The eel parasites are small worms that invade the eel's body during its growth process and multiply rapidly after entering the eel's body. There is no way to completely eradicate them, so you have to heat them thoroughly.
When cleaning eels, it is recommended to wear rubber gloves, which can prevent the parasites in the eel body from infecting the body through the breaks in the skin, so it is not recommended to kill eels directly with bare hands.