ABSTRACT
In the last decade, partial resistance to Praziquantel [PZQ] in treatment of schistosomiasis appeared in some villages in Egypt. This happened following the invasion of the irrigation system by hybrid snails of the indigenous, vector snail Biomphalaria alexandrina and the introduced Biomphalaria glabrata. The objective of this study was to investigate if the distribution of the hybrid snails in the irrigation system represents a factor, between others, which is related to the appearance of [PZQ] resistance. Therefore, three groups of mice were infected with Schistosoma mansoni cercariae obtained from infected B. alexandrina, B.glabrata and hybrid snails. Six weeks later, the animals were treated with.the usual curative dose of PZQ [500mg/kg body weight for two consecutive days] and sacrificed two weeks post-treatment. The results showed that worms reduction in the group infected with cercariae from hybrid snails was significantly less than that in the other two groups 86.1% versus 95.1% and 92.8%, respectively. The number of dead ova in the same group was also less, being 81.5% versus 97.5%, and 95.1% respectively. The numbers of ova/g liver was 56.6%, in the same group while 64.2 and 70.9 in the other two groups. The reduction in numbers of ova/g intestine was 81.9% in this group versus 86.1% and 88.4% in the other two groups.The present results give indication that the appearance of PZQ resistance against schistosomiasis in Egypt may return at least partially to the wide distribution of the hybrid Biomphalaria snails in this country