THURSDAY, March 7, 2002 (HealthDayNews) -- New research has found a better way to treat onchocerciasis, the "river blindness" that affects more than 20 million people in the tropical regions of Africa and Latin America.
A single course of a widely available antibiotic, doxycycline, could preserve the sight of people infected with the parasitic worm that has traditionally been described as the cause of the disease, says a report in tomorrow's issue of Science.
That's because animal studies indicate it's not the worm itself, but the bacteria inside it that trigger the severe inflammatory response of the immune system that damages the eyes, says Eric Pearlman, lead author and associate professor of medicine and ophthalmology at Case Western Reserve University in Cleveland.
"What we show is that when you get rid of the bacteria, which we did by a couple of approaches, you get much less disease," Pearlman says.
Current treatment is aimed at killing the parasitic worms that infect more than 200 million people worldwide, says Calvin Baerveldt, a spokesman for the International Eye Foundation.
That treatment involves ivermectin, a medication marketed in the United States as Mectizan by Merck & Co., the drug company that has donated millions of doses for the fight against river blindness.
"Some 30 million people are treated annually for river blindness by this drug," says Mary Allerman, director of the Mectizan Donation Program, an organization in Atlanta involved in distribution of the drug. "It is not a cure, but is used to control symptoms."
Treatment is handled by a number of groups in different countries, she says. The International Eye Foundation is one of those organizations.
"All indications are that it does seem to be moving toward the progress we anticipate," Baerveldt says of the program.
However, Pearlman thinks more progress could be made.
While ivermectin kills larvae of the worm, it does not kill adult worms, "so you must treat people year after year," Pearlman says. "A single treatment regimen of doxycycline, daily for six weeks, renders the adult worms sterile."
That belief comes from studies done in Pearlman's laboratory, and from collaborators at the Institute for Tropical Medicine in Hamburg, Germany, and the Liverpool School of Tropical Medicine. The researchers have done a painstaking study of the life cycle of the parasitic worm and the reaction it precipitates in the body.
"The adult worm lives in subcutaneous tissues," Pearlman says. "There are millions of small larvae that travel through the skin and are picked up by blackflies that breed in rivers. When the blackfly bites, another individual is infected."
The new report describes a study in which extracts of the parasitic worm were injected into the animals' eyes. Careful study showed the eye-damaging inflammatory response was caused by a species of bacteria called Wolbachia, rather than by the worms themselves, Pearlman says. Without those bacteria, the worms cannot reproduce, he adds.
"Wolbachia have emerged as the only target for a chemotherapy that results in the long-term sterility of the worms in human onchocerciasis," the journal report says.
Antibiotic treatment could also be effective against lymphatic filariasis, a skin condition related with other parasites that carry Wolbachia, Pearlman says.
There are no plans to change the program for attacking river blindness, Baerveldt says. The work by Pearlman and his colleagues "hasn't been very well circulated among people in the field," he says.
What To Do: Fortunately, river blindness is not a danger in the United States. A primer on the disease is offered by the World Health Organization and the Centers for Disease Control and Prevention.
