Nigeria’s Experience in Determining that Loiasis Presented No Risk to Ivermectin Treatment for Onchocerciasis

Nigeria accounts for approximately 40% of the global onchocerciasis burden, affecting more than 50 million people. Onchocerciasis constitutes a major social and public health problem and therefore cannot be taken for granted. The discovery and free donation of ivermectin (Mectizan®) encouraged Nigeria and other endemic countries to implement Mass Drug Administration (MDA) in atrisk population. Unfortunately, reports from some onchocerciasis-endemic African countries where onchocerciasis is co-endemic with Loa loa indicate that Severe Adverse Events (SAEs) may occur in patients who have taken ivermectin. This threatens the success of the onchocerciasis control/elimination programme in many of these onchocerciasis-endemic African countries where Loa loa is coendemic. Nigeria commenced MDA in 1988 in endemic communities of Kwara and Kaduna States and later expended MDA to nearly all the transmission zones and tens of millions of people have been treated with ivermectin including areas presumed to be onchocerciasis- loiasis co-endemic zone. One striking observation is that there was no evidence of SAEs in Nigeria. Of the 758 SAEs reported to the Mectizan Donation Program between 1990 and 2014, only one suspicious case (0.1%) was reported in Nigeria (around Kwara State, a non- loiasis belt). The international scientific community has continued to ask questions concerning this. For instance, the WHO Loa loa Expert Committee met in Paris, France, August 28-30, 2024 and wanted to know the Nigerian experience in determining that loiasis presented no risk to ivermectin treatment for onchocerciasis. In doing so, the Expert Committee asked the following questions: (a) what are the Rapid Epidemiological Mapping of Loiasis (RAPLOA) exercises in Nigeria; (b) what is the more recent data collected on Loa loa microfilaria density that led Nigeria to determine that MDA for onchocerciasis was safe; (c) do Nigerians think that the RAPLOA data differed so much from the microfilaria density data?, and (d) did loiasis endemicity change over time or is the relationship between RAPLOA and mf density different in Nigeria? As the Chairman of Nigerian Onchocerciasis Elimination Committee (NOEC), the present work addresses these programmatic questions.