Ultraviolet sensitivity of WASH (water, sanitation, and hygiene) -related helminths: A systematic review

Abstract

Helminthiases are a group of disabling neglected tropical diseases that affect billions of people worldwide. Current control methods use preventative chemotherapy but reinfection is common and an inter-sectoral approach is required if elimination is to be achieved. Household and community scale water treatment can be used to provide a safe alternative water supply for contact activities, reducing exposure to WASH (water, sanitation, and hygiene) -related helminths. With the introduction of ultraviolet light emitting diodes (UV-C LEDs), ultraviolet (UV) disinfection could be a realistic option for water treatment in low-income regions in the near future, to provide safe alternative water supplies for drinking and contact activities such as handwashing, bathing, and laundry, but currently there is no guidance for the use of UV or solar disinfection against helminths. A qualitative systematic review of existing literature was carried out to establish which WASH-related helminths are more susceptible to UV disinfection and identify gaps in research to inform future studies. The search included all species that can infect humans and can be transmitted through water or wastewater. Five online databases were searched and results were categorized based on the UV source: sunlight and solar simulators, UV-A and UV-B (long wavelength) sources, and UV-C (germicidal) sources. There has been very little research into the UV sensitivity of helminths; only 47 studies were included in this review and the majority were carried out before the standard protocol for UV disinfection experiments was published. Only 18 species were studied; however all species could be inactivated by UV light. Fluences required to achieve a 1-log inactivation ranged from 5 mJ/cm² to over 800 mJ/cm². Larval forms were generally more sensitive to UV light than species which remain as an egg in the environment. This review confirms that further research is required to produce detailed recommendations for household or community scale UV-C LED or solar disinfection (SODIS) of water for preventing helminthiases. Helminth infections are currently controlled by mass administration of anthelmintic drugs which are effective at treating the diseases but cannot prevent reinfection. As we work to eliminate these diseases, complimentary control methods such as improving access to water, sanitation, and hygiene will be crucial to reduce re-exposure and cut transmission. UV disinfection is a widely used form of water treatment but it is often seen as incompatible with low income regions. Recently developed UV-C LEDs and SODIS offer alternative sources of UV light that may be more suitable for this context, but there is little guidance about how we can use this technology to prevent helminth infections. We carried out a systematic review to establish which helminths are more sensitive to UV light and identify the areas which need further research. This will enable the production of design guidelines for household and community scale UV water treatment, so that the WASH community will be able to take full advantage of the recent developments and standardizations in UV disinfection technology.