Kill the Larvae, Spare the Worm

Ivermectin, the only drug used in mass drug administration (MDA) programs for onchocerciasis (river blindness), kills microfilariae — the larval offspring — but leaves adult worms alive. Adult female worms live 10–15 years and resume microfilariae production continuously. Because elimination requires stopping transmission, not merely suppressing it year by year, ivermectin-only MDA cannot achieve elimination and must be continued indefinitely. The leading macrofilaricidal candidate, emodepside (developed by DNDi and Bayer), has completed Phase II Part 1 trials in Ghana and DRC with favorable safety signals, but cannot be administered by mass campaign in the highest-burden zones of Central Africa because of a dangerous drug interaction with Loa loa co-infection.

Approximately 220 million people across 31 countries are at risk of river blindness, with 1.15 million already living with vision loss from the disease. In Loa loa co-endemic zones — particularly DRC, Cameroon, and the Central African forest belt — rapid killing of microfilariae in heavily co-infected individuals triggers potentially fatal encephalopathy, a known risk that has caused deaths in previous MDA campaigns and forced the suspension of ivermectin distribution in entire regions. Without a macrofilaricidal drug that can be safely deployed in these zones, the areas with the highest transmission burden are precisely the areas that cannot be treated at population scale.

Ivermectin MDA, running since the 1980s through the African Programme for Onchocerciasis Control and successor programs, has reduced transmission in many areas but cannot achieve elimination as long as adult worms survive. Doxycycline, which kills Wolbachia endosymbionts that adult worms require, is effective as a macrofilaricide, but requires a full 4–6 week daily oral course — making it structurally incompatible with mass administration in rural settings with limited health infrastructure. Emodepside's Phase II Part 1 data (Ghana, DRC) are promising, but the drug will face the same Loa loa constraint as ivermectin in MDA contexts unless either a Loa loa rapid diagnostic test (RDT) can be deployed at point-of-distribution to screen out high-risk individuals, or a dosing regimen is found that avoids triggering encephalopathy. The LoaScope (a phone-based microscopy tool to count Loa loa microfilariae in blood) was developed as a point-of-care diagnostic but has not been operationalized at MDA scale. No fully validated, deployable pre-treatment screening protocol currently exists for community use.

A validated, rapid, low-cost point-of-care test for Loa loa microfilariae load — one that can be administered by community health workers in the field before drug distribution — would allow emodepside MDA to proceed safely in co-endemic zones by excluding high-risk individuals. Alternatively, a macrofilaricidal regimen with a slower microfilaricidal action profile that avoids triggering encephalopathy could remove the constraint entirely. Either pathway would unlock elimination campaigns in DRC and Cameroon, the current bottleneck for regional elimination.

A team with microfluidics, optics, or mobile diagnostics experience could investigate what minimal Loa loa detection specification is needed to safely gate MDA access — and whether existing lateral flow or phone-based platforms can meet it at the cost and durability required for community health worker deployment. A health systems or operations research team could model the tradeoff between screening cost, false-negative risk, and lives saved under different sensitivity thresholds, to define the target product profile. A pharmacology or drug delivery team could investigate whether slower-release formulations of emodepside could decouple macrofilaricidal and microfilaricidal kinetics.