SchistoTrack

Rationale

Schistosomiasis is a neglected tropical disease caused by the parasitic flatworm of the genus Schistosoma. Over 700 million people worldwide live in areas with ongoing pathogen transmission with an estimated 250 million current cases. More than 90% of current cases are in sub-Saharan Africa where S. mansoni is common and causes intestinal schistosomiasis. For intestinal schistosomiasis, chronic infection can lead to severe disease including enlarged spleen/liver, liver fibrosis, portal hypertension, upper gastrointestinal tract bleeding, and ultimately premature death.

There exists widespread treatment for schistosome infections, but no routine, widely available treatment or management strategies for the disease caused by chronic infection. Praziquantel is administered in a blanket treatment without diagnosis to individuals in at-risk areas. This strategy of mass drug administration aims to treat infections before disease develops and does not prevent reinfection. Residual schistosomiasis-related morbidities remain after mass drug administration and pose complex problems to health systems where schistosomiasis is not commonly managed. More information is needed to understand the risk factors for schistosomiasis-related morbidity within the context of repeated mass drug administration and to identify the determinants of severe disease progression as well as management strategies that can be implemented within local health systems.

Establishment

The SchistoTrack Cohort is a close partnership between the Division of Vector Borne Diseases and Neglected Tropical Diseases at the Uganda Ministry of Health and Big Data Institute and Nuffield Department of Population Health at the University of Oxford. SchistoTrack is part of the Oxford-Uganda Collaboration on Schistosomiasis led by Associate Professor Dr Goylette Chami (Oxford) and Dr Narcis Kabatereine (Uganda).

There are core multidisciplinary teams involved in the project: sonographers, malacologists, surveyors, technicians, nurses, doctors, counsellors, data scientists, epidemiologists, and statisticians. Additional project support and expertise is frequently provided from village health teams, district and national politicians, hospital and primary health centre workers, ethics committees, and importantly the study participants and local community leaders. 

Cohort

SchistoTrack is a prospective community-based cohort in rural Uganda, which collects clinical, socioeconomic, and environmental data to better understand transmission and morbidity of schistosomiasis. The primary aim of the cohort is to understand infectious causes of liver disease progression, with a secondary focus on gut and splenic disease. The cohort is based in Eastern and Western Uganda in Pakwach, Buliisa, and Mayuge Districts where there are diverse populations, risk factors, and disease.

SchistoTrack was established in 2022, initially with 38 villages, >1450 households, and >2800 clinical participants. In 2023, the Cohort expanded to include 52 villages, >1900 households and >3800 enrolled clinical participants. In 2024, the Cohort expanded again to include 52 villages, >2200 households, and >4500 enrolled clinical participants. Villages are sampled to be within five kilometres of the Nile River, Lake Albert, or Lake Victoria. Households were randomly sampled within villages. And, within each household, one child 5-17 years and one adult 18+ years were sampled by the household head to be followed yearly for clinical measurements. By revisiting the same participants yearly, long-term risk factors and disease progression can be monitored. Annual follow-up is planned until the year 2026. The main outcome is periportal fibrosis as diagnosed via ultrasound. The key exposures are schistosome, malaria, hepatitis B, and HIV infections as well as current alcohol use.

Teams of surveyors first visit new households to collect detailed survey information for every person in the home regarding water, sanitation and hygiene behaviours, water contact patterns, socioeconomic information, health access, medical histories, and availability of physical infrastructure. Every year clinical teams examine the same two participants per household. Stool, blood, and urine samples are assessed; abdominal palpations and ultrasound scans are conducted; and praziquantel and antimalarial treatment are provided through government health outreach. For all village members, ancillary care is offered. Government nurses provide medical referrals and transportation is provided. Annual community engagement at national, district, and community levels is completed to receive study feedback, build local clinical capacity, and share medical findings. Study teams also revisit participants one time each to assess praziquantel efficacy or parasite clearance approximately 3-4 weeks after treatment during the annual timepoint.

Schistosoma parasites are transmitted via snails that reside in freshwater; therefore, water contact is strongly associated with parasite transmission. To capture this step in the parasite lifecycle, water contact and malacology (snail collections) also are conducted. Trained teams of malacologists record annually the abundance, diversity of snail species, and the prevalence of snail infection. All potential water contact sites within study villages are visited. Water contact observations are measured by household surveys, direct water contact observations, and GPS loggers worn by study participants. A seasonal timepoint was incorporated to capture variation in schistosomiasis and malaria prevalence as well as differences in malacology.