Research Article: The Neglected Tropical Diseases of Latin America and the Caribbean: A Review of Disease Burden and Distribution and a Roadmap for Control and Elimination

Date Published: September 24, 2008

Publisher: Public Library of Science

Author(s): Peter J. Hotez, Maria Elena Bottazzi, Carlos Franco-Paredes, Steven K. Ault, Mirta Roses Periago, Patrick J. Lammie

Abstract: The neglected tropical diseases (NTDs) represent some of the most common infections of the poorest people living in the Latin American and Caribbean region (LAC). Because they primarily afflict the disenfranchised poor as well as selected indigenous populations and people of African descent, the NTDs in LAC are largely forgotten diseases even though their collective disease burden may exceed better known conditions such as of HIV/AIDS, tuberculosis, or malaria. Based on their prevalence and healthy life years lost from disability, hookworm infection, other soil-transmitted helminth infections, and Chagas disease are the most important NTDs in LAC, followed by dengue, schistosomiasis, leishmaniasis, trachoma, leprosy, and lymphatic filariasis. On the other hand, for some important NTDs, such as leptospirosis and cysticercosis, complete disease burden estimates are not available. The NTDs in LAC geographically concentrate in 11 different sub-regions, each with a distinctive human and environmental ecology. In the coming years, schistosomiasis could be eliminated in the Caribbean and transmission of lymphatic filariasis and onchocerciasis could be eliminated in Latin America. However, the highest disease burden NTDs, such as Chagas disease, soil-transmitted helminth infections, and hookworm and schistosomiasis co-infections, may first require scale-up of existing resources or the development of new control tools in order to achieve control or elimination. Ultimately, the roadmap for the control and elimination of the more widespread NTDs will require an inter-sectoral approach that bridges public health, social services, and environmental interventions.

Partial Text: The neglected tropical diseases (NTDs), a group of chronic, debilitating, and poverty-promoting parasitic, bacterial, and some viral and fungal infections, are among the most common causes of illness of the poorest people living in developing countries [1]. Their control and elimination is now recognized as a priority for achieving United Nations Millennium Development Goals (MDGs) and targets for sustainable poverty reduction [1]–[3]. Approximately 40% of the estimated 556 million people living in the Latin American and the Caribbean region (LAC) live below the poverty line, including 47 million people who live on less than US$1 per day, and another 74 million people who live on less than US$2 per day [4],[5]. Relative to sub-Saharan Africa and Asia, where NTDs also occur, the character of poverty in LAC is unique. In terms of income distribution, LAC exhibits the highest inequality anywhere [6], with the richest one-tenth of the population earning 48% of total income and the poorest tenth earning only 1.6% [7]. Of LAC’s estimated 213 million impoverished people, approximately one-third live in rural poverty as subsistence farmers, ranchers, and fishermen [8], typically in communities of indigenous and African descent where they face a high level of social exclusion and social inequity [9], including lack of access to safe water and health care services [10],[11]. Two-thirds of the region’s poor live in favelas, asentamientos pobres, barrios pobres, turgurias, and áreas periféricas, i.e., urban and peri-urban communities where poverty combines with the conditions of unsafe water, poor sanitation, and the proliferation of rodent animal reservoirs and vectors [8],[12].

The NTDs in LAC may be characterized by two major patterns of disease distribution. The first is a pattern of widespread endemicity such as that seen for the soil-transmitted helminth (STH) infections, Chagas disease, and dengue; the second pattern is one of geographically restricted endemicity as the result of concerted public health interventions and ecological conditions as seen for onchocerciasis, lymphatic filariasis (LF), and schistosomiasis in areas such as the Caribbean and Guyana shield. The latter group may represent a distinct situation from other parts of the world, as they may be said to represent a “last stronghold” of endemic focal communicable diseases, that can be eliminated in a region but are not yet. In this sense, the presence of such NTDs represents a moral burden as well as an epidemiological burden. Because they are seen by some as illustrations of the failure of primary health care implementation [13], the NTDs also represent a moral imperative for action to complete primary health care implementation where it has failed and make it accessible to all.

The NTDs in the Americas are concentrated not only within pockets of intense poverty, but also among selected vulnerable populations, especially some indigenous populations and communities of African descent. In LAC, it is estimated that 7% of the total population and 40% of the rural population belong to a unique ethnic group [20]. Rural poverty disproportionately affects indigenous people, particularly in Bolivia, Colombia, Ecuador, Guatemala, Mexico, and Peru, where 80% of these populations live [9]. In Guatemala and in the neighboring states of southern Mexico, the indigenous populations suffer from some of the highest rates of STH infection in the Americas [19], as well high rates of onchocerciasis [35] and Chagas disease [48]. Some of the indigenous populations acquire their infections in agricultural labor camps and on plantations [9],[66]. Similarly, the indigenous people of Bolivia and Peru experience high rates of fascioliasis, cysticercosis, and plague [20],[39],[67],[68]; those in Colombia are at risk for leishmaniasis, Chagas disease, and yellow fever [15]; and in Brazil, there are several well-documented examples of high levels of STH infection and subsequent growth stunting among indigenous people [69]–[72], as well as trachoma [55]. Indigenous people also often bear the brunt of vector-borne NTDs that emerge during conflict [15],[48]. In addition to LAC’s indigenous communities, poor populations in communities of African descent, such as those found in parts of the Caribbean, Central America, and Brazil, suffer from high prevalence rates of NTDs, especially N. americanus hookworm infection, LF, onchocerciasis, and schistosomiasis. These infections were introduced into the region during the Middle Passage, so that their prevalence among the poor represents a tragic living legacy of the Atlantic slave trade [73].

There have been some extraordinary successes in both national and regional efforts to take measures for controlling several of the most important NTDs in LAC. First among them has been great progress towards the elimination of LF and onchocerciasis. With respect to the former, Brazil has reduced LF transmission from 11 known foci to one to two small areas, and the at-risk populations in the Caribbean region, particularly in Haiti and Dominican Republic, are receiving MDA [20],[33],[34]. Similarly, all six onchocerciasis-endemic countries have met their full treatment goals and no new ocular disease has been found in recent years; MDA with ivermectin continues in the foci with active transmission [35],[36]. In addition, the prevalence of both trachoma and leprosy has been declining in the region in recent decades [20] and there is optimism that these two ancient scourges could be eliminated in the coming decade. In the Caribbean, the incidence of schistosomiasis has been dramatically reduced [31],[32] and the disease seems potentially eliminatable. Through expanded use of insecticides, improved housing, and other interventions, great gains have been made by Iniciativa de Salud del Cono Sur (INCOSUR) in their efforts to eliminate Chagas disease from South America’s southern cone [50]. An exciting new effort to eliminate Chagas disease throughout the region by 2010 has been launched through a new Global Network for Chagas Elimination [43]. Some countries, including Argentina, Belize, Ecuador, Haiti, Honduras, and Nicaragua, have recently initiated major expansions of their STH control programs.

In sub-Saharan Africa an important approach to NTD control relies on the concept of integration and the simultaneous targeting of the most highly prevalent NTDs, i.e., ascariasis, trichuriasis, hookworm infection, schistosomiasis, LF, onchocerciasis, and trachoma, through MDA with a “rapid-impact” package of drugs [1]. In most of LAC, however, the distribution of the NTDs is not as widespread and therefore not always amenable to the same African control strategies. With the exceptions of some areas of eastern Brazil where STH and schistosome infections are also co-endemic with LF (Pernambuco and Alagoas States), and in the Amazonian basin where, particularly among indigenous people, STH infections overlap with onchocerciasis and trachoma (northern Brazil), there are limited opportunities to administer a full rapid-impact package in the Americas. Instead, the pattern of NTD endemicity in the most impoverished areas of LAC has a unique regional character, typically with STH infections or Chagas disease, the most widespread NTDs, co-endemic with a few other NTDs, especially zoonotic NTDs.

In recognition of the severe NTD disease burden in the Americas, the PAHO/WHO, together with the LAC governments, their national disease control programs, the US Centers for Disease Control and Prevention, and the Global Network for Neglected Tropical Diseases [1] will be embarking on efforts to further control, or in some cases, eliminate the region’s NTDs. To this end, a strategic plan is being developed, which will be important to MDG targets for health and sustainable poverty reduction in LAC by 2015 [81] (Table 10). The plan uses the existing epidemiological data and adapts an ecosystems approach (Tables 8 and 9) in order to define the most effective interventions that will tackle the multifactoral determinants responsible for the persistence of NTDs, placing health within the context of social and economic development and key MDGs [72].

Rather than a strictly disease-centered approach [4],[9],[72],[82], comprehensive public policies aimed at community development and poverty reduction will be adopted. These policies will be then implemented at the local level through the mobilization and involvement of various agencies [9],[72] under the responsibility of different government sectors (inter-sectoral action) so that they can come together in a synergistic and synchronic manner. Together with strong social participation and appropriate technologies, the inter-sectoral action completes the three pillars advocated in a primary health care strategy and will contribute towards health systems strengthening. Examples of such inter-sectoral partnering were recently reviewed [72],[82]. The collateral benefits of NTD control and elimination also provide multiple entry points for linking diverse programs and projects within the health sector and among different sectors [9],[72],[82], and could build on several PAHO/WHO and World Bank initiatives to combat disease and deprivation [8],[9]. A new generation of control tools, including vaccines, some under development by product development partnerships that include research, development, and manufacturing institutions in LAC, would represent additional innovations to fold into these infrastructures [83]. Among them are new drugs and human vaccines for dengue, hookworm (and hookworm–schistosomiasis co-infections), leishmaniasis, and leprosy [76],[84],[85], as well as transmission-blocking interventions for Chagas disease, cysticercosis, fascioliasis, leptospirosis, and leishmaniasis, which target major animal reservoir hosts [48],[84]. Overall, the control and/or elimination of NTDs represent a highly cost-effective mechanism for providing new investment opportunities in areas currently plagued with these diseases and freeing up their economic potential, i.e., for tourism and ecotourism, ecologically sound mining and oil exploration, infrastructure for rural community transportation, and sustainable crop production (traditional and non-traditional crops). The treatment and prevention of the NTDs have also been revealed as an ethical imperative to respond to the fundamental human right to health [86], particularly for LAC’s poorest people, its indigenous populations and people of African descent.



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