Objective To understand the differences in the external morphology between Schistosoma japonicum miracidia and S. sinensis miracidia, explore the optimal egg incubation temperature and observation time of Schistosoma japonicum and S. sinensis in the liver tissues of mice, and provide reference for the surveillance for S. japonicum infection in wild mice in endemic areas where S. sinensis exist.

Methods The miracidia of the two species of Schistosoma were fixed with iodine, and 75 miracidia of the two species with better morphology were randomly selected. The body length, shoulder width, head length, tail width and middle width of the miracidia were measured to compare the external morphological characteristics of the two species. The morphology, range and speed of miracidia of the two species in movement in a conical flask were observed with dissecting microscope. The dynamic automatic identification system of Schistosoma miracidia was used to identify the two kinds of miracidia. Three egg concentrations (180, 360 and 540 eggs per bottle) and three incubation temperatures (20℃, 25℃ and 28℃) were set for incubation, and the observation time was 10min, 20min, 30min, 1h, 2h, 4h and 8h to explore the optimal incubation temperature and observation time. Software SPSS 23.0 was used to analyze the five indicators of the two kinds of miracidia of Schistosoma by two independent samples t-test, and the egg incubation rates at different temperatures were analyzed by χ² test. Excel 2021 was used for statistical analysis on the best egg incubation temperature and observation time.

Results The average body length, shoulder width, head length, tail width and middle width of the miracidia of S. japonicum were (112.48±10.63), (32.61±4.64), (19.17±4.13), (29.91±3.36) μm and (39.31±4.42) μm, respectively. The average body length, shoulder width, head length, tail width and middle width of the miracidia of S. sinensis were (106.22±9.55), (30.72±5.09), (17.48±4.36), (22.63±4.44) μm and (36.18±5.63) μm, respectively. The differences in body length (t=−3.795), shoulder width (t=−2.378), head length (t=−2.436), tail width (t=−11.295), and middle width (t=−3.781) between the two species of Schistosoma were significant (all P<0.05). There was no significant difference in the shape, range and speed of the miracidia between the two species of Schistosoma. The dynamic automatic identification system identified the two kinds of miracidia. The differences in egg incubation rates of S. japonicum at 20℃, 25℃ and 28℃ were not significant (χ²=2.677, P>0.05). The differences in egg incubation rates of S. sinensis at 20℃, 25℃ and 28℃ were significant (χ²=31.692, P<0.05). There were significant differences in egg incubation rates between S. japonicum and S. sinensis at 20℃, 25℃ and 28℃ (χ²=98.464, 35.169, 9.720, all P<0.05). In the eggincubation at 20℃ and 25℃, the number of miracidia reached the peak 1 hour later. In the eggs incubation at 28℃, the number of miracidia peaked 30 min later in all cases. The cumulative number of miracidia incubated from eggs of two Schistosoma species at the three temperatures reached a high value at 2-4 hours, and the number of miracidia hatched from eggs of two Schistosoma species decreased gradually after 1 hour of incubation.

Conclusions The external morphology and movement patterns of S. sinensis miracidia and S. japonicum miracidia were highly similar, and the egg incubation conditions of two species of Schistosom were also similar. Therefore, the existing of S. sinensis has certain interference in the surveillance for wild mice infected with S. japonicum in Yunnan province, and the surveillance program should be adjusted according to local conditions.