A Bed Net to Rule Them All: Accelerating Lymphatic Filariasis Elimination Through Malaria Control Programmes

by Corrado Minetti

In rural areas of Africa, Lymphatic Filariasis (LF) is primarily transmitted by night-biting Anopheles mosquitoes, which also transmit malaria. Currently, the two major ways of controlling malaria vectors are the indoor residual spraying (IRS) of insecticides and the use of bed nets. It has been estimated that the combination of these two interventions, in the decade 2000-2010, has prevented  more than 200 million new cases and more than 1 million deaths due to malaria.

In areas where both LF and malaria occur and are transmitted by the same mosquitoes, should we then promote vector control alongside mass drug administration (MDA) to accelerate the elimination of LF through a better and more cost-effective integration of LF and malaria control programmes at the national level?

The answer is yes.

The importance of vector control for lymphatic filariasis elimination

Reducing mosquito numbers and preventing people being bitten has a significant impact in reducing the burden of LF and, ultimately, pushing towards its elimination. As it has been reported in various countries around the world the use of bed nets, IRS and/or reducing the mosquito breeding sites can all result in a significant reduction of LF transmission even in the absence of MDA. For example, in Papua New Guinea the deployment of insecticidal bed nets in communities where MDA was stopped 10 years before resulted in a reduction of the LF transmission potential down to zero within only 11 months following distribution.

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A long-lasting insecticidal net (LLIN) in Agyan (Ghana) (Photo: Corrado Minetti)

Mathematical models have clearly shown the strategic impact of implementing vector control alongside MDA for LF: reducing the human-mosquito exposure allows reaching the community and vector infection thresholds below which LF transmission will be interrupted faster and earlier compared with using MDA alone. As a result less rounds of MDA may be needed to reach elimination if vector control is in place, with important savings for the programme.  Furthermore, sustained vector control may avoid the resurgence of LF in treated communities in a post-elimination setting (after MDA has been stopped) due to the potential re-introduction of the disease through human movement.

The way forward: integration of lymphatic filariasis and malaria control programmes

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Mass distribution of ivermectin for LF elimination (on the left, source: www.mectizan.og) and bed nets for malaria control (on the right, source: www.usaid.org)

Given the importance of vector control for LF elimination; with LF and malaria being transmitted by the same mosquito vectors in West and rural Africa, integrated vector management (IVM) becomes crucial. There is a tremendous opportunity to effectively integrate the LF and the malaria control programmes, making both more efficient and cost-effective.

Establishing a synergy between MDA for LF and bed nets distribution/indoor insecticide spraying for malaria can have two major effects which will be extremely beneficial for the fight of both diseases. Firstly, a more efficient use of resources: the same community distributors delivering the drugs can distribute bed nets at the same time leading to important savings in terms of time and human resources. Secondly, a higher impact on the burden of both diseases: MDA campaigns can facilitate the distribution and penetration of bed nets in the community and vice-versa.

The beneficial effects of an integration of MDA and bed nets distribution has been clearly shown in Nigeria, where the concomitant delivery of nets alongside MDA resulted in a significant improvement in insecticide-treated bed net ownership and use (up to 9-fold) and it did not negatively affect the MDA coverage.

Following the above evidence, in 2014 Nigeria has been the first country in Africa to launch a Nationwide Malaria and LF elimination Co-Implementation Plan alongside specific guidelines.

We now have the tremendous opportunity to promote a better cross-talk between the vector borne disease-specific communities, stakeholders and policy-makers in order to raise awareness on the importance of a sustained and better planned vector control leading to a more cost-effective and effective use of resources across disease control programmes.

Within the COUNTDOWN research consortium, we recognize that the scale-up of MDA won’t be enough to achieve the London Declaration 2020 targets for the elimination of lymphatic filariasis. In particular, following the example of Nigeria, we are seeking opportunities in Ghana for an integration of the national LF elimination and malaria control programmes to co-ordinate MDA distribution and delivery of vector control interventions and to evaluate the impact of such synergy on service delivery, community participation and cost-effectiveness.

Find more information on COUNTDOWN’s activities here.

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Patience and prior knowledge: simple requirements for schistosomiasis control

By Suzy Campbell

Schistosomiasis is challenging and complex whichever way you look at it! From its five-syllable name, to its subtle but extensive disease burden, to its lifecycle in aquatic and mammalian hosts, to its control with preventive chemotherapy and – dare we hope – to its elimination by intersectoral action.

Take for example the schistosomiasis life cycle (see below). It’s so complicated that despite many attempts it was only unravelled 100 years ago, by a parasitological pioneer, Robert T. Leiper. Before this, it was not known that there was more than one type of schistosomiasis. Added to this the snail hosts’ roles were not clear and as a result little could be done to develop control strategies in any meaningful way. This meant that schistosomiasis struck fear in the hearts of many.

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There are so many interesting points to emerge from Leiper’s work. He first identified the separate African schistosome species; a contribution of tremendous value to parasitology because one (Schistosoma mansoni) is linked to intestinal schistosomiasis and the other (Schistosoma haematobium) to urogenital schistosomiasis.

Importantly, Leiper also identified and applied simple water safety measures as versatile ways to reduce schistosomiasis transmission. This included simple filtration, water boiling, use of disinfectants and resting water for 24 hours before use. In addition, his clarification of the snail intermediate hosts paved the way for attempts to remove or destroy the snails. These were all practical control strategies which were useful in schistosomiasis control, well in advance of deworming tablets being developed. All that was needed was a little patience and adequate temporary water storage.

Roll forward 100 years. Some things have changed. We are very fortunate in that we have very effective deworming tablets, although they only reach a small portion of the people who need them, and possibly not at the right frequencies to sufficiently control disease.

However, some things have not changed. The subtle morbidity of schistosomiasis is still under-recognised: for example the clinical significance of schistosomiasis in very young children and the importance of female and male genital schistosomiasis. Environmental strategies, such as water safety measures, seem to have largely been forgotten. In particular, our behaviour and perceptions of how water is used should be questioned. Water is not always safe (see below). Until we recall the prior knowledge imparted by the likes of Leiper, schistosomiasis should still strike fear in our hearts. It will not go away.

 

 

This is a village in Cameroon, showing a public tapstand as an improved water supply. But ‘run off’ water flows as an open stream, continuing through the centre of the village. Had a snail intermediate host been residing in this stream, schistosomiasis could have been prevalent despite the improved water source. (Photos: R. Stothard, S. Campbell)

A newly-released Special Issue Review in Parasitology gives an entertaining and thorough biography of Leiper’s contributions to parasitology and the developing field of ‘medical malacology’. This review covers 100 years of the history – and at times controversy – since Leiper’s elucidation of the Schistosoma life cycle and development of practical control strategies. The review goes on to illustrate how Leiper’s contributions still have relevance today, indicating a need for integrated control mechanisms, and introducing the COUNTDOWN research consortium which focuses on implementation research to provide tangible health improvements.

Globally, there is a paradigm shift for schistosomiasis, from morbidity control to transmission control, and eventual elimination as a public health problem. More than ever we are going to need to be guided by integrated and broad-based control strategies. This has been well-recognised by the World Health Organization (WHO), with their recent release of the Water, Sanitation and Hygiene (WASH) for Neglected Tropical Diseases (NTDs) Global Strategy 2015-2020. This calls for intersectoral collaboration to address NTDs by augmenting current control programmes with additional WASH activities.

Progression of a global NTD integration agenda is being increasingly recognised by NTD practitioners, researchers, and other policy makers. International consortia, such as the Schistosomiasis Control Initiative, and now COUNTDOWN, will play a part in driving this agenda. Some of the integration and WASH concepts will be elaborated upon at the annual COR-NTD meeting in November 2016. Work is also progressing within COUNTDOWN on two manuscripts to address aspects of environmental frameworks for schistosomiasis transmission control. The imperative lies with all NTD partners to ensure that Leiper’s work will continue resonating true today.

Find more information on COUNTDOWN’s activities.