Morbidity control of schistosomiasis by mass drug administration: how can we do it best and what will it take to move on to elimination?

Abstract

The World Health Organization (WHO) has, for some time, encouraged countries endemic for schistosomiasis to control morbidity from this disease through mass drug administration (MDA) of the well-tolerated drug, praziquantel (PZQ). With the London Declaration in January 2012 and the promise by Merck Serono to eventually donate 250 million PZQ tablets per year, most endemic countries in sub-Saharan Africa have now developed national plans to do MDA for schistosomiasis morbidity control. More recently, based on two World Health Assembly (WHA) resolutions (WHA 54.19 & WHA 65.21) on schistosomiasis, countries are further encouraged to eliminate schistosomiasis, where feasible. The fight against schistosomiasis is therefore in a critical period of tremendous opportunities and equal challenges. How do we do the most effective job of MDA? What tools do we need to do this job better? How will we know when to move from morbidity control to elimination? What combinations of interventions, beyond MDA, are needed to eliminate transmission? The Schistosomiasis Consortium for Operational Research and Evaluation (SCORE) has its Secretariat at the University of Georgia and with programs in more than 26 institutions in 19 countries it is trying to answer these very practical questions through multiple large field-based studies and the evaluation or development of better diagnostics for schistosomiasis. This presentation will summarize the current status of morbidity control and elimination programs and the operational research by SCORE that we hope will provide much-needed answers for national program managers so they can most effectively pursue these critical public health programs.

Keywords: Control; Diagnostics; Elimination; Mass Drug Administration; Operational Research; Schistosomiasis.

Fig. 1.

Photographs of Egyptians with schistosomiasis mansoni. A) An adolescent male with periportal fibrosis of the liver, esophageal varices and hepatosplenic disease. B) A group of (mainly) grade school children in a village with ~80% prevalence of Schistosoma mansoni infection in this age group.

Fig. 2.

Cartoon of human schistosome life cycles depicting adult worms, eggs of the three main human schistosomes, a miracidium, snail vector, cercariae, and schistosomula and showing the means by which and the points at which transmission can be controlled (red bars).

Fig. 3.

Photographs of the Point-of-contact Circulating Cathodic Antigen (POC-CCA) assay being done in western Kenya and of the POC-CCA cassettes with one cassette (orange arrow) showing a positive “test” line, in addition to the internal control line seen in all the cassettes.

Fig. 4.

Diagram of the large SCORE field studies of Gaining control (starting prevalence of >/= 25%) and Sustaining control (starting prevalence of 10%–24%). Each arm is comprised of 25 villages or schools and the red arrows indicate that some of the studies are finishing their Year 2 and others are finishing their Year 3 of four years of MDA and 5 years of data collection. CWT = Community-wide Treatment; SBT = School-based Treatment. These studies are being done in four African countries: Cote d’Ivoire, Kenya, Tanzania and Mozambique. For more detail please see the SCORE website: http://score.uga.edu