(NewsNation) — The Colorado Department of Public Health and Environment is urging people who attended an adoption event in one Colorado city last month to contact health officials due to possible exposure to rabies.

Officials said a rabies-positive puppy arrived from Texas and has since been euthanized, as this is the only way to test for rabies in an animal.

The puppy was one of 11 littermates who were part of an adoption event at Moms and Mutts Colorado Rescue for Pregnant and Nursing Dogs in Englewood on July 20.

“Anyone who attended the event and interacted with the July Shepherd Mix litter (may also be referred to as ‘The Celebrity Kids’ litter) of puppies should contact public health officials to determine if they need to receive prophylaxis,” officials said.

Attendees can also call the health department at 303-692-2700 or email cdphe_zoonoses@state.co.us.

Officials said animals who’ve already been vaccinated for rabies and may have encountered the puppy litter may need a booster shot.

In a letter to adoptees, Moms and Mutts Colorado Rescue for Pregnant and Nursing Dogs wrote the puppy from the Celebrity Kids litter didn’t show symptoms until July 29; it presented as rabies on Aug. 1. Additionally, they wrote the last time the infected puppy was with its littermates was at the adoption event.

“Rabies is extremely rare and this is the first time we have encountered such a horrible situation. You do not have cause for concern for your adopted puppy or any of the available puppies,” the organization wrote.

Rabies is a viral disease that is deadly if not treated before symptoms start, according to the CDC. It’s spread to people and animals primarily through bites or scratches from an infected animal.