A one-year-old male Siberian tiger at Winnipeg's Assiniboine Park Zoo died suddenly on Monday, according to zoo officials.

Reka, a tiger that was born at the zoo in July 2011, started appearing lethargic and ill on Sunday, said Dr. Chris Enright, the zoo's head veterinarian.

Zoo staff were about to examine Reka on Monday morning, but he stopped breathing shortly after being tranquilized for the exam.

The young tiger went into cardiac arrest and died at about 9:55 a.m. CT.

Enright said it is too early to say what killed Reka, as it may take 10 to 14 days for tests to determine how it died.

However, he said it appears the tiger may have had some kind of infectious disease.

"There were some indications of an infection being present — we don't know what type of infection at this point, but I'm certainly concerned for remaining tigers," he told CBC News.

Distemper a possible cause?

Enright added that he is investigating whether canine distemper from raccoons could be the cause.

"I'd really be looking more at sort of wild animals either in and out of the exhibit, or across the top of the exhibit," he said.

"That's the sort of thing where urine, saliva, or feces could contact from a wild animal to a zoo animal."

While tigers are susceptible to distemper, which has recently been found in raccoons around Winnipeg, Reka had been vaccinated, said Enright.

"It's extremely unusual. This is a young, healthy animal," he said.

"He's actually been vaccinated just like sort of a puppy or kitten, [with a] series of vaccinations.  He was vaccinated at eight, 12 and 16 weeks of age."

Enright said it is possible that the vaccine may not have worked, or perhaps an infected raccoon may have crawled over the tiger enclosure and defecated inside."

Siberian tigers are an endangered species, and Reka is one of the few remaining animals in captivity, Enright said.

Reka was born on July 29, 2011, and unveiled to the public on Oct. 3, 2011.

The Assiniboine Park Zoo has three other Siberian tigers: Baikal, Kendra and Sarma.

Enright said the remaining tigers are under quarantine, but they will remain on exhibit.