Inferring Clearance and Reinfection Dynamics of Schistosoma mansoni from Kato-Katz and Circulating Cathodic Antigen-based Diagnostics.

Tue16  Apr12:39pm(3 mins)
Renold C16


J Clark1; P H Lamberton2; J M Prada3
1 Faculty of Health & Medical Sciences, University of Surrey, UK;  2 Institute of Biodiversity, Animal Health and comparative Medicine, and Wellcome Centre for Parasitology, University of Glasgow, UK;  3 University of Surrey, UK


Schistosomiasis is a debilitating disease causing chronically poor health with over 240 million people infected. The World Health Organization has set ambitious control and elimination goals, though key to their success, are suitable diagnostic tools and efficacious treatment programmes. The predominant intervention strategy is mass drug administration (MDA), implemented in response to baseline infection prevalence estimates. However, though treatment may immediately reduce infection prevalence and intensity, prevalence commonly returns to pre-treatment levels within 6 months. This suggests that successful clearance is followed by rapid re-infection, however, as adult Schistosoma clearance and reinfection cannot be directly observed these dynamics remain unclear. The clarification of these dynamics is further hindered by reliance on excreted egg counts and antigen detection as proxy infection measures. The egg-count based Kato-Katz (KK) technique, which is highly Schistosoma specific, lacks sensitivity when infection burdens are low, including post-treatment. Alternatively, Circulating Cathodic Antigen (CCA) tests have proven to be more sensitive to low intensity infections, but suffer from inconsistencies in the interpretation of “trace” results, leading to highly divergent epidemiological and drug efficacy estimates. To understand post-treatment dynamics, and to improve upon prevalence estimates, a hidden Markov model was developed drawing on longitudinal KK and CCA diagnostics data, to infer the proportion of children in a cohort that experience clearance and reinfection. In addition to the conventional “trace”, +, ++, +++ scale of CCA results, a newer 1-10 scale was used, allowing for increased precision, particularly at low antigen levels. This work provides valuable insight into Schistosoma infection dynamics and emphasises the strengths and short-comings of current diagnostic strategies.

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