The society first issued a warning about the pet shop chain and distemper last week.
Dakota, a four-month-old dachshund, is fighting for her life. Her owner doesn't know if he'll be forced to put her down. "It's unfathomable. I can't think about that," said Bryan Phillips, owner.
The dog has distemper, a rare, often-fatal, and highly-contagious dog illness, marked by vomiting, diarrhea, and infection. Those symptoms came to light shortly after Phillips bought Dakota last month at the Happiness is Pets store in Naperville.
Phillips says he took Dakota to a veterinarian recommended by the store who said nothing about distemper. When he became suspicious about the medicine prescribed, Phillips says he went to another vet who quickly diagnosed the illness.
"Even if she does survive this illness right now, her long term prognosis, she could still have neurological issues, gastrointestinal issues," he said.
Dakota is one of three dogs purchased from three different Happiness is Pets locations that, according to the Humane Society, have recently contracted distemper.
Earlier this month, James Hollensteiner and Natalie Sallee adopted four-month-old Lucy from a family who purchased her from the Arlington Heights store. Soon, the yellow lab began shaking uncontrollably. The illness had spread to her brain and spine.
The couple ended Lucy's suffering Tuesday.
"She was ours, and she was our little Lucy, and we just told her how much we loved her," said Sallee. "She was our little baby."
"We're adults, and we're going through this. I can't imagine what a little kid would have to go through, you know?" said Hollensteiner.
Bryan Phillips is trying to remain hopeful. The store has refunded him $800 but he's still saddled with vet bills, heartache and unanswered questions.
"Since all these dogs are all puppies, they're all about the same age, you'd have to think they were all together at one point in time," said Phillips.
The owner of the pet store chain did not return ABC7's calls for comment.