"The victims are getting younger as girls, mainly those in rural areas, are more likely to focus on the positive stories of those who made it to Europe and didn't end up in prostitution,"
A promising student who dreamed of going to university, Mary was 16 when a woman approached her mother at their home and offered to take the Nigerian teenager to Italy to find work.
Pushed to go by her family who hoped she would lift them out of poverty, Mary ended up being trafficked into prostitution.
Her voice faltering, Mary described three years of being forced to sell her body, beatings, threats at gunpoint and being made to watch as a 14-year-old virgin was raped with a carrot before being sent on to the streets of Turin in northwest Italy.
After being arrested by Italian police, Mary was repatriated to Nigeria's southern Edo state in 2001, but she was rejected by her family and left feeling like a failure.
"I returned with nothing," Mary, now 35, told the Thomson Reuters Foundation from Benin city in Edo. "I hated myself."
While Mary's ordeal ended 15 years ago, a soaring number of Nigerian girls like her are being trafficked to Europe - mainly Italy - and forced to sell sex by gangs taking advantage of the chaos caused by the migrant crisis, anti-slavery activists say.
Thousands of women and girls are lured to Europe each year with the promise of work, then trapped by huge debts and bound to their traffickers by a religious ritual - the curse of juju.
"The victims are getting younger as girls, mainly those in rural areas, are more likely to focus on the positive stories of those who made it to Europe and didn't end up in prostitution," said Katharine Bryant of the Walk Free Foundation rights group.
She spoke ahead of the launch of the third Global Slavery Index, which found Nigeria has the world's eighth highest number of slaves - 875,500 - and is a key source country for women trafficked to Europe and sold into sex work.
BOUND BY JUJU
More than nine in 10 of the Nigerian women trafficked to Europe come from Edo, a predominantly Christian state with a population of about 3 million, according to the United Nations.
While Edo is not among the country's poorest states, its history of migration to Italy has fuelled locals' hopes of easy money in Europe - leaving people vulnerable to traffickers, the International Organization for Migration (IOM) says.
Before going to Europe, women and girls must sign a contract with traffickers to finance their move, racking up debts of up to $100,000. They then must seal the pact with a juju ritual.
"I was taken to a native doctor's shrine, and told to bite the neck of a chicken to add its blood to a concoction made with bits of my hair and fingernails, and my underwear," Mary said.
This belief in black magic means victims fear they or their family may fall ill or die if they do not pay off their debts.
Most of the women and girls know they will have to sell sex but are pressured by their families and deceived by traffickers, said Nigeria's anti-human trafficking agency (NAPTIP).
Many have no idea they will live under the control of older "madams" and be forced to work for several years to clear their debts, according to the U.N. Office on Drugs and Crime (UNODC).
Madams, who make up almost half of traffickers in Nigeria, are mostly former victims who target others in order to escape prostitution - perpetuating a cycle of exploitation, the UNODC said in its latest global report on human trafficking.
Traffickers and gangs in Nigeria are now exploiting Europe's migration crisis - moving girls to lawless Libya, before crossing the Mediterranean to Italy on flimsy, overloaded boats, said Bryant from the Walk Free Foundation.
More than 5,600 Nigerian women and girls arrived in Italy by sea last year, up from 1,200 in 2014, and at least four in five were trafficked into sex work, the IOM said.
At least 1,250 Nigerian women have landed in Italy this year, up from 373 for the same period in 2015, IOM data shows.
Traffickers also take victims to Europe by plane, using forged documents and flying via other West African countries to avoid suspicion, said Mikael Jensen of the UNODC.
British airports such as Gatwick are increasingly used as entry points by Nigerian trafficking gangs with forged documents, Spanish police said earlier this year.
"Many traffickers are careful with their goods, they don't want to risk them on a dangerous sea crossing," Jensen said.
About 3,770 migrants and refugees died in 2015 crossing the Mediterranean, making it the deadliest year on record for those fleeing conflict and poverty, according to the IOM.
Human trafficking by Nigerian organised crime gangs is one of the greatest challenges facing police forces across Europe, according to the EU's law enforcement agency Europol.
A lack of coordination between European states and Nigeria is allowing traffickers to act with impunity, said Kevin Hyland, who was appointed Britain's first anti-slavery chief in 2014.
"There has been some progress, but it's been a piecemeal plan, and responsive rather than proactive," Hyland said.
Nigerian anti-trafficking official Arinze Orakwe said more European nations should criminalise the purchase of sex to curb the number of Nigerians trafficked into prostitution in Europe.
"If nobody is buying, nobody will sell," said the official at NAPTIP, which has rescued some 1,340 victims in Nigeria over the past year, and works with NGOs to support them.
The Women Trafficking and Child Labour Eradication Foundation (WOTCLEF) clothes and feeds victims, provides counselling and attempts to reunite them with their families.
"But sometimes families are hostile, and not interested in getting them back," said WOTCLEF coordinator Veronica Umaru.
Disillusioned by her parents' disappointment at her return home, Mary hoped to go back to Italy before being resocferred to Girls' Power Initiative, a Nigerian NGO that housed her, trained her to run a business and encouraged her to help other victims.
Yet Mary says many former victims have been re-trafficked to Italy, and fears not enough is being done to stop traffickers or persuade women and girls not to go abroad and into prostitution.
"Girls today, unlike me, know exactly what they are in for when they agree to go to Italy to work," Mary says tearfully.
"But they do not understand the trauma they will face."