Status of Onchocerciasis transmission after more than a decade of mass drug administration for onchocerciasis and lymphatic filariasis elimination in central Nigeria: challenges in coordinating the stop MDA decision

Background This study was undertaken in five onchocerciasis/lymphatic filariasis (LF) co-endemic local government areas (LGAs) in Plateau and Nasarawa, Nigeria. Annual MDA with ivermectin had been given for 17 years, 8 of which were in combination with albendazole. In 2008, assessments indicated that LF transmission was interrupted, but that the MDA had to continue due to the uncertain status of onchocerciasis transmission. Accordingly, assessments to determine if ivermectin MDA for onchocerciasis could be stopped were conducted in 2009. Methods We evaluated nodule, microfilarial (mf) skin snip, and antibody (IgG4 response to OV16) prevalence in adults and children in six sentinel sites where baseline data from the 1990s were available. We applied the 2001 WHO criteria for elimination of onchocerciasis that defined transmission interruption as an infection rate of
Author Summary Both lymphatic filariasis and onchocerciasis are treated with ivermectin-based mass drug administration (MDA) regimens in Africa. Where the infections are co-endemic, ivermectin treatments cannot be stopped until both infection transmission cycles are broken. This report follows a previous determination that the LF transmission cycle had been interrupted in five districts (LGAs in Nigeria) but evidence was needed on the status of the onchocerciasis transmission cycle prior to halting MDA. In this report we determined (based on WHO guidelines) that most likely the transmission of onchocerciasis has been interrupted in Plateau and Nasarawa States and we conclude that ivermectin MDA could be stopped.