this front. As an alternative or complementary approach to STH control, there has been a concerted effort to develop a recombinant anthelmintic vaccine, which would prevent reinfection following deworming.30 In chapter 11, I will discuss the efforts of our nonprofit product development partnership, known as the Human Hookworm Vaccine Initiative, to develop a new hookworm vaccine as an important antipoverty measure.
Summary Points: “The Unholy Trinity”
STH infections are caused by intestinal worms, with Ascaris roundworms, Trichuris whipworms, and hookworms being the most common.
Ascariasis, hookworm infection, and trichuriasis are the world’s most common NTDs.
STH infections are highly prevalent in sub-Saharan Africa, Asia, and the Americas, especially in areas where rural poverty overlaps with tropical environments and adequate rainfall.
Children typically exhibit heavier STH infections with higher worm burdens than do adults.
The STHs live for years in the gastrointestinal tract.
In children, chronic STH infections impair physical growth and development as well as cognition, memory, and school performance. Therefore, STHs produce educational deficits as well as ill health. These poverty-promoting features probably result from parasite-induced malnutrition.
Hookworms cause malnutrition by producing intestinal blood loss, which leads to iron deficiency anemia, especially in children and pregnant women with low underlying iron reserves. The DALYs lost to hookworm infection rank the highest for any worm infection.
Global control of STH infections currently focuses on morbidity reductions through frequent and periodic deworming with BZAs. School-based deworming is being frequently emphasized in order to target at-risk children.
There are both theoretical and actual concerns about BZA drug resistance; a human hookworm vaccine is under development.
Notes
1. The Greek derivation of “helminth” is from Faust et al., 1970, p. 251. References to the historical documentation of human ascariasis and hookworm infection are found in Cox, 2002; Grove, 1990; and Sherman, 2006, p. 349–352.
2. Prevalence numbers are modified from Bethony et al., 2006.
3. The impact of STHs on child growth and development and cognition is summarized (with references) in Bethony et al., 2006; and Crompton and Nesheim, 2002. The Crompton and Nesheim reference also describes the nutritional basis of these deficits.
4. The results of the nationwide parasite survey are summarized in Hotez et al., 1997. The survey was later repeated (but on a smaller scale) between 2002 and 2004 and demonstrated that the incidence had since decreased dramatically in areas of economic development. The new Chinese prevalence numbers are reported in Li et al., 2010.
5. These observations are summarized in Hotez, 2002.
6. These observations are reported in Fenghua et al., 1998.
7. From de Silva et al., 2003.
8. Factors underlying the relationship between STH infection and poverty are described in Raso et al., 2005; Holland et al., 1988; and Hotez, 2008.
9. The exact mechanisms by which STHs impair growth and development are still poorly understood. An excellent review of the literature is found in Crompton and Nesheim, 2002.
11. The link between STHs and impaired cognition and memory has been studied extensively by D. A. P. Bundy and his colleagues. Two important papers include Nokes et al., 1992; and Sakti et al., 1999. However, the mechanisms by which worms impair cognition and memory are not well understood.
12. Bleakley, 2007.
13. The GBD 2010 study is found in Murray et al., 2012, and Vos et al., 2012.
14. Original maps of the distribution of all three STH infections can be found in de Silva et al., 2003.
15. An excellent historical account of hookworm in the United States is found in Ettling, 1981. A more global perspective can be found in Farley, 2004. Whether or not hookworm or other STH infections are still endemic in the United States is not known, given that no major studies have been conducted in more than 30 years; see Starr and Montgomery, 2011.
16. Humphreys, 2001, p. 110–111.
17. A summary of the impact of sanitation and health education on STH infections is found in Asaolu and Ofoezie, 2003; and Ziegelbauer et al., 2012. A study showing the absence of a relationship between wearing shoes and avoiding hookworm infection is found in Bethony et al., 2002.
18. Descriptions of the hookworm life cycle and the clinical manifestations of hookworm are found in Hotez et al., 2005; and Hotez et al., 2004.
19. Studies showing a high hookworm prevalence and intensity in coastal regions (regions with sandy soils) are in Mabaso et al., 2003; and Mabaso et al., 2004.
20. The biochemical mechanism by which hookworms digest blood is described
