Verification Of The Absence Of Wuchereria Bancrofti Transmission After Ten Years Of Albendazole And Ivermectin Administration In Four Districts, Ghana

Abstract

Lymphatic filariasis (LF) is one of the seven neglected tropical diseases (NTDs) identified by the World Health Organization (WHO) as controllable and potentially eliminable with effective interventions. It is a vector borne parasitic infection transmitted by mosquitoes which belong to the Anopheles, Culex, Aedes, Mansonia, Coquillettidia and Ochlerotatus genera. The nematode parasites responsible for causing the disease are Wuchereria bancrofti, Brugia malayi and Brugia timori. These parasites have no animal reservoir and are largely found in rural areas even though they can be found in urban areas. Mass drug administration (MDA) is the approved strategy for elimination of the disease. Between 4 and 6 rounds of yearly MDA with at least 65% treatment coverage has been found to be enough to interrupt transmission. Transmission Assessment Surveys (TAS) is the primary tool recommended for deciding when to stop MDA and for post-MDA surveillance in LF elimination programs. In Ghana, four districts, Awutu Senya, Effutu, Agona East and West have stopped MDA after ten rounds with microfilaria and antigen prevalence below 1% and 2% respectively. Surveillance is ongoing in these areas to ensure the detection of early recrudescence. These areas have passed the pre-TAS based on the WHO criteria for an area to pass pre-TAS or otherwise and therefore the need to conduct TAS to monitor for recrudescence in both humans and vectors of the disease. The aim of this study was to conduct post-MDA surveillance in four endemic areas that have stopped MDA to detect early recrudescence using periodic surveys. Three surveys were conducted; school-based, household and xenomonitoring surveys. Approximately 1,600 school children aged 6-10 years from selected schools and 1,000 community members aged 11-60 years were sampled annually for four years to participate in the longitudinal school-based and household surveys respectively. Daytime finger-prick blood samples were collected from all consenting participants and tested using a rapid card test (ICT) and Enzyme Linked Immunosorbent Assays (OG4C3 and Wb123). Night time blood was collected for blood smear from participants who tested positive for ICT. Mosquitoes were captured from households using the Pyrethrum Spray Catch (PSC) method for the xenomonitoring survey. All mosquito species were pooled by community with an average pool size of fifteen mosquitoes. Loop Mediated Isothermal Amplification (LAMP) and Polymerase Chain Reaction (PCR) assays were conducted to detect Wuchereria bancrofti parasites in the mosquitoes. Results obtained show that microfilaria prevalence in humans remained below the 2% threshold required for post-MDA surveillance to be conducted and was fairly stable over the study period [2010=0.07%, 2012=0%, 2013=0.12%, 2014= 0.12%] among 6-10-year-old children sampled and tested as well as the older population [2010=1.1%, 2012=1.0%, 2013=0.17%, 2014=0.60%]. Mosquitoes collected in 2013 and 2014 numbered 7,268. This consisted of 4628 Anopheles gambiae s.l., 146 An. funestus, 5 An. pharoensis, 2430 Culex spp. and 59 Mansonia spp. Six (0.08%) pools (five An. gambiae spp. and one Culex spp.) tested positive for W. bancrofti. Surveys in both humans and mosquitoes revealed very low antigen, antibody and microfilaria prevalence four years after last MDA. Mosquito biting rates were low (2013 = 0.057; 2014 = 0.058) but infection rates were high; 0.97 (CI: 0.17-3.17) in 2013 and 1.3 (CI: 0.36-3.65) in 2014 per 1,000 mosquitoes for Anopheles gambiae complex, while that for Culex species was 0.86 (CI: 0.05-4.15) in 2013 per 1,000 mosquitoes. These results depicted that mosquitoes harbored parasites making recrudescence possible. However, results from this study have shown that four years post-MDA is not enough to detect recrudescence and therefore the earliest occurrence of recrudescence goes beyond four years post-MDA. Continued surveillance is therefore recommended.