and cognitive effects, such as improvements to short-term and long-term memory, problem solving, language, and cognition.11,24 Michael Kremer and Ted Miguel, economists at Harvard University and the University of California, Berkeley, respectively, have recently confirmed the benefits of deworming in promoting educational advancement, while additional economic analyses conducted by Kremer and Miguel together with Sarah Baird and Joan Hicks, as well as Hoyt Bleakley of University of Chicago, suggest that these effects may also translate into economic benefits for the community.10,11,24
Every May, the world’s ministers of health meet at the annual World Health Assembly, held at WHO headquarters in Geneva, Switzerland. At the 54th World Health Assembly in 2001, a resolution was adopted (Resolution 54.19) that urged member nations to attain a minimum target of regular deworming of at least 75% and up to 100% of all at-risk school-age children (www.who.int/wormcontrol). Since then, there has been heightened advocacy by the WHO and other international agencies for the administration of BZAs, typically a single dose of either albendazole or mebendazole, on a large scale. Increasingly, annual deworming is being practiced in schools because of the cost-effectiveness and efficiencies of having teachers rather than health care practitioners administer anthelmintic drugs.25 This approach includes using schoolteachers who are specially trained to deliver the deworming tablets alongside health education messaging.24 In many African and Asian countries, deworming is linked with school feeding programs sponsored by the World Food Programme (www.wfp.org) and through the FRESH Partnership (Focusing Resources on Effective School Health), an interagency initiative of the World Bank, UNICEF, UNESCO, and WHO (www.freshschools.org), as well as nongovernmental organizations such as the Partnership for Child Development (www.child-development.org) and Deworm the World (www.dewormtheworld.org).24 Such interventions can be achieved for extremely low costs. For example, in Ghana and Tanzania, hundreds of thousands of children have been treated for as little as US$0.03 and $0.04 per capita.24,25 In addition to the fact that the BZAs are often donated for free, another reason that the costs of school-based deworming are so low is that the excellent safety profile of a single dose of a BZA allows children to be treated regardless of whether they are infected with STHs. Instead, once it is established that the overall community prevalence of STH infections exceeds 50%, it no longer is necessary to conduct fecal examinations on each child. Authorities can then blanket the school with a single dose of either mebendazole or albendazole. This practice eliminates the high cost of bringing trained microscopists and laboratory equipment to the school. I believe that the advocacy efforts of two individuals, namely, Lorenzo Savioli at WHO and Don Bundy, now at the World Bank, were especially instrumental in promoting global deworming and advancing the agenda leading to Resolution 54.19.26
More than 300 million children in 77 countries received low-cost deworming in 2010.27 While this number is impressive, it is still far short of the almost 900 million children who would need to be treated annually in order to meet the targets specified by World Health Assembly Resolution 54.1927 (Fig. 2.11). Because many school-age children do not attend school in developing countries, as an alternative or complementary approach to school-based interventions, many children are being targeted worldwide through community-based interventions, such as child health days. In such programs, deworming is linked to vitamin A distribution as well as to some immunizations, such as measles vaccinations.24 Child health days and other community-based interventions are particularly suitable in regions of STH infection endemicity where preschool children, i.e., children under the age of five, also suffer from moderate and heavy infections. By some estimates, almost 200 million children have received vitamin A in more than 50 countries,24 so that this mechanism provides an added opportunity to scale up deworming. Also, as pointed out earlier, in some developing countries pregnant women are at high risk for hookworm infection, and the WHO and other international agencies have therefore expanded their recommended targets to include this group in areas of high transmission.
Although for most school-based and community-based interventions a single dose of either mebendazole or albendazole is provided on an annual basis, in areas of intense transmission deworming may need to be conducted more frequently. STH reinfection can occur over a period of just a few months, so that sometimes two or three dewormings must take place in a single year. Currently, the WHO recommends two or three deworming treatments annually in areas of high prevalence (typically greater than 70% prevalence) or high intensity (where more than 10% of the population have moderate or heavy infections).
Figure 2.11 Proportion of children (1 to 14 years of age) by country requiring preventive chemotherapy for soil-transmitted helminthiases, worldwide, 2010. (See http://gamapserver.who.int/mapLibrary/Files/Maps/Global_STH_2010.PNG [© 2011 WHO].)
When frequent and periodic dewormings are required in order to control STH infections for large populations, there are concerns that STH parasites, like any other infectious agent, could over time become resistant to either mebendazole or albendazole. Indeed, BZA resistance is now widespread among intestinal helminth parasites of sheep and cattle in Australia, New Zealand, South America, South Africa, and elsewhere in the Southern Hemisphere.28 The mechanisms by which BZA resistance occurs will be discussed later (in chapter 11). To date, there is no convincing evidence of the emergence of drug resistance to the BZAs used for human STH infections. However, a systematic review conducted by Jennifer Keiser and Juerg Utzinger from the Swiss Tropical and Public Health Institute revealed that single-dose mebendazole currently exhibits a cure rate for human hookworm infection of only 15%, with egg count reductions for N. americanus hookworm infections ranging from 0 to 68%.28 Thus, while albendazole is still generally effective for N. americanus hookworm infection, single-dose mebendazole can no longer be considered a standard treatment for hookworm infection. Today, the high rate of drug failures for single-dose mebendazole and high rates of STH infection in areas of high transmission, coupled with emerging evidence of BZA resistance in animal nematodes, have led to international calls for increased monitoring of the effectiveness of the BZAs and for the development of new-generation STH drugs.
Given the enormous health and educational benefits of deworming, I believe that we should try to do everything possible to scale up the use of BZAs in developing countries. We now have in hand some very promising geostatistical tools for increasing the efficiencies of deworming in resource-poor settings.29 At the same time, however, we must try to develop backup control tools. Unfortunately, the absence of a commercial market for such drugs has hampered a substantive research and
