Often they are forced to undergo a Juju oath-swearing ritual that commits them to repaying the money on pain of death or insanity.
When they arrive in Europe, they discover the only way they can do this is by agreeing to work in the sex trade.
They work with "brothers", men who are in charge of physically trafficking the "babies", as girls forced into prostitution are called.
In the following account Chiara Caprio, an Italian journalist who was involved in the making of the film, describes what they found out in southern Italy.
The ghetto of Destra Volturno, an assembly of houses once used by Neapolitan tourists, is surrounded by flowers as it hosts the funeral of Mary Morad, a seven-year-old from Ghana. But in Castel Volturno, more than one-third of the 25,000 official citizens are African and, in particular, Ghanaian and Nigerian.
But it's an easy game for them in Italy also for another reason: the high number of Italian clients who look for prostitutes night and day," says Giovanni Conzo, a prosecutor at the anti-mafia section in Naples. We should stop them before they take full control of our region," he adds. Using voodoo to enslave Isoke Aikpitanyi, a former victim of trafficking and now the main reference point for Nigerian women in Italy, knows how this business is managed in Caserta's area.
As she walks in Castel Volturno's historic centre, she explains: "Today in Italy there are almost 10,000 madams, each one in control of an average of two or three girls." Madams are the key, she explains. They force girls into prostitution and ask for money to repay the debt.
A Juju priest who is involved in the trade justifies the use of ritual practices on the grounds that he is offering a service to the community.