Most types of cyanobacteria that produce neurotoxins occur in marine environments, where they can cause red tides. A few species are found in freshwater around the world, and they sometimes kill dogs, cattle and other animals that drink from or swim in contaminated water bodies.
“One of the biggest unresolved issues is why there seems not to have been collateral mortality,” said Chris Thouless, head of research at Save the Elephants, an organization based in Kenya. “That is one of the reasons we originally said this was not a probable explanation, because other animals didn’t seem to be dying.”
Elephants account for the majority of wildlife in the area, but cattle are also found there, Dr. Thouless said. He has not been able to verify, however, whether cattle drink from the same bodies of water used by elephants.
That said, he added, “While no suggested cause is a perfect fit to observations, this one is less improbable than the others, so I am inclined to accept it, particularly since this is supported by lab results.”
There are several possible explanations for why only elephants died, said Roy Bengis, a veterinary wildlife specialist at the University of Pretoria in South Africa, who formerly served as chief state veterinarian at Kruger National Park.
It could be that elephants are “exquisitely sensitive” to whichever particular neurotoxin killed them, whereas other species are more resistant, Dr. Bengis said. “We know this happens — different species of animals have different tolerances.”
Elephants also drink copious amounts of water, up to 40 gallons a day, so they would be taking in a larger dose of toxin than a smaller animal. Additionally, unlike most other species, elephants “actually go and frolic in the water and roll in the mud and spray themselves,” Dr. Bengis said. The neurotoxin might have been absorbed through their skin.