Is mass drug administration against lymphatic filariasis required in urban settings? The experience in Kano, Nigeria

Abstract

BackgroundThe Global Programme to Eliminate Lymphatic Filariasis (GPELF), launched in 2000, has the target of eliminating the disease as a public health problem by the year 2020. The strategy adopted is mass drug administration (MDA) to all eligible individuals in endemic communities and the implementation of measures to reduce the morbidity of those suffering from chronic disease. Success has been recorded in many rural endemic communities in which elimination efforts have centered. However, implementation has been challenging in several urban African cities. The large cities of West Africa, exemplified in Nigeria in Kano are challenging for LF elimination program because reaching 65% therapeutic coverage during MDA is difficult. There is therefore a need to define a strategy which could complement MDA. Thus, in Kano State, Nigeria, while LF MDA had reached 33 of the 44 Local Government Areas (LGAs) there remained eleven ‘urban’ LGAs which had not been covered by MDA. Given the challenges of achieving at least 65% coverage during MDA implementation over several years in order to achieve elimination, it may be challenging to eliminate LF in such settings. In order to plan the LF control activities, this study was undertaken to confirm the LF infection prevalence in the human and mosquito populations in three urban LGAs.MethodsThe prevalence of circulating filarial antigen (CFA) of Wuchereria bancrofti was assessed by an immuno-chromatography test (ICT) in 981 people in three urban LGAs of Kano state, Nigeria. Mosquitoes were collected over a period of 4 months from May to August 2015 using exit traps, gravid traps and pyrethrum knock-down spray sheet collections (PSC) in different households. A proportion of mosquitoes were analyzed for W. bancrofti, using dissection, loop-mediated isothermal amplification (LAMP) assay and conventional polymerase chain reaction (PCR).ResultsThe results showed that none of the 981 subjects (constituted of <21% of children 5–10 years old) tested had detectable levels of CFA in their blood. Entomological results showed that An. gambiae s.l. had W. bancrofti DNA detectable in pools in Kano; W. bancrofti DNA was detected in between 0.96% and 6.78% and to a lesser extent in Culex mosquitoes where DNA was detected at rates of between 0.19% and 0.64%. DNA analysis showed that An. coluzzii constituted 9.9% of the collected mosquitoes and the remaining 90.1% of the mosquitoes were Culex mosquitoes.ConclusionDespite detection of W. bancrofti DNA within mosquito specimens collected in three Kano urban LGAs, we were not able to find a subject with detectable level of CFA. Together with other evidence suggesting that LF transmission in urban areas in West Africa may not be of significant importance, the Federal Ministry of Health advised that two rounds of MDA be undertaken in the urban areas of Kano. It is recommended that the prevalence of W. bancrofti infection in the human and mosquito populations be re-assessed after a couple of years.

Low transmission of Wuchereria bancrofti in cross-border districts of Côte d’Ivoire: A great step towards lymphatic filariasis elimination in West Africa

“…quinquefasciatus infectivity rates of 6.3% and 6.0% in Nigeria, respectively. Similar findings have been reported in West African countries such as Guinea [47] and Nigeria [48], and in East African countries including Tanzania [49]. A high parity rate is expected to imply that vectors could have sufficient lifespan thus allowing the completion of W. bancrofti worm life cycle, from stage L1 to L3 before transmitting to humans [2].…”

Prevalence of Wuchereria bancrofti infection in human and vector populations from Center-East, East and South-West regions of Burkina Faso: preliminary results

“…The detection of Wuchereria bancrofti L3 within mosquitoes was realized by conventional PCR [8,16,17] using DNA from heads and thoraces of mosquitoes grouped by pool before PCR processes. This technique permitted to analyze the An.…”

Testing a method of sampling for entomological determination of transmission of Wuchereria bancrofti to inform lymphatic filariasis treatment strategy in urban settings

“…Currently, urban, rural or peri-urban areas inside implementation units (IUs) are treated based on the IU Transmission Assessment Survey (TAS) result. MDA in urban settings presents significant challenges and costs, and often coverage is inadequate [3][4][5][6][7].…”

“…While presence of LF in urban areas has been demonstrated, transmission of W. bancrofti itself has been a subject of debate [5][6][7]. Where mapping results have led to treatment in urban areas, elimination was achieved with three or fewer yearly rounds of treatment or without recourse to MDA [7] implying the TAS results may not reflect on-going local transmission [6,7].…”

“…While presence of LF in urban areas has been demonstrated, transmission of W. bancrofti itself has been a subject of debate [5][6][7]. Where mapping results have led to treatment in urban areas, elimination was achieved with three or fewer yearly rounds of treatment or without recourse to MDA [7] implying the TAS results may not reflect on-going local transmission [6,7]. In addition, the findings that West African Culex, the most abundant urban mosquitoes appears to be less susceptible to W. bancrofti, have led to the hypothesis that urban cases of LF could be due to transient inward migration from rural areas rather than be the result of local transmission [4,5,7].…”