Graphical abstractArachidonic acid interacts with the surface double lipid bilayer shield of larval, developing and adult schistosomes, leading to its disintegration and eventual parasite attrition.

Schistosoma mansoni is one of the parasites causing schistosomiasis, a disease which threatens millions of people all over the world. Traditional chemical drugs are not fully effective against schistosomaisis due to the evolving drug resistant worm strains, so exploring new remedies derived from natural products is a good way to fight schistosomiasis. In the present investigation two natural products, Nigella sativa oil and Chroococcus turgidus extract were used separately or in a combination to explore their effect on S. mansoni. The infected mice treated with Chroococcus turgidus extract or/and sativa seed oil showed a significant decrease in the total worm burden. The total number of deposited eggs by females of S. mansoni was significantly decreased in the liver of mice treated with Chroococcus turgidus extract or/and sativa seed oil. However, in the intestine, the number of eggs was significantly reduced in mice treated with algal extract and those treated with both algal extract and oil. Fecundity of female S. mansoni showed a significant decrease from mice treated with algal extract or/and sativa seed oil. According to SEM investigations the tegmental surface, oral and ventral suckers of worms also showed considerable changes; as the tubercles lost their spines, some are swollen and torn out. The suckers become edematous and enlarged while the tegmental surface is damaged due to the treatment with Chroococcus turgidus extract or/and sativa seed oil. In conclusion, the Nigella sativa oil and Chroococcus turgidus extract are promising natural compounds that can be used in fighting schistosomiasis.

Seventy albino mice were infected with~ 80 S. mansoni cercariae and were classified into: GI: infected non-treated group, GII: treated with C. procera alcoholic extract after infection (therapeutic), GIII: treated with C. procera aqueous extract after infection (therapeutic), GIV: treated with C. procera alcoholic extract before infection (prophylactic alcoholic), GV: treated with C. procera aqueous extract before infection (prophylactic aqueous), GVI: treated with praziquantel, treated group with praziquantel combined with aqueous extract of C. procera and G.VII: infected and treated with half dose of Praziquantel combined with aqueous plant extract. Seven weeks post infection, all mice were autopsied, and livers and ilea were parasitological examined (Tissue egg load) and histological assessments (Number & size of hepatic granulomas). Schistosomes recovered from all groups were processed to calculate total worm burdens.The results showed that mice treated with C. procera alcoholic and aqueous extracts showed more significant reduction in total worm burden (43.7% & 46.4%), total egg tissue load (60% & 50.7%) and number of hepatic granuloma (45.9% & 55.5%) than mice in prophylactic aqueous or alcoholic groups (38.3% & 36%, 27.2% & 44%, 25.6% & 39%, respectively). Female worms recovered from mice of aqueous or alcoholic treated groups showed less fecundity than those recovered from mice of prophylactic groups (1475±181 & 2821±200, corresponding to 3674±1447 & 3023±709, respectively). Mice treated with praziquantel or treated with praziquantel combined with C. procera aqueous extract showed the highest reduction in total tissue egg load (86.4% & 97.4%, respectively). Mice treated with praziquantel combined with C. procera aqueous extract showed higher reduction in total egg tissue (97.4%), number and size of hepatic granuloma (72.3% & 31.4%) than those treated with praziquantel (86.4%, 55.5% &10.8%, respectively).

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