine the cause of the die-off. To help achieve this in such a challenging landscape, we will use advanced molecular biology methods to sample invertebrate (mosquito and tick) vectors, and bioanalysis to detect traces of toxins in environmental samples. Importantly, existing evidence including the location and timing of deaths will be compiled and assessed by an international network of experts to assist the Botswana government in their interpretation. A spatial model will evaluate the relative likelihood of environmental and infectious factors and their interaction. The capacity of partner laboratories in Botswana, and field workers, to investigate future events like this in the globally important Okavango ecosystem will be enhanced by this collaboration and by setting up new analyses there. Government, conservation organisations, local communities and other interested parties in Botswana and internationally will be engaged in the research throughout and come together in a stakeholder forum at the end of the project to discuss outcomes and plan for future responses to wildlife die-offs as well as engaged research in wildlife health in the area using a One Health perspective.