Control of schistosomiasis in Cameroon: searching for evidence

By Russell Stothard and Louis-Albert Tchuem-Tchuenté

Schistosomiasis, also known as Bilharzia, is a disease that often doesn’t show any symptoms for several months or even years. Worms that cause schistosomiasis live in fresh water. Having been infected with these parasites that burrow through the skin, it is only after some time that people might get a high temperature, cough, diarrhoea and then progressive damage to the internal organs such as the bladder and bowel. Symptoms might disappear after a while too, but the parasite stays in the body causing serious long-term ill health, for example, infertility in women. The parasite also continues to be transmitted back into the environment, spreading further.

This neglected tropical disease needs more attention. De-worming tablets can make all the difference, and COUNTDOWN’s second integrated complementary strategy theme (ICST-2) is going to research the effectiveness and acceptability of expanded access to this deworming medication in Cameroon and Ghana.

For example, Cameroon only provides annual praziquantel (PZQ) treatment by mass drug administration to school-aged children. It’s possible to buy PZQ over the counter in local pharmacies, but the availability of this drug within the general health system is poor. Pre-school aged children and women of reproductive age are vulnerable here because without regular treatment they will continue to suffer. The parasites continue to be fed back into the environment, via stool or urine, first infecting snails then others in the community.

Over the coming years, COUNTDOWN will seek to foster the scale-up and wider access of PZQ treatment to people who are not currently targeted within national control programmes. We will also assess acceptability and find out it is both sustainable and cost-effective at the community level. In addition, expanded access to PZQ treatment could also accelerate progress towards the reduction of schistosomiasis transmission in the environment.

Water, sanitation and hygiene

The parasites that cause schistsomiasis – also known as schistosomes – live inside freshwater snails. Schistosomes are able to multiply themselves to enormous numbers each day and although the stages are short lived – they typically dying within 24 hours – a new wave of parasites are released the next day from infected snails.

While this is well known to many parasitologists, its importance and significance has been largely ignored within the water, sanitation and hygiene (WASH) community and agenda. Put simply, any aquatic habitat that people use and that contains infected freshwater snails is a high-risk location for schistosomiasis. Some very simple water hygiene measures – if used daily – can make the water safe, yet they remain out of reach for millions in rural Africa.

Furthermore, any efforts to make water safe needs to be tailored specifically to each demographic group in the population, as they each have different requirements and abilities to accept change. Mothers, for example, collect water for their domestic chores and typically bathe their children with it.

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A child washing at Barombi Kotto

Eliminating schistosomiasis

How can we eliminate schistosomiasis? It’s a big question. The influential and heavily cited paper by Rollinson et al. (in which we both played a part) first outlined the need to develop a guiding framework for the surveillance of schistosomiasis in the environment. This has become ever more pressing and an issue for even closer consideration within the European health sector, given the recent focus of urogenital transmission on Corsica. Developing a strategic framework is especially important in the context of the WHO 2020 Roadmap targets. Here, certification of elimination of transmission will be needed or any reasons for its failure will need to be explored.

It is obvious that PZQ treatment should be expanded to all groups at risk of infection, as highlighted by the World Health Organization. It is less popular, however, to justify its use in reducing schistosome transmission. This year, several mathematical modelling studies suggest we should no longer overlook the significant environmental transmission of schistosomiasis from groups outside school-aged children. Moreover, as we slowly gain control of the disease, the relative roles each group plays in sustaining local transmission will also be dynamic.

With this in mind, we are looking for examples in Cameroon where COUNTDOWN activities are able to develop new coordinated intersectoral actions. This will provide a more holistic vision of how to expand access to treatment for people who need it, alongside environmental studies that measure reductions in transmission.

Cameroon: searching for evidence

In Cameroon, the communities at Barombi are at greatest risk of urogenital schistosomiasis, largely because of the presence of a key species of Bulinus, the genus of freshwater snail that are permissive hosts for Schistosoma haematobium in Africa. It is the absence of other snail species at Barombi that allows us to focus on urogenital schistosomiasis alone.

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A snail distribution map of Barombi Kotto with species indicated in green and blue

Our recent field surveys undertaken in June 2016 in the crater lakes of Barombi Mbo and Barombi Kotto are starting to reveal the need to further develop a guiding strategic framework. It would measure schistosome infection alongside local environmental transmission. The sampling framework is appropriate and implementable with resources typically at hand in the sub-Saharan African region.

Since urogenital schistosomiasis also has links with female health, we can better research reasons why this parasite, which is transmitted in urine and not stool, remains a considerable health burden at Barombi Kotto and Barombi Mbo. Significant investment at Barombi Mbo has meant the building of safe water sources with piped water available to all households. However, we need to assess how current WASH interventions can be further refined to dampen local parasite transmission. For example, social science investigations could reveal why some people are unable to benefit from these interventions or continue to use unsafe water.

The two locations of Barombi are important areas for multidisciplinary studies. Here, our research will test the effectiveness and acceptability of expanded access of de-worming PZQ treatment and record any changes in environmental transmission. The research also examines biannual treatment schedules, as a way to promote equity of treatment, but also to accelerate reduction in transmission and elimination. Evidence is needed to support elimination, as there is currently no formalised WHO framework to do this. While guidelines for lymphatic filariasis with transmission assessment surveys (TAS) exist, there are none for schistosomiasis. Both national and international policies are lagging behind in this area. It is a great opportunity for our COUNTDOWN research to make an impact.

Our initial results will be presented on the 14th and 15th June at the meeting Global Schistosomiasis Alliance in China, so please watch this space!

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