Parasitic illnesses afflict millions of people in poor countries, mostly in Africa and Asia. But many are known as "neglected diseases," because most drug companies don't make the medicines necessary to treat people who cannot afford to pay.
"These people don't represent a market," said Nicolas de Torrente, executive director of Doctors Without Borders' U.S. office. "There is no return on investment there."
However, neglected tropical diseases are finally getting some attention from the San Francisco-based Institute for OneWorld Health, the nation's first not-for-profit pharmaceutical company.
Company founder Victoria Hale, a former pharmaceutical scientist, came up with a solution: Look for existing drugs that have been dropped by the big companies, but could be used to cure neglected diseases.
Her first target was black fever, which is almost 100 percent fatal.
"You hemorrhage and die," Hale said. "It's a terrible way to die."
Using an off-patent drug called paromomycin and funding from the Bill and Melinda Gates Foundation, OneWorld Health has finished clinical trials in India that cured 94 percent of the patients. It's great progress, but there are a lot of other parasites out there.
For instance, more than 40 million people have been disfigured by elephantiasis. River blindness has blinded more than 250,000. Sleeping sickness, also fatal, is spread by the tsetse fly. And the really big killers are malaria and children's diarrhea.
"The problem with infectious diseases is the bug that you're going after changes -- it mutates, it develops resistance," Hale said. "So you have to keep developing new medicines. And it is that which is not happening."
Drug companies, of course, are businesses, not charities. But some are getting involved. For instance, Merck took an existing heartworm medicine for dogs and turned it into a very effective treatment for river blindness in people.
"We were lucky enough to find something that worked, and we've done what we can to make it available," said Jeffrey Sturchio of Merck. "In fact, we've donated more than a billion tablets."
Even so, the diseases that afflict 90 percent of the world's population get only 10 percent of the health dollars. Most of those dollars go to Western lifestyle problems -- like cholesterol, digestive problems and erectile dysfunction.
"I am frustrated," Hale said. "I understand it, though. And I believe that the way to address it is not to go in and change this enormous system that exists, but to build a system that can work with what already exists and to make it happen."
ABC News' Judy Muller originally reported this story for "World News Tonight" on Oct. 30, 2005.