الفهرس 
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Abstract
There is no doubt that schistosomiasis is one of the major communicable parasitic diseases with socio-economic and health hazards in the developing world. Controlling the snail intermediate hosts of this parasite by molluscicides is still one of the most promising means in the battle against this parasite.
The present study was planned to evaluate the molluscicidal properties of carbamide perhydrate, copper and magnesium chlorophyllin (Cu-chl and Mg-chl) against Bulinus truncatus snails, the intermediate host of Schistosoma haematobium. Also, snails’ fecundity and infectivity of S. haematobium miracidia to infect these snails and cercarial production from infected ones were determined post snails exposure to the sublethal concentrations of these agents. As well as, some biochemical parameters, e.g. total protein, the activities of AST, ALT and AKP enzymes were evaluated in tissue homogenate of treated snails. Moreover, histological changes in the digestive and hermaphrodite glands and steroid sex hormones were recorded in B. truncatus snails treated with the tested agents.
The data of the present experimental tests are as follow:
1- Carbamide perhydrate was the most toxic agent to B. truncatus snails followed by Mg-chl, while the least toxic one was Cu-chl. Their LC50s were 91.73, 395.1 and 571.4 ppm, respectively.
2- The snail’s fecundity (Mx) and the reproductive rate (R0) of B. truncatus snails were suppressed post 24 hours of maintenance with the three tested agents followed by 4 or 8 weeks of recovery in clean water. The reduction rate of R0 for snails treated with LC25 of carbamide perhydrate, Mg-chl and Cu-chl were 76.66 %, 83.5 % and 50.8 %, respectively.
3- The biochemical parameters evaluated in tissue homogenate of B. truncatus snails treated with LC90 of the thee tested agents revealed that:
a- The levels of total protein, albumin and globulin were less than those of control groups. The concentrations of total protein for snails treated with carbamide perhydrate, Mg-chl and Cu-chl were 6.99, 27.3 and 21.3 mg/g tissue, respectively compared to 44.3 mg/g tissue for the control group. Similar observations were recorded for concentrations of albumin and globulin.
b- The activities of transaminases AST and ALT and alkaline phosphatase enzymes were elevated in tissue homogenate of snails treated with the tested agents in comparison with control group.
4- The concentrations of steroid sex hormones progesterone and 17-β estradiol that were evaluated in tissue homogenate of snails treated with LC50 of the three tested agents were reduced in comparison with those of control snails. For the hormone testosterone, although its concentrations were decreased in tissue homogenate of B. truncatus snails treated with carbamide perhydrate and Cu-chl, they were elevated in snail groups treated with Mg-chl compared to the control group.
5- The histological sections in the digestive and hermaphrodite glands of B. truncatus snails treated with LC50 and LC90 for 24 hours from the tested agents displayed deleterious effects in tissues and cells of these glands compared to control ones. Fore digestive gland the changes in its tissues and cells were represented by swelling and deformation of the secretory cells, rupturing and disintegration of digestive cells, epithelial cells lost their regular shape and necrotic changes of the digestive tubules and enlargement of the lumen between them. Also, the hermaphrodite gland exhibited deleterious histological deteriorations represented by acini deformation, varying degrees of degeneration and lesions among different cell types, atrophy and rupture of connective tissue. The most prominent damages were vacuolated ova, degenerations of sperms as well as the disintegration of acinus’ germinal epithelial layer that leads to ceasing snail’s oviposition for some weeks during the experimental period.
6- Infection of B. truncatus snails with S. haematobium was suppressed as a reflection of their exposure to LC10 of the three tested agents at 7 and 21 days post miracidial exposure. So, the infection rates of snail groups exposed to LC10 of carbamide perhydrate and Mg-chl at 21 days post miracidial exposure were 36.7% and 20.0%, respectively compared to 53.3% for control the group. The results displayed that B. truncatus snails treated with LC25 of these experimental agents at 7 and 21 days post miracidial exposure did not tolerate these stresses and died before shedding cercariae.
7- The results revealed that the values of the prepatent period, durations of cercarial shedding and life span of infected B. truncatus snails treated with the tested agents at 7 and 21 days post miracidial exposure were not significantly different from those of control groups.
8- S. haematobium cercarial production/infected treated snail throughout its life span was significantly less than that of the infected control group (p< 0.01). The recorded values of cercarial production/infected snail treated with LC10 Cu-chl and Mg-chl at 21 days post miracidial exposure were 568.7 and 224.3 cercariae/infected treated snail, respectively, compared to 1588.4 cercariae / infected control snail.
It is concluded that the tested agents carbamide perhydrate, Cu-chl and Mg-chl exhibited an acceptable molluscicidal activity against B. truncatus snails, the intermediate host of S. haematobium, causing deleterious biological, biochemical and histological effects to them. In addition to minimizing the production of S. haematobium cercariae from infected snails, which is the mile stone in transmission of this parasite. This might render these agents to be the considered in an integrated program for schistosomiasis control. However, it is suggested that more comprehensive studies are needed to define the proper technique(s) for the application of such tested agents in field operations for controlling this disease aiming also, to minimize or prevent water pollution with chemicals and saving the non- target organisms in treated water bodies.