Cryptosporidium spp. and Giardia duodenalis emissions from humans and animals in the Three Gorges Reservoir in Chongqing, China

Abstract

Cryptosporidium spp. and Giardia duodenalis are two waterborne protozoan parasites that can cause diarrhea. Human and animal feces in surface water are a major source of these pathogens. This paper presents a GloWPa-TGR-Crypto model that estimates Cryptosporidium and G. duodenalis emissions from human and animal feces in the Three Gorges Reservoir (TGR), and uses scenario analysis to predict the effects of sanitation, urbanization, and population growth on oocyst and cyst emissions for 2050. Our model estimated annual emissions of 1.6 × 1015 oocysts and 2.1 × 1015 cysts from human and animal feces, respectively. Humans were the largest contributors of oocysts and cysts, followed by pigs and poultry. Cities were hot-spots for human emissions, while districts with high livestock populations accounted for the highest animal emissions. Our model was the most sensitive to oocyst excretion rates. The results indicated that 74% and 87% of total emissions came from urban areas and humans, respectively, and 86% of total human emissions were produced by the urban population. The scenario analysis showed a potential decrease in oocyst and cyst emissions with improvements in urbanization, sanitation, wastewater treatment, and manure management, regardless of population increase. Our model can further contribute to the understanding of environmental pathways, the risk assessment of Cryptosporidium and Giardia pollution, and effective prevention and control strategies that can reduce the outbreak of waterborne diseases in the TGR and other similar watersheds.

Spatially explicit model of the Cryptosporidium and Giardia disease burden from surface and ground waters in urban and rural areas of the Three Gorges Reservoir watershed in Chongqing, China

“…This study constructed a modified GloWPa-TGR-Crypt-Giar C1 model based on the original GloWPa-TGR-Crypto model described in detail by Hofstra et al ( 2013 ) and Huang et al ( 2020 ) and focused on model modifications and input variable changes. Figure 1 shows a schematic of the model components.…”

“…The GloWPa-TGR-Crypt-Giar C1 model simulated monthly human and livestock Cryptosporidium and Giardia loads from point and nonpoint sources into the TGR and soils (Hofstra et al 2013 ; Huang et al 2020 ). The model computed monthly spatial outputs from human or livestock populations, fecal pathogen shedding, sanitation coverage, wastewater treatment removal, storage survival, and surface runoff.…”

“…The model computed monthly spatial outputs from human or livestock populations, fecal pathogen shedding, sanitation coverage, wastewater treatment removal, storage survival, and surface runoff. Unlike in Huang et al ( 2020 ) where a constant annual (oo)cyst excretion per person in developing countries was used, we calculated annual (oo)cyst excretion per person by multiplying annual feces per person in China, daily (oo)cyst excretion rate per infected person, and cryptosporidiosis and giardiasis prevalence in China. A statistical distribution for monthly storage survival and surface runoff parameters were applied to distinguish the effects of seasonal meteorological parameters on the loads.…”

“…In contrast to surface water, which is susceptible to fecal contamination from point and nonpoint sources (Huang et al 2020), groundwater is generally considered to be of higher quality due to the contaminant attenuation capacity of the overlying (sub)soil (Chique et al 2020). However, field studies and outbreak investigations both indicate that groundwater systems can be significant sources of enteric pathogens including Cryptosporidium and Giardia (Daniels et al 2018;Chique et al 2020).…”

“…This is one of the world’s largest comprehensive hydropower projects and a major source of drinking water for the region which includes a highly urbanized coastal area (He et al 2011 ). Human and livestock feces enter the TGR directly with minimal or no pre-treatment, leading to serious Cryptosporidium and Giardia pollution (Xiao et al 2013 ; Liu et al 2019 ; Huang et al 2020 ). However, there is currently no comprehensive understanding of the risk and disease burden attributable to parasitic pathogens consumed via TGR surface and ground waters.…”