Police have closed down a circus in southern Italy after a terrified 19-year-old woman was forced to swim in a tank full of piranha fish while her younger sister endured the company of snakes and tarantulas.

Three men have been arrested and charged with holding the Bulgarian women in slavery and breaching international human rights conventions.

The trio, who are accused of running a "circus of horrors," were named as Enrico Raffaele Ingrassia, 57, the owner, his son William Ingrassia, 33, and his son-in-law Gaetano Belfiore, 25.

The Marino Circus has been offering shows at Petina, south of Naples in southern Italy, in a tent with 200 plastic seats inside it.

Ingrassia's daughter, who was not named, told police that a Bulgarian couple and their two daughters, aged 19 and 16, had been held as slaves "in a state of fear" since January.

They were forced to work 15 to 20 hours a day for about $200 a week instead of the promised $957, with $757 deducted as "expenses for their upkeep."

An appalled spectator tipped off the police after seeing the show, in which Giusi, the 19-year-old woman, tried to escape from the piranha tank "trembling with terror" her head was held down by Ingrassia.

Her 16-year-old sister, Olga, was bitten by snakes that she was forced to drape on her body, and she had injuries to her stomach where the snakes had wound themselves too tightly around her. The circus owners had rubbed ointment on snake bites on her legs but had refused to take her to a doctor.

Police said the Bulgarian family had lived in the back of a cockroach-infested lorry used for animal transport. The only meat they had been given since January consisted of leftovers from the circus owners' Easter lunch last weekend.

Reports said Giusi had a tumour on her ear for which she had twice been operated in Bulgaria. Doctors had told her never to get water in her ears, especially cold water. However the water tank in which she was forced to swim with eight piranhas was kept at a temperature just above zero in order to make the piranhas lethargic.

The Bulgarian family has now been taken to "safe premises." Police said the raid on the circus followed an undercover operation in which plain clothes officers took their families with them as cover and filmed the show as evidence. They said the arrested men appeared surprised but made no attempt to justify their behavior.

Corriere della Sera said the incident appeared to be "something out of the 19th century" but showed that slavery was still "very much a reality" in modern Italy. La Stampa said the treatment of the Bulgarians was "unfortunately not an isolated incident" of illegal immigrant labor, with many East European women brought to Italy as street prostitutes.

Police said they were investigating "trafficking in humans" by organized crime to supply circuses with cheap labor. The Bulgarian women's mother worked as a cook at the site while their father moved tents and equipment and cleaned the camper vans and lorries. The mother had once tried to run away but had been captured and beaten, police said.

Livio Togni, a former left wing senator whose family ran Italy's best known circus for generations, said "I've never in my life heard anything like this. There is a strong sense of solidarity in the circus world, and violence is not part of it."