Ultraviolet disinfection of schistosome cercariae in water
File(s)
Author(s)
Hazell, Lucinda
Type
Thesis
Abstract
Schistosomiasis is a tropical disease that is contracted by skin contact with water containing cercariae, larvae of the Schistosoma parasite. Providing safe water for contact activities (e.g. laundry, bathing) can help reduce transmission. UV disinfection is a widely used form of water treatment and its application in low-income settings is now becoming a reality through solar-powered units. This thesis examines the effectiveness of UV LED disinfection against schistosome cercariae for use in endemic regions. A systematic review revealed that low UV fluences (5–14mJ/cm2 at 253.7nm) were required to achieve a 1-log10 reduction in worm burden in animal hosts, but the direct effect on cercariae had not been quantified. There were insufficient published data to produce UV disinfection guidelines, therefore experiments were carried out to determine the fluence-response of Schistosoma mansoni cercariae at four peak wavelengths in the germicidal range (253.7nm, 255nm, 265nm, and 285nm). The morphology and motility of cercariae were studied under the microscope to determine if they were alive or dead. At the most effective wavelength (265nm) 247mJ/cm2 was required to achieve a 1-log10 reduction in alive cercariae but this reduced to 127mJ/cm2 and 99mJ/cm2 if samples were stored for 1–3 hours post-exposure, respectively. Fluences were much higher than those required to achieve the same reduction in worm burden in previous studies and further research was needed to investigate the potential disinfection mechanisms. Using an immunological assay to detect dimer formation it was found that DNA was damaged at lower fluences (10–50mJ/cm2, depending on wavelength), but this damage would not be expressed until cercariae penetrate the skin and transform into schistosomula. Further research is required to confirm if cercariae are non-viable at these fluences, until then a conservative approach based on the death of cercariae is appropriate. Due to the high fluences required to kill cercariae, UV disinfection alone is unlikely to be an energy- or cost-efficient water treatment method for combatting schistosomiasis, however improvements in efficiency combined with cheaper production costs may make UV LED technology more competitive in the near future.
Version
Open Access
Date Issued
2021-11
Date Awarded
2022-03
Copyright Statement
Creative Commons Attribution NonCommercial Licence
License URL
Advisor
Templeton, Michael
Sponsor
EPSRC Global Challenges Research Fund
EPSRC Centre for Doctoral Training in Sustainable Civil Engineering
Grant Number
EP/P028519/1
EP/L016826/1
Publisher Department
Department of Civil and Environmental Engineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)