Understanding the sub-optimal response to ivermectin and implications for onchocerciassis control

Onchocerciasis, or African river blindness, has been subject to extensive public health interventions designed to reduce the burden of disease over the past two decades. Spraying programs for vector control followed by ivermectin treatment for affected communities (mass drug administration) have been successful in dramatically reducing the public health burden of the disease. These initiatives have been so successful that the WHO has prepared for a move from a public health control strategy towards a goal of elimination. However, there is emerging evidence that the parasite, Onchocerca volvulus, may be evolving under the selective pressure brought by treatment programs. Ivermectin failure would be of grave concern from a public health perspective.

Emerging population genetic data on the parasite, generated by A/Prof Warwick Grant and his team at Latrobe University with support from the WHO, suggest that the response of Onchocerca volvulus to ivermectin is a continuously variable polygenic trait, ranging from a “good response” to a “sub-optimal or poor response”. Working with A/Prof Grant, we are developing new within-host and community-level models of ivermectin treatment that account for the features of quantitative traits. Through a better understanding of the emerging genetic and population data on the host-response to ivermectin, we aim to evaluate current control programs and provide recommendations on revised treatment strategies to ensure maintenance of control.