The Interruption of Transmission of Human Onchocerciasis by an Annual Mass Drug Administration Program in Plateau and Nasarawa States, Nigeria

Abstract

Plateau and Nasarawa states in central Nigeria were endemic for onchocerciasis. The rural populations of these two states received annual ivermectin mass drug administration (MDA) for a period of 8-26 years (1992-2017). Ivermectin combined with albendazole was given for 8-13 of these years for lymphatic filariasis (LF); the LF MDA program successfully concluded in 2012, but ivermectin MDA continued in areas known to have a baseline meso-/hyperendemic onchocerciasis. In 2017, serological and entomological assessments were undertaken to determine if MDA for onchocerciasis could be stopped in accordance with the current WHO guidelines. Surveys were conducted in 39 sites that included testing 5-to < 10-year-old resident children by using ELISA for OV16 IgG4 antibodies, and Onchocerca volvulus O150 pooled polymerase chain reaction (PCR) testing of Simulium damnosum s.l. vector heads. Only two of 6,262 children were OV16 positive, and none of 19,056 vector heads were positive for parasite DNA. Therefore, both states were able to meet WHO stop-MDA thresholds of an infection rate in children of < 0.1% and a rate of infective blackflies of <1/2,000, with 95% statistical confidence. Transmission of onchocerciasis was declared interrupted in Plateau and Nasarawa states by the Federal Ministry of Health, and 2.2 million ivermectin treatments/year were stopped in 2018. Post-treatment Surveillance was launched focusing on entomological monitoring on borders with neighboring onchocerciasis-endemic states. An apparent positive impact of the LF MDA program on eliminating hypo-endemic onchocerciasis was observed. This is the first stop-MDA decision for onchocerciasis in Nigeria and the largest single stop-MDA decision for onchocerciasis yet reported. This achievement, along with the process used in adapting and implementing the 2016 WHO stop-MDA guidelines, will be important as a potential model for decision makers and national onchocerciasis elimination committees in other African countries that are charged with advancing their programs.

Scaling-Down Mass Ivermectin Treatment for Onchocerciasis Elimination: Modeling the Impact of the Geographical Unit for Decision Making

“…Our analysis focused on APOC’s original target area, excluding the following: (1) untreated low-endemic areas that were not previously prioritized for treatment by APOC and still remain to be delineated by onchocerciasis elimination mapping [ 23 ]; (2) areas reporting elimination of the vector and/or parasite [ 14 , 24 , 25 ]; (3) areas where MDA was stopped before 2019 as elimination was deemed to have been achieved [ 16 , 26 , 27 ]; (4) meso- and hyperendemic areas identified recently, which were not covered by APOC; and (5) Liberia, as it is geographically separate from the rest of APOC. We include 123 separate MDA implementation units (henceforth referred to as “projects” following APOC’s terminology) in 15 African countries.…”

“…Applying the definition becomes more difficult in areas where multiple transmission zones may be contiguous, as in most endemic countries in west and central Africa. Nigeria has chosen a pragmatic approach, taking the state as the unit for stopping MDA in Plateau and Nasarawa without explicitly considering transmission zones [ 16 ].…”

Emodepside targets SLO-1 channels of Onchocerca ochengi and induces broad anthelmintic effects in a bovine model of onchocerciasis

“…This regimen also suppresses the release of new Mf from the adult female worm for several months [ 4 ]. In foci with seasonal transmission, MDA with IVM (which may include semi-annual treatments) has also been demonstrated to be capable of breaking transmission, typically after an interval of 15–25 years [ 5 , 6 ]. The long period of MDA required to abrogate transmission is due to the longevity of the adult worms [ 7 ], as the female can be reproductively active for more than 10 years and is only temporarily sterilised, not destroyed, by IVM treatments.…”

Entomological Assessment of the Impact of Long-term Mass Administration of Ivermectin in Onchocerciasis – Endemic Communities in Kaduna State, Nigeria.

“…In 2020, evidence of onchocerciasis elimination through annual mass drug administration was documented in Plateau and Nasarawa states in Nigeria [4].…”