kill the larvae, spare the worm

Problem statement

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.

Why this matters

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.

What’s been tried and why it hasn’t worked

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.

What would unlock progress

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.

Entry points for student teams

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 desk study on published prevalence, microfilarial-density and encephalopathy-risk data. A team with microfluidics, optics, or mobile diagnostics experience could work out what minimal Loa loa detection specification safely gates MDA access and audit whether existing lateral flow or phone-based platforms meet it on cost and durability for community health worker use, benchmarking published LoaScope performance and building a bench rig read on spiked microsphere or fixed-microfilaria phantoms; testing on human blood in a co-endemic zone belongs to DNDi and its country partners, so the deliverable is the specification and the bench-validated optics. A pharmacology team could ask whether a slower-release formulation decouples macrofilaricidal from microfilaricidal kinetics by modeling it rather than making it — emodepside is a DNDi/Bayer development compound no student team can obtain, but its population pharmacokinetics and exposure–adverse-event relationship are published from 142 phase I subjects (Assmus et al., PLoS Negl Trop Dis 2022; Gillon et al., Br J Clin Pharmacol 2021), enough to simulate what absorption profiles a modified-release form would have to hit and which are physically reachable. Any wet formulation work should use a licensed veterinary or human anthelmintic as a release-kinetics surrogate; the filaricidal kinetics themselves need specialized animal models that are not a semester project.