A couple of years ago over a span of three weeks, around 200,000 saiga antelope in Central Kazakhstan died off suddenly. At the time, scientists felt that one of two pathogens Pasteurella and Clostridia—already present in the saiga population—must be a part of the mysterious die-off. Saiga antelopes had had mass-die offs before, but nothing even remotely on the scale of what was being seen. The Atlantic has an update, two years in the making, and the conclusions that scientists have reached concerning what exactly happened to the saiga antelope.
Pasteurella multocida normally lives in the saiga’s respiratory tract, but Kock’s team found that the microbe had found its way into the animals’ blood, and invaded their livers, kidneys, and spleens. Wherever it went, it produced toxins that destroyed the local cells, causing massive internal bleeding. Blood pooled around their organs, beneath their skin, and around their lungs. The saigas drowned in their own bodily fluids.
But that answer just led to more questions. Pasteurella is common and typically harmless part of the saiga’s microbiome. In livestock, it can cause disease when animals are stressed, as sometimes happens when they’re shipped over long distances in bad conditions. But it has never been linked to a mass die-off of the type that afflicted the saigas. What could have possibly turned this docile Jekyll into such a murderous Hyde?
After putting together a 13-page list of the potential explanations, scientists tested and checked and cross-checked to see what the variable could possibly have been. The conclusion was the warmer and more humid climate that the saigas were living in in 2015.
It’s still unclear how heat and humidity turn Pasteurella into a killer, and the team is planning to sequence the bacterium’s genome to find out more. But for now, Kock says the connection makes sense. In laboratory studies, rats that are exposed to Pasteurella are more likely to get infected if you crank the humidity up. The idea of humidity as an environmental trigger also explains how the die-off happened so broadly, suddenly, and totally. It’s something pervasive, which would hit all the saiga at once, and influence the bacteria that they all already harbor.
Climate change will have effects we can predict and others we cannot. In the case of the saigas the hope is that these animals are able to once again fight off extinction and return to more robust numbers.