Towards Evidence-based Control of Opisthorchis viverrini

Abstract

Transmission of the carcinogenic liver fluke Opisthorchis viverrini is ongoing across Southeast Asia. Endemic countries within the region are in different stages of achieving control. However, evidence on which interventions are the most effective for reducing parasite transmission, and the resulting liver cancer, is currently lacking. Quantitative modelling can be used to evaluate different control measures against O. viverrini and assist the design of clinical trials. In this article we evaluate the epidemiological parameters that underpin models of O. viverrini and the data necessary for their estimation, with the aim of developing evidence-based strategies for parasite control at a national or regional level. Assessing InterventionsControl initiatives against the liver fluke O. viverrini are driven by two related aims. Firstly, to reduce transmission of the parasite, leading to its elimination (see Glossary). Secondly, to halt the progression of O. viverrini-induced liver pathology, and thus prevent new cases of cholangiocarcinoma [1]. In endemic regions, definitive hosts become infected through consumption of raw or insufficiently cooked freshwater fish encysted with metacercariae and perpetuate the life cycle by defecating into water sources containing snails of the Bithynia genus. Programmes to control O. viverrini therefore have a number of interventions available to them, including health education to promote safe eating habits; case diagnosis and anthelmintic treatment; improvements to sanitation; and food safety controls [2]. Parasite-induced liver pathology can be tackled with ultrasound screening to detect periductal fibrosis, an early warning sign of cholangiocarcinoma; and operative surgery to improve survival rates [3]. With such a variety of tools on offer, policy makers, international health organisations, and affected communities are entitled to ask: what works? Which measures are most effective at interrupting transmission of the parasite and reducing mortality in a cost-effective, sustainable manner?The traditional method for answering this question is through randomised controlled trials, which are the gold standard for assessing interventions [4]. Such trials, however, are costly, take many years, and require substantial manpower and expertise. It is also unethical to conduct trials in contexts where public health initiatives are ongoing and would have to be withdrawn for participants allocated into the control arm of a trial. An alternative approach is to use quantitative models to make predictions on the effectiveness of different control strategies. These models take myriad forms, can be parameterised from routinely collected field data, and provide considerable insight for a fraction of the cost of a trial. Different types of models that can capture macroparasite dynamics are summarised in Box 1.When the need to conduct a clinical trial is unavoidable, for example on novel therapeutics or diagnostics, dynamic simulations can provide powerful insights into trial design, power HighlightsH...

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