60,000 dead saigas dot the landscape in central Kazakhstan, in May 2015. Over a four period, the entire herd — about 60,000 saigas — died off. Workers struggled to keep up with the mass dying, quickly burying the dead animals in heaps. Photo: Sergei Khomenko / FAO

By Tia Ghose
2 September 2015

(Live Science) – It started in late May.

When geoecologist Steffen Zuther and his colleagues arrived in central Kazakhstan to monitor the calving of one herd of saigas, a critically endangered, steppe-dwelling antelope, veterinarians in the area had already reported dead animals on the ground.

"But since there happened to be die-offs of limited extent during the last years, at first we were not really alarmed," Zuther, the international coordinator of the Altyn Dala Conservation Initiative, told Live Science.

But within four days, the entire herd — 60,000 saiga — had died. As veterinarians and conservationists tried to stem the die-off, they also got word of similar population crashes in other herds across Kazakhstan. By early June, the mass dying was over. [See Images of the Saiga Mass Die-Off]

Now, the researchers have found clues as to how more than half of the country's herd, counted at 257,000 as of 2014, died so rapidly. Bacteria clearly played a role in the saigas' demise. But exactly how these normally harmless microbes could take such a toll is still a mystery, Zuther said.

"The extent of this die-off, and the speed it had, by spreading throughout the whole calving herd and killing all the animals, this has not been observed for any other species," Zuther said. "It's really unheard of." […]

Mass burial of saigas in central Kazakhstan, in May 2015. Over a four period, the entire herd — about 60,000 saigas — died off. Workers struggled to keep up with the mass dying, quickly burying the dead animals in heaps. Photo: Sergei Khomenko / FAO

Tissue samples revealed that toxins, produced by Pasteurella and possibly Clostridia bacteria, caused extensive bleeding in most of the animals' organs. But Pasteurella is found normally in the bodies of ruminants like the saigas, and it usually doesn't cause harm unless the animals have weakened immune systems.

Genetic analysis so far has only deepened the mystery, as the bacteria found were the garden-variety, disease-causing type.

"There is nothing so special about it. The question is why it developed so rapidly and spread to all the animals," Zuther said.

A similar mass die-off of 400,000 saigas occurred in 1988, and veterinarians reported similar symptoms. But because that die-off occurred during Soviet times, researchers simply listed Pasteurellosis, the disease caused by Pasteurella, as the cause and performed no other investigation, Zuther added. [more]

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