SLINGER - A strange virus is affecting cats in Wisconsin, killing some and forcing at least one shelter to make big changes.

The Washington County Humane Society reportedly saw the first case of this feline virus. Maribeth Marshall said some of the symptoms they've seen in their cats include oral ulcers, nose ulcers and upper respiratory infections.

"Sometimes you'll see them drooling from the mouth, not eating," she said.

It's a mutant strain of a traditional virus in cats, called the calicivirus. The shelter has more than 20 cats affected. Most of them have died.

"It's very hard to have to see the symptoms and the signs, to see what the cats are going through. It breaks our heart," Marshall said.

The healthy cats at the shelter won't find new homes soon either. For now, all adoptions are on hold to prevent the spread of this potentially deadly virus.

It jumps from cat to cat, but humans can also be carriers. You can pick up the virus by touching a door handle, it can be on your clothes, hands or shoes. If you touch a cat, it is then at risk.

Veterinarians are worried about this virus becoming an epidemic as most cats are not vaccinated against the mutant strain of calicivirus.

"We're just seeing the early stages of this, and we don't know what the ramifications are going to be at this point," said Dr. Dale Schneider.

There is a new vaccine that protects cats from this form of the virus. Schneider recommends cats get that vaccine.

The virus has been detected in some cats outside the Washington County Humane Society.

The virus does not affect humans.