Officials say the firefighter was bitten Thursday while trying to stop the dog, a cane corso mix, from biting a 3-year-old girl, The Palm Beach Post reported. Fire-rescue crews had responded after a 13-year-old girl was bitten.
The dog may also have attacked an older woman, its owner's granddaughter.
Officials say the dog did not have a license and was not current on its rabies vaccination. Brain samples were taken to determine if the animal was infected with rabies.
The cane corso is an Italian breed used as a guard and hunting dog.