The present study was undertaken to observe the morphological changes of Clonorchis sinensis obtained from experimentally infected rats treated with praziquantel (Biltricide) which is a new anthelmintic agent with high activity against a broad spectrum of cestode and trematode species. For this study, the rats were infected experimentally with about 50 metacercariae of C. sinensis and were given praziquantel a single dose of 600 mg per kg of body weight at 5 weeks after infection. The Clonorchis worms were isolated from the bile ducts of the rats which were autopsied on the 4th day after treatment. After isolation the parasites were observed their shape and motility in the medium of 37 degrees C physiological saline solution, and then the fine structure of the tegument of C. sinensis was studied by means of light, scanning and transmission electron microscope. The findings of the observation were compared with those of untreated parasites. The results are as follows: 1. All the isolated worms moved actively in the medium of physiological saline solution (37 degrees C). A majority of the parasites obtained from the treated rats showed a large balloon shaped structure on the surface between oral and ventral suckers. But such structure has never seen in the parasites obtained from control rats. 2. By the scanning electron microscopic observation, the regular pattern of the tegumental ridges was significantly changed on the outer surfaces of parasites obtained from the treated rats as compared with those of the control rats. 3. By the transmission electron microscopic observation, the numerous mitochondriae in the syncytial tegumental layer of the treated parasites appeared to be degenerated and formed small vacuoles, and the tegumental ridges were also degenerated and showed somewhat flattened. 4. In the parasites obtained from the treated rats, a different size of vacuoles interspersed in the distal part of the syncytial tegument and also in subepithelial region of the urinary bladder. These vacuoles are fused each other and lead to the disruption of the apical region of syncytial tegument along the basement layer. Finally the basement layer was dislocated. So that the tegumental layer appeared as a large balloon.

A total of 48 subjects harbouring Trichuris trichiura, Ascaris lumbricoides, hookworm and/or Enterobius vermicularis were treated with oxantel/pyrantel pamoate tablets (100 mg of each) in a single dose of 20 mg base per kg of body weight. In all 37 cases of A. lumbricoides and 8 cases of A. duodenale infections cured completely, and the mean recovered worm-load was 3.8 with a range of 1-21 and 5.8 with a range of 3-9 respectively. In T. trichiura infection, 32(71.1%) of 45 cases cured completely and the average egg reduction rate was 90.8 per cent. The mean recovered worm-load was 14.6 with a rnage of 1-77 worms. On the other hand, in E. vermicularis infection, 37 (84.1%) of 44 patients were negative eggs by anal swab tests on the 10 to 11th days and 27 (61.4%) on the 20 to 21st days after treatment. The mean recovered worm-load was 17.7 with a range of 1-62. Only one patient with Trichostrongylus orientalis treated with this drug showed no eggs in his stools throughout the post-treatment examinations. Side effects were not noted in all treated cases. These findings demonstrate that a single dose of oxantel/pyrantel pamoate tablets can be considered a drug of choice for multiple infections with these nematodes.