Reduced transmission of human schistosomiasis after restoration of a native river prawn that preys on the snail intermediate host

Abstract

Eliminating human parasitic disease often requires interrupting complex transmission pathways. Even when drugs to treat people are available, disease control can be difficult if the parasite can persist in nonhuman hosts. Here, we show that restoration of a natural predator of a parasite’s intermediate hosts may enhance drug-based schistosomiasis control. Our study site was the Senegal River Basin, where villagers suffered a massive outbreak and persistent epidemic after the 1986 completion of the Diama Dam. The dam blocked the annual migration of native river prawns (Macrobrachium vollenhoveni) that are voracious predators of the snail intermediate hosts for schistosomiasis. We tested schistosomiasis control by reintroduced river prawns in a before-after-control-impact field experiment that tracked parasitism in snails and people at two matched villages after prawns were stocked at one village’s river access point. The abundance of infected snails was 80% lower at that village, presumably because prawn predation reduced the abundance and average life span of latently infected snails. As expected from a reduction in infected snails, human schistosomiasis prevalence was 18 ± 5% lower and egg burden was 50 ± 8% lower at the prawn-stocking village compared with the control village. In a mathematical model of the system, stocking prawns, coupled with infrequent mass drug treatment, eliminates schistosomiasis from high-transmission sites. We conclude that restoring river prawns could be a novel contribution to controlling, or eliminating, schistosomiasis.

Infection with schistosome parasites in snails leads to increased predation by prawns: implications for human schistosomiasis control

“…Initial field trials in Senegal have shown fewer infected snails in waters stocked with predatory prawns, and reduced schistosomiasis prevalence in an adjacent village (Sokolow et al, 2015). In several other case studies, changes in the abundance of snail predators have been linked to changes in schistosomiasis incidence in people.…”

Hydrology and density feedbacks control the ecology of intermediate hosts of schistosomiasis across habitats in seasonal climates

“…Snail demographic data consisted of relative abundance counts between May through July 2014 and October 2015. A time-based snail sampling technique was used analogously to the ones previously used in similar malacological studies ( 6,7,30). Along with snail sampling, a network of wireless micrometeorological stations was installed in each village, allowing for the continuous monitoring of microclimatic and hydrological parameters, including air temperature, water level, conductivity and temperature, and precipitation (36).…”

“…10) have been at the heart of a debate (11,12) on whether or not they must be seen as a key ecological process for the demography of the intermediate hosts of schistosomes. Density feedbacks have been alternatively accounted for (6,13,14) or ignored (15,16) in spatially implicit mathematical models of schistosomiasis transmission that include snail demography. Ecological approaches have also highlighted the role of environmental forcings in limiting snail abundance, including water temperature for Bulinus globosus in permanent streams in Zimbabwe (17) and water level fluctuations for Oncomelania hupensis (the intermediate host of Schistosoma japonicum) in irrigation canals in China (18).…”

“…The population dynamics of B. globosus have been labeled as "density vague" (17), suggesting that, under natural conditions, snail abundance is controlled by adverse environmental conditions preventing crowding levels at which negative density feedbacks are appreciable. Occasionally, however, crowding was observed to occur in particularly favorable environments (6). Notably, a large body of literature exists on statistical methods for density feedback detection (19)(20)(21)(22).…”

Blockade of PD-1 Signaling Enhances Th2 Cell Responses and Aggravates Liver Immunopathology in Mice with Schistosomiasis japonica

“…Schistosomiasis is an infectious disease that affects at least 220 million people worldwide and causes serious morbidity and economic problems in developing countries [1,2]. During infection with Schistosoma japonicum ( S .…”