Artificial preparation, indoor passage, and nature breed of Oncomelania hupensis infected with Schistosoma Japonicum.

Objective: To prepare the infected Oncomelania hupensis by artificial method for the research on the activity, vaccine, and genetic variation of Schistosoma Japonicum (S. Japonicum).
Methods: The mature eggs of S. Japonicum were collected by Nylon silk method and the miracidia were incubated under appropriate conditions. Negative snails were infected with miracidia in different proportion by means of individual or collective infection to seek the best method and proportion of infection between miracidia and snails. Infected snails were divided into 12 groups in total. I-VI groups were for individual infection and VII-XII groups were for collective infection. There were 200 snails in each group. The infection ratios between snails and miracidia in Group I-VI or VII-XII were 1:0,1:5,1:10,1:15,1:20,1:25, respectively. The infected snails were screened, numbered, and reared singly. The amount of cercariae was calculated once every 10 days until the infected snails died. Then cercariae shedding quantity, infection quantity, and mortality of infected snails in every group were compared to find the best infection method and the best infection proportion between miracidia and snails. The cercariae were collected from the first generation of infected snails and were used to infect experimental animals. The mature eggs of S. Japonicum were saved from the infected experimental animals and incubated to get miracidia. The snails were artificially infected by miracidium to get the second generation of infected snails. The developmental rates of adult worms, the egg density in fecal and liver were compared between artificially and naturally infected snails. Results In individual infection Group I-VI,the average infection value of snails were 0 ± 0,22.7 ± 4.2,31.7 ± 4.5,53.0 ± 5.3,39.3 ± 5.9,32.7 ± 4.7,the average fatality of snails were 21.7 ± 3.1,25.0 ± 3.6,31.3 ± 4.9,44.7 ± 6.5,78.3 ± 9.5,89.7 ± 13.6, and the average value of cercariae shedding from infected snails were 0.0 ± 0.0,308.0 ± 96.6,428.1 ± 146.2,527.0 ± 171.1,571.4 ± 148.9,602.9 ± 356.3, respectively. In collective infection Group VII-XII,the average infection value of snails were 0 ± 0,12.3 ± 2.5,18.7 ± 4.7,28.3 ± 4.2,33.3 ± 4.7,29.3 ± 5.5,and the average fatality of snails were 22.7 ± 3.8,23.7 ± 4.5,28.3 ± 5.5,47.0 ± 9.5,75.7 ± 8.5,86.3 ± 12.2, and the average value of cercariae shedding from infected snails were 0 ± 0,244.5 ± 57.3,292.3 ± 74.8,347.1 ± 100.8,477.2 ± 142.1,447.3 ± 161.4, respectively. The second generation of artificially infected snails was obtained successfully. The average infection rate and fatality rate for the second generation of artificially infected snails were 24.65% and 24.50%, both of which were not obviously different from that of the first generation of artificially infected snails (P>0.05). In the animal experiment, the worm growth rate for the naturally infected snails, the first or second generation of artificially infected snails were 68.50%,73.50% or 71.00%. There was no obvious difference among them (P>0.05). The fecal (or liver) eggs per gram for the naturally infected snails, the first or the second generation of artificially infected snails were 1 503 ± 269,1 683 ± 233, or 1 541 ± 117 (or 6 641 ± 1 819,6 272 ± 1 419, or 7 263 ± 1 643). There was no significant difference among the 3 groups (P>0.05).
Conclusion: Infected snails can be obtained through the artificial method by using S. Japonicum miracidia to infect snails. Individual infection has the advantage over collective infection. The optimal proportion of infection between snails and miracidia is 1:15. There was no significant difference between the first and the second generation of artificially infected snails in the average of cercariae shedding, infection, and fatality average of snails. There was no significant difference between artificially and naturally infected snails in the developmental rate of adult worms, fecal and liver eggs per gram.