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

Abstract

BackgroundThis 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.MethodsWe 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 <0.1% in children (using both skin snip and OV16 antibody) and a rate of infective (L3) blackflies of <0.05%.ResultsAmong adult residents in sentinel sites, mean mf prevalence decreased by 99.37% from the 1991–1993 baseline of 42.95% (64/149) to 0.27% (2/739) in 2009 (p<0.001). The OV16 seropositivity of 3.52% (26/739) among this same group was over ten times the mf rate. No mf or nodules were detected in 4,451 children in sentinel sites and ‘spot check’ villages, allowing the exclusion of 0.1% infection rate with 95% confidence. Seven OV16 seropositives were detected, yielding a seroprevalence of 0.16% (0.32% upper 95%CI). No infections were detected in PCR testing of 1,568 Simulium damnosum s.l. flies obtained from capture sites around the six sentinel sites.ConclusionInterruption of transmission of onchocerciasis in these five LGAs is highly likely, although the number of flies caught was insufficient to exclude 0.05% with 95% confidence (upper CI 0.23%). We suggest that ivermectin MDA could be stopped in these LGAs if similar results are seen in neighboring districts.

Evaluation of an OV-16 IgG4 Enzyme-Linked Immunosorbent Assay in Humans and Its Application to Determine the Dynamics of Antibody Responses in a Non-Human Primate Model of Onchocerca volvulus Infection

“…37 In Nigeria, the comparison of OV-16-specific antibody levels among adults living in communities that had received annual IVM for about 17 years showed lower reactivity in 2009 when compared with baseline values from the 1990s, suggesting that some seroreversions had likely taken place. 38 In the NHPs, the IgG4 response was closely related to the detection of microfiladermia and the decline in reactivity was associated with the disappearance of parasites. Although seroreversion was seen in one NHP, it occurred in the context of an infection that produced few microfilariae.…”

Evaluation of Lymphatic Filariasis and Onchocerciasis in Three Senegalese Districts Treated for Onchocerciasis with Ivermectin

“…The Ministry of Health of Senegal decided to start MDA with albendzole and ivermectin in 2015 in the three district of the Kédougou region. This study provides another example of the complexities that encompass the stop MDA decision in onchocerciasis and LF co-endemic areas [19]. This challenge was described by Katabarwa et al in the Wadelai focus of Uganda [20] where ivermectin-based MDA for onchocerciasis could not be stopped due to ongoing transmission of LF.…”

Challenges to Making the Decision to Stop Mass Drug Administration for Onchocerciasis: Lessons Learned from Nigeria

“…A previous study from a subset of the sites included in this study noted the challenge of collecting a sufficient number of black flies using human landing capture (HLC). 5 The present study made use of the Esperanza window trap, which can allow capture of up to five times the number of flies as an individual HLC. 6 However, the trap eliminates the ability to determine a biting rate, which in turn eliminates the ability to calculate the annual transmission potential, a key indicator of transmission in areas with low vector density.…”