A shocking sudden death event has affected tens of thousands of endangered saiga antelopes in Kazakhstan earlier this month. According to the Tech Times, the rare antelopes have lost nearly 120,000 individuals since the event was reported to officials from Kazakhstan’s agriculture ministry.

So far, nearly 40 percent of the total saiga antelope population in Kazakhstan has perished. Animal conservationists and veterinarians have been scrambling to determine the cause of the die-offs, but so far they don’t have a solid idea of what exactly is responsible.

According to Richard Kock, the lead veterinarian at the Royal Veterinary College in Hatfield, England, “It’s very dramatic and traumatic, with 100 percent mortality. I know of no example in history with this level of mortality, killing all the animals and all the calves.”

Preliminary investigations have shown that the saiga antelopes all exhibited some respiratory problems, in addition to severe cases of diarrhea. The team of veterinarians from the RVC was able to offer three possible explanations for the unprecedented deaths.

The first suspect is an infection called pasteurellosis, which can transfer quickly between animals through direct contact, and usually results in death within 8 to 24 hours.

The second possible cause for the die-offs is a virus called epizootic hemmohagic disease, which affects white-tailed and mule deer typically. The virus is usually transferred by mosquito bites.

The third possibility is toxicity produced by the clostridia bacteria, which infect saiga antelopes through contaminated food.

The widespread death of saiga antelopes in Kazakhstan has troubled officials as well as local agricultural groups who rely on the herds. The population in central Asia has dropped from more than a million in the mid nineties to about 260,000 in 2014.