Chlorination of Schistosoma mansoni cercariae

Abstract

Background Schistosomiasis is a water-based disease acquired through contact with cercaria-infested water. Communities living in endemic regions often rely on parasite-contaminated freshwater bodies for their daily water contact activities, resulting in recurring schistosomiasis infection. In such instances, water treatment can provide safe water on a household or community scale. However, to-date there are no water treatment guidelines that provide information on how to treat water containing schistosome cercariae. Here, we rigorously test the effectiveness of chlorine against Schistosoma mansoni cercariae. Method S. mansoni cercariae were chlorinated using sodium hypochlorite under lab and field condition. The water pH was controlled at 6.5, 7.0 or 7.5, the water temperature at 20˚C or 27˚C, and the chlorine dose at 1, 2 or 3 mg/l. Experiments were conducted up to contact times of 45 minutes. 100 cercariae were used per experiment, thereby achieving up to 2-log 10 inactivations of cercariae. Experiments were replicated under field conditions at Lake Victoria, Tanzania. Conclusion A CT (residual chlorine concentration x chlorine contact time) value of 26±4 mg�min/l is required to achieve a 2-log 10 inactivation of S. mansoni cercariae under the most conservative condition tested (pH 7.5, 20˚C). Field and lab-cultivated cercariae show similar chlorine sensitivities. A CT value of 30 mg�min/l is therefore recommended to disinfect cercariainfested water, though safety factors may be required, depending on water quality and operating conditions. This CT value can be achieved with a chlorine residual of 1 mg/l after a contact time of 30 minutes, for example. This recommendation can be used to provide safe water for household and recreational water activities in communities that lack safe alternative water sources.

The efficacy of soap against schistosome cercariae: A systematic review

“…The results suggest that soap is less toxic to schistosome cercariae than other chemicals, such as niclosamide and chlorine [42,43]. For example, the 50% lethal dose of niclosamide when treating cercariae for 4 hours was 3650 times lower than that associated with endod [42].…”

Parameters for effective sand filtration of Schistosoma mansoni cercariae from water

“…An alternative to reducing the filter volume using a Pitchford funnel would be to kill the cercaria in the one-litre effluent, for example with chlorine or iodine. Inactivated cercariae sink to the bottom, allowing the top layer of cercaria-free water to be poured or pipetted off (Braun et al 2020). The remaining effluent can then be examined under the microscope.…”

Study of the behavior of snails intermediate hosts of Schistosoma spp. under different maintenance conditions and their resistance to salinity in an african laboratory environment

“…Moreover, in the delta of the SRB, the population density of this species is higher in areas with lower salinity ( Bakhoum et al., 2019 ). On the other hand, such laboratory research could help to better understand snail population dynamics and preferred habitat, predict their behavior to global environmental change ( Yacoubi et al., 2007 ) and develop control measures such as those attempting to control cercariae through water chlorination ( Braun et al., 2020 ).…”