A woman who believes her pet died of a new "mysterious dog illness" has warned owners to avoid doggie parks.

Trang Huyen, a beauty business owner, thinks her shih tzu Chowder died from an unknown condition that's spreading across the United States.

More than 200 cases have been documented and possible cases have been reported in Colorado, California, Indiana, Washington and Georgia.

Chowder fell ill in late October and his symptoms appeared minor until he began struggling to breathe and died days later.

Now Trang is warning other dog owners "to take safety precautions such as limiting time at dog parks and areas with other dogs."

The new mystery illness was described by the Oregon Department of Agriculture as an "atypical canine infectious respiratory disease."

Reported symptoms of the disease include a cough that can last for weeks, runny eyes and sneezing.

Another possible symptom is pneumonia which can lead to death in 36 hours.

According to Trang, who didn't wish to reveal her age, Chowder's initial symptoms matched the new disease.

The pup was lethargic. He also refused to eat and had a cough.

The pet's tongue also turned blue in the later stages of his illness.

Trang, from Pensacola, Florida, USA, said: "It started with a small dry cough and being more lethargic each and every day after that.

"It did not [seem serious]. Chowder would have seasonal allergies so I thought nothing of it.

"Things started to change when his breathing was much heavier and he did not want to eat or drink."

Trang believes that her case was too early for the vets to correctly diagnose but that the symptoms match the new illness.

Vets diagnosed him with pneumonia but disagreed on causes, one suggested allergies and another liquid aspiration.

Trang explained: "We went to the ER vet and visited multiple veterinarians. Not one veterinarian knew about the mystery dog illness at the time of my visit.

"I realized that many others were going through the same thing with their pet.

"They all had the same symptoms: cough and severe respiratory issues."

Trang spent roughly $4,000 on treatments. Chowder was x-rayed, put in an oxygen chamber and medicated.

Sadly, the treatment had no effect and Chowder passed away just days after his symptoms began showing.

Trang, who has had Chowder for more than ten years, said: "Chowder meant the world to me.

"He was a significant part of my family. He followed me everywhere.

"For the past decade, he was my constant companion, my source of comfort during the darkest times and the one who brought boundless joy into my life."

The cause of the disease remains unknown but researchers at the University of New Hampshire claim a previously unknown germ may be causing the illness.