A new study by researchers at the Big Data Institute has shown that having current water contact is not necessarily indicative of a current schistosome infection. The study highlights the complex human-environmental drivers of transmission, showing that drivers of water contact and infection were largely distinct. The study is published in Nature Communications.
Schistosomiasis is a neglected tropical disease which affects 250 million people globally. More than 700 million people live in endemic areas which are predominantly in sub-Saharan Africa. Schistosome infection is caused by parasitic flatworms and occurs when people have contact with freshwater sources such as lakes and rivers. This enables the parasite to bore through the skin and establish an active infection in the human host.
There is no vaccine for schistosomiasis. At-risk communities are repeatedly treated with praziquantel through mass drug administration campaigns, but individuals are often reinfected rapidly. Consequently, mass drug administration programmes need to be combined with other control measures such as behaviour change strategies to meet the World Health Organization's (WHO) 2030 goals for eliminating schistosomiasis as a public health problem. One major challenge in devising multifaceted control strategies is that there is limited knowledge about the groups most at risk of exposure to schistosomes and the factors determining risk of exposure.
In this study, researchers from Oxford Population Health and the Uganda Ministry of Health surveyed 2,867 individuals across 38 diverse villages in Eastern and Western Uganda. The individuals were all part of SchistoTrack, a community-based study aiming to better understand schistosome exposure and resulting infection.
The researchers collected information on a variety of socio-demographic and environmental factors, as well as detailed information on participants’ water contact activities. To determine the current schistosome infection status of participants, the team collected stool samples examining them for parasite eggs using microscopy. Researchers then used advanced statistical modelling to separately identify relevant predictors of water contact and infection.
Key findings:
- Among study participants, 43% were infected with schistosomes and 47% reported having contact with freshwater bodies at least once per week. The median frequency was six times per week and the median duration eight hours per week among those with water contact;
- There were clear gender differences in water contact, as women and children predominantly engaged in domestic water contact while men mostly engaged in fishing;
- Reported water contact rapidly decreased with household distance from water bodies as 80% of all reported water contacts occurred in households within 430m of water sites. However, infection rates did not follow this same trend and remained elevated even at 1km water site distance;
- There was no significant correlation between infection status and having any water contact. Trends in infection and water contact over age were also different. Infection rates peaked at age 15, whereas water contact peaked at age 30;
- Environmental variables and other variables at the village and household level were comparatively more important for predicting water contact than for infection. Among the 10 variables which were relevant for water contact, only 50% were selected as predictors for infection.
Goylette Chami, Associate Professor and Robertson Fellow at Oxford Population Health and senior author of the study, said ‘This study highlights the complexity of human exposure and the need for future research and implementation work to identify how water contact reduction interventions could be best integrated within mass drug administration programmes. It also calls on the WHO or other stakeholders to create tools for assessing water contact as part of country monitoring and control programmes.’
Narcis Kabatereine, co-investigator of the SchistoTrack study, remarked ‘This study has implications for control efforts because of the potential to use precision mapping for isolating the communities with highest exposure and targeting these areas through spatially-targeted interventions while saving drugs and resources in lower risk communities.’
Fabian Reitzug, DPhil student at Oxford Population Health and lead author, added ‘A key challenge for exposure studies has been reliable water contact measurement. Self-reported measures have been the most widely used but are considered less reliable than direct observations or wearable GPS data.
‘We show that self-reported water contact provides valid population-level estimates. Still, there remains a need for future research to understand the fine-scale dynamics of water contact and better link human behaviour and environmental risk. So, some of my ongoing work uses data from wearable GPS loggers within the SchistoTrack study to build granular models of human water contact behaviour.’