(SOUNDBITE) (English) CLAUDIA, SEXUAL EXPLOITATION VICTIM, SAYING: "I feel like I paid the ultimate price for my family." Claudia dropped out of college in 2012 when her family was hit with hard times.
So, like millions across Africa, she left Nigeria to find work in much bigger countries.
She says she ended up in Russia, but instead of finding work she was forced into prostitution -- 20 men a day -- another victim of the modern slave trade.
(SOUNDBITE) (English) CLAUDIA, SEXUAL EXPLOITATION VICTIM, SAYING: "I thank God I made it back alive." The world marks 400 years this month since the first African slave landed in the Americas, but hidden away from public view it's never stopped.
It affects young and old, often lured away with job promises, instead held captive.
Estimates 40 million people are trapped in it across the world.
Blessing was only six when she became a housemaid in Nigeria.
She wasn't paid, but her family was promised she'd receive an education instead.
That didn't happen either.
Worked round the clock.
Forced to eat rotten food.
(SOUNDBITE) (English) FORMER CHILD SLAVE VICTIM, BLESSING, SAYING: ''She (my captor) would tell me that my mother is coming that I should not tell her what is happening to me, that I am not even going to say anything, that she will not allow me to say anything.
She will only allow me to greet (my mother) and tell her all these things, that if she asks me how am I doing I should say that I am doing fine, if not if she goes what she will do to me: I will regret why my own mother brought me to the house." Claudia and Blessing aren't their real names.
They want to stay anonymous, fearing for their safety.
And they're the lucky ones.
Both were saved by immigration and anti-trafficking groups.
Margaret Ukaegbu is with Nigeria's National Commission for Refugees: (SOUNDBITE) (English) MARGARET UKAEGBU, NIGERIA'S NATIONAL COMMISSION FOR REFUGEES, SAYING: "There are some states in the country that the parents see it as a pride that the child has gone abroad (...) The Middle East is becoming another hotbed because a lot of Nigerians are being deceived by agents who tell them they will take them to the Middle East for employment.
Employment such as being a nanny, a cook, hair dresser, and whatever, these menial jobs (...) They actually have legitimate visas but when they get there it becomes another story." Human traffickers will often steal a victim's passport, so that they become stranded and totally dependent on them in a foreign land.