**4.1 Current strategies for schistosomiasis control and elimination**

Recent years have witnessed an increased interest in the control and, finally, elimination of Neglected Tropical Diseases (NTDs), and today the control of schistosomiasis has again become a priority on the agenda of many governments, donors, pharmaceutical companies and international agencies [40]. WHO has developed several road maps for NTDs, and many African countries have made significant progress by rolling out national Schistosoma *Hybridizations and Risk of Emerging Zoonosis in Africa: Time to Think of a One… DOI: http://dx.doi.org/10.5772/intechopen.103680*

action plans and programs targeting schistosomiasis control and elimination [41, 42]. Preventive chemotherapy is the main strategy for schistosomiasis control in Africa, supplemented with water, sanitation and hygiene (WASH) interventions in some regions [43].

#### *4.1.1 Preventive chemotherapy*

#### *4.1.1.1 An overview of preventive chemotherapy: Praziquantel*

Current control of human schistosomiasis in Africa is based on preventive chemotherapy, whereby populations are mass-treated with anthelminthic praziquantel administered in the standard single oral dose of 40 mg/kg body weight. Treatment with praziquantel is currently the strategy of choice and is endorsed by WHO [41, 43]. The ambitious goals of control and eventual elimination are underpinned by targets that require countries to reach at least 75% treatment coverage of school-age children and at-risk adults, with mass drug administration schedules and the designation of target groups depending on schistosomiasis endemicity [43]. This coverage goal is endorsed for schistosomiasis and soil-transmitted helminths in the 2012–2020 WHO road map for NTDs, in which preventive chemotherapy was identified as a key strategy for tackling NTDs [42, 44].

Over the past decade, significant progress has been made on large-scale treatments through integrated control of schistosomiasis and other NTDs. It is estimated that at least 236.6 million people required preventive treatment for schistosomiasis in 2019, of which more than 105.4 million (about 45%) were reported to have been treated [45]. In Africa, 17 countries out of the 40 that require preventive chemotherapy had not achieved the 75% treatment coverage target for school-age children during 2018, when a total of 69.1 million school-age children were treated, representing overall coverage of 62.9% [46]. In general, annual mass drug administration of preventive chemotherapy has had a significant effect on infection prevalence, intensity and associated morbidity among school-age children [47–49]. However, disease reoccurrence and persistent transmission suggest a need for more intense control measures to achieve the goal of schistosomiasis elimination.

Since the adoption of the World Health Assembly Resolution WHA 65.21 and NTDs road map 2021–2030, schistosomiasis control programs have shifted from morbidity control to disease elimination [41]. However, gaps continue to be observed in the implementation of control programs in Africa. Mass drug administration programs commonly overlook large numbers of preschool-age children, adolescents and adults, thus increasing health inequality and the risk of reinfections of previously treated groups [50]. Schistosomiasis cannot be eliminated in communities where mass drug administration is not ongoing. In the past, a key bottleneck to the implementation of preventive chemotherapy for control of schistosomiasis in Africa was the limited access to praziquantel [51]. Though there is now growing access to this medication for schistosomiasis control in Africa, it is not at the level that is projected to be necessary to reach all people who are at risk or who require treatment [52]. Analysis of data reported on treatment coverage for schistosomiasis shows that utilization of available praziquantel by NTD programs is not yet optimal in many countries [46, 52].

#### *4.1.1.2 Strengths and weaknesses of preventive chemotherapy*

Praziquantel is the drug of choice for the treatment of schistosomiasis, as it is considered cost-effective, relatively safe, inexpensive and efficacious; also, donor organizations are willing to provide the drug [53]. Despite increased efforts to control schistosomiasis using preventive chemotherapy, several challenges still exist in reaching the target populations. Until recently, preschool-age children, as well as at-risk adults such as fishery workers, have not been included in many mass drug administration programs despite the evidence of schistosomiasis infection among these populations [54, 55]. This increases health inequality and the accumulation of potentially irreversible morbidities due to prolonged infection [56].

A major challenge now lies in the unavailability of a child-size formulation of praziquantel [56, 57]. The currently available formulation presents several limitations: (a) It is a large tablet, which is difficult for young children and infants to swallow and thus must be broken and crushed to allow for safe uptake. (b) It has a very bitter taste, and so is often mixed with a sweetener to make it palatable to young children. (c) The current formulation of 600 mg does not allow for flexibledose adjustments for this age group.

#### *4.1.2 Water, sanitation and hygiene (WASH) interventions*

Clean water provision, sanitation and hygiene are critical components of the global NTD roadmap [41]. For schistosomiasis, improved sanitation across the entire community to prevent contaminated feces and urine from reaching surface water can reduce or eliminate transmission, by stopping worm eggs in feces and urine from entering water sources, which are the snail habitat [58]. The aim of United Nations Sustainable Development Goal 6 (SDG 6) is to ensure the availability and sustainable management of water and sanitation for all by 2030. WASH interventions are among the most important measures used to control water-related diseases in Africa. However, sanitation, hygienic practices, and access to clean water are inadequate in large parts of Africa where schistosomiasis is endemic [59]. According to the United Nations Children's Fund, in 2020 more than two-thirds of the African population did not have basic sanitation services and about 18% practiced open defecation. Ethiopia, Uganda, Kenya and Tanzania had the largest numbers of people in the continent without access to basic sanitation services, while Eritrea, South Sudan and Ethiopia had the largest proportions and numbers of people practicing open defecation [60]. Furthermore, in Eastern and Southern Africa, about 50 million (over 27%) of school-age children had no access to sanitation services, while 117 million (62%) had no access to hand-washing facilities at school [60]. It has also been reported that nearly half of Africans do not have access to clean water and two-thirds lack access to sewage infrastructure [61]. A systematic review and meta-analysis of the relationship between safe water, adequate sanitation, good hygiene and schistosomiasis found that people with access to safe water were significantly less likely to acquire a *Schistosoma* infection than those who, while they had access to adequate sanitation, did not have safe water access [62].

#### **4.2 A different approach to schistosomiasis control: one health**

#### *4.2.1 The concept of one health and the one health disease control approach*

The Centers for Disease Control and Prevention define One Health as a collaborative, multispectral transdisciplinary approach applied at the local, regional, national and global levels, with the goal of achieving optimal health outcomes that recognize the interconnection among people, animals, plants and their shared environment

Schistosoma *Hybridizations and Risk of Emerging Zoonosis in Africa: Time to Think of a One… DOI: http://dx.doi.org/10.5772/intechopen.103680*

[63]. The One Health approach is a collaborative effort between the human health, animal health and environmental sectors to attain optimal health for people, animals and the environment. Over 60% of emerging, re-emerging and endemic human diseases have their origins in animals [64]. Humans are at increased risk of contracting diseases of animal origin because of a wide range of interconnected variables, including mass urbanization, large-scale livestock production and increased travel [64]. Therefore, efforts to unite the sectors working to protect humans and animals and the ecosystem are of paramount significance.

#### *4.2.2 Schistosomiasis control and elimination under the one health approach*

The recurrent hybridization between *Schistosoma* species in nature increases the distribution of schistosomiasis and ultimately challenges current elimination efforts. Animal reservoirs can maintain transmission with zoonotic parasites even while the disease they cause in humans seems to be effectively controlled [65]. To be successful, schistosomiasis elimination programs cannot ignore the animal reservoirs of infection in Africa; this requirement demonstrates the need to consider control measures within a One Health framework [40]. The rapid occurrence of reinfection with schistosomiasis further highlights the need for a One Health approach. An anthropocentric or disjointed sectoral approach to controlling human schistosomiasis in Africa, such as the NTD intervention strategies applied alone, may be insufficient to eliminate schistosomiasis. For example, in the Mekong subregion of Southeast Asia, relying solely on deworming to prevent schistosomiasis did not prevent reinfection, but required parallel activities within the One Health framework [66]. Measures should focus on health aspects of the environment, animals and humans. They should also involve state-of-the-art approaches to schistosomiasis diagnosis and surveillance that encompass the environment (water and snails), animals (both domestic fauna and wildlife) and humans to enable an understanding of transmission ecology and the evolution of schistosomiasis across all hosts (**Figure 5**) [6].

#### *4.2.2.1 Environmental health measures*

*Schistosoma* species depend entirely on the presence of freshwater environments harboring susceptible snails to complete their life cycle. Control measures should therefore focus on preventing excreta (fecal or urine) contamination of freshwater sources. The following control measures are ideal for preventing excreta contamination of freshwater sources:


#### **Figure 5.**

*Schematic presentation of the proposed one health framework for controlling zoonotic schistosomiasis in Africa.*

Snail control can be attempted through snail habitat modifications such as altering flow rate and water levels so as to disturb snail habitat and disrupt snails' food sources. Such modifications include constructing V-shaped banks in irrigation channels, removing vegetation and draining water sources that serve no special purpose for humans, wildlife or livestock [67]. Biological control of snails using nonsusceptible competitor snails has been reported to be successful in the Caribbean region [69], although it is important not to run the risk of importing potentially invasive snails. Snail control may also be accomplished through molluscicide application; however, since molluscicides have not been notably effective in past efforts, and may cause damage to other organisms [70], the application should be targeted, and carefully monitored rather than widespread [67].

#### *4.2.2.2 Human health measures*

As part of ongoing mass drug administration campaigns, other human interventions should be considered. Therefore, WASH providers must prioritize the reduction of inequality to align with the Sustainable Development Goals agenda, as developed in the recent WASH strategy to accelerate and sustain progress on NTDs [71]. Water scarcity can result in the sharing of water sources between people and animals, which can increase the risk of zoonotic diseases. Improving access to clean water by supplying tap water or wells at homes [65], accompanied by behavioral changes such as avoiding swimming, wading, washing or bathing in contaminated ponds, rivers and lakes, would help to prevent human contact with *Schistosoma*-infested waters. It is safest to consider all freshwater bodies in endemic areas as potential transmission

Schistosoma *Hybridizations and Risk of Emerging Zoonosis in Africa: Time to Think of a One… DOI: http://dx.doi.org/10.5772/intechopen.103680*

sites [67]. Furthermore, while safe water is unlikely to contain cercariae, its provision often will not prevent all human contact with infested water. In some settings, such as fishing communities, it is important to account for considerable occupational water contact that the availability of safe water supplies would not prevent [72]. Hence, periodic examination and treatment of workers and people at constant risk of infection may be the most feasible approach to controlling schistosomiasis [67]. Interventions to reduce the contamination of water bodies with *Schistosoma* eggs could reduce the potential for disease transmission in both humans and animals [65]. Stakeholders should scale up the provision of improved sanitation services through the construction of latrines (including aboard boats). Also, public toilets along river basins in schistosomiasis-endemic areas must be provided to stop human excrement from entering freshwater sources [67]. In addition, interventions such as the construction of big systems like sewage treatment ponds and constructed wetlands, or home-based smaller systems, would help prevent contamination of water sources. Basically, if the urine and feces of people and animals could be kept from entering water bodies, there would be no more schistosomiasis transmission. This can be seen in two highly infested bodies of water, Lake Victoria and Lake Malawi, where, thanks to local initiatives, there are actually 'safe beaches' with no schistosomiasis [1].

#### *4.2.2.3 Animal health measures*

The most effective way of controlling zoonotic schistosomiasis in livestock is also through keeping susceptible domestic animals from coming into contact with infested water. This can be achieved by preventing livestock grazing in infested wetlands, fencing infested water sources and supplying drinking water to the animals in troughs [73]. Apart from reducing the risk of infections to the animals, these measures will also prevent contaminated excreta from livestock from entering freshwater sources. Susceptible animals used in wetland areas for agriculture purposes should be replaced with nonsusceptible species or with farm machinery if the purpose of animals' use is mechanical management. Periodic examination and treatment of susceptible livestock should be conducted. However, reinfection may occur quickly if the source of contamination is left uncontrolled. Regarding wild animals, high-density populations of susceptible wildlife increase the potential for disease transmission. Interaction between livestock and wildlife should be prevented wherever possible, and supplementary feeding of wild animals close to water sources should be avoided. Lastly, scientists and funders should invest in finding *Schistosoma* vaccines for animals and humans [67].
