Also known as blinding trachoma, this disease is one of the most prevalent causes of blindness in the world. Researchers estimate that 500 million people are affected by the highly contagious disease, with 7 million to 9 million of them going blind from the effects of repeated infection. The disease is found worldwide, with its highest concentrations in the Southern Hemisphere [source: Mayer].
Trachoma is caused by a strain of chlamydia, the bacterium that causes a widespread sexually transmitted disease of the same name. Trachoma infects the inner eyelid, causing inflammation and swelling that can turn the eyelashes until they rub against the eye. This rubbing is what causes the blindness; it scuffs and scratches the cornea until it grows too cloudy to see through [source: WHO]. The infected eye releases a discharge onto towels, skin, and insects like eye-seeking flies. Since trachoma is highly asymptomatic (many infected people show no symptoms), it's easy for a person to spread the disease without even knowing he or she is a carrier.
In areas where the disease is prevalent, as many as 90 percent of local children may carry trachoma [source: WHO]. This statistic, along with the disease's easy spread through hands, towels and simple contact between parent and child, mean trachoma is a difficult adversary for the world's public health crusaders.