The cause of river blindness, a tropical disease that affects some 18 million people, may have its roots in bacteria, not worms, as was previously thought. This finding, detailed in the current issue of the journal Science, suggests that the devastating ailment could be treated with antibiotics.
Humans develop river blindness from the bite of the blackfly, which deposits parasitic worms that burrow into the skin. The worms reproduce repeatedly, sending millions of offspring throughout the body. Some of these offspring reach the eyes, where their eventual death triggers a severe immune response that results in inflammation, gradual loss of vision and eventual blindness. Previous efforts to fight river blindness have targeted the blackflies and parasitic worms, but the new research indicates that antibiotics may be the most effective weapon.
The worms, it turns out, carry Wolbachia bacteria, which they need in order to reproduce successfully. What is good for the worms is not good for humans, however. Eric Pearlman of the University Hospitals of Cleveland and Case Western Reserve University and his colleagues infected two groups of mice with extracts from the parasitic worms. One group received extracts of worms that had been treated with doxycycline, an antibiotic that kills Wolbachia; the other group received untreated extracts. Mice infected with the treated extract, the team found, exhibited fewer of the expected symptoms. The researchers concluded that the bacteria, not the worms, trigger the human hosts violent immune response.
"These data show that Wolbachia itself has a major role in the disease's pathology," Pearlman says. Eliminating the bacteria with antibiotics could therefore not only ease the symptoms of individuals infected with river blindness, it could also prevent the spread of the worms. If such treatment proves effective, it could help resolve a crisis that has vexed public health officials for decades.