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 form is responsible for hematuria, female genital schistosomiasis, and squamous cell carcinoma of the bladder. Genital lesions increase the risk of HIV/AIDS transmission.
Intestinal and liver schistosomiasis caused by S. mansoni accounts for approximately one-third of the cases in Africa and 1 million cases of schistosomiasis in Brazil. This form is responsible for bloody diarrhea, abdominal pain, and liver involvement (hepatomegaly and fibrosis).
The major approach to control of schistosomiasis today is mass drug administration of praziquantel. It has led to the near elimination of schistosomiasis in some middle-income countries and to significant morbidity reductions in some sub-Saharan African countries.
Notes
1. The estimate of 400 to 600 million people is based on studies by Charles King and his colleagues at Case Western Reserve University. They determined that earlier estimates do not adequately consider the number of people who go undiagnosed with schistosomiasis because of variabilities in parasite egg excretion or the difficulties in detecting parasite eggs in human feces and urine; see King, 2010. However, not everyone agrees with this assessment. Instead, a previous and more conservative estimate of approximately 200 million people is more commonly cited; see Steinmann et al., 2006.
2. Historical accounts of schistosomiasis are found in Hulse, 1971; Hotez et al., 2006; Cox, 2002; Fenwick et al., 2006; and Grove, 1990.
4. This incident is described in Kernan, 1959. Because the article is not easy to find, readers may also wish to read a summary of this information in Farley, 1991.
5. Information is contained in Lampton, 1974.
6. Information is found in Horn, 1969, p. 94–106; Hotez, 2002; Utzinger et al., 2005; and Farley, 1991, p. 201–215.
7. Wei, 1958, quoted in Farley, 1991, p. 206.
8. The impact of dam construction projects on the emergence of human schistosomiasis is described in Fenwick, 2006; and Hotez et al., 1997.
9.
