Whole villages in southern Mexico are threatened with mass blindness as an obscure disease sweeps the tropical, coffee-growing state of Chiapas. Thus far Government sanitary brigades have only sized up the enemya kind of filaria or threadworm, whose eggs are spread from victim to victim by gnats. The eggs develop into hairlike parasites, some 20 inches long, which work their way through the body toward the head and shoulders. There they reproduce and multiply into tangled masses, forming cysts.
When the victim becomes lumpy around the face and head, he is doomed to blindness unless the cysts are cut away before the...