Is resistance developing to river blindness drug?

4 Feb 2008

Paul Chinnock

Source: Institut de Recherche Pour le Développement (see original article)

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Genetic changes, thought to indicate drug resistance in the parasite which causes onchocerciasis (river blindness), have been reported by researchers from the Institut de Recherche Pour le Développement in Paris.

An estimated 37 million people are infected with Onchocerca volvulus, a nematode worm. About 99% of those infected live in Africa. Infected subjects suffer severe skin lesions and also eye damage that can lead to irreversible loss of sight. Since 1995, the African Programme for Onchocerciasis Control (APOC) has been covering 19 of the continent’s 28 countries hit by the disease. Mass treatment with ivermectin now reaches the majority of the seventy million people at risk in those countries and this has resulted in a great reduction in the number of people suffering from the effects of the diseases. However, the doubling of cases of infection in certain communities of Ghana between 2000 and 2005, in spite of annual treatments, has led to fears of the emergence of ivermectin-resistant strains of the parasite.

Since 1994, a team of researchers from the Recherche Pour le Développement (IRD), working jointly with Cameroon researchers and others from McGill University of Montreal, has been monitoring a group of Cameroon patients receiving repeated treatments with ivermectin. Regular parasite sampling from the patients took place over a 13-year period in order to follow the changes in the genetic structure of the parasites. They focused on the gene required to make β-tubulin, a protein involved in the organization of the parasite’s cells. The gene is known to act as a marker of resistance to ivermectin in other nematode species that are parasites of cattle. The researchers have concluded that, in this group of patients, the proportion of parasites which have a reduced susceptibility to ivermectin has increased from 21% to 69%.

The researchers say that ivermectin is still effective and their results should not lead to any change in current control strategies for onchocerciasis. However, at some point in the future an alternative to ivermectin will be needed.