Otieno is certain it will work. She believes a demon sent by an envious relative or neighbor is making her sick. She knows there is a disease called AIDS, she has watched it decimate her community, but she doesn’t like to think of herself as another of its victims. Drugs to treat her tuberculosis are out of the question; she can hardly feed her three children and wouldn’t know how to start raising $7 a week for treatment. A follower of Legion Maria–one of the myriad sects that have grown out of the poverty of Nairobi’s slums–told her that at his church people get cured all the time. They get “prayed over” and have their demons cast out.

After Otieno’s first mass, she stood outside the church–a shack of corrugated-iron sheeting–with a dozen others, praying but also keeping an eye on the three exorcists working their way down the line toward her. When her turn came, she dropped to her knees, whispered her name and closed her eyes. By the time she was deemed purged of her demon, she had been repeatedly struck and shouted at, forced to the ground and had “blessed” water poured into her mouth and ears. “I have often wondered about the psychological impact of so much violence on an individual,” says Alex Zanutelli, an Italian, Roman Catholic missionary who lives among the poor in the slum. For her part, “I already feel better,” says Otieno.

Healing has always been central to African religious belief. But as AIDS decimates the continent, the belief that sickness can be healed through prayer or exorcism compounds the challenge of fighting the plague–obscuring its origins and giving many the impression they are no longer contagious. Nowhere is the faith in religious healing stronger than in Nairobi’s slums, where 2 million people live with little hope of growing old. There, sects like Legion Maria celebrate not one but five services a week: each mass lasts all day and brings new converts. On any given block, at least two or three sects compete for space, recognition and followers. They have names like Israel Roha, Fire of the Holy Spirit and African Divine, and all proclaim the power of prayer over disease.

Thanks to a landmark revision of Kenyan law this week, the government will now be able to import cheap generic drugs to treat HIV/AIDS, raising hopes for 2 million HIV-positive Kenyans. Still, at a cost of between $30 and $100 a month, antiretrovirals from India or Brazil will be well beyond the means of Nairobi’s slum dwellers. For the poorest of the poor, prayer and exorcism will remain the only option.

“If you believe you can be cured, you can be cured,” explains Joseph Alexus Okan, a Legion Maria priest at Saint Theresa’s church in Gorokocho, the most violent of Nairobi’s slums. Legion Maria, one of the oldest and largest sects, with 53 churches in Nairobi’s slums alone, holds a deliberately ambiguous position on HIV/AIDS. Most of its 50,000 followers join in hope of getting healed. But while church leaders acknowledged earlier this year that HIV/AIDS might not be curable through exorcism, no announcement was ever made to the crowds of believers.

Legion Maria leaders stop short of promising healing in exchange for money. But down the street from Saint Theresa’s, at the God’s Power Church and World Center of Healing, Rev. John Nduati tells it as it is: “The more you give, the more you are healed. Somebody say amen.” The church, another shack, reverberates with the sound of 3,000 amens. Because Nduati’s healing session is strictly for HIV/AIDS, he assumes that most, if not all, congregants are infected with the virus.

Nduati starts with a teacher. “Why are you here?” he asks Bernard Ageri, 42. “Because I have tried different kinds of treatments and none has worked,” comes the reply. Eventually, Nduati announces, “As I am standing here, I tell you, you have been healed,” to loud applause, cheering and weeping. After the mass–eight hours long–Ageri simply says: “I believe I am healed.” Next to him, a 21-year-old woman, who used the pseudonym Nancy, says she too believes she has been healed. Asked whether she would get tested to make sure, she flashes a radiant smile: “There is no need.” Nduati lets out a delighted laugh. Wearing an expensive suit and a gold watch, he says, “This is not the movies. This is life.”

Zanutelli, the Catholic missionary, knows life in the slum. Each evening he leaves his shack in the heart of Gorokocho looking for terminal AIDS victims, bringing not just the comfort of prayer but the message that they are not alone. “People come to the slum to die, they come to hide,” he says. In the dark home of a childless woman abandoned by her husband and unlikely to survive the week, he gathers a cheerful crowd and celebrates the mass. Each participant offers a prayer and a song for Mama Jessica, whose tuberculosis is so advanced she has trouble sitting up. Zanutelli reads from one of the gospels: the story of a woman healed by the strength of her faith in Jesus. He promises nothing. But as he steps outside into the damp night, the woman is crying and smiling at the same time.