A new study by researchers at the Big Data Institute indicates that current World Health Organization (WHO) guidelines for monitoring the control and elimination of schistosomiasis-related disease, especially severe disease such as periportal fibrosis (PPF), may not give an accurate picture of how many people are affected. The study is published in The Lancet Global Health.
Schistosomiasis is a tropical disease caused by a parasitic flatworm that is transmitted to humans through contact with freshwater sources such as lakes and slow-moving rivers. It is estimated to affect around 250 million people every year and more than 700 million people live in endemic areas where infections are common.
PPF is a late-stage complication of schistosomiasis where chronic and repeated infection causes damage to the vessels that supply blood to the liver and eventually in its most severe form to the liver tissue itself. Current WHO guidelines use information about the intensity of a schistosomiasis infection in place of actually diagnosing the disease to estimate how many people are affected by PPF.
To assess whether the current guidelines were able to accurately estimate how many people had PPF according to their infection status and intensity, researchers conducted a systematic review. This review included all published studies (40 studies) to date without language restriction, where cases of PPF had all been diagnosed using ultrasound, and where current infection status or intensity was diagnosed in the same participants.
Key findings:
- People with any current infection were 2.65 times more likely to have PPF when compared with uninfected individuals;
- Infection status was not associated with PPF in studies that used the Niamey protocol (the recommended WHO ultrasound protocol);
- Infection status was not associated with PPF in studies in sub-Saharan Africa after mass drug administration programmes became widespread;
- Infection intensity, which is the only proxy indicator used now by the WHO, rather than status, was not found to be associated with PPF.
Dr Lauren Wilburn, Research Facilitator at Oxford Population Health, and joint lead author, stated ‘Many global targets for schistosomiasis control and elimination focus on parasitic infection intensity. However, this review highlights that infection intensity is not associated with the severe disease, periportal fibrosis. It is clear that to better monitor schistosomiasis morbidity, updated guidance is needed to more accurately estimate disease burden.’
Goylette Chami, Associate Professor at Oxford Population Health, and senior author said ‘Our study has found that current schistosome infection status and intensity of infection are only tenuously associated with risk of PPF, and no longer relevant in the context of repeated mass drug administration. There is a need for the WHO to urgently develop guidelines for schistosomiasis-related morbidity that focus on the disease and not current infection to help endemic countries progress towards providing more equitable healthcare for schistosomiasis.’