NASSAU COUNTY, Fla. -- Dozens of cats at the Nassau County Animal Shelter were quarantined Thursday night because animal experts suspect the animals may have a contagious parasite that can affect people.

Fifty of the shelter's 90 cats are under quarantine.

Officials with the shelter are worried the felines may have been infected with a parasite called cryptosporidium, which causes vomiting, diarrhea, dehydration and can be deadly.

One cat in the shelter has already tested positive for the parasite. The 50 quarantined animals have been tested, but their results have not come back.

Until animal officials know for sure whether they're healthy, they said the cats must be kept separate.

"It's very contagious among kitty cats and other animals," said Dr. Richard Williams, of the Hidden Hills Animal Hospital in Jacksonville.

He said scientists are still studying the parasite, hoping to learn more about it. What they do know he said is that it can affect animals and humans.

"The cat form is thought to truly only infect cats at this point, but they're not sure because they get a lot of conflicting information from different testing facilities and stuff like that," Williams said.

Workers at the Nassau County shelter said they have contacted everyone who recently adopted a cat or kitten from their facility to let them know about the issue.

"It's very, very difficult to treat. There is no known actual cure. You can't just put them on a pill and cure them," Williams said.

The quarantined cats are expected to remain separate for at least 20 days.

For more information about cryptosporidium visit www.CDC.gov/Crypto/.