DENVER (KDVR) — Dog owners across Colorado are being warned by local veterinarians who are seeing an increase in a deadly respiratory disease sweeping across the state.

“We’ve had cases that require oxygen, some require surgery and there have been fatalities with this throughout the region, unfortunately,” said Dr. David Israel, medical director of the Veterinarian Emergency Group on Colfax Avenue.

Israel said that right now, his clinic and other emergency clinics around Colorado are seeing multiple cases of this infection daily.

“We are seeing one or two or three or even more of these cases coming up,” Israel told FOX31.

Over the past several months, Israel said the clinic has seen dogs with a respiratory disease similar to kennel cough, but this year, the regular treatments aren’t working.

“It’s progressing to pneumonia, which is infection in the lungs, and getting much sicker than we’ve seen in the past,” Israel said.

Sadly, Tina Castro said her dog, a 2-year-old doodle named Luna, died from this illness.

“She was very lethargic. It wasn’t my Luna,” Castro said.

Castro told FOX31 her cousin’s dog was sick back at the end of September and they had gone to daycare on the same day. She said she decided to take Luna out of daycare for a few weeks but took her back for one day. Four days after that, Luna started coughing.

“They did everything they could,” Castro said.

Luna was coughing badly, Castro said, and spitting white phlegm. She said she took Luna to the vet on Tuesday and by Wednesday had to make the decision to put her down.

She said Luna was a young and healthy dog with no issues.

“Me, my son and my dad were all with her when we put her down, lots of emotions,” Castro said. “She was my later-in-life baby.”

Colorado State University is working on research on this illness.

Israel is letting dog owners know symptoms include coughing, white foam when they cough, trouble breathing with their head and neck extended and lethargy.

“Any contact puts them at risk,” Israel said. “So if they are nose to nose with each other, they are at risk.”

The doctor and Castro say to avoid situations where dogs are around each other like dog parks, boarding/day camp centers and indoor situations with longer contact.

With holidays on the horizon, Israel said it’s best to look into pet sitter options so your dogs have less contact with others.

“I want to warn people: Make sure you know where you are walking. It just takes a sniff or a lick, because it’s that contagious,” he said.