More than 350 elephants in Botswana have mysteriously died since May, in a phenomenon that some scientists have charachterised as a “conservation disaster”. No full investigation has been conducted so far, no explanation provided, however there have been some tests on a number of carcasses, which have exclused some of contageious deseases, typical for the speaces, but the cause of death remains unexplained.

The elephants — which massively died in the swampy Okavango Delta — still had their tusks intact, suggesting that the ivory poaching was not behind it. A flight over the delta in May by researchers with Elephants Without Borders, a wildlife conservation organization, first spotted 169 carcasses, that number increased rapidly to 356 in June, when the conservationists took another flight over the area.

Botswana’s Ministry of Environment, Natural Resources Conservation, and Tourism is aware of the problme, and the relevant department has verified 275 of those elephant carcasses, according to a statement from the African Wildlife Foundation.

Already, officials have ruled out anthrax, the carcasses tested negative for that bacterium, said Scott Schlossberg, a research consultant for Elephants Without Borders.

The bacterium that causes anthrax disease, called Bacillus anthracis, occurs naturally in soils, where it can stay inactive as spores for decades, scientists reported in 2019 in the journal Proceedings of the Royal Society B. Grazing animals can ingest anthrax-tainted soils along with plants or while drinking from watering holes.

This isn’t the first elephant die-off in the region; more than 100 elephants died over a two-month period in the fall of 2019 in Botswana’s Chobe National Park, primarily driven by drought. Some of those deaths may have been due to anthrax, as the elephants would have ingested soil (possibly contaminated with anthrax spores) while grazing around dried-up watering holes and across wilted grasslands.