Study On Early Detection And Therapy Evaluation Of Schistosoma Japonicum Infection In A Rabbit Model By PCR

A detection assay for Schistosoma japonicum DNA in rabbit fecal and serum samples based on the Polymerase Chain Reaction (PCR) was developed and evaluated. Specific primers were designed based on the genome of S.japonicum and a 230bp sequence DNA was amplified by PCR from Schistosoma japonicum male and female adult worms, liver homogenate, eggs and feces. The expected PCR product was observed when 0.021 egg-equivalents of DNA purified from the eggs and 1.1 egg-equivalents of DNA from feces was used as a template, and there is no cross-reaction with S.mansoni.Three groups of rabbits were infected with 1500 (Group I), 500 (Group II) and 200 (Group III) cercariae of S. japonicum respectively. After the infection, rabbit sera were collected weekly for 7 weeks or 20 weeks, depending on the cercarial dose. The rabbits of Group II were treated with two praziquantel doses on the seventh and eighth week post-infection, and the sera were collected weekly for 23 weeks after treatment. Serum anti-worm IgG was tested for 20 weeks in Group III and for 30 weeks post-infection (23 weeks post-treatment) in Group II by ELISA and COPT. ELISA and COPT gave the positive results at 4 weeks and 5 weeks in Group II respectively. The parasite eggs were detected in feces at 7 weeks in the three groups. In contrast, S.japonicum DNA was detected in the sera at 1 week post-infection, i.e. 3-6 weeks earlier than the other methods in the rabbit model, and it became negative at 10 weeks post-treatment, whereas the COPT become negative at 20 weeks post-treatment, and the anti-worm IgG was still at high levels at 23 weeks post-treatment. These data suggest that the PCR is a potential tool for the early diagnosis and evaluation of chemotherapy in S. japonicum infection.