Veterinarians say parvovirus is prevalent in Texas, and young animals are especially at risk.
The Zeffer family first saw their little pup, Sugar, on East Dallas Pet Rescue's website.
"My daughter fell in love with her, I fell in love with her, my husband. All of us just instantly knew that was the puppy for us," said Brittney Zeffer.
The latest news from around North Texas.
The rescue group said the dog had a clean bill of health, but Sugar wasn't home long before the Zeffers noticed something wasn't quite right.
"Sugar was very lethargic, and as soon as she got home there was some diarrhea," Zeffer said.
She reached out to the rescue, and both sides agreed Sugar needed to see a vet.
Zeffer took the puppy to a vet whom the rescue routinely uses.
Sugar was diagnosed with having a parasite, and the vet prescribed antibiotics and sent her home, but Zeffer still had a feeling it was more than a simple parasite.
A second vet confirmed her fears.
Sugar had parvo, even though she already received two rounds of vaccinations for parvo through East Dallas Pet Rescue.
It took seven days of treatment and more than $5,400 in vet bills to get the puppy healthy again.
East Dallas Pet Rescue says it has refunded the adoption fee to the Zeffer family, started a GoFundMe campaign and will also hold a happy hour fundraiser all to help with the Zeffers vet bills.
The rescue group reiterated to NBC 5 Responds it had no knowledge the puppy would become ill.
When picking a new pet, how do you know you're adopting one that's truly healthy and not one in need of thousands of dollars worth of care?
Dr. Cynthia Rachal, with the Animal Health Care Center in Arlington, says when animals are young they can pick up illnesses anywhere as their immune system is still developing.
She said it's important to know as much as you can about where an animal came from even before it arrived at a shelter.
"I have 10 rescues that I work with. The ones I work with, I work with for a reason. I know they take excellent care of their animals," Rachal said.
She said Sugar could have easily gotten parvo from just about anywhere, because it's very prevalent in North Texas and contagious.
She added when puppies are young it's almost impossible to prevent it until fully vaccinated.