Is it possible that the parasite that causes onchocerciasis – also known as river blindness – is developing resistance to ivermectin, the only available treatment? This is the question being put by researchers at the IRD (the French Institute of Research for Development) who recently conducted a study in Cameroon.
Onchocerciasis is a parasitic infection caused by Onchocerca volvulus, a nematode worm transmitted to man by tiny simuliid flies known as black flies. The illness causes skin lesions and severe eye disorders that can lead to irreversible blindness.
Although ivermectin – the only treatment available against this condition – is very effective, several teams of researchers are warning about possible resistance. This is certainly true at the IRD where scientists are monitoring a group of patients who have been treated with ivermectin since 1994. Their most recent study shows a “genetic selection of parasite populations associated with a modification in their fertility”.
In other words, the researchers think that parasites with a particular genotype – homozygote in this case – may be more sensitive to the molecule. They are therefore gradually disappearing over the course of the treatment and being replaced by other – heterozygote – parasites that are more resistant. “These results are not confirmation that Onchocerca volvulus is gradually becoming refractory to ivermectin. What they show is that certain parasites are more sensitive than others to treatment”, concludes the IRD.