Investigating the freshwater snails of Lake Albert, Uganda: A lesson in Neglected Tropical Diseases

By John Archer

Infection with parasitic trematodes, giving rise to debilitating and life-threatening diseases such as schistosomiasis and fascioliasis, affect more than 500 million people and a countless number of other vertebrate hosts globally. For transmission of such diseases to take place, just three simple ingredients are required; the presence of infected freshwater snail intermediate hosts; a suitable aquatic habitat in which they can survive; and repeated human, or animal, water contact with this habitat.

As a postgraduate student at the Liverpool School of Tropical Medicine embarking upon his Masters’ dissertation, I was recently fortunate enough to conduct fieldwork along the shoreline of Lake Albert, Uganda. My project aims to investigate not only freshwater snail population dynamics in this region, but also the human and animal trematode infections they may, or may not, be transmitting; building on recently published work with a similar focus along the same shoreline. In addition, the trip gave an eye-opening and invaluable opportunity to witness and experience first-hand communities so heavily burdened with Neglected Tropical Diseases (or NTDs), that they are an ingrained part of everyday life.

Our research

Freshwater snails collected from aquatic habitats at the lake’s edge were screened on-site for trematode infection using a shedding analysis; a procedure that involves placing snail hosts into individual shedding trays containing bottled drinking water throughout the day (you can imagine my guilt using clean water in this way given the environment we were in). The bottled water is then examined using a dissecting microscope for the presence of shed cercariae; the free-swimming trematode larval stage responsible for human and animal infection.

A variety of different cercariae species were found; each with their own distinctive swimming behaviours and morphologies. Furthermore, staining the cercariae by adding a drop of Lugol’s iodine to the water sample and pipetting it onto a glass slide for observation under a compound microscope allowed for closer morphological analysis, as well as providing a great opportunity to take pictures of our findings.

Photo collage

Above (left):  Melanoides, Biomphalaria and Bulinus freshwater snails capable of transmitting trematodes infections.  (Middle): Myself and Russell Stothard collecting freshwater snail samples at Lake Albert’s edge. (Right): Three trematode cercariae of different species shed from collected freshwater snails capable of infecting humans, birds and amphibians.

Collecting samples at the lake’s shore across a multitude of villages truly emphasised its significance as a resource essential for both human and animal survival. Whether utilised as a source of drinking water, a place to bathe, an area to catch fish, or just as a means of recreation, one thing was clear; contact with these potentially dangerous waters is currently both completely necessary and patently inevitable.

As such, until enhanced and repeated access to donated treatment, an increased awareness of disease transmission and a reduction in water-contact through means such as improved sanitation are implemented, trematode disease transmission will, undoubtedly, persist in these villages.

uganda lake 2

The lake’s edge at Butiaba; people interacting with potentially dangerous waters is a common sight.

Looking ahead

Having returned to Liverpool, I’m very much looking forward to the next steps in my project; assessing the population dynamics of both snail hosts and trematodes using GIS mapping and statistical analysis; employing molecular methods to further characterise and quantify snail trematode infection status’ and transmission potentials, as well as visiting and working with world-leading experts in this field at London’s Natural History Museum. Watch this space.

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The Neglected Tropical Disease hotspot puzzle requires multidisciplinary investigation

Sally Theobald, Margaret Gyapong, Mike Osei-Atweneboano, Sheila Addei, Alexander Adjei, Adriana Opong, Samantha Page and Kate Hawkins Dr Benjamin Kofi Marfo, Deputy Director of the Neglected Tropical Disease (NTD) programme in Ghana, is fizzing with energy as he explains the NTD hotspot conundrum in Ghana. Hotspots, or areas with persistent NTD prevalence above a threshold set by the World Health Organisation, present the final hurdle to elimination of certain NTDs. The COUNTDOWN team meeting in Accra brought together the Ghana Health Service (GHS) NTD team, colleagues from Dodowa Health Research Centre, the Council for Scientific and Industrial Research, Liverpool School of Tropical Medicine and Pamoja Communications. Together we discussed the map of hotspots for Lymphatic Filariasis (LF) in Ghana – bringing to mind a detective story – we debated different explanatory possibilities:

  • Border areas: All but four of the 22 hotspot areas are either on the border or next to a border district – with the Cote D’Ivoire (West of Ghana), and Burkina Faso (North of Ghana), but intriguingly not Togo (East of Ghana). These borders, carved up by colonial powers, separate families and communities and in reality are porous with regular movement and trade across them. Could it be that people here are missing Mass Drug Administration as they move from one country to the other? Dr Marfo and his team discussed the importance and challenge of cross border NTD collaboration and the possibility of synchronising approaches to MDA to minimise losing people from the process.
  • Genetic variation in human population: Why is it that in some families people get LF and others don’t although their exposure is arguably similar. Are there some genetic factors at play which predispose certain individuals or communities to LF?
  • Genetic variation in parasite or vector population that we don’t understand: Are there some genetic changes in some population of parasites and/or vectors and some geographically specific adaptation going on that needs further investigation?
  • Context specific socio-cultural beliefs or practices: Or is there something specific about the understanding, livelihoods and socio-cultural realities of these communities that lead to additional vulnerability or challenges in accessing and adhering to drugs (or in NTD language are there more persistent non-compliers in hotspots?)
  • Health system challenges: Or could it be that there are some health systems challenges and bottle necks within the hotspots? Challenges relating to distribution or possibly community based drug distributors feeling under motivated and undervalued?

Or does the explanation lie in a mixture of some or all of the factors above? Trachoma is on the road to elimination in Ghana. However, with the exception of the Upper East Region, it is more problematic in the Northern and Upper West Regions of Ghana. Why is the Upper East Region less affected? Dr Marfo explained how this district has benefitted from different Non-Governmental Organisations conducting water, sanitation and hygiene programmes, which have supported access to fresh water and the construction of latrines. There is also an eye hospital in the Region which has enabled earlier access to treatment. The trachoma story highlights the importance of understanding the context and historical evolution of the Regions when looking at NTDs. It also illustrates the positive legacy of interventions in water and sanitation and the importance of multisectoral partnership in efforts to address the debilitating and disabling effects of NTDs. The tricky conundrum presented by hotspots demands multidisciplinary investigation and multi-sectoral engagement to understand which factors play out in different contexts to shape hotspots. COUNTDOWN brings together social scientists, health systems researchers, health communication experts, health economists, parasitologists, molecular biologists and modellers to work in partnership with NTD programmes in Ghana, Cameroon and Liberia to support NTD programmes. Watch this space as we bring different disciplines to bear to understand and address hotspots.

Hot topics in schistosomiasis

COUNTDOWN has been busy this week at the mini-symposium on ‘hot topics’ in schistosomiasis at Leiden University Medical Center in the Netherlands. Russell Stothard represented the Consortium and says:

“I am delighted to present at Leiden amongst friends and colleagues who have contributed so much to the advancement of tropical parasitology. I will present our recent experiences in Uganda and Namibia where we have used the CCA test and also uncovered that there are still barriers to its effective deployment within the health system. This is something which we will hope to address more specifically in COUNTDOWN to ensure that preventive chemotherapy approaches against schistosomiasis have the future impact we expect of them.”

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