Alternative Strategies for Onchocerciasis Control

Alternative Strategies for Onchocerciasis Control

Onchocerciasis (river blindness) is a vector-borne disease caused by the parasite Onchocerca volvulus. It manifests as severe itching, visual impairment and irreversible blindness. It is common and widespread in Cameroon. The current control strategy is mass drug administration (MDA) with ivermectin; a drug that kills the immature, transmissible form of the parasite in skin, but leaves adult worms alive. The WHO recommends annual MDA for 15-17 years with high population coverage, as this should be sufficient to interrupt transmission in most settings.

MDA has been delivered in South West Cameroon for 12 years using Community-Directed Treatment with ivermectin (CDTi), yet higher than expected prevalence and intensity of onchocerciasis persists. The geographic overlap between L. loa and O. volvulus provides a possible explanation for the lower than expected benefit from CDTi: lack of adherence to treatment due to fear of adverse reactions and poor perception of the treatment in general. The World Health Organization (WHO) recommends either doxycycline or vector control as alternative strategies in L. loa co-endemic areas, yet implementation research on the integration of these interventions is lacking. Therefore an urgent need exists to validate and implement such alternative strategies. The overall aim of the Cameroonian onchocerciasis work is to implement a test-and-treat strategy for onchocerciasis control using the WHO-endorsed macrofilaricidal treatment, doxycycline, in tandem with focal vector control, to reduce the blackfly biting rate.

Doxycycline differs from ivermectin as it acts directly on adults worms; permanently sterilising them, thus preventing the production of skin infecting micofilariae, and significantly reducing adult worm lifespan. Offering an alternative treatment to ivermectin will help counter the poor community perception of the current strategy. Biological monitoring will be undertaken to determine the impact of this alternative strategy on the prevalence of onchocerciasis microfilariae in the skin, using traditional parasitological techniques. The focal vector control aspect of the study consists of adapting tools used with huge success on a large scale in the onchocerciasis control programme (OCP) for use in small targeted areas. Rather than applying larviciding chemicals from the air, as was done during the OCP, larvicides will be applied from the riverside to local tributaries and rivers within the vector control area.

Social science approaches will be used to help identify risk factors for the poor efficacy of the current CDTi strategy, alongside the capture of societal and health economic data to assess the acceptability and feasibility of the test and treat and vector control strategies.


Neglected Tropical Diseases