A new drug to be tested in three African countries could greatly reduce cases of onchocerciasis, commonly called "river blindness," health officials said.

"This is a devastating illness that has plagued 30 African countries for centuries," said Dr. Uche Amazigo, director of the African Program for Onchocerciasis Control. More than 100 million Africans are at risk of infection from the disease, Amazigo said.

The drug, moxidectin, developed by Wyeth Pharmaceuticals, kills the larvae and adult worms of Onchocerca volvulus, which gives the disease its name. Moxidectin is to be tested for the next couple of years on 1,500 people at four clinical sites in Ghana, Liberia and the Democratic Republic of the Congo, the World Health Organization said in a release Friday from its Geneva, Switzerland, headquarters.

For more than 20 years, river blindness has been controlled with ivermectin, a drug developed by Merck & Co. Ivermectin, however, kills only the larvae so treatments of at least 11 to 14 years are needed to ensure disease control.

Onchocerciasis is transmitted by a black fly that breeds in fast flowing rivers. Blindness is the most incapacitating symptom of the disease, which also causes debilitating skin ailments, WHO officials said.