Ever wonder what happens to those people who have a rare disorder or physical attribute and whose bodies represent a scientific gold mine? An incredible piece in the Guardian's Observer magazine offers us one sad answer. It profiles Agnes, a Nigerian prostitute who for the past 30 years has been having sex with about 12 men a day, working 12-hour shifts from 6 a.m. to 6 p.m. in the slums of Nairobi, Kenya. Still, she barely ekes out a living for her family of five children. She makes between one and two bucks a job, earning only enough to buy some food and pay rent on two one-room, dirt-floored shacks, one for her family and one for her work. Yet she's also a scientific celebrity of sorts -- a woman who has had unprotected sex with thousands of men but who has never contracted AIDS.

The story -- an excerpt from "Twenty-Eight: Stories of AIDS in Africa" by Stephanie Nolen -- highlights the ironies rarely addressed in journalism about AIDS or third-world medical research. Though medical workers have gotten grants to teach Agnes about the dangers of unprotected sex, they offer her help to actually avoid it by getting another job. Meanwhile, over the past 20 years Agnes has been donating her blood to a project that is studying the miraculous immune systems of Agnes and a few other Nigerian prostitutes like her. The project has generated $43 million in research funds aimed at discovering their bodies' secrets. But Agnes' life -- the poverty, the sex work she yearns to escape -- remains essentially the same.

As Nolen puts it: "Agnes's frustration with her life in sex work raises troubling ethical questions about research, the kind that bedevil investigations into AIDS vaccines, prevention technologies and treatment, all of which, by definition, involve large groups of poor Africans, the people most at risk. What obligation does a researcher ... have to the women who have given him their blood for 20 years? What does this project owe Agnes?"

There are no answers here, but it's provocative stuff on a topic where most writing feels both distancing and not terribly profound.