Chlorine-and sodium chloride-induced resistance in Australorbis glabratus.

Australorbis glabratus tempered to sodium chloride, or water with a free chlorine residual, became resistant to ICI 24223, Bayer 73, and WL 8008. The most practical control measure against schistosomiasis at present appears to be the destruction of the snail transmitters by chemical means. Three molluscicides, Bayer 73, ICI 24223, and WL 8008 are very effective against Australorbis glabratus, the intermediate host in the western hemisphere, and intensive research activities in various laboratories have had as their objectives obtaining concentration-mortality data (Ritchie et al., 1963; Frick et al., 1964). However, little has been done on the capacity of snails to develop resistance to these compounds. In our laboratories it was found that a free chlorine residual of about one part per million in the water of the toxicological test solution inactivates both Bayer 73 and ICI 24223 to a remarkable degree (Fox, Aleman, et al., 1963). This phenomenon could be explained by one of two hypotheses: Either chlorine reacts with the molluscicide to form less toxic compounds outside the snail; or chlorine stimulates detoxifying or excretory mechanisms inside the snail. The purpose of this report is to present results of laboratory experiments which support the latter hypothesis and to point out its relationship to resistance in snails to molluscicides. MATERIALS AND METHODS Bayer 73 was received from the Chemagro Corporation, Kansas City, Mo., on 14 November 1963 labeled as follows: Bayer 73, 70% Wettable Powder. Active ingredients, Ethanol amine salt Received for publication 2 April 1965. *This investigation was supported in part by NIAID (Research Grant AI-06083 and Graduate Research Training Grant 5 T1 AI 15), WHO, and the Puerto Rico Department of Health. of 2',5-dichloro-4'-nitrosalicylanilide-71%; Inert ingredients-29%, Control No. 863. ICI 24223 (hydrochloride) was received from Imperial Chemical Industries Limited, Pharmaceutical Division, Fulshaw Hall, Wilmslow, Cheshire, England on 7 February 1963 (