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article image'Climate envelope' responsible for mass deaths of Saiga antelopes

By Karen Graham     Jan 18, 2018 in Science
Over the span of three weeks in 2015, more than 200,000 saiga antelope suddenly died in central Kazakhstan from hemorrhagic septicemia caused by a normally harmless bacteria called Pasteurella multocida type B. Now, scientists know what happened.
In May 2015, the die-off of nearly 200,000 saiga antelopes in far-away Kazakhstan captivated the Internet, all the deaths occurring in a period of about three weeks.
The saiga antelope had been roaming Central Asia since the time of the woolly mammoth. It is a goat-sized, fawn-colored creature best characterized by its tubular nose. Even without the mass die-off, hunting and habitat loss have depleted its numbers so that the saiga is now a critically endangered species, according to the International Union for Conservation of Nature (IUCN).
The 2015 die-off of saiga antelopes
The mystery illness, which started on May 10, 2015, causes severe diarrhea and breathing difficulties and has a 100 percent mortality rate. At that time, a team of veterinarians and scientists, led by Richard Kock of the Royal Veterinary College in Hatfield, UK was called in to investigate.
Digital Journal followed the story from the beginning, including the followup in the investigation. Scientists did find the "garden-variety" bacteria, Pasteurella multocida type B. Interestingly, Pasteurella is normally found in ruminants, such as the saiga, and usually don't cause problems, unless the animal has a weakened immune system.
Scientists figured the only environmental cause for the mass die-off could be the unusually hard winter that past year, and the overly wet spring that resulted in an abundance of lush vegetation and standing water. They thought this could have helped to spread the bacteria more easily, however, they decided further research was needed.
Rapid environmental change at fault
Finding out that harmless P. multocida caused the die-off wasn't enough. Now, according to a new study published in Science Advances on January 17, 2018, researchers say they have found a deeper connection - The infection and subsequent die-off was strongly linked to warmer weather and higher humidity.
“The fact that P. multocida infection in saigas... appears strongly linked to high humidity and temperature is of concern going forward, given that a climate change-induced increase in temperature is projected for the region over the short to medium term, writes the international team of researchers in the study. This means that going forward, saiga antelopes are at extreme risk of extinction.
Dr. Koch, who witnessed the "rapidly accelerating deaths," talked with National Public Radio recently, He said the antelopes showed clear signs of a form of blood poisoning called hemorrhagic septicemia. The bacteria "very rapidly goes into the bloodstream," causing hemorrhaging. "It's so toxic and so devastating that the animal doesn't show a lot of pathology actually, other than the hemorrhage and rapid death," he added.
In the study, the scientists say they believe "virtually 100 percent of adults" already had the organism present in their bodies, and an environmental factor led to the bacteria proliferating, leading to the death of all the animals at the same. Kock says the culprit was a period of unusual heat and humidity in the ten days leading up to the mass death.
Using computer modeling, the team was able to correlate the most recent die-off with temperature and humidity anomalies observed in two previous similar events in the same region, one in 1981 and another in 1988, where the saigas are also believed to have died because of hemorrhagic septicemia. Environmental factors, such as temperature, rainfall, wind and the state of the vegetation were also included.
"You have unusually high levels of humidity each day over that 10 day period. And by doing that we could really tease it out and get a significant correlation," says Kock.
"That makes sense," he says, "because the bacteria in the tonsils, they're quite close to the environment of the air and they then basically, presumably, respond to that change in atmosphere. And that triggers them to start growing."
Of the 30,000 saiga antelopes that survived, they have proven to be resilient and their numbers are growing. However, it is really not clear if they could go through another environmental event like the one in 2015. "If we get a similar event, and all the animals are within a sort of weather envelope, it could be total extinction. It could happen in a week," says Kock.
The bottom line? With all the unusual weather patterns and extreme weather events we have been experiencing recently, other animal populations could be at risk, from reindeer and musk oxen to - well, you pick an animal. "We may be looking at a much more global effect," Kock adds.
More about saiga antelopes, May 2015, hemorrhagic septicemia, climate envelope, Climate change