In vitro. bioassay screening of 346 methanol extracts originated from 281 native and cultivated plant species growing in Egypt, and related to 81 families, was carried out for schistosomicidal activity. The extracts were bioassayed at 100 µg/mL on viable Schistosoma mansoni. mature worms in culture medium. Viability of worms was examined after exposure for 24 h, and mortality determined. Negative (DMSO) and positive (praziquantel) controls were used. Of the tested plant extracts, 72 were found to possess reproducible in vitro. antischistosomal activity. These active extracts were further subjected to determination of their LC₅₀ and LC₉₀ values. Strong antischistosomal activity was found in the extracts of 15 species (possessing LC₅₀ ≤ 15 µg/mL), viz. Agave americana. L. var. marginata. Trel. (Agavaceae), A. lophantha. Schiede (Agavaceae), Furcraea selloa. C.Koch. (Agavaceae), Calotropis procera. (Aiton) W.T.Aiton (Asclepiadaceae), Pergularia tomentosa. L. (Asclepiadaceae), Asclepias sinaica. (Boiss.) Muschl. (Asclepiadaceae), Alkanna orientalis. (L.) Boiss. (Boraginaceae), Khaya grandifoliola. DC. (Meliaceae), Swietenia mahogani. (L.) Jacq. (Meliaceae), Pimenta racemosa. (Mill.) J.W.Moore (Myrtaceae), Pinus canariensis. C.Sm. (Pinaceae), Verbascum sinaiticum. L. (Scrophulariaceae), Solanum elaeagnifolium. Cav. (Solanaceae), S. nigrum. L. (Solanaceae), and Brachychiton rupestris. (Lindl.) K.Schum. (Sterculiaceae). These 15 species could represent promising bioactive sources that deserve further investigation, with the aim of finding novel antischistosomal agents. The current study represents the first report on a systematic screening of schistosomicidal activity utilizing a large number of plant species.

Context: This study is a continuation of our previous work in which a bioassay screening of 346 methanol extracts from 281 Egyptian plant species was carried out for in vitro schistosomicidal activity. Objective: Another 309 methanol extracts from 278 plant species were subjected to the bioassay screening using the same technique on viable Schistosoma mansoni Sambon (Schistosomatidae) mature worms in specialized culture medium (Roswell Park Memorial Institute medium 1640) in a trial to discover a source for a schistosomiasis drug from Egyptian flora. Material and methods: The methanol plant extracts were tested in vitro against viable S. mansoni mature worms in culture medium. Viability of worms was examined after exposure to 100 μg/ml of the extract in the medium for 24 h. Negative (dimethyl sulfoxide) and positive (praziquantel) controls were simultaneously used. Extracts showing schistosomicidal activity were further subjected to determination of their (Lethal concentration) LC₅₀ and LC₉₀ values. Results: Confirmed in vitro antischistosomal activity was found in 42 extracts. Of these, 14 plant species possessed considerably high antischistosomal activity (LC₅₀ ≤ 15 µg/ml), viz. Callistemon viminalis (Soland. Ex Gaertn) Cheel, C. rigidus R.Br., C. speciosus (Sims.) DC, C. citrinus Stapf, Eucalyptus citriodora Hook, E. rostrata Dehnh., Eugenia edulis Vell, E. javanica Lam syn. Syzygium samarangense (Blume) Merril, Melaleuca leucadendron (L.) L., M. stypheloides Sm. (all belong to Myrtaceae), Cryptostegia grandiflora R.Br. (Asclepiadaceae), Zilla spinosa (L.) Prantl (Cruciferae), Ficus trijuja L. (Moraceae) and Fagonia mollis Delile (Zygophylacae). Discussion and conclusion: These species may represent additional natural sources of bioactive material that deserve further investigation for drug discovery against schistosomiasis.