Published December 5, 2023
6 min read
When hundreds of African savanna elephants dropped dead in Botswana’s Okavango Delta in 2020, conservationists were alarmed. As the death toll rose—from dozens in March to more than 350 animals by July—their concerns increased, especially because nobody knew what was happening.
A short time later, the mystery deepened when 34 more individuals of the endangered species died across the border in northwestern Zimbabwe in a three-week period, with one more found in November.
“It was very quick,” says Chris Foggin, a veterinarian with Victoria Falls Wildlife Trust who examined the elephant carcasses in Zimbabwe. “That was what was so dramatic.”
African savanna elephants in the five-country Kavango-Zambezi Transfrontier Conservation Area, or KAZA, represent the majority of what’s left of that species, notes Steve Osofsky, director of the Cornell Wildlife Health Center in Ithaca, New York. Around 350,000 African savanna elephants remain, and given the already significant set of threats to their survival, “a new disease could be what tips that last domino towards extinction,” says Osofsky, who wasn’t involved in the new research.
In September 2020, the Botswana government attributed the deaths of elephants in the Okavango Delta to cyanobacteria in the water that elephants drank, although without data to support it, scientists have questioned this conclusion. Meanwhile, the Zimbabwe carcasses showed no evidence they died from those toxic algae.
And so, the cause of the die-offs continued to elude experts. They ruled out poaching because the tusks were intact, and they found no bullet wounds. Poisoning was unlikely because no other animals, such as vultures feeding on the carcasses, were affected. (Read about the search for answers in Botswana’s elephant deaths.)
Now, new research published recently in Nature Communications points to a different culprit, at least for the Zimbabwe elephants—a bacterium not previously found in elephants of any species, called Bisgaard taxon 45, that causes a massive systemic blood infection called septicemia.
Bisgaard taxon 45 is related to another bacterium, called Pasteurella multocida, that can cause septicemia in cattle and was linked to the death of 200,000 endangered saiga antelope in Kazakhstan in 2015. Yet while it shares many of the same lethal genes, Bisgaard taxon 45 is a separate species.
“It’s a disease we know can kill a reasonable number of elephants in a short space of time,” says Foggin, co-leader of the study. And “it has the potential to kill a lot more given the right circumstances.”
What those are, however, remains unknown—yet it’s pressing to find out. Aerial population surveys in KAZA in 2022 found a high number of new elephant carcasses.
Search for answers
Finding Bisgaard taxon 45 was no easy task. Scientists examined as many elephant carcasses as they could,