They found the first carcasses in late December, on the frozen steppes of Mongolia’s western Khovd province.
By the end of January, officials in the region had recorded the deaths of 2,500 endangered saiga antelopes — about a quarter of the country’s saiga population — and scientists had identified a culprit: a virus called peste des petits ruminants, or P.P.R.
, also known as goat plague.
It was the first time the disease, usually seen in goats, sheep and other small livestock, had been found in free-ranging antelopes. For the saiga, an ancient animal that once roamed the grasslands of the world with the woolly mammoth and the saber-toothed tiger, the outbreak was potentially catastrophic.
The antelope’s numbers, once in the millions, have been severely depleted by illegal hunting, habitat loss and competition for food. The species is described as critically endangered on the International Union for Conservation of Nature’s Red List.
They found the first carcasses in late December, on the frozen steppes of Mongolia’s western Khovd province.
By the end of January, officials in the region had recorded the deaths of 2,500 endangered saiga antelopes — about a quarter of the country’s saiga population — and scientists had identified a culprit: a virus called peste des petits ruminants, or P.P.R., also known as goat plague.
It was the first time the disease, usually seen in goats, sheep and other small livestock, had been found in free-ranging antelopes. For the saiga, an ancient animal that once roamed the grasslands of the world with the woolly mammoth and the saber-toothed tiger, the outbreak was potentially catastrophic.
The antelope’s numbers, once in the millions, have been severely depleted by illegal hunting, habitat loss and competition for food. The species is described as critically endangered on the International Union for Conservation of Nature’s Red List.
In 2015, 211,000 saigas in Kazakhstan — more than half of the entire antelope species — were wiped out by a bacterial infection in less than a month.
“It’s just one thing on top of another,” said Dr. Richard Kock, a professor of wildlife health and emerging diseases at the Royal Veterinary College in London who, with colleagues, concluded that climate change had contributed to the Kazakhstan die-off.
“Once you’re down to very low numbers, a species is vulnerable to extinction,” Dr. Kock said. “You have to wake up to the fact that these populations really are on the brink, and you can’t do anything about it if it’s gone.”
Dr. Kock, who has studied both saigas and P.P.R. in wildlife, recently returned from Mongolia, where he was part of a United Nations crisis team called in to investigate the mass deaths there. He and other scientists predicted that before the virus had run its course, thousands more saigas from the Mongolian population will die.
And the appearance of P.P.R. in the antelope, which probably contracted the virus from close contact with livestock that graze on the steppe, raised fears that it could spread to other threatened species, like Bactrian camels and Mongolian gazelles.
“Potentially, this could be an 80 percent mortality,” said Eleanor J. Milner-Gulland, a zoology professor at Oxford and chairwoman of the Saiga Conservation Alliance. “It could be completely disastrous.”
Dr. Milner-Gulland noted that the spring, when the antelopes gather together to calve, could be an especially risky time for the spread of the virus, and there is concern that it could spread to antelopes remaining in Kazakhstan.
The saigas are well adapted to the harsh conditions of the Mongolian steppe, their thick hair insulating them in the winter and their Bullwinkle noses warming frigid winter air before it reaches the lungs. The Mongolian saiga is a subspecies, smaller and stockier than its Kazakhstan counterparts, with horns of a different shape and a slightly more refined proboscis.
But both subspecies are valuable to wildlife traffickers, who poach the animals and market the horns for medicinal use in Asian countries.
Enkhtuvshin Shiilegdamba, an epidemiologist and the Wildlife Conservation Society’s country director in Mongolia, said that scientists believe the virus traveled to Mongolia from China, one of 76 countries around the world where P.P.R. is active. Livestock in Khovd province began to fall ill in September, Dr. Enkhtuvshin said.
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She added that the number of deaths so far was probably an underestimate, because the antelope are smallish animals and “this area is quite a large area and there is snow, so it makes it difficult to find them.
“It’s likely that we already lost about 50 percent of the saiga population,” she added. Even before the virus hit, a fiercely harsh winter in 2015 had reduced the population to approximately 10,000 saigas from about 15,000. P.P.R. is also suspected in the deaths of 22 black-tailed gazelles and at least one ibex.
Dr. Kock said that many of the dead antelope they examined were in poor physical condition, probably contributing to their susceptibility to disease.
The die-off, he said, came at the worst time of year, during the winter, when the animals’ resistance is lower. “That is extremely bad luck and that will be reflected in the mortalities,” he said.
About 11 million sheep and goats in Khovd and in a second province where saigas live were vaccinated against P.P.R. after the initial outbreak, but the vaccine was apparently not effective in preventing the virus from spreading to wildlife, suggesting that some animals were missed or that there were storage problems with the vaccines.
“I think there is commitment in the country and the political will to address the situation,” said Bouna Diop, who is directing a United Nations campaign to eradicate P.P.R. by 2030.
But, he added, “there are some gaps that need to be improved, to make sure when they are vaccinating they are using good vaccine, and the vaccination is done properly.”
If the saiga does survive, it may be its capacity for rapid reproduction that finally saves it. Two-thirds of pregnant female antelopes give birth to twins, and although the species plummeted to a low of 50,000 saiga in the 1990s, it rebounded with conservation efforts, reaching several hundred thousand by the time of the Kazakhstan die-off.
“It has gone down to low levels before and then gone back up again, so we’re always hopeful,” Dr. Milner-Gulland said.
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