Late last year, news trickled in about the horrific mass dying of the saiga antelopes of central Kazakhstan, of which it has been estimated that over 200,000 of the animals dropped dead over a matter of days, with scenes of entire herds of the antelope, made up of mothers with calves, littering the landscape.

What caused this sudden widespread mortality initially baffled biologists and zoologists who struggled to find the culprit.

It now seems that the mystery is finally over, with the cause being narrowed down by the Saiga Conservation Alliance to a normally benign bacteria suddenly becoming deadly — although the cause of why that happened is not known.

When researchers first discovered the dead and dying animals on the Kazakhstani grasslands, they had no idea as to the scale of the disaster.

The first accounts were still shocking, putting the number of dead saiga in the tens of thousands, but as more reports came out conservationists realized the full extent of the die-off.

It is thought that as much as 88% of the antelope from the Betpak-Dala desert of Kazakhstan succumbed, accounting for roughly 70% of the entire global population of the already endangered antelope.

Now, after continued analysis of samples taken from the carcasses of the saiga, multiple laboratories have come to the same conclusion and identified the bacterium Pasteurella multocida as the cause. It is thought that the bacteria, which naturally lives in the respiratory tract of the animals and normally has no impact on their health somehow became deadly, leading to hemorrhagic septicemia.

The symptoms of the condition include a high fever, salivation, and shortness of breath, followed by death within 24 hours. This is consistent with what was observed in the field.

It is not unknown for domestic animals to suffer from the same condition, but what is particularly unusual is the 100% mortality rate seen in the saiga herds. The reasons behind this are less clear, but could be related to earlier suggestions that unusual weather conditions may have been stressing the animals, many of which were mothers who had just given birth.

As the Saiga Conservation Alliance says, the investigation into the animals’ deaths is still ongoing, with questions such as these still to clear up. With a next calving season creeping up, many biologists are waiting with baited breath to see what will occur.

Before the mass dying, the antelope numbers stood at around 300,000. They were previously heavily hunted, mainly for their horns, which were used as a replacement for rhino in traditional medicine. In a terrible case of poor lack of judgment, the WWF is thought to have had a hand in the decline of the species during the 1990s.

At the start of the decade, there were thought to have been around a million of the antelopes roaming the steppes of central Asia, but in a bid to try and ease the poaching of rhinos for their horn, the WWF actually encouraged the use of the saiga horn, leading to their populations to crash.