Forgotten People, Forgotten Diseases. Peter J. Hotez
plagued humankind for centuries. This historical link is well documented through the accounts and descriptions of some of the dramatic clinical manifestations of the NTDs, particularly leprosy, dracunculiasis, schistosomiasis, hookworm infection, and trachoma, in ancient texts including the Bible, Talmud, Vedas, writings of Hippocrates, and Egyptian medical papyri.7 One exception to this persistent state is selected NTDs that can sometimes reappear after their earlier near elimination because of public health breakdowns resulting from civil or international conflicts. Later (in chapter 7), we will see how this situation has tragically unfolded in Angola, the Democratic Republic of Congo, and Sudan and has resulted in a reemergence of human African trypanosomiasis and kala-azar.
4 The NTDs are chronic conditions. Another distinguishing feature of the NTDs is that unlike many infectious diseases with which we are familiar, they are mostly chronic infections lasting years and sometimes even decades. In some cases, poor people can suffer from NTDs for their entire lives.6
5 The NTDs cause disability and disfigurement. Even though they are infectious diseases because they are caused by microbial or multicellular pathogens, which are transmitted either from person to person or through contact with contaminated soil or water or through exposure to arthropod vectors (e.g., mosquitoes, sandflies, assassin bugs, and copepods), the NTDs frequently do not exhibit the classic features of most infections. That is to say, they do not typically cause acute febrile illnesses, which either resolve or kill. Instead, the NTDs mostly cause chronic conditions that lead to long-term disabilities and, in some cases, disfigurement.6 I will highlight the specific disabling features of each of the NTDs when they are treated separately (in chapters 2 to 9), but to provide some specific examples here, the long-term effects of chronic hookworm infection and schistosomiasis in childhood produce a long-standing anemia, which is associated with physical growth retardation, impaired memory, and cognitive growth delays; in pregnant women, the anemia from hookworm infection and from schistosomiasis results in poor birth outcomes such as low neonatal birth weight and increased maternal morbidity and mortality. Onchocerciasis and trachoma cause impaired vision and blindness. Chagas disease causes a chronic and severely disabling heart condition. LF, onchocerciasis, guinea worm infection, leishmaniasis, Buruli ulcer, and leprosy cause either limb disuse or profound disfigurement (including genital deformities), which often prevent afflicted individuals from either obtaining or maintaining employment (Fig. 1.2).
6 The NTDs have a high disease burden but low mortality. An estimated 530,000 people die annually from the NTDs.8 While this number of people is significant and more than twice the number estimated to have perished in the 2004 Christmas tsunami, for example, the reality is that these numbers pale in comparison to the number of annual deaths from HIV/AIDS or malaria (about 1 to 2 million deaths annually from each disease). Therefore, placing NTDs on the global health radar screen of world leaders and policymakers and motivating them to tackle these conditions in a substantive way require focusing advocacy efforts on something more than simply looking at deaths as an end point. While it is obvious that the individuals shown in Fig. 1.2 are having their lives ruined by the long-term consequences of their NTDs, these compelling images by themselves do not provide an obvious metric that we can use to justify to the global community investments either in this group of diseases or in the people who suffer from them. Instead, we need another mechanism to convince policymakers that the “other diseases” deserve the same international attention as HIV/AIDS and malaria.Table 1.4 Major attributes of the NTDsFigure 1.2 Disfiguring effects of the NTDs. (Top) Elephantiasis of the leg due to filariasis, Luzon, the Philippines. (Bottom) Guinea worm infection, with female worm emerging from the patient’s foot. (Images from Public Health Image Library, CDC [http://phil.cdc.gov].)One approach to measuring the full health impact of the NTDs is to use the disability-adjusted life years, or DALYs, which consider the number of healthy life years lost from either premature death or disability. Because of the chronic, disabling, and disfiguring components of the NTDs, the DALYs ascribed to them are substantial. Shown in Table 1.5 is a ranking of HIV/AIDS, malaria, tuberculosis, and the NTDs by deaths and DALYs. One of the greatest values of DALYs is that they facilitate the comparison of one condition with another. The data illustrate that the total disability resulting from the NTDs is almost as great as the disability from HIV/AIDS and even more than the disability resulting from malaria or tuberculosis.8 A newer estimate from studies conducted at the Institute for Health Metrics and Evaluation (University of Washington) ascribes fewer DALYs to the NTDs, but still a substantial number.The devastating comparison between the NTDs and the “big three” diseases—HIV/AIDS, malaria, and tuberculosis—has multiple implications for international efforts to control or eliminate infectious diseases. Today, much of the global enterprise targeting infections focuses primarily on HIV/AIDS, malaria, and tuberculosis. The DALY measurements suggest a strong rationale for considering the NTDs an important fourth leg of the chair. The rationale goes beyond merely comparing DALY estimates and pointing out the high disease burden resulting from the NTDs. Instead, an increasing body of evidence indicates not only that the NTDs exhibit geographic overlap and coendemicity with each other but also that the NTDs are coendemic with AIDS and malaria. The geographic overlap and coendemicity between the NTDs and malaria and AIDS will be further elucidated elsewhere (chapter 10). However, to briefly mention it here, there is new evidence that the morbidities resulting from the NTDs are additive with malaria and that some NTDs actually increase susceptibility to HIV/AIDS. Therefore, there is an important rationale for not simply tackling the big three conditions in isolation, as currently advocated by the Global Fund, PEPFAR, and PMI, but also for embracing the NTDs to take on what is really a “gang of four.” This concept of integrating NTD control measures with those for malaria and HIV/AIDS will become clearer when we outline possible intervention strategies for NTD control (in chapter 10) and give the reason why we need to consider bundling treatment strategies for the NTDs together with those for HIV/AIDS and malaria (and even possibly why the Global Fund should incorporate NTD control into its programs).Table 1.5 Ranking of the “gang of four” by deaths and DALYsaModified from Hotez et al., 2006a.bModified from Murray et al., 2012.
7 The NTDs are stigmatizing. Not surprisingly, the blinding and disfiguring features of NTDs are stigmatizing and cause individuals to be ostracized by their families, their communities, and sometimes even health care professionals.6 In some societies, NTDs are considered a sign of a curse or an “evil eye.” The social stigma of the NTDs strikes young women particularly hard, and as a result, these women are frequently abandoned by their husbands, prevented from holding or kissing their children, or unable to marry altogether. Specific examples of these stigmatizing consequences of the NTDs will be illustrated in the chapters dealing with LF, Buruli ulcer, and leishmaniasis (chapters 4, 6, and 7, respectively).
8 The NTDs have poverty-promoting features and other socioeconomic consequences. The health impact of the NTDs may also represent only the tip of the iceberg in terms of their adverse effects on international development. Because of their chronic and disabling features, the NTDs also produce important and serious socioeconomic consequences that keep affected populations mired in poverty. The NTDs not only occur in the setting of poverty; they also actually promote poverty. For example, the cognitive and intellectual impairments resulting from hookworm-associated iron deficiency and anemia severely affect childhood education in terms of school performance and school attendance. Reduced school attendance leads to reduced future wage-earning capacity, while chronic hookworm infection among agricultural