The worm, Dracunculus insignis, can grow to almost a foot long and must emerge from its host to lay eggs that hatch into larvae. It forms a blister-like protrusion in an extremity, such as a leg, from which it slowly emerges over the course of days to deposit its young into the water, the vets said.
Often found in wildlife such as raccoons, it had never before been seen in cats, they said.
It does not infect humans.
"The cats that contracted the Dranunculus insignis worms likely ingested the parasites by drinking unfiltered water or by hunting frogs," Cornell veterinary researcher Araceli Lucio-Forster said.
There are no drugs to treat a D. insignis infection, the researchers said, so worms must be removed surgically.
"Although rare in cats, this worm may be common in wildlife and the only way to protect animals from it is to keep them from drinking unfiltered water and from hunting -- in other words, keep them indoors," Lucio-Forster said.