The contribution of the anticholinesterase activity of Pedialanthus tithymaloide to its molluscicidal activity

Abstract

Experiments were conducted to evaluate the molluscicidal and anticholinesterase activity of aqueous leaf and stem-bark extract of Pedialanthus tithymaloide (Family- Euphorbiaceae) Lymnaea (Radix) acuminata (Lamarack) and Indoplanorbis exustus (Deshyas) – intermediate hosts of endemic schistosomiasis and fascioliasis diseases in cattle and livestock. The toxic effect of both extracts was time- as well as dose-dependent. There was a significant negative correlation between LC values and exposure periods observed, thus the LC₁₀ values of P. tithymaloide leaf decreased from 24.7 mg/L (24 h) to 15.4 mg/L (96 h); LC₅₀ decreased from 69.4 mg/L (24 h) to 27.4 mg/L (96 h); LC₉₀ decreased from 194.6 mg/L (24 h) to 48.9 mg/L (96 h) against L. acuminata and LC₁₀ values of P. tithymaloide leaf decreased from 5.5 mg/L (24 h) to 0.6 mg/L (96 h); LC₅₀ decreased from 35.8 mg/L (24 h) to 4.3 mg/L (96 h); LC₉₀ decreased from 233.1 mg/L (24 h) to 32.1 mg/L (96 h) against Indoplanorbis exustus. Similar trend was also observed for the aqueous stem-bark extract of P. tithymaloide. Sub-lethal exposure at 24h and 96h of the aqueous leaf and stem-bark extract of P. tithymaloide caused significant (P < 0.05) time- and dose-dependent inhibition of the activity of enzyme acetylcholinesterase (AChE) in the nervous and hepatopancrease tissues of L. acuminata after 24 h or 96 h exposure periods. Withdrawal study also shows that there was a significant recovery in the acetylcholinesterase activity in both the tissues of snail after the 7th day of the withdrawal of treatment. Thus, the aqueous extract of P. tithymaloide leaf and stem-bark are environmentally safe candidate molluscicides for controlling vector snails of schistosomiasis and fascioliasis.

Key words: schistosomiasis and fascioliasis, Pedialanthus tithymaloide, molluscicidal, anticholinesterase activity

Afr. J. Trad. Comp. Alt. Med. Vol.2(3) 2005: 326 - 336