DNA Detection Of Low-intensity Schistosoma Japonicum Infection And Study The Sources And Metabolic Dynamics Of The Parasitic DNA In Serum Of Host

In this study, a DNA detection assay for Schistosoma japonicum in low-infection rabbit model based on nested-PCR was evaluated. In our previous studies, standard PCR and LAMP based method have been proved a potential tool for the direct detection of parasite DNA in a rabbit model. However, the previous rabbit models were middle and heavier intensity of infection. As the human prevalence rate of S. japonicum has gradually been lowered year by year, it was very valuable to investigate the sensitivity of nucleic acid detection methods in serum samples of low-infections host, in order to evaluating the practical application of DNA detection as a diagnostic approach in the field, especially for efficacy evaluation.Firstly, four low-infection rabbit models of 200, 100, 50 and 30 S. japonicum cercariae infection were established, and the rabbits blood were collected at 0, 3 day and 1, 2, 3, 4, 5, 6, 7, 9, 11, 13, 15, 17, 19 weeks post-infection. Nested-PCR detection results shown that the S. japonicum DNA were detected from the 3rd day to 19th week post-infection even at the level of worm burdens was 3 pairs. Compared with the standard PCR assay, the nested-PCR assay was a more sensitive and specific DNA detection method for amplifying a purpose fragment of DNA from a large complex mixture of DNA, showing a ten times less detection limit of 10.2 copies per reaction, and the electrophoretic bands were clearer.Secondly, in order to further understanding the pathogenic character for DNA detection instruction, we focus our attention on the source and metabolic dynamics of parasitic DNA in the blood of host. Rabbit model with monosexual and bisexual cercariae infection was employed to compare the efficacy of egg laying for DNA detection and thus indirectly reflected where the parasitic DNA came from, the worm or eggs? Then, in order to study the metabolic dynamics of parasitic DNA in the blood of host, praziquantel treatment was applied to the same rabbits mentioned above which would led to worm elimination and clearance of worm origin DNA from serum. The experiment results suggested that, in the first 4 weeks post-infection the parasite DNA in serum primarily came from the residual body of dead schistsomula and / or tegument shedding of worm growing but not eggs, while during the spawning stage of adult female Schistosoma it might relate to the disintegration of inactive eggs. The duration from treatment to total elimination of worm origin DNA from serum was projected to not exceed 3 weeks. But, the inactive eggs release DNA with a more slowly kinetics which could last for more than 16 weeks.At last, on the base of the encouraging results from animal model, the nested-PCR assay was employied to detect 100 cases sera of patients. The results of detection showed that it could detected 78 positive cases (positive rate was 78%). These data suggested that nested-PCR is a potential tool for early diagnosis and therapy evaluation in S. japonicum infection.