Developing a trap for African Chrysops flies to accelerate onchocerciasis elimination in areas co-endemic for loiasis: proof of concept in Cameroon

To determine whether horizontally polarised light can be used to effectively attract and trap African Chrysops species in communities which require mass drug administration for onchocerciasis

River blindness (onchocerciasis) is an eye and skin disease affecting millions of people in many parts of the world including Cameroon. The current core strategy for eliminating (interrupting transmission) of onchocerciasis is population-based treatment (also known as mass drug administration or MDA) with ivermectin.

A major challenge for onchocerciasis elimination efforts in Africa is co-endemicity of loiasis (‘African eye worm’). Individuals with a high load of Loa loa cannot receive ivermectin due to risk of fatal adverse reaction by the Loa loa parasite. In addition to being excluded from treatment, individuals who are infected with both loiasis and onchocerciasis may perpetuate continuous transmission post MDA.

To address this long-standing challenge of onchocerciasis and loiasis co-endemicity this research aims to develop and optimise a novel trap that catches the blood-sucking Chrysops flies that are responsible for spreading Loa loa.

Added value of this study

This research builds on earlier work (done outside Africa) to optimise trap design for ‘Tabanidae’ group of flies (known as ‘horse’ and ‘deer’ flies), which Chrysops are part of. Expanding research to Cameroon is needed as tabanids’ response to traps differs between species and locations.

In this study the proposed trap design builds on existing evidence which demonstrated that Chrysops are attracted to horizontally polarized light. Following polarized light enables flies to locate water for egg laying, finding mates and hydration. Horizontally polarised lights can also be produced by black shiny surfaces, which forms the basis of this research.

Policy and practice implications

Once the Chrysops trap is developed and has proven to be effective in catching these flies, further research may consider:

• How the spatial deployment of traps maybe optimised to reduce Chrysops abundance and biting rate
• Impact on Loa loa transmission levels
• Impact on Loa loa infection load in humans and numbers who will be able to safely take ivermectin