Every night as dusk falls in Piazza Gastone in the Noce district of Palermo, a tall, imposing Ghanaian woman dressed in traditional west African robes stands before a small congregation sweating in rows of plastic chairs before her.

The Pentecostal Church of Odasani has been converted from an old garage in a backstreet into a place of worship, albeit one unrecognised by any formal faith group. But what many of the congregation – largely young Nigerian women – have come for tonight is more than prayer; it is freedom.

“Nigerian women come to me for help, they have bad spirits that have been put inside their bodies by people who want to make money from them,” says the self-proclaimed prophetess, as she prepares to start her service.

She gestures to her devotees, who sit nervously fiddling with their phones as they wait for her to begin. “The spirit is forcing them to remain in a life of prostitution. When they come to Europe and realise they can’t live this life, they come to me and I help free them of this juju forever.”

She says she has spent the past 10 years battling the juju curses that are potentially keeping tens of thousands of Nigerian women under the control of human traffickers across Europe.

The abuse of religious and cultural belief systems in Nigeria has proved a deadly and effective control mechanism for traffickers involved in the recruitment of women destined for the sex trade in Europe. A hugely profitable and well-organised criminal industry has been operating between Italy and Nigeria for more than two decades but the UN’s International Organisation for Migration says it has seen an almost 600% rise in the number of potential sex trafficking victims arriving in Italy by sea over the past three years.

In 2016 its staff registered more than 11,000 Nigerian women at landing points in Sicily, with more than 80% of them victims of trafficking and destined for a life of forced prostitution on street corners and in brothels across Italy and Europe. Before they left Nigeria, many of them will have been made to undergo traditional oath-taking ceremonies involving complicated and frightening rituals often using the women’s blood, hair and clothing. These rituals – which have become known as the “juju” – bond the woman to her trafficker and to any debts she will incur. The rituals make it clear that failure to pay off those debts will result in terrible things happening to the woman and her family.

“This juju might seem like something small or meaningless to people here in Europe, but to the women these curses are real and they are terrifying,” says Princess Inyang Okokon, who runs Piam Onlus, an anti-trafficking NGO and who was herself taken from Nigeria to Italy in 1998. “Using these very old belief systems passed down through generations is a psychological form of control that is much stronger than any violence that can be done to them.”

Psychologists in hospitals across Sicily say they are witnessing a growing mental health crisis in these women among Nigerians who have been persuaded to leave their traffickers by the authorities or NGOs. At the Vittorio Emanuele hospital in Catania, 20 Nigerian women are being treated by the psychiatric department – double the number last year. “These women, who are brought to us by our emergency staff, have been abused, they have been raped, imprisoned and blackmailed. Some of them are as young as 12,” says Dr Aldo Virgilio.

He says that 80% of those coming to the outpatient clinic are asylum seekers. “Already this year we have seen 80 cases of women being brought to us, but many refuse food and treatment, they are afraid something is coming to hurt them. We cannot convince them that this is not the case.

“We can treat their symptoms with drugs but this doesn’t resolve the deep-set psychological fractures that have occurred. So aside from the drugs there is little we can do for them.”

At the Paolo Giaccone hospital in Palermo, Dr Filippo Casadei and Dr Maria Chiara Monti are trying to help five Nigerian women referred by migrant reception centres and shelters.

They say that while they understand the women’s psychotic episodes, hallucinations, panic attacks, insomnia and fits to be the physical signs of post-traumatic stress disorders, the women themselves see them as proof that the juju is coming to punish them for leaving their traffickers and breaking their oaths.

“On top of the terrible abuse they have faced while being trafficked, the juju is a constant source of strain on these women, they feel under constant threat and this creates a kind of psychological dependency and addiction,” says Monti. “So when they leave their traffickers, the pressure of the years of carrying this curse on their shoulders can break them.” Casadei says that they recently had a young patient who had been trafficked from her home town in Edo state and had been referred to the hospital after escaping her traffickers.

Sister Mary Anne Nwiboko has helped more than 300 women who have come to her convent in Syracuse. Photograph: Francesco Bellina / Cesura

“She had been doing so well. We were so proud of her. She’d escaped her captors, had been living independently,” Casadei says. “But then one day she received a package in the post from her home town. She couldn’t tell us what was inside but we knew it was related to the juju curse that she’d been made to undergo before her journey to Europe. She had a severe psychotic episode, a very violent reaction to whatever was in that package and we never saw her again.”

Casadei and Monti admit they are at a loss to know how to help the women. “It is pointless trying to say that these curses are not real, these women need to believe in a treatment or solution and there is an impenetrable wall between our two belief systems,” says Casadei. “Our approach of western psychology is virtually useless in these cases.”

Prosecutors say that the juju’s hold over the women is hindering their fight against the traffickers. “Because of the juju, Nigerian women become the perfect victims of sexual slavery,” says Salvatore Vella, a prosecutor in Agrigento. “Gangs know they can trust them, they know women are not going to report them to the police because they are afraid of the consequences for breaking the juju. And this makes our investigation harder. It is almost impossible to find witnesses among Nigerian prostitutes because of the ritual. Maybe one in 20 is ready to speak out. The rest of them are stuck in a wall of silence and fear.’’

There is also evidence of Nigerian criminal gangs in Sicily being in touch with the traditional priests who conduct the rituals. “They are providing the traffickers in Italy with all the information they need to terrify and control their victims. When the women arrive the traffickers know their names, real ages, names of their relatives, and above all the name of the “priest” who conducted the juju ceremonies. You don’t need to use violence if you have this sort of control.”

Some local African leaders on the island are trying to form a bridge between the authorities and victims to try to break the psychological chains.

Sister Mary Anne Nwiboko, a Catholic nun working in a convent in Carlentini in Syracuse, says she has helped more than 300 Nigerian women escape their traffickers since 1998. A trained counsellor and psychotherapist, she works with the police to help identify and approach potential victims. “I have always battled the juju,” she says. “I do not believe in these ceremonies but I understand the power that they hold over these women.”

In recent months, she says the number of women independently seeking her out to help them escape the juju curses has risen sharply. She says she invites them into her convent and uses prayer and song to try to get them to trust her.

“These women are very far away from their home. I know their language, their world, it helps me explain that they don’t need to be afraid. Behind every one of these ceremonies is money and I try to show this to the women. That this is not magic, it is just a way to keep them under their control.”

The influence of a handful of west African self-styled Pentecostal priests and traditional healers who are claiming to exorcise juju spells is also on the rise.

Small informal churches, like the one in Noce, have sprung up in disused buildings and private homes.

This is concerning charities such as Médecins sans Frontières who believe they are often working in tandem with traffickers to keep the women under their control. “Sometimes these preachers are the very same people who are reminding the women that they must not fail to pay their debt,” says Lilian Pizzi, a psychotherapist with MSF.

The Odasani “priestess” vigorously denies that she is doing anything but using “her power” to save the lives of the women who come to her door.

This evening, after she has started her service, she invites a young woman asking to be freed of her traffickers to stand in the middle of a circle. The congregation starts to chant and pray, their voices getting louder and faster as the ceremony progresses. The priestess blesses water and oil before conducting a traditional ritual of purification, dousing the woman and commanding the bad spirits to leave her forever.

“I ask the spirit, what is your name? And the spirit answers. And I say, in the name of the Lord depart from my daughter,” she says, raising her arms to the sky. “For many when they leave here the juju has departed their bodies. If they believe this then they are healed and they are free. But if they don’t believe then it is no good. If they don’t believe then there is nothing I can do to help them.”