Forgotten People, Forgotten Diseases. Peter J. Hotez
treatments with praziquantel can sometimes reverse both urinary tract and liver pathology, particularly if children receive these treatments early in their lives. Building on these breakthrough medical observations were the low-cost synthesis and production methods for manufacturing generic praziquantel by the Korean pharmaceutical company Shin Poong. These manufacturing improvements have dramatically reduced the price of the drug, possibly by as much as 90%.10 As a result, by the 1990s, it became possible to launch praziquantel mass treatment programs for schistosomiasis in several middle-income countries, including Brazil, China, Egypt, Morocco, the Philippines, Saudi Arabia, and Tunisia, as well as Puerto Rico.10,13,17 Several of these initiatives were funded by the World Bank. Praziquantel mass drug administration in these countries has been largely successful, particularly in Morocco and Puerto Rico, where the disease is close to being eliminated (zero transmission) partly because of parallel poverty reduction measures that were enacted.10
Despite the promise that praziquantel offers for controlling human schistosomiasis, up until recently it has not been made widely available.17 Previously (in chapter 2), we learned how in 2001, the 54th World Health Assembly adopted a resolution calling for treatment with a benzimidazole anthelmintic drug of at least 75% of school-age children at risk of acquiring schistosomiasis and soil-transmitted helminth infections by 2010. Based on the experiences and successes of mass drug administration of praziquantel, the resolution was written to include this drug along with either albendazole or mebendazole for the treatment of school-age children. In many regions of the developing world, especially in sub-Saharan Africa and Brazil, it is common for children to be polyparasitized with both soil-transmitted helminths (especially hookworm) and schistosomes,18 so that they could benefit from combination therapy with a benzimidazole anthelmintic and praziquantel. Unfortunately, the World Health Organization (WHO) estimates that in 2010 only about 33 million of the 236 million children at risk for schistosomiasis actually received praziquantel, just a little over 10%.19 The low drug coverage results from the absence of political will in expanding mass drug administration, together with limited availability of praziquantel. In response, in January 2012, the Bill & Melinda Gates Foundation partnered with the major pharmaceutical companies, the World Bank, WHO and other international agencies, and key nongovernmental organizations in a London Declaration to reaffirm support for control of neglected tropical drugs through mass drug administration.20 The announcement coincided with a commitment by a German company, Merck KGaA, to dramatically ramp up praziquantel donations.
A key implementing partner that provides technical assistance to the African health ministries in order to facilitate praziquantel administration (usually together with albendazole for soil-transmitted helminth coinfections) through mass drug administration is the Schistosomiasis Control Initiative (SCI), a public-private partnership established by Alan Fenwick at Imperial College London (www3.imperial.ac.uk/schisto). Previously, Fenwick had acquired a wide-ranging experience in large-scale control of schistosomiasis through his leadership in World Bank-and USAID-funded projects in Egypt and Sudan. Working in collaboration with ministries of health in almost a dozen sub-Saharan African countries as well as Yemen, together with WHO, the SCI facilitates once-yearly praziquantel treatments using donated praziquantel from Merck KGaA, as well as generic praziquantel from MedPharm and other sources. SCI operates through algorithms based on the schistosomiasis prevalence determined in local school surveys. The number of praziquantel tablets administered to each individual is based on an easy-to-use height pole that approximates a dose of 40 mg of drug per kg of body weight, and the delivery and distribution of praziquantel are carried out in health centers, in schools, or through community-based drug distributors.10
To date, SCI and its partners have made some impressive public health gains, scoring significant and dramatic reductions in either the prevalence or intensity of schistosomiasis in several African nations.21 Such successes and the prospects of expanded mass drug administration campaigns and ongoing donations of praziquantel have led some investigators to suggest that global schistosomiasis elimination is a potentially attainable goal.22 Indeed, in 2012 the World Health Assembly adopted a resolution that affirmed the feasibility of elimination.22 Here the term “elimination” refers to reduction in the prevalence of human schistosomiasis to the point where transmission has been interrupted, but unlike eradication, elimination may require ongoing implementation of public health control measures.
There are a number of important but still unanswered questions about the impact of praziquantel mass drug administration on sustainable poverty reduction in developing countries. Current population-based approaches with praziquantel are focused on reducing the morbidity of this condition in areas where high-intensity infections and serious urogenital, intestinal, and liver morbidities are present. However, it is unclear whether mass treatment will also reduce transmission and prevent reinfection in the community.23 This uncertainty is a serious concern, since ongoing low levels of schistosomiasis reinfection could lead to subtle but persistent clinical problems, including anemia, growth stunting, and diminished productive capacities.23 In addition, there are potential worries that frequent and periodic use of praziquantel could lead to anthelmintic drug resistance. These issues have prompted some nascent efforts to develop alternative or complementary control tools for schistosomiasis, just as they have for human hookworm infection. These activities include exploration of new drug development, including the antimalarial artemisinin, artemether, which also exhibits antischistosomal properties.24 Still another approach has been efforts to develop a recombinant vaccine for schistosomiasis, and several candidate vaccines have entered into early clinical trials (discussed in chapter 11).25 However, our major approach to schistosomiasis control still relies on mass drug administration of praziquantel or of praziquantel and albendazole or mebendazole in areas of schistosomiasis and soil-transmitted helminth coinfection. We will further explore (in chapter 10) how these treatments might link with mass drug administration for other neglected tropical diseases, including lymphatic filariasis, onchocerciasis, and trachoma.
Summary Points: Schistosomiasis
Significant impact on the modern history of China and Egypt
One of the most common and clinically important human helminth infections
Schistosomiasis is a waterborne infectious disease transmitted by a snail intermediate host.
Approximately 400 to 600 million cases worldwide, with more than 90% of the infections in Africa
Children and adolescents are at highest risk. All forms of chronic schistosomiasis are associated with anemia, undernutrition and growth impairments, poor school performance, and reduced productive capacity.
Urogenital schistosomiasis caused by S. haematobium accounts for approximately two-thirds of the schistosome infections in Africa. This