Mystery disease kills saigas

Before the end of the last Ice Age, saigas roamed by the millions in a range stretching from England to Siberia, even into Alaska. Eventually, they moved to the steppes of Central Asia, where they continued to thrive – until the 20th century, when these strange-looking antelopes began flirting with extinction.

Hunted for its horns, 95 per cent of the population disappeared, and the saiga was declared critically endangered. After the implementation of strict anti-poaching measures, the population recovered, from a low of 50,000 to about 250,000 last year. “It was a big success story,” said Eleanor J Milner-Gulland, the chairwoman of the Saiga Conservation Alliance.

Now, that success is in jeopardy. Last month, a mysterious disease swept through the remaining saiga herds, littering the steppes with carcasses. The so-called die-off claimed more than a third of the world’s population in just weeks. “I’m flustered looking for words here,” said Joel Berger, a senior scientist at the Wildlife Conservation Society. “To lose 120,000 animals in two or three weeks is a phenomenal thing.”

An international team of wildlife biologists is now examining tissues taken from dead saigas, hoping to figure out what killed them. Whatever it is, it has the potential to undo years of conservation efforts, further endangering the species. “Once we know what’s causing it, then we need to think very hard about how to avoid it in the future,” said Aline Kuehl-Stenzel, the terrestrial species coordinator of the Convention on the Conservation of Migratory Species of Wild Animals.

Saigas are remarkable creatures. In the spring, they migrate across the steppes by the thousands, the females pausing just long enough to give birth, usually to twin calves. Saigas can travel more than 50 miles a day on their migrations, and can run more than 40 mph.

Naturalists are quick to note their improbable, cartoonish faces, anchored by enormous noses somewhat resembling elephant trunks. “It’s a remarkable structure, really,” said Aline, who has studied saigas since 2003. “In the rutting season, the male’s nose swells even more, and then they shake their heads and it makes a squishy sound.” Females may be attracted to the fleshy noses of males. But scientists also suspect these noses also protect saigas from dust rising up from the dry ground.

From time to time, saigas have faced widespread die-offs. The last major one occurred in 2010, when 12,000 animals died. The causes are still uncertain, because biologists did not reach the animals until long after they expired. “There’s no data at all, and so people go on speculating,” said Richard A Kock, an expert on wildlife disease at the Royal Veterinary College in London.

On May 13, Aline started receiving reports from government officials in Kazakhstan, one of five countries in which the antelope remain, that another die-off was beginning. Hundreds of carcasses were discovered, many of them dead mothers with their offspring. As the days passed, the losses mounted. The die-off is now 10 times bigger than the 2010 event. And because the saiga population was at a precariously low level, the die-off has claimed an astronomical proportion of the species, from one-third to perhaps a half.

As soon as the reports of the die-offs began emerging, Richard and other wildlife disease experts swung into action, travelling to Kazakhstan to study the outbreak as it unfolded. They examined dead animals, performing necropsies on 15 of them. Richard was astonished by the deadliness of the disease, whatever it is: Once it struck a herd, every animal died, in a matter of days. He and his colleagues found that the saigas were infected with two species of deadly bacteria, Pasteurella and Clostridium. But Richard says he suspects that these infections became deadly only when something else crippled the animals.

There are two reasons for this suspicion. One is the speed with which the animals died: so fast that they would not have enough time to spread a virulent strain of Pasteurella or Clostridium to other animals. And Pasteurella and Clostridium are common in healthy animals. Only when the animal becomes weakened do these microbes turn deadly.

So what is killing the saigas? One possibility is that an unknown virus has swept through the herds. Richard said it will take three or four weeks to isolate any agent in the necropsy tissues. Changes in the environment also may have contributed. This year’s heavy rainfalls may have led to a lush growth of plant species that make saigas dangerously bloated, for example.

Central Asia has also had heavy chemical pollution over the decades from factories and farms. There had been speculation that the saigas were poisoned by fuel from Kazakhstan’s rocket programme, but Aline said she doubted the hypothesis. Determining whether the environment contributed to the die-off may take years. “We have some simple stories, but it’s probably more complicated,” Richard said. “We have to do the science and let the evidence speak.”

Joel said that it was urgent to figure out what killed the saigas to ensure long-term survival of the species: “We’re not going to get ahead of the curve if we don’t understand what’s doing this.”