The deaths of 19 of the St-Félicien Zoo's 21 caribou in a two-week span have got zoo biologists scratching their heads.

"We found one animal dead and another one the next day, and two others the next day... it was too much. We knew something was going on," said biologist Christine Gagnon.

Now just two caribou remain after nearly the entire herd died in July.

"It's still a mystery for us," Gagnon said. "We are still waiting for the final report."

Initial tests seem to point to a blood parasite, but Canadian and American labs are working to definitively identify the cause of the deaths.

Caribou have lived at the zoo and animal conservatory for more than 50 years.

This is the first time so many caribou have died all at once, Gagnon said.

"It's the first time that we hear of this quick, fast and devastating death of our animals. It happened over a short period of time," she said.

"It's really, really hard on the animal keepers who work with these animals. They are great animals, we have had the herd for a long time," Gagnon continued.

Gagnon said the remaining two caribou are doing well, and that the zoo plans to rebuild its herd over the next couple of years.

St-Félicien is located in Quebec's Saguenay-Lac-St-Jean region, north of Quebec City.