1. Laboratory of Parasitic Diseases, National Institutes of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD 20892.
2. Swiss Tropical Institute, Basel CH 4051, Switzerland.
3. Onchocerciasis Control Programme/World Health Organization, Ouagadougou, Burkina Faso.
4. Wilmer Ophthalmological Institute and School of Hygiene and Public Health, Johns Hopkins University, Baltimore, MD 21205.