Researchers at Oxford Population Health have found wide variations in the diagnosis of liver fibrosis resulting from a parasitic infection that causes schistosomiasis. The research suggests that the current protocols recommended by the World Health Organization (WHO) need to be revised. The study is published today in PLOS Neglected Tropical Diseases.
Schistosomiasis is a tropical disease that affects around 250 million people every year. Over 90% of the people at risk of schistosomiasis live in sub-Saharan Africa. Schistosomiasis is caused by a parasitic worm that is transmitted to humans through contact with freshwater sources such as lakes and slow-moving rivers.
The intestinal form of schistosomiasis can cause periportal fibrosis (PPF), which in severe cases can result in excessive liver scarring that blocks blood flow to the liver and prevents it from working properly. This blockage causes enlarged veins in the oesophagus and, if not treated, will burst resulting in the vomiting of blood. There are three species of parasite that can cause PPF: Schistosoma mansoni, S. japonicum, and S. mekongi.
PPF is diagnosed using an ultrasound scan. Sonographers and radiologists then use staging systems to describe how much scar tissue has built up in the liver and the pattern of scar tissue across the liver and the vessels that supply blood to the liver.
Ultrasound staging systems have been developed since the late 1980s in an attempt to standardise the collection of data in studies on schistosomal PPF. The latest staging system for S. mansoni-related disease is the Niamey protocol, which was first published in 1996 and last updated in 2000 by the WHO. A staging system for S. japonicum-related disease was published by the China Centre of Disease Control, also in 2000.
The researchers reviewed 192 studies that were carried out between 1979 and 2019 to find out whether or not these protocols were being used consistently over time and whether the protocols were appropriate for current disease control. They also wanted to see whether data collection procedures and the available technologies for diagnosis had changed over time and whether there was a case for reviewing the guidance.
Key findings:
- Ultrasound procedures, interpretation of the ultrasound, the users of the ultrasound, the type of technology used, and the definition of PPF were reported inconsistently across all of the studies. When this information was reported consistently, there were wide variations in how it was reported. However, very few studies reported much more than the definition of PPF that they used;
- There was widespread use of only one element (the patterns of liver scarring) of the Niamey protocol to stage PPF as opposed to using the score suggested in the guidance, which takes into account many more elements such as the size of the main portal vein that carries blood to the liver;
- There was a wide range of example use-cases for clinical actions and for accurately staging PPF using ultrasound images. Coupled with the inconsistent interpretation of results from similar use-cases, the findings highlighted a need to specify particular criteria for developing a protocol for ultrasound scans when the use-case was for screening PPF rather than managing already-diagnosed cases or even using the protocol to train new sonographers.
Eloise Ockenden, DPhil candidate at Oxford Population Health and first author of the study, said ‘Our study is the first to review the existing research on using ultrasound scans to diagnose and stage schistosomiasis. Protocols for collecting data on schistosomiasis infections must be updated urgently to take into consideration new technologies and progress in the field, such as advances in machine learning to analyse large datasets, which are underrepresented in work on neglected tropical diseases.
‘We are developing automated diagnostic tools for the staging of schistosomal PPF as part of the SchistoTrack study to support improvements in diagnosis and care for affected communities. My goal is to create an end-to-end pipeline for schistosomal PPF detection that is informed by clinical relevance and impact at each stage. I hope that this can be developed into a diagnostic tool that can impact the communities that need access to PPF diagnosis.’
Dr Goylette Chami, Associate Professor at Oxford Population Health and senior author of the study, notes ‘Both the WHO Department of Control of Neglected Tropical Diseases and the WHO- Regional Office for Africa are considering how to move forward with schistosomiasis surveillance and elimination. Our extensive review will feed into future guidelines on developing protocols to assess morbidity and highlights the considerations needed for particular use cases. We hope that the WHO will bring together experts to reach a consensus on disease guidelines for schistosomiasis and ultrasound protocol revisions.’