Terry Pareja, from the Philippines, was visiting relatives when he became ill a month ago, according to his daughter, Jeffmarey Pareja.
The family believes Mr Pareja's bug was caused by a spider bite, but doctors have said this link is not supported by evidence.
"It's eating him alive, literally," Ms Pareja told the BBC.
"He needs to stay in hospital for about 12 to 18 months."
She said Mr Pareja, 65, had been diagnosed with necrotising fasciitis.
What is necrotising fasciitis?
