Open defecation is the practice of defecating in open spaces, usually in bushes or open fields, in waterways, or any other place outside a designated modern or traditional toilet facility (1). It is a serious public health problem that necessitated its inclusion in the Millennium and Sustainable Development Goals (SDGs). Millennium Development Goal (MDG) number 7 was specific for the control of open defecation. It also targets reducing by half the population of people without access to sustainable water and basic sanitation, including toilet facilities, by 2015 (2), but this was not attained. SDGs were developed in 2015 to renew the efforts to achieve targets that were not met with the MDGs, and controlling open defecation was aptly included in SDG number 6, which focused on providing sustainable access to clean drinking water and basic sanitation for all (2, 3). Projections show that, as 2030 is just a few years away, this target might not be attained in many countries, especially in sub-Saharan Africa (3).

There is historical evidence that open defecation is also a nagging problem in many developed countries, but civilization coupled with technological advancement helped in eradicating the menace (4). Unfortunately, the same cannot be said of countries in the developing world, especially those in sub–Saharan Africa, as many are still grappling with providing drinking water and basic sanitation amenities for their citizens (1). Open defecation is a nagging problem in low- and middle-income countries of the world located in sub-Saharan Africa, South, Central, and East Asia, and others (5). According to the United Nations Children’s Fund (UNICEF), countries would need to triple their current pace to be able to eliminate open defecation by 2030, and only 18 countries are successful in that track (5). Approximately 1.5 billion people lack basic sanitation amenities in most developing countries (6), and as a result, over 400 million people still practice open defecation because of limited toilet facilities. However, the practice of open defecation cannot only be attributed to a lack of latrines, but factors such as dysfunctional or collapsed toilets and the unsanitary nature of the public toilet facilities, especially during times of water scarcity, contribute to the problem (6).

Improper disposal of human feces is another huge sanitation problem in many developing countries. The improper disposal of feces of children highlights the pervading problem of improper disposal of feces in limited resources developing countries already battling with open defecation (7, 8). Aside from the disposal of feces of children, it is important to note that improper feces disposal constitutes a huge problem even in areas and populations that use toilet facilities (9). Improper disposal of human feces is a spectrum of open defecation, as both practices ultimately achieve the same unwanted outcome of fecal contamination of the environment with its attendant health problems (7). However, the academic distinction between the two terms is not the focus of this review; rather, the common impact of contamination of the environment with the resultant hazardous health consequences. Open defecation in this review refers to both direct open defecation and improper disposal of feces, and thus, we define open defecation as the unsanitary disposal of human feces either by direct open defecation or improper disposal of collected feces into the environment resulting in the fecal contamination of soil, water, and food, which poses a danger to human health. Fecal contamination of the environment is a serious public health hazard as human feces contains many pathogenic organisms ranging from millions of viruses and bacteria to several thousand eggs and cysts of parasites (2, 9). This has resulted in feco-orally transmitted diseases such as diarrheal diseases, enteric fever, hepatitis B, poliomyelitis, and several other diseases (2, 9). Control and prevention of open defecation is an active component of the Water, Sanitation, and Hygiene (WASH) strategy, which has contributed significantly to the reduction of waterborne and water-related diseases, including some Neglected Tropical Diseases NTDs (10–12).

Neglected Tropical Diseases (NTDs) are a subset of tropical diseases ( Figure 1 ), characterized by their preponderance and negative impact in poverty-stricken endemic tropical areas of the world, especially in sub-Saharan Africa (10, 11). NTDs are so named to put a spotlight on them in an attempt to make up for the years of inattention in terms of control interventions from important local and international stakeholders (13). Currently, 20 diseases comprise this list, including viral, parasitic, bacterial, and fungal diseases, and others like snake bites, yaws, and Buruli ulcers (10, 11). Of all the NTDs, some are caused by a lack of clean water, poor sanitation, and poor personal hygiene and, thus, are controlled by the WASH intervention initiative (12). WASH initiative, through the adequate provision and access to drinking water and sanitation, is believed to have a direct and indirect positive impact on the prevention and management of all NTDs including zoonotic parasitic NTDs ( Table 1 ) (12, 14). The WASH intervention activities directly prevent some NTDs, such as Soil-transmitted helminthiasis (STH), Taeniasis and Cysticercosis, Schistosomiasis, dracunculiasis, Foodborne Trematodiasis, and Trachoma, which can be termed WASH-related NTDs ( Figure 1 ). While the provision of WASH can interrupt the transmission route of these WASH-related NTDs (12), some of them are directly driven by open defecation (pathogens found in feces) such as STH, Taeniasis, and Cysticercosis, Foodborne Trematodiasis, and Schistosomiasis, and hence, can be referred to as Open Defecation Driven NTDs ( Figure 1 ).

WASH has recorded some successes in controlling these NTDs; however, this accomplishment has been uneven as many endemic areas, especially in sub-Saharan Africa, still have a high burden of open defecation driven NTDS (10, 11). The Unfortunate expectation of not meeting the SDGs targets of 2030, coupled with the projected human population explosion, and increasing poverty in many developing nations, makes it highly likely that the problem of open defecation will worsen (3, 15). This foreboding projection calls for a more pragmatic, integrated, and holistic approach to dealing with this problem. One Health provides a platform to help control, prevent open defecation, and provide lasting solutions to WASH-related and open defecation-driven NTDs (16, 17). This is particularly important since open defecation not only poses a threat to human health, as environmental contamination of human feces also affects animals and other biotic components of the environment (18).

One Health is the science that looks at the interconnectedness of human, animal, and environmental health (19–21), and in essence, prevention of diseases involving humans, animals, and the environment is at the center of One Health (20). It provides a holistic, integrated, and cost-effective preventive approach after assessing and understanding the magnitude and ramifications of interconnected health problems of humans, animals, and the environment (19). All these require a multidisciplinary and interdisciplinary collaborative effort involving multiple sectors with a unifying agenda of simultaneously improving the health of humans and animals, as well as the health of the environment in which they live (19).

The One Health approach has been applied to understand the epidemiology of NTDs, as well as their control, especially to help achieve the NTDs 2030 road map goals (10, 11, 21, 22). The One Health concept has been applied to WASH interventions where the provision of clean water and sanitation has been extended to animals and livestock (10, 11, 22). One Health has aptly broadened the scope of open defecation to include animal feces, a welcome development since animal feces are known to cause a variety of human diseases (17). Thus, a One Health definition of open defecation is the unsanitary disposal of human feces either by direct open defecation or improper disposal of collected feces into the environment, resulting in the fecal contamination of soil, water, and food, posing a danger to the health of both humans and animals. For this reason, we added Echinococcosis (primarily driven by dog feces) to STH, Taeniasis and Cysticercosis, Foodborne Trematodiasis, and Schistosomiasis on the list of Open defecation driven NTDs. There is a vicious cycle between animals and humans involving fecal contamination of the environment with subsequent contamination of food, water, and soil ( Figure 2 ). All these Open defecation-driven NTDs are endemic in sub–Saharan Africa except foodborne trematodiasis, which is a group of trematodes, flukes acquired through the ingestion of seafood and water vegetables contaminated by the larvae of the parasites as a result of the fecal contamination of water bodies.

The World Health Organization is strongly advocating for an integrated approach in the control of NTDs, especially in the race to meet the 2030 targets (10, 11), and such an integrated approach will oversee several NTDs involving multi-sectoral and inter-disciplinary collaborations (10, 11).

The control of open defecation of humans and animals can be an integrated One Health approach that can simultaneously control multiple NTDs. Feces from animals or humans should be considered a biohazard, a harbinger of disease and death, and their proper management should be a priority for all stakeholders (61). However, this is not easy owing to the complex problems influencing open defecation in endemic areas, especially in Sub-Saharan Africa, such as poverty, poor education, lack of infrastructure, and lack of political will (62).

The major control effort against open defecation has targeted human feces, probably because humans produce the largest amount of feces, with an individual producing an average of 250 grams of feces daily (63). In poor developing countries, preventing open defecation is a Gordian knot due to a lack of infrastructure, poor finances, population expansion, poor perception of the dangerous effects of open defecation practices, and lack of awareness of the negative impacts of open defecation on the community (64). Some of these adverse community practices are so entrenched in places that control programs, even with proper community engagement, have trouble initiating or achieving success in open defecation control campaigns (22). Also, the fact that it took developed countries several years with millions of dollars invested in improving sanitation and stopping open defecation, proves that this will be a daunting task for developing countries, especially in sub–Saharan Africa, where there is little to no resources and political will to achieve it (62).

The control of open defecation of animals has not enjoyed the same attention as that of humans, even though animal feces contribute significantly to environmental contamination with attendant health consequences for both animals and humans (61, 65, 66). In many developing countries, humans are more exposed to animal feces than human feces, and they pose a greater threat to human health. This is because animals, especially domestic animals, live with humans in households, providing the opportunity for possible health problems (61, 65, 66).

By and large, humans and animals produce about 4 trillion tons of feces per year, so massive that it is metaphorically likened to filling 1.6 million Olympic-sized swimming pools (61). A significant amount of these feces contributes to the menace of open defecation driven NTDs and other diseases resulting from open defecation. While WASH interventions should be intensified and further expanded to include control of open defecation from animals, harnessing the usefulness of these feces vis-à-vis their use in manure and other by-products might be the way to go (67). It is now important that a relatively cheaper alternative means of recycling feces is a venture that should be considered, as has already been done in some countries like Kenya, Madagascar, and other places where feces have been converted to fertilizer, fuel, and biogas (68). Safe recycling of human and animal feces to benefit humans, animals, crops, and the ecosystem is the ultimate One Health strategy in the control and prevention of open defecation (68, 69).

Open defecation of both animal and human feces directly impacts some NTDs, termed Open defecation-driven NTDs, a category of WASH-related NTDs affecting millions in endemic areas. A One Health evaluation of the burden of open defecation, highlighting both human and animal feces, provides a platform for an integrated and holistic approach to the control of open defecation. Despite the challenges, this might be a useful inclusion in the WASH interventions strategy in the fight against NTDs, providing a sustainable control that might contribute significantly to the prevention of open defecation driven NTDs and other diseases related to fecal contamination of the environment.