Drug Resistance In River Blindness

Armen Hareyan's picture

River Blindness

Study has found that ivermectin, the only drug available to treat onchocerciasis, or river blindness, is triggering the very genetic changes that are building drug resistance in the parasite that causes the disease.

The study, to be published in the inaugural edition of the new journal PLoS Neglected Tropical Diseases, was previewed online Aug 30.


Dr. Prichard, who is James McGill Professor at the University's Institute of Parasitology, published a study in The Lancet in June documenting the growing rate of ivermectin resistance in onchocerca volvulus in the West African nation of Ghana. The current study, conducted in Cameroon, proves the genetic basis of this resistance. Samples of the parasite were taken from people in an area where ivermectin treatments had never been administered. Three years later, samples were taken from the same people after intensive treatment.

"We were then able to compare the parasites obtained after treatment with those obtained before," explained Prichard. "And we found significant changes in one of the genes that is involved in drug resistance in other species of parasites."

River blindness, which is the second-leading infectious cause of blindness worldwide after trachoma, is caused by the filarial nematode parasite onchocerca volvulus, a worm transmitted by black fly bite. It leads to visual impairment, blindness and, in some cases, pathological changes in the skin. Adult worms can survive as long as 10 to 15 years in a human host, releasing millions of tiny worms (microfilariae) each year. An estimated 37 million people are infected worldwide, primarily in Sub-Saharan Africa but also in parts of Central and South America and, to a lesser extent, the Middle East.