Onchocerciasis and Loa loa co-endemicity — DTM&H MCQ

Correct answer: B — Assess Loa loa risk before community ivermectin distribution

The correct answer is B, assess Loa loa risk before community ivermectin distribution. Ivermectin mass drug administration for onchocerciasis is highly effective, but individuals with high Loa loa microfilarial loads are at risk of severe, sometimes fatal, post-treatment encephalopathy because rapid microfilarial killing in areas of forest co-endemicity (Central Africa) can provoke this reaction. Transient Calabar swellings and eye-worm migration in villagers are clinical clues to significant loiasis burden, meaning the community may fall into the co-endemic risk category recognised by WHO/APOC control programmes. The recommended approach is to use a rapid assessment tool such as RAPLOA (history of eye worm prevalence) or, where available, individual microfilarial load screening (LoaScope) before deciding whether to proceed with standard mass ivermectin, apply precautions, or use alternative strategies, rather than treating blindly. Why the other options are wrong: A. Proceed with ivermectin without further mapping: this ignores the documented signal of heavy Loa loa exposure and risks triggering serious neurological adverse events, which is precisely what pre-treatment risk assessment is designed to prevent. D. Replace ivermectin with primaquine: primaquine is an antimalarial with no filaricidal activity and has no role in onchocerciasis or loiasis management. C. Control snails before drug administration: snail control targets schistosomiasis intermediate hosts, not the blackfly (Simulium) vector of onchocerciasis or the tabanid vector of Loa loa, so it is irrelevant here. E. Use yellow fever vaccine as a campaign prerequisite: yellow fever vaccination is a travel and routine immunisation issue unrelated to filarial mass treatment safety and does not address the Loa loa encephalopathy risk. Key point: In Loa loa/onchocerciasis co-endemic forest areas, community-level risk assessment (for example RAPLOA or microfilarial load testing) must precede mass ivermectin distribution to avoid triggering Loa loa encephalopathy.

Reference: Filaria Journal (WHO/APOC-supported study): Rapid Assessment Procedures for Loiasis (RAPLOA) combined with onchocerciasis REA to identify communities at risk of Loa loa post-ivermectin encephalopathy before mass treatment, PMC1090603, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1090603/