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

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.