The current strategy for interrupting transmission of lymphatic filariasis (LF) is annual mass drug administration (MDA), at good coverage, for 6 or more years. We describe our programmatic experience delivering the MDA combination of ivermectin and albendazole in Plateau and Nasarawa states in central Nigeria, where LF is caused by anopheline transmitted Wuchereria bancrofti. Baseline LF mapping using rapid blood antigen detection tests showed mean local government area (LGA) prevalence of 23% (range 4–62%). MDA was launched in 2000 and by 2003 had been scaled up to full geographic coverage in all 30 LGAs in the two states; over 26 million cumulative directly observed treatments were provided by community drug distributors over the intervention period. Reported treatment coverage for each round was ≥85% of the treatment eligible population of 3.7 million, although a population-based coverage survey in 2003 showed lower coverage (72.2%; 95% CI 65.5–79.0%). To determine impact on transmission, we monitored three LF infection parameters (microfilaremia, antigenemia, and mosquito infection) in 10 sentinel villages (SVs) serially. The last monitoring was done in 2009, when SVs had been treated for 7–10 years. Microfilaremia in 2009 decreased by 83% from baseline (from 4.9% to 0.8%); antigenemia by 67% (from 21.6% to 7.2%); mosquito infection rate (all larval stages) by 86% (from 3.1% to 0.4%); and mosquito infectivity rate (L3 stages) by 76% (from 1.3% to 0.3%). All changes were statistically significant. Results suggest that LF transmission has been interrupted in 5 of the 10 SVs, based on 2009 finding of microfilaremia ≥1% and/or L3 stages in mosquitoes. Four of the five SVs where transmission persists had baseline antigenemia prevalence of >25%. Longer or additional interventions (e.g., more frequent MDA treatments, insecticidal bed nets) should be considered for ‘hot spots’ where transmission is ongoing.

This paper describes a pilot initiative to incorporate lymphatic filariasis (LF) elimination and urinary schistosomiasis (SH) control into a mature onchocerciasis control program based on community-directed ivermectin treatment in central Nigeria. In the same districts having onchocerciasis we found LF (as determined by blood antigen testing in adult males) in 90% of 149 villages with a mean prevalence of 22.4% (range 0-67%). Similarly, SH, as determined by dipstick reagent testing for blood in urine from school children, was found in 91% of 176 villages with a mean prevalence in school age children of 24.4% (range 0-87%). Health education and treatment interventions for SH resulted in 52,480 cumulative praziquantel treatments, and 159,555 combined onchocerciasis and LF treatments (with ivermectin and albendazole) as of the end of 2000. Treatments for onchocerciasis and LF were separated by at least 1 week from treatments for SH. There was no negative impact on the coverage of the onchocerciasis program by the addition of LF and SH activities.

Background

The rapid immunochromatographic card test (ICT) for Wuchereria bancrofti circulating filarial antigen is being used to map areas endemic for lymphatic filariasis. However, the ICT is expensive; thus, surveys based on this test must be relatively limited. Our study was conducted to determine if village-based hydrocele surveys could be used to supplement the ICT surveys in the mapping activities. We compared in 144 Nigerian villages the two assessment methods, ICT and examination for clinical hydrocele, in random samples of 30 adults selected using a procedure that obtained 15 younger males (reported age ‫ס‬ 16−39 years old) and 15 older males (Ն 40 years), based on the assumption that hydrocele rates may be more prevalent in older age groups. The men were asked if they had scrotal swelling, then examined and tested by the ICT. We found a weakly positive correlation between village prevalence determined by the ICT and hydrocele (r ‫ס‬ 0.041, P < 0.001). Only villages with hydrocele rates of 20% or greater were also consistently classified as having endemic filariasis by the ICT. There was no correlation between an individual's ICT positivity and clinical presence of hydrocele, and questioning about scrotal swelling was not predictive for presence of hydrocele. More research is needed to determine if community level hydrocele prevalence surveys can offer an economical and broadly applicable supplement to the ICT for determining the endemicity of filariasis.

Background: Members of the Anopheles gambiae complex are important vectors of lymphatic filariasis (LF) in sub-Saharan Africa, but little is known about the relative contributions of all mosquitoes to lymphatic filariasis transmission in this area.

Abstract. An average of six annual rounds of ivermectin and albendazole were distributed in Plateau and Nasarawa States, Nigeria, to eliminate lymphatic filariasis. From 2007 to 2008, population-based surveys were implemented in all 30 local government areas (LGAs) of the two states to determine the prevalence of Wuchereria bancrofti antigenemia to assess which LGA mass drug administration (MDA) could be halted. In total, 36,681 persons from 7,819 households were examined for filarial antigen as determined by immunochromatographic card tests. Overall antigen prevalence was 3.05% (exact upper 95% confidence interval [CI] = 3.41%) with an upper 95% CI range by LGA of 0.50-19.3%. Among 3,233 children 6-7 years of age, overall antigen prevalence was 1.71% (exact upper 95% CI = 2.19%), too high to recommend generally halting MDA in the two-state area. However, based on criteria of 2% antigenemia among persons 2 years of age, stopping MDA was recommended for 10 LGAs.

In central Nigeria Anopheles mosquitoes transmit malaria and lymphatic filariasis (LF). The strategy used for interrupting LF transmission in this area is annual mass drug administration (MDA) with albendazole and ivermectin, but after 8 years of MDA, entomological evaluations in sentinel villages showed continued low-grade mosquito infection rates of 0.32%. After long-lasting insecticidal net (LLIN) distribution by the national malaria program in late 2010, however, we were no longer able to detect infected vectors over a 24-month period. This is evidence that LLINs are synergistic with MDA in interrupting LF transmission.

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.