BIOCHEMICAL STUDIES ON TISSUE EXTRACTS OF FRESH WATER SNAILS "SPECIFIC INTERMEDIATE HOSTS FOR BILHARZIASIS''

Abstract

A new approach for the control of schistosomiasis through the intermediate host, which is considered the weakest link in the parasite life cycle, may be achieved by several means such as the use of certain compounds which may induce some changes in the snail's biochemical parameters. These changes may render the snails less susceptible to infection by the parasite as the host parasite relation-ship is highly specific and depends on a typical biochemical constitution with the snail's body. The present work is a trial to evaluate the effect of some chemical compounds which are already used in the field like fertilizers (urea, ammonium nitrate, ammonium sulphate and sodium dihydrogen phosphate) and an organophosphorus insecticide (Dichlorvos) on the snails' tissue.

Most fertilizers used in this study and the insecticide exerted a toxic effect on Biomphalaria alexandrina snails. The mortality rates of snails treated with urea, ammonium nitrate and ammonium sulphate increased with the time and dose, while sodium dihydrogen phosphate had non-toxic effect on snails at a concentration of up to 2000 PPm. The insecticide dichlorvos had also a toxic effect on the snails, which increased with increment of the dose.

The hazardous effect of these compounds may be due to changes in osmotic pressure in snails media due to liberation of unionized ammonia from nitrogen­ containing fertilizers. also to the mutagenic effect exerted by inorganic phosphorus (NaH2P04) and organophosphorus (DDVP) compounds which alter the biochemical nature of the macromolecules in the snails' tissue.