BIOCHEMICAL STUDIES ON STEROIDS OF FRESH-WATER SNAILS

Abstract

Schistosomiasis. Is a parasitic disease which reqmres specific intemiediate hosts. The parasite-host relationship is highly adaptive and requires high biochemical specificity of the host. In the present work, studies on B. alexandrina snails, which are susceptible to schistosome infection, were perfmmed and compared with L. truncatula and P. acuta snails which are non­ susceptible to infection. The studies included the determination of the steroidal pattern of these snail species (different sterols and male and female steroid sex hormones) m different maturity stages of the snails (juvenile, adult and senescent) by GC/MS and HPLC. Moreover, the effects of schistosoma! infection as well as exposure to chloroform extract of the plant Haplophyllum tuberculatum on adult B. alexandrina snail steroidal pattern, reproduction and cercaria! shedding were also investigated. The results indicate that L. truncatula snails had the highest steroidal content when compared with B. alexandrina and P. acuta snails. On the other hand, adult B. alexandrina snails had the highest steroidal content as compared to juvenile and senescent B. alexandrina snails. However, infection of adult B. alexandrina snails with S. mansani parasite caused a great decrease in the level of testosterone in infected snails. Treatment with the molluscicide H. tuberculatum decreased egg-laying capacity of B. alexandrina snails with a concomitant decrease in phenoloxidase activity as well as a drastic decrease in testosterone content. The total output of cercanae by the snails also decreased upon using •the molluscicide. Histochemical examination of hepatopancreas-ovotestis complex of B. alexandrina snails showed that the two tissues were greatly affected by the plant molluscicide.