Lymphatic filariasis control in Tanzania: effect of six rounds of mass drug administration with ivermectin and albendazole on infection and transmission

Abstract

BackgroundControl of lymphatic filariasis (LF) in most countries of sub-Saharan Africa is based on annual mass drug administration (MDA) with a combination of ivermectin and albendazole, in order to interrupt transmission. We present findings from a detailed study on the effect of six rounds of MDA with this drug combination as implemented by the National Lymphatic Filariasis Elimination Programme (NLFEP) in a highly endemic rural area of north-eastern Tanzania.MethodsThe effect of treatment on transmission and human infection was monitored in a community- and a school-based study during an 8-year period (one pre-intervention and 7 post-intervention years) from 2003 to 2011.ResultsBefore intervention, 24.5% of the community population had microfilariae (mf) in the blood, 53.3% had circulating filarial antigens (CFA) and 78.9% had specific antibodies to the recombinant filarial antigen Bm14. One year after the sixth MDA, these values had decreased considerably to 2.7%, 19.6% and 27.5%, respectively. During the same period, the CFA prevalence among new intakes of Standard 1 pupils in 10 primary schools decreased from 25.2% to 5.6%. In line with this, transmission by the three vectors (Anopheles gambiae, An. funestus and Culex quinquefasciatus) as determined by dissection declined sharply (overall vector infectivity rate by 99.3% and mean monthly transmission potential by 99.2% between pre-intervention and fifth post-intervention period). A major shift in vector species composition, from predominantly anopheline to almost exclusively culicine was observed over the years. This may be largely unrelated to the MDAs but may have important implications for the epidemiology of LF in the area.ConclusionsSix MDAs caused considerable decrease in all the measured indices for transmission and human infection. In spite of this, indices were still relatively high in the late period of the study, and it may take a long time to reach the recommended cut-off levels for interruption of transmission unless extra efforts are made. These should include increased engagement of the target population in the control activities, to ensure higher treatment coverage. It is expected that the recent initiative to distribute insecticide impregnated bed nets to every household in the area will also contribute towards reaching the goal of successful LF elimination.

Lymphatic filariasis control in Tanga Region, Tanzania: status after eight rounds of mass drug administration

“…whereas the density was higher in the post-MDA 8 period. The previously reported [16,18] shift in vector composition from being predominantly anophelines during the pre-MDA period to being predominantly Culex quinquefasciatus in the later part of the study was still clearly seen. None of the dissected vector mosquitoes from post-MDA periods 7 or 8 were found to carry filarial infections.…”

“…Since launching of the LF control programme in Tanga Region in 2004, the present project has monitored the effect of MDA on LF infection and transmission in rural areas of Tanga District through repeated human cross sectional surveys in communities and schools and continuous vector and transmission surveillance [16][17][18]. As infection and transmission indices had reached relatively low levels, and for logistical reasons, most activities were suspended in 2012.…”

“…With a range of 46-56%, these were markedly lower than the minimum of 65% required for reaching LF transmission interruption within reasonable time [5]. Treatment coverages moreover appeared to have declined when compared with previous years [16,18]. To attain and maintain high treatment coverage has been a commonly reported challenge for LF control programmes, both in Tanzania [41] and elsewhere [42].…”

“…During 2004-2011 the present study monitored the effect of the NLFEP MDA activities on LF transmission and human infection in communities and primary schools in rural areas of Tanga District [16][17][18]. It was seen that the level of transmission and human infection initially decreased considerably, but also that the effect leveled off and became less pronounced in subsequent years.…”

Population genomics of the filarial nematode parasite Wuchereria bancrofti from mosquitoes

“…In the first 13 years, over 4.4 billion treatments have been distributed in 56 endemic countries reducing the risk of infection by 46% from previous estimates in the year 2000 (Hooper et al 2014;Ramaiah & Ottesen 2014). However, the programme has identified some outliers regions where prevalence is rebounding after an initial reduction (Won et al 2009;Simonsen et al 2013;Lau et al 2014;Rebollo et al 2015).…”