Chlorination of Schistosoma mansoni cercariae.

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-log₁₀ 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-log₁₀ 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 cercaria-infested 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. Author summary: Schistosomiasis is a preventable yet serious disease in many developing countries. Although schistosomiasis control strategies include the provision of water and sanitation facilities, specific WASH solutions are often lacking. Control programs generally focus on preventive chemotherapy with praziquantel which is effective in killing adult worms in humans but does not prevent re-infection. Communities lacking safe alternative water sources therefore have no choice but to rely on unsafe water for their daily water contact activities, even if this exposes them to high risk of infection. Water treatment can provide communities with safe water on a household or community scale. However, to-date there are no guidelines for treating cercaria-contaminated water. We rigorously tested the effectiveness of chlorine against S. mansoni cercariae in lab and field settings. The resulting chlorination recommendation can be used to treat water and provide schistosomiasis-endemic communities with safe water facilities (e.g. laundry or bathing stations). [ABSTRACT FROM AUTHOR]