Animal influence on water, sanitation and hygiene measures for zoonosis control at the household level: A systematic literature review

Introduction Neglected zoonotic diseases (NZDs) have a significant impact on the livelihoods of the world’s poorest populations, which often lack access to basic services. Water, sanitation and hygiene (WASH) programmes are included among the key strategies for achieving the World Health Organization’s 2020 Roadmap for Implementation for control of Neglected Tropical Diseases (NTDs). There exists a lack of knowledge regarding the effect of animals on the effectiveness of WASH measures. Objectives This review looked to identify how animal presence in the household influences the effectiveness of water, hygiene and sanitation measures for zoonotic disease control in low and middle income countries; to identify gaps of knowledge regarding this topic based on the amount and type of studies looking at this particular interaction. Methods Studies from three databases (Medline, Web of Science and Global Health) were screened through various stages. Selected articles were required to show burden of one or more zoonotic diseases, an animal component and a WASH component. Selected articles were analysed. A narrative synthesis was chosen for the review. Results Only two studies out of 7588 met the inclusion criteria. The studies exemplified how direct or indirect contact between animals and humans within the household can influence the effectiveness of WASH interventions. The analysis also shows the challenges faced by the scientific community to isolate and depict this particular interaction. Conclusion The dearth of studies examining animal-WASH interactions is explained by the difficulties associated with studying environmental interventions and the lack of collaboration between the WASH and Veterinary Public Health research communities. Further tailored research under a holistic One Health approach will be required in order to meet the goals set in the NTDs Roadmap and the 2030 Agenda for Sustainable Development.


Introduction
Neglected zoonotic diseases (NZDs) have a significant impact on the livelihoods of the world's poorest populations, which often lack access to basic services. Water, sanitation and hygiene (WASH) programmes are included among the key strategies for achieving the World Health Organization's 2020 Roadmap for Implementation for control of Neglected Tropical Diseases (NTDs). There exists a lack of knowledge regarding the effect of animals on the effectiveness of WASH measures.

Objectives
This review looked to identify how animal presence in the household influences the effectiveness of water, hygiene and sanitation measures for zoonotic disease control in low and middle income countries; to identify gaps of knowledge regarding this topic based on the amount and type of studies looking at this particular interaction.

Methods
Studies from three databases (Medline, Web of Science and Global Health) were screened through various stages. Selected articles were required to show burden of one or more zoonotic diseases, an animal component and a WASH component. Selected articles were analysed. A narrative synthesis was chosen for the review.

Results
Only two studies out of 7588 met the inclusion criteria. The studies exemplified how direct or indirect contact between animals and humans within the household can influence the effectiveness of WASH interventions. The analysis also shows the challenges faced by the scientific community to isolate and depict this particular interaction. PLOS

Neglected tropical diseases and zoonoses
Neglected tropical diseases (NTDs) are a group of communicable diseases estimated to affect over a billion people globally, particularly those with least economic resources, access to health care, good nutrition, clean water and sanitation facilities; the weak political influence of affected groups as well as the complex nature of these diseases has resulted historically in a lack of attention and resources, precipitating the use of the term "neglected" [1]. This has been acknowledged by the World Health Organisation (WHO) and a global Roadmap was released in 2012 to focus on reducing the burden of 17 NTDs. This "Roadmap for Implementation" [2] includes five 'key strategies to combat NTDs by 2020' of which one aims to improve veterinary public health at the human-animal interface, and another emphasises the provision of safe and clean sources of water and effective sanitation infrastructure, and ensuring appropriate hygiene practices (WASH) [3]. The Roadmap, together with the 2015 WHO global strategy on WASH and NTDs [4], espouses a holistic approach to disease control and elimination.
The new global development framework enshrined in the Global Goals of the United Nations' 2030 Agenda for Sustainable Development [5] sets out a One-Health approach to poverty, inequalities, health and the environment, in contrast with the siloed structure of the previous Millennium Development Goals (MDGs), whose agenda ended in 2015. Global Goal 3 within this agenda sets ambitious targets for improving health and wellbeing, including NTDs, and acknowledges the importance of addressing social and environmental determinants of health [6]. A One Health approach that addresses the animal-human interface and defines disease control strategies that enhance livelihoods and reduce poverty can contribute to the achievement of the Global Goals, but also represents a departure from current prevailing practices. Further knowledge on effective programming approaches is therefore urgently needed.
Several of the NTDs are zoonotic diseases-infections transmitted between animals and humans, and are therefore referred to as Neglected Zoonotic Diseases (NZDs). These include cysticercosis, rabies, echinococcosis, foodborne trematodiases, zoonotic African trypanosomiasis and schistosomiasis. Several of these are related to WASH elements in terms of prevention and/or treatment. Other diseases recognised by WHO in its "Research Priorities for Zoonoses and Marginalized Infections" include toxoplasmosis, cryptosporidiosis and bacterial zoonoses, for which improved sanitation has proven effective in reducing transmission [3]. The global burden of these zoonotic diseases is considerable. Cystic echinococcosis causes, on average, the loss of 2 million annual disability-adjusted life years (DALYs), with associated costs rising up to US$ 3 billion for human treatment and livestock industry losses [7]. Taenia solium, the causal agent of taeniasis and cysticercosis, is responsible for an estimated cost of 2.8 million DALYs globally [8]. Mortality due to cysticercosis in humans increased by 58% between 1990 and 2010 [9], and the disease is estimated to affect over 50 million people globally, causing up to 30% of all epilepsy cases [10]. Zoonoses are estimated to contribute to up to 10% of the total DALYs lost, and 26% of DALYs lost due to infectious diseases in low income countries [11]. Zoonoses affect human health directly, but by affecting animal health, they can also cause important economic losses and limitations for affected rural communities that depend on animals for working fields, transportation, as a source of protein and as a source of income when sold in local markets [12]. For example, cysticercosis has been reported to cause $12,6 million in annual losses in Cameroon [13], $150 million in India [14] and 18.6 to 34.2 million US dollars in East Cape, South Africa [15].

One Health approach to NZDs
These zoonotic diseases are neglected due to the relatively low mortality associated with them, their tendency to affect predominantly poor and marginalised populations, and the complex, intersectoral measures required to control them, which include community infrastructure and capacity building, health promotion programmes, improved diagnostics and treatment, vaccination and prevention programmes and policy adaptation at local, regional, national and international level [11]. Zoonotic pathogens have complex life cycles that commonly include different phases in human hosts, animal hosts and the environment before completion. Overlooking one or more of these three elements facilitates the perpetuation of the cycle, and with it, reinfection. A One Health approach to controlling zoonotic transmission is needed, considering animals, people and the environment in a comprehensive approach to public health. Since zoonoses are influenced directly and indirectly by multiple factors, focusing solely on transmission routes wrongfully overlooks socio-cultural, economic, anthropological and ecological elements that may affect transmission as well as delivery of control programmes.
The need for intersectoral control measures is especially evident in low income countries [16], where the rural population accounts for an average of 69% of the total [17]. Not only do poor, rural communities have fewer resources and less access to healthcare, they also possess less political influence and power than other population groups to demand services and resources from government authorities [18][19][20]. A One Health approach helps create resilient solutions for disease transmission by setting measures that can be implemented in the long term by community and government action, meeting the objectives for sustainability set by the Sustainable Development Goals [21]. In poor, rural settings, smallholder animal production of indigenous species of pigs, poultry and ruminants is dominant [22], and hence human and animal interaction within the household is more common in these settings, requiring special attention to this interaction in the control of zoonotic diseases [23]. However, given the dependence of rural households on animals as a major source of livelihood and as an alternate source of income in emergencies, certain measures that may support disease control objectives may not be feasible in practice [24]. For example, pig-corralling is recommended as a main method for control of cysticercosis, and hence programmes may be put in place to improve this practice amongst farmers [25]. However, for many households and communities in middle-low income countries, this is not economically feasible [26], since this would require the family to assume the added cost of feeding the pigs, instead of allowing the animals to forage for themselves [27]. Similarly, protecting water sources from animal access prevents contamination of water for human use with animal faeces and secretions. However, the need to provide livestock and humans with sufficient clean water from a protected source poses a challenge for many communities [28].
A One Health approach can help identify such multi-factorial elements and avoid omitting valuable programme components, including human, environmental and animal factors. Human behaviour factors such as conflict, migration and socio-cultural practices, shape disease patterns, due to relocation, high human density and reduced hygiene levels [29]. Similarly, economic and agricultural development will reshape the land and demands of society, changing animal farming and animal product consumption practices, increasing the risk of foodborne disease transmission and zoonotic influenza [30]. An example of an animal factor to consider is how wildlife reservoirs can help perpetuate infective cycles within local livestock. This poses a great challenge for zoonotic disease control in pastoral communities due to the difficulty of limiting direct and indirect interaction between wildlife and livestock species [30,31]. Additionally, ecological factors like climate change and deforestation have a direct impact on the distribution of vector-borne diseases by altering the habitats of the vector and reservoir species, as well as allowing vectors to sustain their life cycle in new areas due to a rise in average temperatures, leading to emergence and re-emergence of these diseases in new parts of the world [30,32]. Another example of One Health approaches helping to tackle ecological problems can be found in the reuse of animal excreta as crop manure, as incorrect use can lead directly to disease transmission through contact and clothes and indirectly through water contamination [33]. Use of animal excreta as crop manure can also alter the chemical properties of the soil, endangering the environmental sustainability of the area, and subsequently increasing the exposure of humans and animals to contaminated sources of infection [33]. Authors like Nguyen-Viet, Zinsstag and Charron propose an integration method as a solution for optimising the use of human and animal excreta as manure, by combining cross-sectoral knowledge and stakeholder engagement under a One Health framework [33,34]. Such a framework enables the implementation of sustainable control strategies for NZDs in countries where economic resources are scarce.

One Health challenges for WASH programmes
Water, sanitation and hygiene (WASH) programmes can plausibly contribute to control of zoonotic disease given the knowledge about pathogen transmission cycles, through provision of sanitation infrastructure that safely removes human and animal faecal waste from the human environment, provision of clean water sources, and improvement of hygiene practices at the community and household level [4]. The WHO WASH and NTDs strategy is a step towards developing collaboration between WASH and NTDs programmes, both of which reference integration of control measures, but do not offer specific guidance or methods of monitoring on collaboration between the sectors [4]. However, the much needed guidance to encourage a One Health approach through engagement of other sectors such as agriculture and veterinary public health is not included in the remit of the WASH and NTDs strategy [5,35]. The positive relationship between WASH programmes and reduction of NTDs incidence has been proven, yet many of these programmes still lack the multifactorial approach needed to cover the impact of other elements that affect disease transmission [36], such as animal presence within the household and human-animal interaction. Because of this, there are limitations to understanding why WASH programmes may not result in the expected disease control outcomes and how they can be optimized. No systematic research has been done to date on the impact of demand-side sanitation programmes on NZDs transmission [3].
Although the evidence base on the interaction of animals with sub-standard sanitation facilities is weak, it is plausible that the presence of free-roaming household animals alongside conditions of open defecation or poor containment of faeces can contribute to intensified disease transmission [37]. As mentioned in the WHO WASH and NTDs Strategy [4], and as several authors argue [36, [38][39][40], it is necessary to gather more information regarding WASH-related interventions and disease burden reduction. This is particularly relevant for zoonotic diseases, as, out of the existing reviews relating to WASH and disease burden, few focus specifically on zoonotic diseases. Those that do, often disregard the presence of animals in the household and its impact on the effect of WASH interventions on zoonotic disease. There is need to identify these linkages and knowledge gaps that require further study. The aim of this work was to conduct a systematic review to identify the existing published data, on how the presence of animals in the household impacts the efficacy of WASH interventions for zoonotic disease control.
The objectives of this review were: to identify how animal presence in the household influences the effectiveness of water, hygiene and sanitation measures for zoonotic disease control in low and middle income countries; to identify gaps of knowledge regarding this topic based on the amount and type of studies looking at this particular interaction.

Protocol
A review protocol was designed to inform and direct the review steps before conducting the systematic review. The protocol was designed based on the guidelines given by "CRD's guidance for undertaking reviews in health care" and the "WHO Handbook for Guideline Development" [41,42], as well as example systematic review protocols found in various academic sources, approved by peer academic experts. The complete protocol can be found in Text S1.

Search strategy
Three databases were used: Medline, Web of Science and Global Health. These were chosen based on other systematic reviews conducted in the area of sanitation, hygiene and NTDs [43][44][45], and on expert academic advice solicited by the authors. The three databases were systematically searched for publications dating 1980 to 30 th April 2016.
The search terms relative to WASH were chosen based on other WASH literature reviews and scientific articles. Animal terms were selected based on literature and expert advice, including those species most likely to interact with humans within the household, in low-and middle-income countries. The terms were then divided into four pools: The terms amongst pools were combined by the Boolean operator "OR", while those between pools were combined by the Boolean operator "AND".
Diseases chosen for the terms were based on the list of neglected zoonotic diseases described in the WHO NTDs Roadmap [2]. The results obtained were sorted by "author" in descending order. Studies were selected through a three-stage process, first by title and abstract screening, then by full text analysis, based on the selection criteria for each stage, and finally by a quality control checklist. References were managed with the use of reference management software EndNote X7.

Inclusion/Exclusion criteria
For the first stage, title and abstract screening, studies were included if the abstract mentioned a zoonotic disease term together with a WASH term, if a full text version was available and if the article was published in English or Spanish. Studies not meeting these requirements, and review articles, were excluded.
The full text versions of studies selected in this first stage were retrieved and analysed for further selection. In this second stage, articles that did not quantify burden of disease in human or animal populations, did not analyse the role of animals in zoonosis transmission in relation to WASH measures, or did not meet the requirements of the quality check described in the protocol, were excluded from the review. The type of study and its design were not deemed to be crucial inclusion/exclusion criteria, due to a low number expectancy of final study retrieval.

Quality assessment
Studies selected for the last stage of the systematic review were analysed using a quality checklist based on the guidelines for public health studies from the National Institute for Health and Clinical Excellence [49].

Data extraction and synthesis
Articles included in the full text review were subjected to data extraction based on the protocol, with special attention to the study population regarding burden of disease, the diagnostic method used, the WASH measures in place, description of animal presence within the household, and the statistical analysis approach taken by the study. Due to the consideration of various types of studies in the inclusion criteria and the expected low count of final studies making the last selection, pooling was not deemed possible. Therefore, a narrative approach was chosen for addressing data synthesis. Zoonotic diseases in which WASH measures play a relevant role in control were included in the analysis and synthesis of the results, as long as the selected study included it in its own analysis, even if said diseases were not considered to be neglected by inclusion in the WHO reference list.

First screening
Seven thousand five hundred and eighty-eight (n = 7588) studies where obtained after introducing the search terms into the three databases (Fig 1). Screening of titles and abstracts retrieved a total of 80 studies (n = 80) meeting the inclusion criteria for the first stage of the review: 46 from Medline, 28 from Global Health, and six from Web of Science. Of these 80, 13 were duplicates and three were unable to be retrieve in full-text form and were therefore discarded. The total number of articles selected for the next stage of the review was 64.

Second screening
Full text for the remaining 64 articles was obtained, analysed and considered for review inclusion. After data extraction and analysis, two articles [50,51] were identified that quantified the burden of disease in humans or animals and analysed the role of animals in zoonosis transmission in relation to WASH measures, hence meeting the final inclusion criteria as set out in the protocol. Due to the low count of studies included in the final review, the 64 articles analysed in this phase were summarised in the form of tables that show the research tendencies when addressing WASH and NZDs. The complete list with the main data extracted from each one can be found in Table 1, including location, type of study, number of participants in the study, disease of interest, diagnostic test used to address presence of disease, WASH and animal component studied, the type of statistical method used for the analysis, and a summary of the results of the study.
More than half of the studies (29) focused on cysticercosis, while 12 focused on toxoplasmosis (Table 2). Humans appear as the most studied species, with 36 studies looking at human burden of disease, while pigs were second with 26 citations. Fifty one out of 64 were designed as cross-sectional studies, 46 of these establishing a prevalence value through a serological test and combining it with a questionnaire for associated risk factors. Table 3 shows the study count for each of the categories for water, hygiene and sanitation components, and the proportion of studies that included one, two, or the three types is shown in Fig 2. Three studies had at least one factor in each of the categories.
The summarised data suggests the existence of a relationship between NZD epidemiology and the contact of humans and animals in the household, generally showing a negative impact of animal presence on WASH measures or an enhanced negative effect of animal presence on the impact of poor WASH conditions. In the case of cysticercosis, studies show contradictory results regarding the impact of WASH measures and animal presence on disease prevalence.

Final review
Due to the small number of studies that were selected based on the criteria, the outcome of the quality control check was not considered for further exclusion.
The study by Holt et al. (2016) was designed as a cross-sectional study examining prevalence of hepatitis E virus (HEV), Japanese encephalitis virus and Trichinella spiralis in both humans and pigs, as well as Taenia spp. solely in humans in two provinces of Lao PDR, with a multiple correspondence analysis and a hierarchical clustering of several components deemed relevant to disease transmission. Three clusters were identified: one referential (cluster 1) with the best sanitation and lowest pig contact; cluster 2, with moderate sanitation levels and slaughtering of pigs as the main source of animal contact; and cluster 3, with lower sanitation levels and a relative higher rate of free-roaming pigs. The risk of human infection, measured through Odds Ratio (OR), for each of the diseases and clusters when compared to cluster 1 are shown in Table 4. HEV had a very similar OR for risk of infection between clusters 2 and 3, despite the superior WASH conditions of cluster 2. For Taenia spp. and Cysticercosis, risk of infection Animal influence on WASH and zoonosis: Systematic review Animal influence on WASH and zoonosis: Systematic review proved higher in cluster 3 than cluster 2, but with a significant increased risk of infection in cluster 2 compared to the control, despite solid practices of hand washing and water boiling amongst the population. Finally, Japanese encephalitis showed an increased risk of infection in cluster 2 over cluster 3, despite better WASH conditions. Data regarding pig seropositivity was not clustered and WASH factors were not found to be significant in T. spiralis and HEV infection. The other study (Bulaya et al. 2015) was a comparative study pre-and post-community-led total sanitation (CLTS) intervention for porcine cysticercosis control, identifying prevalence performing an Ag-ELISA test. There was no randomization in village selection or house  Cysticercosis  29  11  21  1  -------Toxoplasmosis  12  6  -2  3 1 -----

Type of water source 29
Latrine/toilet presence in the village/household 22

Type of water drainage 3
Latrine/toilet type in the village/household 2

Hygiene knowledge 1
https://doi.org/10.1371/journal.pntd.0006619.t003 Animal influence on WASH and zoonosis: Systematic review  Animal influence on WASH and zoonosis: Systematic review selection, and instead selected based on village characteristics and willingness to participate, respectively. The prevalence pre-intervention was 13.5%, (6.8-20.1, 95% C.I.), compared to a value of 16.4% (12-20.8, 95% C.I.) post-intervention, although this increase was deemed nonsignificant by the author. After the intervention, latrine presence improved from 67.2% to 83.1%, with the percentage of free-roaming pigs changing from an 89.8% to a 30.3% of them free roaming, 43.8% partially free roaming and 25.8% penned. Home slaughter of pigs increased from 49.15% baseline to 80.90% post-intervention. Despite the improvement in latrine presence, animal husbandry was not improved enough to avoid direct and indirect contact between animals and humans within the household.

Discussion
This review showed examples of the way animal-human interaction can affect the effectiveness of WASH interventions for zoonosis control. Importantly, it also highlighted the dearth of studies looking specifically at this interaction. After the search retrieved 7588 articles for this review, 64 were selected in the first screening, of which only 2 were selected for the final review after the second screening. This outcome is likely due to the sectoral focus of the studies. Traditionally, research groups investigating the effectiveness of WASH interventions focus on human factors as positive or negative influences. Similarly, the Veterinary Public Health community focuses more on animal-related factors and disease-transmission routes. The interaction between these two aspects is a research and programming 'blind spot', as was demonstrated by this review, and needs to be addressed with further intersectoral research studies. As noted by Zinsstag in 2015 [33], a study in Vietnam showed how a One Health approach for WASH programmes integrates all factors into one framework. This helps identify the relationship between the factors, while exposing the missing links and the areas in need for further research, of which the main one stated is "the boundaries of the sanitation problem". Sanitation and hygiene programmes have proven effective in reducing NTD burden in numerous studies, as backed by various systematic reviews [43][44][45]. However, effective, full-coverage implementation of control programmes considering both human and animal sanitation aspects can be challenging in practice. As described by Guilman et al. in 2012 [26], some communities may not have sufficient resources to change their animal farming system to one that limits animal-human contact. In other cases, the community may actually benefit economically from this new farming system [114], but as long as the population believes this is not the case, no change will be embraced by the community [115]. This reinforces the importance of accompanying these type of logistic measures with strong education and hygiene promotion campaigns that involve the community and show the importance and benefits of adopting them.
The study by Holt et al. [51] compared Odds Ratio of infection in several pig zoonoses between different sanitation and pig contact factors. For HEV, lower levels of sanitation, as described in the results section, proved to be a risk factor for virus presence, without significant differences between these lower levels specifically. However, increased contact with pigs, particularly through handling and slaughtering, proved significant in its influence on the effectiveness of WASH measures in disease control, as the cluster with moderate sanitation and close pig contact had equal risk of infection as the cluster with poorer sanitation. Pig contact has been described as a risk factor for HEV transmission previously [116], but according to this study, pig corralling impede their access to the household would not make a significant difference in disease transmission as long as the animals are still being slaughtered at home, due to direct human contact with pig blood. In the case of Trichinella, socioeconomic status acted as a confounder, since the main risk factor is pork consumption [117,118], which in this study was associated with higher status due to availability and affordability cost, as are good sanitation and hygiene conditions. In the case of JEV, the cluster with higher direct contact with pigs showed a higher risk of infection, despite better sanitation and hygiene conditions, showing an example of how animal contact can severely hinder the effectiveness of WASH measures. This could be due to its vector-borne nature, which correlates to two factors of this particular cluster: unprotected water sources, which facilitates breeding areas for Culex spp.; hygiene practices, latrine use or corralling measures would not make a significant impact in its transmission unless done optimally, avoiding contamination of water that could facilitate Culex spp. reproduction. Regarding Taenia solium and cysticercosis, the cluster with higher rates of free-roaming pigs and open defecation showed the highest risk of infection, as expected. However, the high risk of infection presented by the cluster with moderate WASH and close contact with pigs shows how the latter can affect the effectiveness of the former.
During the selection process of this review, several studies (Table 1) were screened and later revisited, for further insights on the impact of animals on WASH interventions. Some showed presence, usage or condition of latrines and free roaming of pigs to be significant risk factors in disease transmission [84,119,120], but others had non-significant results [107], rather identifying the source of water for consumption and its quality as a risk factor. In contrast, Nkouawa et al. in 2015 [87] identified that despite having a non-potable (unsafe) water source, disease transmission was reduced by improving hygienic practices and corralling pigs. The study by Holt et al. [51] provided robust results on relative impact of animal and WASH factors, meeting the criteria for selection stated in the protocol of the review. However, future studies should ideally be designed in a way that focuses on isolating the influence of animal factors on the effectiveness of WASH measures. This is particularly difficult to achieve given the circumstances of the communities in which these studies need to be conducted: as noted by Schmidt et al. in 2014 [121], designing impact studies on water, sanitation and hygiene and retrieving significant results is a recurrent challenge for the scientific community: Randomised controlled trials are rarely free from bias, while observational studies usually lack a large enough study population or result significance [121]. Additionally, performing randomised controlled trials in the optimal representative geographical areas is logistically and economically challenging. Another factor to take into account is time, since marketing and promotion campaigns can take several years to have a significant effect, deeming any study that withholds investment in WASH services for such an extended period of time unethical [121].
A relevant limiting factor to assess the efficiency of any WASH programme implementation is the correct use, design and upkeep of sanitation facilities. Several studies show that although latrines were present in the community, they were not consistently used for defecation by all household members or kept in a sufficiently hygienic state [84,85]. The incorrect use of latrines is often associated with socio-cultural and psychological factors, as identified by Thys in 2015 [122], such as a sense of reduced privacy, latrines being too close to the village, comfort of use or trust in its efficacy and need of use. Lack of ownership of the need for latrine construction and lack of ongoing support for maintenance and improvement can undermine potential health benefits of basic latrines.
The study by Bulaya et al. in 2015 [50], showed that despite the CLTS intervention resulting in increased latrine presence, net increase in latrine usage and improved pig husbandry, prevalence of disease in pigs increased slightly after the intervention. The study did not specify whether the newly built latrines resulted in safe separation of humans and animals from human faeces. Achieving that level of detail in the analysis is an objective for future studies. Although deemed non-significant, the 95% C.I. shows almost no change in prevalence from pre to post intervention. This was attributed by the authors to infected members of the community still practising open defecation due to lack of resources for latrine construction. Not corralling the totality of the pig population, therefore allowing for interaction of animals and humans within the household, could be the explanation as to why the increase in latrine presence had no effect in decreasing porcine cysticercosis. Free roaming of pigs has been identified as a risk factor for porcine cysticercosis by some of the studies screened before review inclusion [69,75] but was found to be non-significantly others [72]. Similarly, the presence of latrines can be significant [72,73] or non-significant [69] for disease prevalence in pigs, depending on the study, reinforcing the findings by Bulaya et al. (2015). As previously mentioned, low latrine usage has been described as a risk factor for disease transmission [59,84,85] but also as a recurrent sociocultural problem, since many members of the community do not use latrines on a consistent basis for a variety of reasons [59,115,122], or do not keep the latrines in a suitable condition for them to effectively reduce disease transmission [84,115,120]. However, poor programme design, lack of follow up or disputes between NGOs and community leaders on logistics, provisions and payments can be a cause for poor latrine construction and maintenance [123]. This reinforces the suggestion made by Bulaya et al. [50] of the importance of continued hygiene promotion programmes and access to sanitation hardware options in order to ensure the complete effectiveness of sanitation or animal husbandry improvement programmes.
As an example of a multifactorial approach to disease transmission control, prevalence of Schistosomiasis was significantly reduced in three studies in China [70,102,124] by implementing a complete WASH programme with sanitation facilities and hygiene educational programmes, reducing the indirect contact of animals and humans through water and reducing the population of the host snail species for Schistosoma. However, programmes that alter animal husbandry in drastic ways such as changing free-roaming farming systems into stabling farming systems, also alter the local economy of the community [125]. In the case of cysticercosis, the penning of pigs is not always possible in certain communities given the resulting increased costs of feed and infrastructure [125]. Substantial investment and economic compensation to farmers and households would therefore be required to maintain and sustain these programmes consistently over time [126].
In the case of toxoplasmosis, principal and consistent risk factors for infection identified throughout the literature, include unsafe water source, inadequate hygienic conditions of the household and cat presence in the household or the vicinity, and were common to human [52,66] or animal [55,58] infection. While providing clean water sources and creating appropriate hygienic conditions decreases the burden of disease, avoiding the presence of cats within the household could potentially increase the presence of rodents in many communities that use cats as the sole method of rodent control. A study showed how, when combined, the presence of cats and dogs in an area significantly reduced the local rodent population [127], however, more research should be conducted to clarify the impact of cat population control on rodenttransmitted diseases in rural communities.
The review protocol was designed to include animal-focused studies as well as humanfocused studies to ensure a One Health approach to zoonotic disease transmission. Particularly for NZDs, interrupting sustained transmission requires a multifactorial approach considering both zoonotic and anthroponotic transmission paths. Reducing animal burden of disease has a direct effect on human prevalence of disease and vice versa [128], and therefore WASH programmes applied equally to human and animal populations are likely to provide better results than a human-centred approach. The review identified the lack of studies looking at the importance of animal influence in WASH programmes, exposing the existent lack of knowledge in the matter. Further research and programme design need to focus further on animal impact and isolating the study of animal components in the efficiency of WASH control programmes. One of the limitations of the review was the non-inclusion of rodent species in the study. Although rodents are acknowledged to be a source of NZD transmission within the household, they were deemed to overreach the scope and feasibility of this review: on one hand because the review focused in farmed animals kept by the household owners; on the other hand because thorough control of rodent activity in the household is difficult and less reliable than that of farmed animals, mainly due to the complex biological and ecological characteristics of each local rodent species [129,130]. The initial literature review was conducted for fulfilment of an MSc with one student. All three co-authors advised on the approach to be taken and made revisions to the literature. Throughout the writing of the literature there was input from all authors who also held regular review meetings. To further optimise the systematic review, a second reviewer would have performed the search and selection and compared results. Also, had a longer period of time been available, more databases could have been screened, although the final count of studies would most likely be low, since the tendency identified in the review is that of a very low percentage of studies looking specifically at animal influence in WASH measures efficacy. The time constraints were due to the timelines of the MSc. However, all authors had additional input to the manuscript. Whilst the initial literature review was conducted by one student, the manuscript has been prepared after revisions by all authors with additional literature added after further reviews. This has been rewritten to reflect the input following the initial MSc project.

Conclusions
This systematic review demonstrated the relevance of human-animal interaction within the household for the effectiveness of WASH measures for control of NZDs. It also shows the significant lack of specific studies tending to the effect of animals on WASH programmes' effectiveness for zoonotic disease control. Several examples exist in the literature describing prevalence of zoonotic disease and associated risk factors, yet, in the majority of cases, their design fails to assess the specific influence of animal presence in WASH interventions. Further research should be undertaken regarding the influence of animals in WASH programmes, ideally isolating the sanitation component and studying different levels of animal interaction and exposure within the household. Attention to animal burden together with human burden of disease would allow for better understanding and optimisation of WASH programme effectiveness on both disease control and broader development objectives. There exists an evident lack of direct coordination between WHO's WASH and NTDs official programmes. Further developing of a research agenda around the animal-sanitation-disease link can help set out clear actions on which disease control programmes can be based.