Policy Brief
Schistosomiasis is a prominent global disease, second to Malaria in NTD (neglected tropical diseases) where snails are widely known to be its intermediate host. It affects many countries, especially less developed countries such as Africa (Chitsulo, Engels, Montresor, &Savioli, 2000). According to Relman and Choffnes (2011), a basic main feature to the transmission of schistosomiasis disease are related to poverty and underdevelopment; hence poor water sanitation. They are transmitted when humans swim in infected open water which then causes an impact on the socio-economic well-being of countries where it is endemic.
The fight against this parasitic disease using molluscicides is an ongoing effort while useful; it is expensive. Although it is desirable to eradicate the snails to eliminate the parasitic worms, there are concerns in the continuous use of these synthetic molluscicides. Mainly, it being a potential environmental damage; let alone it harms non-target bio life such as fish, tadpoles and other aquatic organisms (Augusto, Mello-Silva, &Correa, 2018; Takougang, Meli, &Angwafo, 2006).
It has led to it being favored (Takougang et al., 2006). Augusto, et al. (2018) stress the importance of taking into account the logistical and environmental costs involved in the Molluscicide programs. Li and Wang (2017), in their article, recognize the effectiveness of the molluscicides. However, they state that its mechanisms and effects on the environment require further investigation as it could potentially lead to adverse environmental outcomes.
Molluscicides have proven to be somewhat effective in combating schistosomiasis in countries such as China, Brazil, Saint Lucia, Iran, Tunisia, Morocco, Saint Kitts and Egypt (Yang et al., 2012; King & Bertsch, 2015; Coelho & Caldeira, 2016).
The World Health Organization (WHO) stressed the importance of using molluscicides in fighting against schistosomiasis (WHO report, 1953; WHO report, 1961) but has also addressed the characteristics that molluscicides needed to have without severely affecting other sectors of biodiversity (Souza, 1995). Such features include having low concentrations of toxicity as this could lead to a chain of effects not just to faunas but humans as well. When consumed, molluscicides could affect biodiversity through its consumption by different types of organisms, whereby these organisms could then potentially be consumed by humans.
The inability of molluscicides implementation can also be attributed to its costly treatment. Molluscicides spraying requires it to be done repeatedly as snails have a high generative rate and that they are able to re-establish themselves after the treatments. In addition, labor cost should be considered in the repeated use of molluscicides. The labor cost for countries such as Tanzania, Zimbabwe, Saint Lucia and Puerto Rico are reported to be costly with Brazil being the highest, accounting for 80% of the national budget (Jordan et al., 1978; Jobin, 1979 as cited in King and Bertsch, 2015). The costly treatment could dissipate Brazil’s economic status as it burdens to keep up with the molluscicide-ing measures.
Recommendations
The arguments against the use of molluscicides outlined above raise the question of which alternative solutions the country can implement to combat schistosomiasis. Such actions as preventive chemotherapy, snail control, and hygiene and sanitation interventions are listed among the possible options (Jobin, 1979; King & Bertsch, 2015; WHO, 2017). The following recommendations will discuss the benefits and limitations of preventive chemotherapy and water-based programs.
Preventive chemotherapy is one of the cost-effective ways to address the infection in humans and cattle. According to Nelwan (2019), this option can be used in children and adults and lower the rate of infection substantially. WHO’s dosing recommendations depend on the spread of the disease and the age of people taking the medication. Nonetheless, this type of treatment does not prevent reinfection, which makes it less effective as a long-term solution – chemotherapy does not reduce the transmission from snails to unprotected people (Augusto et al., 2018). Furthermore, the drug used for this treatment (praziquantel) does not affect immature worms present in the host’s body (Nelwan, 2019). As a result, this medicine may not completely eradicate the infection, especially if it is the only element of the country’s program.
Another set of solutions relies on water-based initiatives and long-term change through education. First, Alzaylaee et al. (2020) suggest using DNA-based xenomonitoring to detect the presence of the infection in tropical freshwaters. This approach is focused on finding water sources that are contaminated to clean them and target specific areas without exposing all bodies of freshwater to chemicals. Moreover, this preventive measure allows scientists to find the most infected places and see how the worms affect different areas. This intervention, however, cannot be used separately from others – it is a necessary step for monitoring the state of freshwater bodies in the country (Secor, 2014). As an outcome, this procedure can help the government to reduce people’s exposure to infections water.
The next part of this intervention is improved water quality and sanitation. The contamination of water happens when fecal matter and urine get into freshwater. Thus, a sanitation system can be a long-term solution for reducing this risk. Although the installation of such systems is rather costly, it can guarantee a long-lasting effect on the health of the citizens (Grimes et al., 2015). An infrastructure of sanitation and clean water may also affect people’s use of freshwater bodies and change the interaction with piped water.
Nevertheless, community efforts are also necessary to educate people about the risks of using contaminated water. WHO (2017) developed a WASH program (water, sanitation, and hygiene) that targets countries with high rates of schistosomiasis. It is a community-led initiative that combines the government’s efforts in sanitation and people’s education about safe hygiene practices, water testing, and malnutrition assessment.
The review of the alternatives shows that several activities have to be considered to ensure the long-term effect and near-complete eradication of the infection. Health education measures will help communities to spread information and change practices. Water quality monitoring will detect the most affected areas that should be targeted first. Government-initiated sanitation and water access should change people’s exposure to contaminated water. Overall, it is clear that the government has to review a combination of community-led initiatives that will lower the risk of the infection and help people understand their role in the process.
References
Alzaylaee, H., Collins, R. A., Shechonge, A., Ngatunga, B. P., Morgan, E. R., & Genner, M. J. (2020). Environmental DNA-based xenomonitoring for determining Schistosoma presence in tropical freshwaters. Parasites & Vectors, 13(1), 63.
Augusto, R. D. C., Mello-Silva, D., & Correa, C. C. (2018). Phytochemical molluscicides and schistosomiasis: What we know and what we still need to learn. Veterinary Sciences, 5(4), 94.
Chitsulo, L., Engels, D., Montresor, A., & Savioli, L. (2000). The global status of schistosomiasis and its control. Acta Tropica, 77(1), 41-51.
Coelho, P. M. Z., & Caldeira, R. L. (2016). Critical analysis of molluscicide application in schistosomiasis control programs in Brazil. Infectious Diseases of Poverty, 5(1), 57.
Grimes, J. E., Croll, D., Harrison, W. E., Utzinger, J., Freeman, M. C., & Templeton, M. R. (2015). The roles of water, sanitation and hygiene in reducing schistosomiasis: A review. Parasites & Vectors, 8(1), 156.
Jobin, W. R. (1979). Cost of snail control. The American Journal of Tropical Medicine and Hygiene, 28(1), 142–154.
Jordan, P., Barnish, G., Bartholomew, R. K., Grist, E., & Christie, J. D. (1978). Evaluation of an experimental mollusciciding programme to control Schistosoma mansoni transmission in St Lucia. Bulletin of the World Health Organization, 56(1), 139-146.
King, C. H., & Bertsch, D. (2015). Historical perspective: Snail control to prevent schistosomiasis. PLoS Neglected Tropical Diseases, 9(4), e0003657.
Li, H., & Wang, W. (2017). Apropos: Critical analysis of molluscicide application in schistosomiasis control programs in Brazil. Infectious Diseases of Poverty, 6(1), 54.
Nelwan, M. L. (2019). Schistosomiasis: Life cycle, diagnosis, and control. Current Therapeutic Research, 91, 5-9.
Relman, D. A., & Choffnes, E. R. (Eds.). (2011). The causes and impacts of neglected tropical and zoonotic diseases: opportunities for integrated intervention strategies. Washington, D.C.: National Academies Press.
Secor, W. E. (2014). Water-based interventions for schistosomiasis control. Pathogens and Global Health, 108(5), 246-254.
Souza, C. P. de. (1995). Molluscicide control of snail vectors of schistosomiasis. Memórias Do Instituto Oswaldo Cruz, 90(2), 165–168.
Takougang, I., Meli, J., & Angwafo III, F. (2006). Field trials of low dose Bayluscide on snail hosts of schistosome and selected non-target organisms in sahelian Cameroon. Memórias do Instituto Oswaldo Cruz, 101(4), 355-358.
World Health Organization. (2017). Eliminating schistosomiasis via MDAs and improved water, sanitation and hygiene. Web.
Yang, G.-J., Sun, L.-P., Hong, Q.-B., Zhu, H.-R., Yang, K., Gao, Q., & Zhou, X.-N. (2012). Optimizing molluscicide treatment strategies in different control stages of schistosomiasis in the People’s Republic of China. Parasites & Vectors, 5(1), 260.