Scientists have discovered how a key anti-parasitic drug kills the worms of tropical diseases such as river blindness and elephantitis, potentially leading to new treatments for the diseases.

The drug ivermectin has been used for decades to treat the filarial diseases, which affect over 140 million people worldwide and majority in equatorial Africa. Elephantiasis is the condition among people who have severe swelling of the legs, arms and torso and caused by tiny worms spread via mosquitos. Black flies spread River Blindness when the worms die in a person's eye causing blindness.

"Ivermectin is one of the most important veterinary and human anti-parasitic agents ever," Charles Mackenzie, a professor of veterinary pathology in the College of Veterinary Medicine and researcher on the project. "Knowing specifically how it interacts with the body's own immune system and kills parasitic worms opens up whole new treatment avenues."

Ivermectin, scientists discovered, is effective in killing the first stage of the worm in the human body, and paralyzes the reproductive tract of the adult female worms, stopping reproduction of new parasites. The study appears in the Proceedings of the National Academy of Sciences. The drug was developed by Merck and Co.

"Understanding how the worms were avoiding the host's immune responses will greatly enhance our ability to manipulate the immune system to the advantage of the host, and perhaps develop vaccines," Mackenzie said. "Also, one of the most important challenges in the overall effort against filarial infections relates to the development of resistance and the loss of efficacy of the drugs we use; this new knowledge provides an important key to understanding and perhaps preventing resistance."