An endearing antelope with a bulbous nose

Saturday, January 27th, 2018

The saiga is “an endearing antelope” that roams Central Asia. Its “bulbous nose gives it the comedic air of a Dr. Seuss character,” Ed Yong says:

It typically wanders over large tracts of Central Asian grassland, but every spring, tens of thousands of them gather in the same place to give birth. These calving aggregations should be joyous events, but the gathering in May 2015 became something far more sinister when 200,000 saiga just dropped dead. They did so without warning, over a matter of days, in gathering sites spread across 65,000 square miles — an area the size of Florida. Whatever killed them was thorough and merciless: Across a vast area, every last saiga perished.

Saiga calf

At first, the team suspected that a new infectious disease had spread through the population, but the pattern of deaths just didn’t fit. The saiga were dying too synchronously and too quickly. Also, all of them had died. “In biology, there’s certain rules, you know?” says Kock. “We accept that sometimes microbes can cause us harm, but not like this. Even very severe viral diseases or anthrax don’t do this. A good proportion of the animals would be fine.”

News of the die-off sparked outlandish explanations about Russian rocket fuel, radiation, and even aliens. But while conspiracy theories raged, a huge international team of scientists, led by Kock, got to work. Vets autopsied as many saigas as they could. Ecologists sampled the soil. Botanists checked the local plants. They couldn’t find any signs of toxins that might have killed the saiga. Instead, the actual culprit turned out to be a bacterium, one that’s usually harmless.

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?

The team considered a list of possible explanations that runs to 13 pages. They wondered if some environmental chemical or dietary change had set the microbe off. They checked if biting insects had transmitted a new infection that interacted with Pasteurella. They considered that Pasteurella might have gone rogue because of an accompanying viral infection, in the same way that Streptococcus bacteria can bloom during a cold, leading to strep throat. “We tested for everything and we couldn’t find anything,” says Eleanor Milner-Gulland from the University of Oxford.

Only one factor fit the bill: climate. The places where the saigas died in May 2015 were extremely warm and humid. In fact, humidity levels were the highest ever seen the region since records began in 1948. The same pattern held for two earlier, and much smaller, die-offs from 1981 and 1988. When the temperature gets really hot, and the air gets really wet, saiga die. Climate is the trigger, Pasteurella is the bullet.

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.


  1. Talnik says:

    The world becomes a much simpler place when everything is due to climate change or race.

  2. Kirk says:

    Talnik, it does, indeed. And, what strikes me as “interesting” is how few of the genius journalists bother to ask the obvious second- and third-order questions in these events, like, What the hell did the Saiga do during the end of the last Ice Age, if they are truly this susceptible to warming conditions? How did they ever survive that?

    Similarly, you see all the articles about the horrid fact that the glaciers are retreating, uncovering massive quantities of artifacts and things like mining sites up in the mountains. This is decried as an awful sign of AGW, and yet none of the great thinkers of the journalism world ask the very obvious question of “Just how the hell did these things get up there, in the first place.? If the mines were originally dug when it was accessible, and now it is again, what does that say about the previous implied period of warming?”

    They don’t ask these questions, because most of these people are dumb as rocks and easily led by any charlatan who can convince them that they are an anointed “expert” on an issue.

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