Department of Civil and Environmental Engineering, Imperial College London, London, United Kingdom.
Wolfson Wellcome Biomedical Laboratories, Department of Life Sciences, Natural History Museum, London, United Kingdom.
PLoS Negl Trop Dis. 2021 Jul 6;15(7):e0009572. doi: 10.1371/journal.pntd.0009572. eCollection 2021 Jul.
Schistosomiasis is a parasitic disease that is transmitted by skin contact with waterborne schistosome cercariae. Mass drug administration with praziquantel is an effective control method, but it cannot prevent reinfection if contact with cercariae infested water continues. Providing safe water for contact activities such as laundry and bathing can help to reduce transmission. In this study we examine the direct effect of UV light on Schistosoma mansoni cercariae using ultraviolet light-emitting diodes (UV LEDs) and a low-pressure (LP) mercury arc discharge lamp.
S. mansoni cercariae were exposed to UV light at four peak wavelengths: 255 nm, 265 nm, 285 nm (UV LEDs), and 253.7 nm (LP lamp) using bench scale collimated beam apparatus. The UV fluence ranged from 0-300 mJ/cm2 at each wavelength. Cercariae were studied under a stereo-microscope at 0, 60, and 180 minutes post-exposure and the viability of cercariae was determined by assessing their motility and morphology.
Very high UV fluences were required to kill S. mansoni cercariae, when compared to most other waterborne pathogens. At 265 nm a fluence of 247 mJ/cm2 (95% confidence interval (CI): 234-261 mJ/cm2) was required to achieve a 1-log10 reduction at 0 minutes post-exposure. Cercariae were visibly damaged at lower fluences, and the log reduction increased with time post-exposure at all wavelengths. Fluences of 127 mJ/cm2 (95% CI: 111-146 mJ/cm2) and 99 mJ/cm2 (95% CI: 85-113 mJ/cm2) were required to achieve a 1-log10 reduction at 60 and 180 minutes post-exposure at 265 nm. At 0 minutes post-exposure 285 nm was slightly less effective, but there was no statistical difference between 265 nm and 285 nm after 60 minutes. The least effective wavelengths were 255 nm and 253.7 nm. Due to the high fluences required, UV disinfection is unlikely to be an energy- or cost-efficient water treatment method against schistosome cercariae when compared to other methods such as chlorination, unless it can be demonstrated that UV-damaged cercariae are non-infective using alternative assay methods or there are improvements in UV LED technology.
血吸虫病是一种寄生虫病，通过与水中血吸虫尾蚴的皮肤接触传播。使用吡喹酮进行大规模药物治疗是一种有效的控制方法，但如果继续接触尾蚴污染的水，仍会再次感染。提供用于洗衣和洗澡等接触活动的安全用水有助于减少传播。在这项研究中，我们使用紫外线发光二极管（UV LED）和低压（LP）汞弧光灯检查紫外线光对曼氏血吸虫尾蚴的直接影响。
使用台式平行光束装置，将曼氏血吸虫尾蚴暴露于四个峰值波长的紫外光下：255nm、265nm、285nm（UV LED）和 253.7nm（LP 灯）。每个波长的紫外线辐照度范围为 0-300mJ/cm2。在暴露后 0、60 和 180 分钟，在立体显微镜下研究尾蚴，并通过评估其运动性和形态来确定尾蚴的活力。
与大多数其他水传播病原体相比，非常高的紫外线辐照度才能杀死曼氏血吸虫尾蚴。在 265nm 时，在 0 分钟暴露后的对数减少需要 247mJ/cm2（95%置信区间（CI）：234-261mJ/cm2）的辐照度才能实现。在较低的辐照度下，尾蚴可见受损，并且在所有波长下，对数减少随着暴露后时间的增加而增加。在 265nm 时，需要 127mJ/cm2（95%CI：111-146mJ/cm2）和 99mJ/cm2（95%CI：85-113mJ/cm2）的辐照度才能在 60 和 180 分钟暴露后实现 1 对数减少。在 0 分钟暴露后，285nm 的效果略差，但在 60 分钟后，265nm 和 285nm 之间没有统计学差异。效果最差的波长是 255nm 和 253.7nm。由于需要高辐照度，与氯化等其他方法相比，紫外线消毒不太可能成为针对血吸虫尾蚴的节能或具有成本效益的水处理方法，除非能够证明使用替代检测方法，或紫外线 LED 技术有所改进，紫外线损伤的尾蚴不具有感染力。
