Effects of agrochemical pollution on schistosomiasis transmission: a systematic review and modelling analysis

Abstract

Background Agrochemical pollution of surface waters is a growing global environmental challenge, especially in areas where agriculture is rapidly expanding and intensifying. Agrochemicals might affect schistosomiasis transmission through direct and indirect effects on Schistosoma parasites, their intermediate snail hosts, snail predators, and snail algal resources. We aimed to review and summarise the effects of these agrochemicals on schistosomiasis transmission dynamics. Methods We did a systematic review of agrochemical effects on the lifecycle of Schistosoma spp and fitted dose-response models to data regarding the association between components of the lifecycle and agrochemical concentrations. We incorporated these dose-response functions and environmentally relevant concentrations of agrochemicals into a mathematical model to estimate agrochemical effects on schistosomiasis transmission. Dose-response functions were used to estimate individual agrochemical effects on estimates of the agrochemically influenced basic reproduction number, R 0 , for Schistosoma haematobium . We incorporated time series of environmentally relevant agrochemical concentrations into the model and simulated mass drug administration control efforts in the presence of agrochemicals. Findings We derived 120 dose-response functions describing the effects of agrochemicals on schistosome lifecycle components. The median estimate of the basic reproduction number under agrochemical-free conditions, was 1·65 (IQR 1·47–1·79). Agrochemical effects on estimates of R 0 for S haematobium ranged from a median three-times increase ( R 0 5·05, IQR 4·06–5·97) to transmission elimination ( R 0 0). Simulations of transmission dynamics subject to interacting annual mass drug administration and agrochemical pollution yielded a median estimate of 64·82 disability-adjusted life-years (DALYs) lost per 100,000 people per year (IQR 62·52–67·68) attributable to atrazine use. In areas where aquatic arthropod predators of intermediate host snails suppress transmission, the insecticides chlorpyrifos (6·82 DALYs lost per 100,000 people per year, IQR 4·13–8·69) and profenofos (103·06 DALYs lost per 100,000 people per year, IQR 89·63–104·90) might also increase the disability burden through their toxic effects on arthropods. Interpretation Expected environmental concentrations of agrochemicals alter schistosomiasis transmission through direct and indirect effects on intermediate host and parasite densities. As industrial agricultural practices expand in areas where schistosomiasis is endemic, strategies to prevent increases in transmission due to agrochemical pollution should be developed and...

Downstream Effects: Impact of Antibiotic Pollution on an Aquatic Host-Parasite Interaction

“…Analysis was conducted over the course of the 9-week experiment and used to parameterize daily mortality rates within our mathematical model. Lastly, we adapted an existing schistosomiasis model (Hoover et al, 2020) and altered parameters in proportion to our data on control versus antibiotic conditions. This analysis was done to further examine how antibiotic contamination may impact human schistosomiasis.…”

“…In order to further understand how antibiotic contamination may alter disease dynamics, we adapted the differential equation model of Hoover et al (2020). We used a base model without predation or agrochemical pollution, including snail reproduction associated with fecundity compensation (Minchella et al, 1981) We used our data to calculate the percent change in snail and parasite life history characteristics in response to antibiotic exposure and altered model parameters accordingly (Table S1).…”

Agricultural Innovations to Reduce the Health Impacts of Dams

“…The breakdown of vegetation, produces both a nutrient-rich amendment for crops while simultaneously offering natural gas that can be used for cooking or for powering generators. By reducing reliance on fertilizers, these approaches might, indirectly, further reduce schistosome transmission [30,31,54,55]. These innovations have great potential for using aquatic vegetation to improve agricultural production and profitability.…”

“…Particularly for recession agriculture, controlled releases can reduce sediment retained by dam barriers, which provides nutrients for cultivation in the floodplain [62]. These controlled releases, in turn, reduce the need for chemical fertilizers, whose use can support medically important snail populations and, by extension, schistosome transmission [31]. Some studies indicate that modifying dam operations in these ways could reduce schistosome transmission [63,64].…”

“…The transition from traditional to modern agricultural regimes also increases reliance on agrochemicals, as the sediment that provides nutrients for recession agriculture remains impounded behind dam barriers along with flood waters. The use of agrochemicals can exacerbate disease dynamics, because insecticides can cause greater harm to snail predators than to snails and fertilizers can promote the growth of both snail food and vegetative habitat [30,31].…”