The cause of a mysterious mass death of African elephants that saw 11 of the world's largest land-based animals die in 24 hours has been unravelled by scientists - but they warn the danger isn't over yet.
Thirty-five African elephants in northwestern Zimbabwe dropped dead under baffling circumstances between late August and November 2020.
"They died over a very narrow window. That’s one of the most enigmatic parts of the whole puzzle.
"That many animals dying quite close together but not right next to each other over such a narrow space of time. It’s really to my mind, rather unique, certainly in this part of the world," said Dr Chris Foggin, a veterinarian at Victoria Falls Wildlife Trust in Zimbabwe, who is a co-author of the study on the cause of the deaths.
Earlier that same year, about 350 elephants in neighbouring Botswana also died suddenly over the course of three months.
Officials and experts were initially at a loss to explain the deaths, which occurred among Africa’s biggest population of elephants.
It turns out a bacterial infection killed the elephants, according to the research based on samples taken from 15 of the animals that died in Zimbabwe.
An analysis, published on October 25 in the journal Nature Communications, showed evidence of infection by a little-known bacterium called Bisgaard taxon 45 that caused septicemia, or blood poisoning.
The deaths took place as food and water resources dwindled during the dry season, forcing the elephants to travel increasing distances to look for water and to forage.
The authors said that heat, drought and population density in that area were likely contributing factors to the outbreak.
With the increased risk of the extreme circumstances coming with climate change, the authors warned similar mass deaths could occur in the future.
Dr Foggin said: "It’s premature to say that climate change has influenced (this) but it may do so in future if we get more and prolonged droughts, or the rainfall patterns (change) and we have a much harsher dry season."
"I do think that if that is the case, then we are more likely to see this sort of mortality event occurring again."
The elephant mortalities in Botswana have been attributed to cyanobacterial neurotoxins, but further details have not been published, the study noted.
Dr Foggin said there was no proven connection between the Zimbabwe and Botswana elephant deaths.
The study noted that only six of the elephants tested positive for Bisgaard taxon 45 but the remains were in "good body condition and unlikely to have died of drought-related starvation or severe dehydration alone."
No elephants had their tusks removed from poaching, and no external signs of trauma were observed. Tests for anthrax were also negative, Dr Foggin added.
The researchers said they failed to detect the bacteria in the other samples - a fact they attributed to poor sample quality and delays in getting the necessary permits that meant it was too late to perform some lab work.
One of the most recognisable animals on Earth the African elephant is listed as endangered on the International Union for Conservation of Nature Red List, population numbers diminished by 144,000 to about 350,000 between 2007 and 2014, with continuing losses estimated at 8% every year, according to the study.
What is known about the bacterium?
Bisgaard taxon 45 has previously been associated with tiger and lion bite wounds in humans. The bacteria have also been found in a chipmunk and healthy captive parrots.
The microorganism, which does not have an official name, is closely related to another, more common bacterium known as Pasteurella multocida, which can cause hemorrhagic septicemia in other animals, including Asian elephants.
That bacterium was also linked to the mass deaths of 200,000 critically endangered saiga antelope in Kazakhstan in 2015, the study noted.
Dr Foggin said researchers had been monitoring wildlife in the area for the presence of the bacteria, but no further elephant deaths as a result of Bisgaard taxon 45 had been confirmed since 2020.
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