New research highlights that even low levels of human contact with open freshwater sources are associated with an increased likelihood of infection with water-borne parasites. The results are published today in PLOS Neglected Tropical Diseases.
Schistosomiasis is a poorly understood tropical disease that is estimated to affect over 250 million people with approximately 779 million people at risk globally. Over 90% of these individuals live in sub-Saharan Africa.
The disease is caused by a parasitic fluke (worm) that lives in the blood stream and is transmitted via human contact with freshwater sources. Water bodies such as lakes, rivers, and streams are inhabited by freshwater snails which release the infectious stage of the parasite. Infections can cause severe liver and spleen damage or bladder cancer, depending on the species of the parasite.
The World Health Organization (WHO) focuses treatment on high-risk groups such as school-age children and fishermen. However, it is not clear to what extent water contact can explain who is at high infection risk. Populations in areas where the infection is common may acquire some immunity through past exposures. The water contact activities people engage in, such as fishing, bathing, and doing laundry, vary between age groups and genders and different activities carry different risks. Infection also depends on environmental conditions that influence the number of snails in the water.
Researchers from the University of Oxford’s Big Data Institute carried out a systematic review of 101 studies involving 192,691 participants in 22 countries across three continents (Africa, Asia, and South America), published between 1984 and 2022. Among the 101 studies, 98 provided data on associations between water contact duration, frequency, and activities with schistosome infection. By analysing these data, the researchers were able to quantify the overall association between water contact and infection, whether the association varied across age groups, and whether different activities carried different risks.
Read the full story and key findings on the Nuffield Department of Population Health website.