"In August 2020, veterinarian Chris Foggin, in the midst of operating on an anthrax-suspected elephant, faced a harsh situation when five more dead elephants were discovered in Zimbabwe, encouraging urgent efforts to collect post-mortem samples before decomposition."
In late August 2020, veterinarian Chris Foggin was wearing a mask and operating on an elephant suspected of having died of anthrax when he received a call that there were more deaths.
The next day, five more dead elephants were found in the scorching Zimbabwean sun.
Foggin knew he and his team couldn't get to all the dead elephants to collect post-mortem tissue samples, but he collected what he could before the carcasses decomposed.
By November, a total of 35 African elephants ( Loxodonta africana ) had died in northwestern Zimbabwe, just across the border from neighboring Botswana, where more than 350 elephants had died months earlier. Concerns grew when poaching, starvation and anthrax, a naturally occurring deadly bacterial disease, were ruled out. In September 2020, the government of Botswana determined that elephant deaths in Botswana were caused by an unspecified blue-green algal toxin that may have contaminated waterholes.
Three years later, another culprit in the mysterious deaths of 35 elephants in Zimbabwe emerged: Pasteurella bacteria similar to a strain called Bisgaard taxon 45, which has been linked to infections in other wildlife but is not known to kill African elephants.
Examining tissue samples at the Victoria Falls Wildlife Trust laboratory, Foggin discovered that several of the dead elephants' organs had been torn from their blood vessels, leading him to suspect hemorrhagic septicemia or blood poisoning.
In all, six of the 15 elephants had genetic or biochemical evidence of Bisgaard's 45 taxa, and no poisons, toxins or viral infections were detected.
Bacterial septicemia adds to the growing list of disease threats to elephant conservation, including tuberculosis, anthrax and virulent poisoning. Foggins and his colleagues write in their paper published in October.
Despite all the epidemiological studies, the source of infection and the route of infection are not known. Elephants are highly social animals, and at least 11 elephants died in about 24 hours in an area of about 50 square kilometers, researchers said.
It was very fast, Foggin told National Geographic that It was so dramatic.
The outbreak was preceded by successive periods of bad rains and the region was in the grip of a drought during the mass deaths.
So one possibility the researchers offer is that the heat and dryness may have somehow triggered bacteria that are thought to be harmless in other animals to infect or spread among the elephants.
In 2015, Pasteurella species killed about 200,000 antelopes during a heat wave in central Kazakhstan.
But there are still many unanswered questions about Bisgaard's taxon 45 and the 2020 death rate in Zimbabwe, veterinary epidemiologist and co-author Laura Rosen wrote in a recent blog about the events.
We still don't know how the bacteria got into this landscape - has it always been here? Is it commonly found in elephants but not previously identified?
To answer some of these questions, the Victoria Falls Wildlife Trust is now equipped to test 45 taxa of Pasteurella Bisgaardi. The organization plans to continue looking for the bacteria in elephants and large carnivores after re-examining samples from previous elephant deaths. The identification of septicemia as a cause of sudden death gives veterinarians and conservationists a new and important differential diagnosis to move forward, Rosen writes.
The study was published in the journal Nature Communications.
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