A mysterious illness is sickening dogs: Hundreds of dogs across at least five U.S. states - Colorado, Rhode Island, Oregon, New Hampshire and Massachusetts - thought to have contracted a mysterious respiratory illness that experts are scrambling to understand. Some are dying.

More mystery diseases. This time of the respiratory nature.

Marie Heckemeyer had every reason to believe her dog was recovering. Six-year-old Thunder, the beloved Siberian husky she raised from a puppy, was back to digging holes, jumping around the house, playing and seeking back scratches.

Thunder had fallen ill after attending a boarding camp while Heckemeyer and her husband were on a trip to Italy for their 20th wedding anniversary. After about two weeks of treatment – and a veterinary bill topping $16,900 – his cough seemed to have retreated.

But within an hour of playing, Thunder was back in the emergency room with respiratory distress. And soon after that, Heckemeyer and her husband, both residents of Colorado, received a call from the vet to come in and say their goodbyes.

“He was so young,” Heckemeyer said through sobs. “. . . For this to just come on so quickly – it’s just so hard.”

Thunder, who died on Nov. 6, is one of hundreds of dogs across at least five U.S. states – Colorado, Rhode Island, Oregon, New Hampshire and Massachusetts – thought to have contracted a mysterious respiratory illness that experts are scrambling to understand.

h/t Orangutan