Newswise — An elegant solution was implemented by a collaborative effort between scientists from the United States and Senegal. Their goal was to reduce the level of infection in the local community by removing the habitat of a parasite-carrying aquatic snail. This approach involved clearing overgrown aquatic vegetation from areas upstream of the Diama Dam in northeastern Senegal. As a result of this initiative, not only did they successfully improve the health of the local communities but also generated additional feed and compost for the benefit of local farmers, thus positively impacting both the health and economies of the region.
"We are presented with a rare and gratifying opportunity when we can discover a potential win-win solution that benefits both human health and livelihoods," expressed David López-Carr, a geography professor at UC Santa Barbara and co-author of a paper published in the journal Nature. The researchers have presented compelling evidence for their hypothesis, indicating that agricultural activities, including the use of fertilizers, contribute to parasitic infections by promoting the growth of aquatic vegetation. This discovery suggests a straightforward remedy that can have a positive impact on the health, society, and economy of northern Senegal, with broader implications for over 700 million people living in schistosomiasis endemic areas worldwide.
Following the construction of the Diama Dam in 1986, local farmers in the region have enjoyed improved access to fresh water for irrigating their fields. However, this new infrastructure has also led to an increase in the prevalence of the schistosoma parasite, a small freshwater flatworm commonly found in Africa, South America, and Southeast Asia. It is estimated that nearly 250 million people worldwide are infected with this parasite.
Although schistosomiasis (also known as bilharzia or snail fever) is not immediately fatal nor transmissible between people, it is a debilitating condition in the long term, particularly among tropical diseases.
López-Carr, an anthropogeographer specializing in human-environment dynamics in the developing world, explained that the disease is most prevalent in impoverished communities lacking access to clean drinking water and proper sanitation. Adult worms reside in blood vessels and lay eggs in tissue, resulting in harmful reactions and damage to organs. The long-term consequences include an elevated risk of cancer and infertility, while infected individuals find it difficult to work and attend school, trapping them in a cycle of poverty. López-Carr emphasized that poor farmers, in particular, can lose up to half of their crop yields due to the burden of infection.
Health agencies and organizations have been diligently combating these infections using effective drugs. However, a major limitation is that the medicine does not provide protection against reinfection, which can occur as soon as individuals come into contact with contaminated water. Past research has explored alternative approaches, such as harnessing the snails' natural predators, such as prawns, to control the parasite population. Unfortunately, the construction of the dam has disrupted this natural balance, cutting off the prawns' access to the affected areas.
In their proactive approach to tackle the disease, the collaborative team closely examined the habitat that sustains the worms' intermediate host—a small snail residing in the Senegal River and its tributaries. Their investigation revealed a significant finding: a prevalent aquatic plant named Ceratophyllum demersum, commonly known as hornwort, can harbor up to 99% of these snails, as they have a mutualistic relationship with it.
Exacerbated by fertilizer runoff from agricultural operations upstream, the overgrowth of c. demersum and other aquatic plants becomes prevalent in local waterways, causing hindrances to daily activities like cooking, irrigation, and laundry.
In a comprehensive three-year randomized control trial encompassing 16 communities, the researchers aimed to understand the impact of removing nuisance vegetation from approximately half of the communities on the presence of snails. They began by measuring baseline infection rates, administering antiparasitic drugs, and then proceeded to eliminate the vegetation. Afterward, they measured reinfection rates in over 1,400 schoolchildren. Throughout the experiment, the research teams successfully removed an estimated 430 metric tons (wet) of aquatic vegetation from water access points.
López-Carr reported that in their randomized controlled trial, the control sites, where submerged vegetation was not removed from water access points, showed a striking 124% higher rate of intestinal schistosoma reinfection. On the other hand, at sites where the researchers removed the vegetation, they observed reduced infection rates.
Moreover, the study revealed a valuable benefit of removing the aquatic vegetation. The material removed could be repurposed to feed livestock or turned into nutrient-rich compost for cultivating crops. This approach substantially lowered costs and significantly increased yields for local farmers. López-Carr emphasized that this method created a compelling economic incentive to clear nuisance vegetation from waterways, while simultaneously restoring nutrients from aquatic plants back to the soil and providing livestock feed. Ultimately, this approach holds the potential to break the cycle of poverty-related diseases and reduce the infectious burden in the region.
"In addition," he added, "a broader benefit lies in the potential of this example to inspire and promote win-win planetary health research and solutions, which can enhance livelihoods while effectively reducing infectious morbidity and mortality."
After conducting these successful trials, the researchers are optimistic about implementing this study in other similar regions to achieve similar health and economic improvements.
Interestingly, this solution might not be limited to developing countries alone. López-Carr suggested that the excess vegetation growth resulting from nutrient runoff could also be utilized as livestock feed in more developed countries, showcasing the versatility and applicability of the approach.
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