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Aim: To study the effect of artemether (Art) on phosphorylase (PP), lactate dehydrogenase (LDH), glucose-6-phosphate dehydrogenase (G-6-PDH), and adenosine triphosphatase (ATPase) of S japonicum., Methods: Mice infected with S. japonicum cercariae for 32-38 d were treated i.g. with Art 100-300 mg.kg-1 and killed 24-72 h after treatment for collection of schistosomes. The activities of PP, LDH, and G-6-PDH were measured by the formation of NADH or NADPH. The activity of ATPase was measured by the rate of release of inorganic phosphate (Pi) from ATP at 37 degrees C., Results: After infected mice were treated i.g. with Art 300 mg.kg-1 for 24-48 h, the activities of total PP and PPa (active form) increased markedly in both male and female worms, while PPb (inactive form) showed no or only a slight increase. At 24-72 h after the above-mentioned mice were treated i.g. with Art 100-300 mg.kg-1, the inhibitory rates of LDH and G-6-PDH were 9%-59% (male) and 41%-75% (female) as well as 22%-42% (male) and 74%-89% (female), respectively. When Art 300 mg.kg-1 was given to infected mice for 24 h, only the activity of Mg(2+)-ATPase showed marked inhibition in both male and female worms. At 48 h, the Ca(2+)-ATPase, Mg(2+)-ATPase, and Na(+)-K(+)-ATPase were all inhibited, the inhibitory rates of 17% (male) and 19% (female), 32% (male) and 48% (female) as well as 29% (male) and 44% (female), respectively., Conclusion: In schistosomes, the increase in the activity of AMP-independent PPa induced by Art may enhance the decomposition of glycogen and the inhibition of LDH by Art could reduce the formation of lactate. Moreover, Art exerts a potent inhibition on the G-6-PDH activity of the female S japonicum.

Aim: To study the effect of artemether (Art) on glyceraldehyde-phosphate dehydrogenase (GAPDH), phosphoglycerate kinase (PGK), and pyruvate kinase (PK) of S japanicum., Methods: Mice infected with schistosome cercariae for 32-38 d were treated ig with Art 100-300 mg.kg-1 and killed 24-72 h after medication for collection of schistosomes. The activities of GAPDH, PGK, and PK of the worms were determined by measuring the formation of NADH or consumption of NAD. The lactate content of the worms was also measured., Results: After the infected mice were treated ig with Art 300 mg.kg-1 for 24 h, the inhibition rates of GAPDH were 13% (Male) and 21% (Female), and 48 h later the inhibition rates of the enzyme were 6% (Male) and 28% (Female). When Art 300 mg.kg-1 was given to infected mice for 24 h and 48 h, the inhibition rates of PGK were 60% (Male) and 48% (Female) as well as 75% (Male) and 62% (Female), respectively. Similar results were seen in PK activity. At 72 h after treatment the reduction rate of lactate content in Female worm was 72%, while that of Male was 48%., Conclusion: In the glycolytic pathway of both Male and Female schistosomes, PGK and PK activities were inhibited by Art. The GAPDH activity of Female worms was also susceptible to Art, While that of Male worms showed only temporary inhibition after treatment with Art. The Art reduced lactate content more in Female than in Male worms.

Aim: To study the effect of artemether (Art) for prevention of schistosomal infection., Methods: Rabbits with single infection or reinfection with Schistosoma japonicum cercariae were treated intramuscularly (i.m.) or intragastrically (i.g.) with Art 5 -20 mg.kg-1 on d 7-15 after the first infection, followed by various regimens., Results: When rabbits were injected i.m. Art 7.5 mg.kg-1 (i.e., one half of the effective dose given i.g. on d 7) followed by once every week for twice, the female worm reduction rate was only 42%. In infected rabbits treated i.g. with Art 10-20 mg.kg-1 given in the same administration schedule, the female worm reduction rates were > 91%. When Art 15 mg.kg-1 was given to rabbits on d 7-14 and the following dose of the drug was given at intervals of 7-14 d, the female worm reduction rates were > 94%. In rabbits reinfected with cercariae, the female reduction rate of Art given i.g. once a week for 3 times since d 8 after the first infection was 96% which was similar to that given once a week twice since d 14 after the first infection., Conclusion: Art should be given i.g. on d 7-15 after infection, followed by repeated dosing once every 7-15 d for a total of 3 doses. Art given i.g. daily for 2 consecutive days or given at 1-wk intervals since 7-15 d after infection also showed preventive effect.

Aim: To study the effect of artemether (Art) on glucose uptake and glycogen content in schistosomes., Methods: Schistosomes recovered from mice treated intragastrically with Art 300 mg.kg-1 for 24-48 h, were incubated in the drug-free medium containing [U-14C]glucose 11.1 MBq.L-1. The glycogen content, [U-14C]glucose uptake, and incorporation of [U-14C]glucose into worm glycogen in both male and female worms were determined., Results: When above-mentioned schistosomes were exposed to drug-free medium containing [U-14C]glucose for 1-24 h, the glycogen contents of male and female worms decreased 27%-61% and 39%-78%, respectively. Only 3 out of 6 male worm groups showed 23%-35% decrease in glucose uptake, while much less glucose uptake was found in female worms in all groups with reduction rates of 18%-38%. Apart from 2 male groups no apparent change in the incorporation of [U-14C]glucose into the worm glycogen was seen., Conclusions: Art-induced glycogen reduction in schistosomes was related to an inhibition of glycolysis rather than an interference with glucose uptake.

Aim: To study effects of antihydatid drugs on glucosephosphate isomerase (GPI) and glyceraldehydephosphate dehydrogenase (GAPDH) in Echinococcus granulosus cyst wall., Methods: Mice infected with the parasite for 8-10 months were treated i.g. with mebendazole (Meb) or praziquantel (Pra). The activities of GPI and GAPDH in the cysts were measured by the formation of NADH or NADPH., Results: GPI activity in the cyst wall was 197 +/- 103 U, while that of GAPDH was 25 +/- 13 U. When infected mice were treated i.g. with Meb 25-50 mg.kg-1.d-1 for 7-14 d, no apparent effect on the GAPDH activity in the cyst was found. In mice treated i.g. with praziquantel (Pra) 500 mg.kg-1.d-1 for 14 d, the GAPDH activity in the cyst wall was inhibited by 26.5%. As to GPI activity only the group treated i.g. with Meb 25 mg.kg-1.d-1 for 14 d showed 33.2% inhibition of the enzyme in the collapsed cyst wall., Conclusion: GPI and GAPDH are not the major targets attacked by the antihydatid drug.

Aim: To study the effect of artemether (Art) on the tegument of schistosomes., Methods: Mice infected with S japonicum cercariae for 7 and 35 d, or with S mansoni cercariae for 49 d were treated intragastrically with Art 200-300 mg.kg-1.d-1 for 2 d. Schistosomes were collected in groups of 2 mice at various intervals after medication for scanning electron microscopic observation., Results: The tegumental changes induced by Art appeared to be similar in S japonicum and S mansoni: swelling and fusion of tegumental surfaces, vesicle formation and collapse of discoid-like sensory structures. In S japonicum the emergence of tegumental alterations was earlier in 7-d-old schistosomulae than that in 35-d-old adult worms., Conclusion: Art injured the teguments of S japonicum and S mansoni.

Unlabelled: To study the histopathological change of the liver of the hosts treated with artemether (Art) or praziquantel (Pra) in early stage after infection with Schistosoma japonicum cercariae., Methods: Dogs infected once with schistosome cercariae were treated ig with Art 10 mg.kg-1 or Art capsule (ArtC) 15 mg.kg-1 on d 7, or praziquantel (Pra) 30-40 mg.kg-1 on d 21 after infection, followed by the repeated dosing once every 1 or 2 wk for 2-4 times. In rabbits, infected with 48-52 schistosome cercariae once every other day for 5 times, were treated ig with Art 10 mg.kg-1 or Pra 30 mg.kg-1 was started on d 7 or on d 21 after the first infection, followed by the repeated dosing every 1 or 2 wk for 2-3 times., Results: After above mentioned dogs or rabbits were treated ig with Art, ArtC or Pra, the female worm reduction rates were 92.1%-100%. Histopathological examination showed that the reduction rates of total granuloma in the liver sections of the dogs and rabbits were 70.9%-97.3% and 76.5%-97.4%, respectively. Meantime, the structure of the hepatic lobules was normal with normal arrangement of the liver bundle., Conclusions: Early treatment with Art or Pra exhibited a promising effect of protection of the liver of the dogs and rabbits infected with schistosome cercariae. Early treatment of infection with schistosome cercariae kills the Female worms before oviposition. Thus, the host will be protected from the damage caused by schistosome eggs. Promising results were obtained when mice and rabbits received an early treatment with artemether (Art) or praziquantel (Pra). This work was to study the liver infected with cercariae and treated by intragastric gavage (ig) with Art, Art capsule (ArtC) or Pra in early stage after infection.

Aim: To explore the existence of glutathione S-transferase (GST) and superoxide dismutase (SOD) in Echinococcus granulosus cyst, and the effect of anthydatid drugs on these 2 enzymes, mice infected with E granulosus protoscoleces for 10-12 months were used., Methods: The activity of GST was measured by conjugation rate of 1-chloro-2,4-dinitrobenzene with glutathione (reduced form), while the activity of SOD was measured by a modified autoxidation of 1, 2, 3-trihydroxy-benzene method., Results: Activities of both GST and SOD in the cyst wall were 12.3 +/- 4.3 to 13.5 +/- 4.8 mumol min-1/mg protein and 4.4 +/- 2.9 to 6.1 +/- 1.4 U min-1/mg protein, respectively. When infected mice were treated ig with mebendazole (Meb) 25 mg kg-1 d-1 for 14 d, the GST activity of both collapsed and full cyst walls were inhibited by 30.1% and 26.8%, respectively. Whereas SOD activity of the cyst walls were activated by 105%-163%. Albendazole 300 mg kg-1 d-1 for 14 d and praziquantel 500 mg kg-1 d-1 for 14 d had no apparent effect on both GST and SOD of E granulosus cyst wall., Conclusion: The results suggested that the inhibition of GST activity in the cyst wall induced by Meb might damage the defence system of the parasite.

Aim: To study the effect of praziquantel (Pra) on the tegument of 21-d-old schistosomula, mice infected with Schistosoma japonicum cercariae for 21 d were treated ig with Pra at a single dose., Method: Groups of mice were killed at different intervals within 48 h, and the worms were collected by perfusion for scanning electron microscopic observation., Results: When the dose used was 300 mg.kg(-1), the worms showed mild or moderate swelling, fusion or even erosion and collapsed of the tegumental ridges, which was characterized by swelling of the discoid sensory structures. At higher dose of 500 mg.kg(-1), similar alterations in the worm surface were seen, but more extensive and serious. When Pra 500 mg.kg(-1) was given daily for 3 d, severe swelling, erosion and peeling of the tegument accompanied by the attachment of the host leukocytes on the damaged surface were seen., Conclusion: Pra exhibited a direct killing effect on 21-d-old schistosomula.

Eighteen and 23 FAA components were detected in the cyst wall and cyst fluid of E granulosus, respectively, by using automatic amino acid analyzer. The concentrations of most of the determined FAA were higher in the cyst fluid than those in the cyst wall, especially the taurine was 5-fold higher. Mebendazole treatment resulted in an increase in the concentration of alanine, valine, lysine, and taurine in both cyst wall and cyst fluid, the most notable being the alanine in the cyst wall. The results are interpreted as a coupling of glycolysis and amino acid metabolism, suggesting an involvement of FAA metabolism in the mechanism of Meb action.

Artemether (Art, beta-methyl ether of artemisinin) first synthesized by Shanghai Institute of Materia Medica, Chinese Academy of Sciences, is effective against not only malaria but also schistosomiasis. When rabbits infected with Schistosoma japonicum cercariae for 7 d were treated ig with Art 10 mg.kg-1, the total worm reduction rates were 74.6-76.7%. If Art (10 mg.kg-1) was given once weekly after the first treatment for 3-4 times, the total worm reduction rate was > 98%, and most of the rabbits were free from female worms. When praziquantel (Pra) was given ig 40 mg.kg-1 to rabbits on d 21 after infection, and repeated once every week for 3 wk, most rabbits showed a total worm reduction rate > 98% with their livers showing normal or mild changes, and their parameters relevant to acute schistosomiasis were negative as compared to the controls. Hence Art and Pra are suggested to be used in field trial for control of acute schistosomiasis or reduction of the intensity of schistosomal infection.

Echinococcus granulosus cyst wall exhibited activities of fumarate hydratase (FH), pyruvate kinase (PK), and phosphoenolpyruvate carboxykinase (PEPCK) with 911-1433, 151-215, and 54-98U, respectively. The ratio of PK/PEPCK was 2.2-2.7, indicating that glycolysis is the main pathway of carbohydrate metabolism in the cyst wall. When infected mice were treated ig with mebendazole, albendazole or praziquantel at the respective daily dose of 25-50, 300, and 500 mg.kg-1 for 7-14 d, no apparent change of FH activity in the cyst wall was found, while PK and PEPCK activities in the cyst wall were markedly inhibited by mebendazole and albendazole. The inhibition rates of PK and PEPCK activities in mebendazole group were 85-88% and 90-92%, respectively, while in albendazole group were 55.3 and 71.6%, respectively. The results suggest that PK or PEPCK in the cyst wall may the important site attacked by effective anti-hydatid drugs.

The first single dose of praziquantel (Pra) was given ig to mice on the day of infection with Schistosoma japonicum cercariae, or 7 d, 14 d, and 21 d after infection. Afterwards, the same dose of Pra was given once at 1-3 wk intervals for 2-3 times. The prophylactic effect was estimated by the reduction of average number of total and female worms, the number of mice without female worm, and the gross change of the liver. When mice were treated with Pra 300-500 mg.kg-1 initially on d 21 after infection and repeated once every 1-2 wk for 2-3 times, almost all the female worms lodged in the host were killed, showing that either the host was protected from the infection of schistosomes or a great decrease in the intensity of the infection resulted.

Echinococcus granulosus cyst wall possess high biochemical activities of malate dehydrogenase (MD) and fumarate reductase (FR), but low activity of succinate dehydrogenase (SD), suggesting that the cyst wall may utilize a partial reverse tricarboxylic acid cycle. When infected mice were given intragastrically with mebendazole, 25-50 mg.kg-1.d-1, albendazole 300 mg.kg-1.d-1 or praziquantel 500 mg.kg-1.d-1 for 7-14 d, no apparent effects on SD and FR activities of the cyst wall were found, while the MD activity was suppressed by all the 3 drugs, the inhibition rates being 34.6-61.6%, 59.8%, and 50.6%, respectively. The results suggested that MD may not be an important target for the antihydatidosis drugs.

The glucose, glycogen, and lactic acid contents in Echinococcus granulosus cyst wall were 3570 +/- 623, 1276 +/- 126, and 267 +/- 29 micrograms.g-1, respectively. The lactate dehydrogenase (LDH) activity in the cyst wall was 4307 +/- 297 U/(min.mg protein). When infected mice were treated ig with mebendazole (Meb) 25 or 50 mg.kg-1.d-1 for 7-14 d, the glucose and glycogen contents in the cyst wall decreased markedly. No apparent changes in lactic acid and LDH activity were seen. The results suggested that Meb had no effect on glycolysis of the cyst wall, but it exhibited an inhibitory effect on the transport of exogenous glucose from the host to the cyst wall, which might further promote the decomposition of endogenous glycogen for energy supply and resulted in a decrease of endogenous glycogen content in the cyst wall.

Mice infected with protoscoleces of Echinococcus granulosus for 12-14 months were treated ig with mebendazole (Meb) 25-50 mg.kg-1 x d-1 for 7-14 d, albendazole (Alb) 200 mg.kg-1 x d-1, cr praziquantel (Pra) 500 mg.kg-1 x d-1 for 14 d. The mice were killed 24 h after the last medication, and acid phosphatase (ACP), alkaline phosphatase (AKP), and adenosine triphosphatase (ATPase) including (Na, K, Mg)-ATPase, (Na, K)-ATPase, and (Mg)-ATPase were determined and compared with those of untreated control group. The results showed that ACP activities of cyst wall in treated groups were lower than the control group. Whereas AKP activity of cyst wall in Pra group increased markedly, this is not the case in Meb and Alb groups. Three ATPase activities of cyst wall were inhibited in both Meb and Alb groups, Meb being more potent. No apparent changes in the ATPase activities were seen in Pra group.

Mice infected with secondary cysts of Echinococcus granulosus were treated ig with mebendazole (Meb) 25 mg.kg-1.d-1 for 7-14 d. At 24 h after the last dose the endocysts in the treated mice were removed out for in vitro cultivation and exposed to [U-14C]glucose 11.1 kBq.ml-1 for 2 min, no apparent difference in radioactivity content in the cyst walls between the treated and control groups was observed. When [U-14C]glucose was given iv to the infected mice 24 h after they had been treated ig with Meb 25 mg.kg-1 or 50 mg.kg-1 daily for 14 d, the radioactivity content in the cyst wall and cyst fluid decreased significantly as compared to the corresponding control group. Nevertheless, no apparent change in the incorporation of radioactivity into the endogenous glycogen of the parasites was observed, although the glycogen in the cyst wall decreased markedly.

Artemether (beta-methyl ether of artemisinin) first synthesized by Shanghai Institute of Materia Medica, Chinese Academy of Sciences(1), appears in colorless crystal and is more lipid-soluble than artemisinin. When artemether was given ig or im to mice infected with Schistosoma japonicum for 32-35 d at the dosage of 1/10-1/2 LD50. Its effects in the two administration routes were similar. After artemether 200 mg.kg.d-1 ig or 100 mg.kg-1.d-1 im for 1-2 d was given to mice infected with S japonicum cercariae at different intervals, d 7 schistosomules were more susceptible to the drug with worm reduction rates of 73.9-92.0%. The d 35 adult worms also exhibited susceptibility to the drug and the worm reduction rates were 47.0-70.1%, but less susceptibility to the drug in other developmental stages of schistosomes. The major morphological alteration of adult worms induced by artemether was sustained shrinkage accompanied by atrophy and degeneration of the worm's reproductive glands, eg, the testis in males and ovary as well as vitelline gland in females. The in vitro tests indicated that artemether showed apparent effects on different stages of schistosomes only when a higher concentration of 40 micrograms.ml-1 was used.

Mice infected with secondary cysts of Echinococcus granulosus were treated ig with mebendazole (Meb), albendazole (Alb), albendazole sulfoxide (AlbSO) or albendazole sulphone (AlbSP) at equal effective dosage. The blood concentrations-time courses of the four drugs were adequately fitted to a liner one-compartment open model analysed with a modified NONLIN program, and the major pharmaco- kinetic parameters were then calculated (Table 1). When Alb was given ig to the infected mice, 76.2-84.5% of the drug absorbed was metabolized to AlbSO. There fore, the pharmacokinetics of AlbSO in Alb group was determined. After ig administration of Meb to the infected mice, the ratio of the drug contents in cyst wall to corresponding plasma concentrations of Meb was 10.6-26.9%, but much less in cyst fluid. In Alb and AlbSO groups, similar AlbSO contents in cyst wall and cyst fluid with higher ratio to plasma concentrations were observed (Fig 3). The results suggest that E granulosus cysts were more susceptible to Meb than to Alb or AlbSO, and improvement of Meb absorption would be favourable for enhancement of efficacy in the treatment of hydatid disease.

Mice infected with 100 and 50 Schistosoma japonicum cercariae for 7 and 35 d respectively were treated with im artemether 100 mg.kg-1.d-1 or arteether 100 and 300 mg.kg-1.d-1 for 2 d. The mice were killed at different intervals within 28 d after medication and the livers were sectioned for histological and histochemical observations. The results showed that both artemether and arteether caused degeneration in the tegument, intestine and genital gland of the hepatic-shifted worms. The glycogen content and alkaline phosphatase (AKP) activity of schistosomula and adult worms decreased 7 d after treatment, especially remarkable in arteether 300 mg.kg-1.d-1 group.

Mebendazole (Meb), albendazole (Alb) or albendazole sulfoxide (AlbSO) were taken rapidly in vitro by secondary cysts of Echinococcus granulosus removed out from mice infected with protoscoleces 8-9 months previously. The amounts of the drugs taken by the cysts were apparently increased followed by exposure of the cysts to the drugs at 10 micrograms.ml-1. The Alb penetrated into the cysts was distributed mainly in cyst wall, whereas the content of Meb in cyst wall was twice as much as that in cyst fluid. The distributions of AlbSO in cyst wall and cyst fluid were similar. When the cysts in the medium were exposed to Alb, some AlbSO and albendazole sulphone were detected in both cyst wall and cyst fluid, indicating that a part of Alb was metabolized by the cysts. In another experiment cysts exposed to the drug for 2 h were transferred to the medium without the drug for another 24 h. The release rates of the 3 drugs from the cysts were alike. In 1-2 h after transfer about 65-70% of the drugs absorbed by the cysts previously were released. Twenty-four hours after exposure the release rates increased to 75-85%, and the release of the drugs from the cyst wall was somewhat faster than that from cyst fluid.

Mice infected with protoscoleces of Echinococcus granulosus for 8-9 months were treated ig with mebendazole (Meb) 50 mg.kg-1.d-1, albendazole (Alb) 300 mg.kg-1.d-1 or albendazole sulfoxide (AlbSO) 150 mg.kg-1.d-1 for 1-7 d. The glycogen contents of cyst wall in each drug groups were 1.0 +/- 0.6 - 1.8 +/- 0.9 mg/g, 1.1 +/- 0.9 - 1.8 +/- 0.8 mg/g and 0.8 +/- 0.5 - 1.5 +/- 0.9 mg/g, respectively, which were less than those 2.2 +/- 1.3 - 2.8 +/- 1.3 mg/g of corresponding control groups with respective glycogen reduction rates of 38-55%, 36-51% and 46-62%. After prolongation of treatment course to 10-14 d, the glycogen contents of cyst wall in Meb and AlbSO groups were further decreased, which resulted in glycogen reduction rates of 73% and 69%, respectively. No further decrease of glycogen contents in Alb groups was seen as the glycogen reduction rates sustained in 32%. Histochemical observation showed that the glycogen contents in germinal layer of the cysts decreased significantly or even disappeared during the treatment of Meb, Alb or AlbSO. The results suggested that the effects of Meb and AlbSO on mice infected with secondary cysts of E granulosus were superior to Alb as evaluated by glycogen reduction rate of cyst wall.

The proliferative response of lymphocytes to Con A and enzyme-linked absorbent assay were used to determine the levels of cellular and humoral immunity of mice infected with ip 2000 protoscolices of Echinococcus granulosus for 2, 4 or 8 months and treated twice with ip BCG 0.2 mg/mouse at an interval of 10 d, or with ip cyclophosphamide (Cy) 10 mg/(kg.d) x 5 d. The results showed that the immune levels of the host were stimulated by BCG, but depressed by Cy significantly. When the mice were treated with ip mebendazole (Meb) 25 mg/(kg.d) x 10 d in combination with ip BCG 0.2 mg/mouse on d 3 before Meb treatment and on d 7 after the beginning of Meb treatment, or with ip Cy 10 mg/(kg.d) x 5 d before Meb treatment, the inhibition rates of cyst weight and the alterations of germinal layers induced by the drugs were similar to those of corresponding groups treated with Meb alone. Cy also exhibited an apparent effect on mice infected with protoscolices for 2 months. Even so, no apparent synergic effect was seen after combined treatment with Cy and Meb. The results suggest that the effect of Meb on secondary cysts of E granulosus was not affected by the host immune level.

[3H]Praziquantel was absorbed rapidly by the cysts in mice infected with metacestodes of Echinococcus granulosus and treated with ig [3H]praziquantel 400 mg/kg (containing 3H 1.48 MBq). Within 24 h after treatment, 3H content in the ectocyst was 27.7-54.9% higher than that in cyst wall. The peak concentration of 3H in cyst wall and cyst fluid were 11.7-15.3% of those found in plasma. However, when the cysts were exposed to [3H]praziquantel 20 micrograms/ml (containing 3H 3.7 kBq), the 3H radioactivity in the cyst wall and cyst fluid reached equilibrium within 30 min-48 h after medication, corresponding to 45.5-63.3% of 3H radioactivity in the medium. Autoradiography showed that [3H]praziquantel entered into the germinal layer through ectocyst and laminated layer. The damage to germinal layer was related closely to deposition of the drug.

Golden hamsters infected with Necator americanus were treated orally with a new anthilmintic tribendimidin (N, N'-[bis-4'-(1-dimethyl amino ethylidene amino)phenyl] 1,4-phenyene dimethylidyne amine) at a single dose of 150 mg/kg. One h after medication, some worms showed cuticular swelling, fusion of transverse striations and attachment of host leucocytes onto the worm's damaged cuticular surface. Four h post treatment, the cuticle revealed a moderate swelling or even erosion. Meanwhile, the ventral cutting plates appeared to be swollen. After 8-24 h, severe cuticular swelling, erosion and peeling in female worm tails and male copulatory bursa were seen. No increases in lesions in the small intestinal mucosa of infected golden hamsters were observed 4-8 h after medication.

Rabbits were infected with 48-52, 198-202 and 498-502 cercariae of Schistosoma japonicum and treated ig with single doses of praziquantel (40 mg/kg) 4 and 8 wk post infection. The worm reduction rates of the 8 wk groups were 87.9, 92.2 and 97%, respectively. These values were significantly higher than 48.5, 52.3 and 58.6% for the corresponding 4 wk groups. The serum antibody titres of the 8 wk post infection rabbits were apparently higher than those of the 4 wk rabbits. Meanwhile, for the same duration of infection, the specific antibody levels in the heavy worm burden groups were also higher than those in the light worm burden groups. The results obtained in the mice infected with S. japonicum at different intensities and treated ig with single doses of praziquantel at 300 mg/kg at different durations were similar to the results in the rabbits. The correlation between efficacy and specific antibody level was confirmed by calculating the coefficient of correlation with r values of 0.454-0.983 (P less than 0.01). The results also indicated that heavy infections with S. japonicum were still more responsive to praziquantel treatment. In addition, the effect of praziquantel on worms was closely related to the specific antibody response in the host.

When protoscoleces of Echinococcus granulosus, maintained in 20% calf serum-RPMI 1640 were exposed to praziquantel 1 microgram/ml for 1-48 h, severe damages to the ultrastructure of protoscoleces were observed. The main lesions of the tegument included indistinct of the matrix, vacuolization and peeling, while vacuolization of perinuclear cytoplasma in tegumental cells, focus lysis in muscle bundles, and destruction in collection ducts and flame cells were also seen. The results suggest that the damages to the tegument, collection ducts and flame cells may interfere with the nutrition and defence functions of protoscoleces, and destroy the osmoregulatory system, which may be the major causes of death in protoscoleces during treatment with praziquantel. When protoscoleces were exposed to albendazole 20 micrograms/ml for 24-72 h, no apparent damage to the tegument was detected, except that some network-like structures appeared in the cytoplasma of tegument and parenchyma cells.