Urine samples may help doctors identify people infected with "river blindness" before they lose their sight. The blindness, found mostly in sub-Saharan African countries, is caused by a parasite that infects humans through black fly bites. Scientists have discovered an unknown molecule in the urine of those infected with the parasite. "Using this molecule, we could make a diagnostic test that can be put in a backpack and diagnose whether people are infected or not," said researcher Daniel Globisch.