Abstract
BackgroundAfter seven annual rounds of mass drug administration (MDA) in six Malian villages highly endemic for Wuchereria bancrofti (overall prevalence rate of 42.7%), treatment was discontinued in 2008. Surveillance was performed over the ensuing 5 years to detect recrudescence.MethodsCirculating filarial antigen (CFA) was measured using immunochromatographic card tests (ICT) and Og4C3 ELISA in 6–7 year-olds. Antibody to the W. bancrofti infective larval stage (L3) antigen, Wb123, was tested in the same population in 2012. Microfilaraemia was assessed in ICT-positive subjects. Anopheles gambiae complex specimens were collected monthly using human landing catch (HLC) and pyrethrum spray catch (PSC). Anopheles gambiae complex infection with W. bancrofti was determined by dissection and reverse transcriptase polymerase chain reaction (RT-PCR) of mosquito pools.ResultsAnnual CFA prevalence rates using ICT in children increased over time from 0% (0/289) in 2009 to 2.7% (8/301) in 2011, 3.9% (11/285) in 2012 and 4.5% (14/309) in 2013 (trend χ 2 = 11.85, df =3, P = 0.0006). Wb123 antibody positivity rates in 2013 were similar to the CFA prevalence by ELISA (5/285). Although two W. bancrofti-infected Anopheles were observed by dissection among 12,951 mosquitoes collected by HLC, none had L3 larvae when tested by L3-specific RT-PCR. No positive pools were detected among the mosquitoes collected by pyrethrum spray catch. Whereas ICT in 6–7 year-olds was the major surveillance tool, ICT positivity was also assessed in older children and adults (8–65 years old). CFA prevalence decreased in this group from 4.9% (39/800) to 3.5% (28/795) and 2.8% (50/1,812) in 2009, 2011 and 2012, respectively (trend χ 2 = 7.361, df =2, P = 0.0067). Some ICT-positive individuals were microfilaraemic in 2009 [2.6% (1/39)] and 2011 [8.3% (3/36)], but none were positive in 2012 or 2013.ConclusionAlthough ICT rates in children increased over the 5-year surveillance period, the decrease in ICT prevalence in the older group suggests a reduction in transmission intensity. This was consistent with the failure to detect infective mosquitoes or microfilaraemia. The threshold of ICT positivity in children may need to be re-assessed and other adjunct surveillance tools considered.
Highlights
After seven annual rounds of mass drug administration (MDA) in six Malian villages highly endemic for Wuchereria bancrofti, treatment was discontinued in 2008
To eliminate Lymphatic filariasis (LF) by 2020, the Global Program to Eliminate LF (GPELF) adopted strategies based on two pillars: annual mass drug administration (MDA) to all eligible residents of the endemic communities and morbidity management [2]
As Bancroftian filariasis was found to be endemic in all eight administrative districts of Mali, ranging from 1% in Timbuktu to > 18% in Sikasso [3], annual MDA using ivermectin and albendazole was initiated sequentially starting from the most highly endemic district in the country [3]
Summary
After seven annual rounds of mass drug administration (MDA) in six Malian villages highly endemic for Wuchereria bancrofti (overall prevalence rate of 42.7%), treatment was discontinued in 2008. To eliminate LF by 2020, the Global Program to Eliminate LF (GPELF) adopted strategies based on two pillars: annual mass drug administration (MDA) to all eligible residents of the endemic communities and morbidity management [2]. As Bancroftian filariasis was found to be endemic in all eight administrative districts of Mali, ranging from 1% in Timbuktu (northern part of Mali) to > 18% in Sikasso (southern part of the country) [3], annual MDA using ivermectin and albendazole was initiated sequentially starting from the most highly endemic district in the country [3]. The baseline data and the impact of six rounds of MDA on human infection and potential transmission in this sentinel site have been previously reported [4]
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