Soil-transmitted Helminthiases

Soil-transmitted helminthiasis (STHs), also known as geohelminthiasis, is an infection spread by parasitic worms that affect 1.5 billion people globally (Becker et al., 2018). They also contribute an estimated 5.18 million disability-adjusted life years (DALYs). DALYs are a measure of overall disease burden, in terms of number of years lost due to ill-health (PAHO/WHO, 2018). STHs are one of two neglected tropical diseases (NTDs) affecting Latin America today, the other being Chagas disease. NTDs are a grouping of predominantly bacterial and parasitic diseases that cause substantial morbidity, but have often received less funding at the international public health level than other, deadlier diseases (Hotez, 2011). However, the beginning of the 21^st century saw a change in this pattern due to renewed advocacy efforts through the branding of these tropical diseases as neglected.

STHs are a grouping of infections by four species, Ascaris Lumbricoides (commonly referred to as roundworm), Trichuris trichiura (whipworm), Necator americanus and Ancylostoma duodenale (hookworm). These organisms often come into contact with humans as a result of unsafe water and poor sanitation, which are daily realities of people living in poverty (Hotez, 2011). Poverty is thus a major contributor to disease burden of STHs. Transmission of these parasites is through the laying of eggs in contaminated food. The Ancylostoma species can also penetrate skin, usually through the feet as a result of walking barefoot in contaminated soil (Colston and Saboyá, 2013). STHs also have a massive impact on the economy of endemic nations, as it is difficult for adults to work when they are sick, and the same is true for children going to school.

Regardless of Hotez’s advocacy efforts, there have been ongoing efforts in Latin America at the regional level for the past century. The Rockefeller Foundation’s (RF) successful Sanitary Commission for the Eradication of Hookworm Disease (1910-1914) in the Southern United States led to the RF attempting their first international infectious disease control campaign aimed at hookworm in Latin America (Birn, 2009). Hookworm’s defining symptom of anemia was one of the reasons it was chosen as the rationale was if hookworm was eradicated, citizens would have the energy to work harder and pull themselves out of poverty, reverting the “backwardness” of these endemic regions. The RF has been described as a “scientific philanthropy” (Birn, 2014), working to rid the world of disease. While the organization’s efforts were honorable, it was also strategic, as diseases with relatively systematic symptoms and effective treatments were chosen to increase chances of success (Cueto and Palmer, 2014). By administering anti-helminthic drugs, promoting shoe-wearing and the use of latrines, and educating the public on STHs, there was a vast reduction in STHs in Latin America. This is actually still the general model for STH control campaigns as these are the same recommendations the WHO/PAHO promotes, and many government agencies thus have adopted these strategies.

A unique aspect of this campaign, in comparison to the RF’s later yellow fever and malaria eradication campaigns, is that local scientists were consulted and included in the organization of this campaign (Cueto and Palmer, 2014). In this sense, the RF was aware of regional efforts before their time, and recognized the knowledge these populations possessed. It should not be overlooked that Brazil's “tropicalistas” discovered hookworm in 1866 and parasitologist Adolfo Lutz’s research into hookworm in 1880s informed much of what we know about the disease today (Cueto and Palmer, 2014). Costa Rica had even already begun the first statewide campaign on the continent in 1907, which the RF then joined 15 years later (Cueto and Palmer, 2014) The RF’s consolidation of efforts under a single entity in Latin America and the campaign’s overall success can explain in part why Latin America has better control of STHs in comparison to other regions of the world. The RF’s technological emphasis on public health interventions and its lasting effects on the international public health world can be seen in the work currently carried out by the Bill and Melinda Gates Foundation. Public health policy and disease elimination campaigns are still therefore loosely modeled on RF’s structure. Overall, the RF’s efforts, including the fact that local experts were included in developing the campaign and thus the campaign was tailored to local public health methods, is an important aspect to take into consideration in understanding the general success in STH control in Latin America.

To control for infection, treatment campaigns, called “deworming campaigns,” are conducted in endemic areas. At-risk populations that are prioritized in deworming campaigns are pre-school age children (aged 2-4 years) school-age children (aged 5-14 years), women of childbearing age, and adults who work in the agricultural and mining sectors (Chammartin and Guimarães, 2013). Small children and pregnant women, specifically, are at-risk because of their weakened immune systems. Children are at risk for the following short and potentially long-term effects of parasites: loss of appetite, intestinal bleeding and obstruction, diarrhea or dysentery, reduced absorption of micronutrients, and impaired growth/development (WHO, 2019). People can be asymptomatic, but of those that do experience symptoms, symptoms tend to be general malaise, such as diarrhea and muscle weakness. This contributes to the difficulty in diagnosis, since such a variety of symptoms can indicate a wide range of illnesses. The antiparasitic drugs albenzadole and mebendazole are effective and provided by PAHO/WHO through partnerships with pharmaceutical companies Johnson & Johnson and GlaxoSmithKline to affected countries, at no cost (PAHO/WHO, 2018). Deworming campaigns are conducted in conjunction with schools because it is another way to keep children in school, as they are also receiving medical care.

The best form of prevention is access to clean sanitation facilities, including ventilated pit latrines and septic tanks. This is due to the how the parasite’s eggs can be transmitted in human feces. In fact, 100 parasite eggs can be found in one gram of infected feces (WHO, 2018). Another equally important form of disease prevention is hand washing and wearing footwear.

In the Americas region, the countries with the highest prevalence of STHs are Brazil, Colombia, Mexico, Bolivia, Guatemala, Haiti, Honduras, Nicaragua, Peru and the Dominican Republic (PAHO/WHO, 2018). Forty-six million children are at risk in this region. For more in-depth case studies of country programs in Latin America, refer to the Regional Meeting to Boost Efforts for the Control of Soil-Transmitted Helminth Infections (Geohelminthiasis) in the Americas, which was held in Lima in August 2016 (see references).

In 2012, the WHO made STHs an international priority by advocating for 75% chemotherapy coverage for all pre-school and school-age children by 2020 (Brooker et al., 2015). In 2015, 100% of endemic Latin American countries had developed action plans to address STHs, which was a major accomplishment for the region. Current data analyses indicate that Latin America will reach the regional goal of 75% preventative chemotherapy coverage by 2020 (PAHO/WHO, 2016). Beyond deworming campaigns, some countries have added the installation of water filters as part of general water, sanitation and hygiene (WASH) programming, as documented in Honduras and El Salvador (PAHO/WHO, 2016).

Looking forward, there are some aspects of this campaign that indicate it may not be able to successfully eliminate STH infections with current practices. For instance, preventive chemotherapy is only donated for school-age children, meaning that pregnant or women of childbearing age and other at-risk populations are not included in deworming campaigns. (PAHO/WHO, 2018). If Latin America is truly to control for STHs, all at-risk populations will need to be included in deworming campaigns. There is also concern that the data available for mapping the prevalence of STHs has not been updated or conducted systematically in many parts of Latin America (Saboya et al., 2013). These are infections that have lasting social and economic consequences for both those infected and the countries they inhabit. Therefore, they must continue to be a public health priority.

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Additional Resources

Becker, S. L., Liwanag, H. J., Snyder, J. S., Akogun, O., Belizario Jr, V., Freeman, M. C., ... & Levecke, B. (2018). Toward the 2020 goal of soil-transmitted helminthiasis control and elimination. PLoS neglected tropical diseases, 12(8), e0006606.

Brooker, S. J., Nikolay, B., Balabanova, D., & Pullan, R. L. (2015). Global feasibility assessment of interrupting the transmission of soil-transmitted helminths: a statistical modelling study. The Lancet infectious diseases, 15(8), 941-950.

Colston, J., & Saboyá, M. (2013). Soil-transmitted helminthiasis in Latin America and the Caribbean: modelling the determinants, prevalence, population at risk and costs of control at sub-national level. Geospatial health, 321-340.

Honduras: : Sin lombrices, Niños sanos. Campaña de Desaparasitación (A video of a de-worming campaign in Honduras produced by PAHO) https://www.youtube.com/watch?time_continue=350&v=LmADidwI4AA

References

Assessing the Efficacy of Antihelminthic Drugs Against Schistosomiasis and Soil-transmitted Helminthiases. (2013). Retrieved April 16, 2019, from https://apps.who.int/iris/bitstream/handle/10665/79019/9789241564557_eng.pdf;jsessionid=0DFFA84BD82AE099D211CAEC2681A948?sequence=1

Birn, A. E., & Fee, E. (2013). The Rockefeller Foundation and the international health agenda. The Lancet, 381(9878), 1618-1619

Birn, A. E. (2014). Philanthrocapitalism, past and present: The Rockefeller Foundation, the Gates Foundation, and the setting (s) of the international/global health agenda. Hypothesis, 12(1), e8.

Chammartin, F., Scholte, R. G., Guimarães, L. H., Tanner, M., Utzinger, J., & Vounatsou, P. (2013). Soil-transmitted helminth infection in South America: a systematic review and geostatistical meta-analysis. The Lancet infectious diseases, 13(6), 507-518.

Guideline: Preventative Chemotherapy to Control Soil-transmited Helminth Infections in At-Risk Population Groups. (2017). Retrieved April 17, 2019, from https://apps.who.int/iris/bitstream/handle/10665/258983/9789241550116-eng.pdf?sequence=1

Hotez, P. J. (2008). Forgotten people, forgotten diseases. George Washington University and Sabin Vaccine Institute. ASM Press, Washington, DC.

Regional Meeting to Boost Efforts for the Control of Soil-Transmitted Helminth Infections (Geohelminthiasis) in the Americas. (2016). Accessed April 12, 2019 from http://iris.paho.org/xmlui/bitstream/handle/123456789/34577/PAHOCHA17012-eng.pdf?sequence=1&isAllowed=y

Saboya, M. I., Catala, L., Nicholls, R. S., & Ault, S. K. (2013). Update on the mapping of prevalence and intensity of infection for soil-transmitted helminth infections in Latin America and the Caribbean: a call for action. PLoS neglected tropical diseases, 7(9), e2419.

Soil-transmitted helminths. (2018). Retrieved April 17, 2019, from www.paho.org/hq/index.php?option=com_docman&view=download&category_slug=fact-sheet-5980&alias=46748-soil-transmitted-helminthiasis-in-the-americas-for-general-public-2018&Itemid=270&lang=en