As if four-time Iditarod Trail Sled Dog Race champ and cancer survivor Lance Mackey hasn't faced enough hardship already this year, another disaster struck on Thursday night.

Iditarod officials reported a three-year-old dog in Mackey's team died of unknown causes while the musher and team were making the 120-mile run from Tanana to Ruby along the Yukon River. The Iditarod said a necropsy was planned to try to determine what caused the death of the dog, Wyatt.

He is the first dog to die while racing in the Iditarod since 2009. One dog did die in 2013 after it was left at a checkpoint to recover. That dog was buried by snow in a storm and suffocated. The Iditarod has since provided shelter for dropped dogs.

A dog also died at this year's ceremonial start when it was struck by a car in Anchorage after getting loose from the team of musher Lachlan Clarke, which was resting at Campbell Tract at the end of the event. Clarke continued in the race.

On Friday, officials with the organization People for the Ethical Treatment of Animals (PETA) condemned the race.

"Three-year-old Wyatt, who died yesterday as a result of 'unknown causes' likely related to the Iditarod is the latest casualty in a long line of dogs . . . who have died during the race," wrote PETA Senior Vice President Daphna Nachminovitch. "This year, other dogs who narrowly escaped disaster include ones used by Yuka Honda, who crashed into a sled, only to be run over by another, and Laura, a 5-year-old dog who is reportedly "blind" and "often seems confused" but who is forced to race anyway by Kelly Maixner. PETA is again calling for this dangerous, cruel race to be canceled permanently to save dogs from a lifetime of isolation, cruelty, and suffering — and before more dogs suffer catastrophic breakdowns on the trail."

Mackey is one of the most popular mushers in the race. He became famous after being diagnosed with cancer and then winning the 1,000-mile Yukon Quest International Sled Dog Race and the 1,000-mile Iditarod back to back. Before he did that, the feat was thought to be impossible.

Mackey went on to win each race three more times, but he is struggling with his health again. He has said this will probably be his last Iditarod because his hands have become so susceptible to cold he can barely use them when the cold gets extreme.

According to the Iditarod website, Mackey arrived in Ruby at 6:16 p.m. Thursday with all 16 dogs after spending 18 hours and four minutes between the checkpoints, which are 119 miles apart.

Mackey was still in Ruby as of 10:45 p.m. on Thursday evening.