| Schistosomiasis caused by Schistosoma,is a serious zoonotic disease.The prevalent disease in China is Schistosomiasis japonica,which is mainly distributed in the swampy lakes in the middle and lower reaches of the Yangtze River.The domestic animals,especially water buffalo,plays an important role in the disease transmission.Water buffalos infected with Schistosoma japonicum(S.japonicum)could self-cure despite they were not treated with drugs.Several epidemiological studies showed that water buffaloes might have resistance to reinfection of S.japonicum.Studies on the degree,process and mechanism of the resistance to reinfection in buffalos may provide scientific basis for the development of anti-schistosome vaccines,finding therapeutic targets,and the establishment of schistosomiasis control strategies.Praziquantel(PZQ)is the first drug of choice for the treatment of S.japonicum infection in domestic animals and plays a very important role in the control of schistosomiasis.Because of the rapid metabolism of PZQ in the body,most researchers generally believe that praziquantel does not produce long-term preventive effects,and the previous studies were mainly conducted based on the direct effect on the parasite.In this paper,we studied the degree,the process and the mechanism of the resistance to reinfection in buffalos,and evaluated the preventive effect of PZQ against S.japonicum infection.1.Study on the degree and mechanism of resistance to S.japonicum reinfection in water buffaloesTwo independent trials,trial 1 and trial 2,were respectively performed in 2016 and 2017.In each trial,the animals were randomly divided into 4 groups,group 1 for the first reinfection,group 2 for the control of the first reinfection,group 3 for the second reinfection and group 4 for the control of the second reinfection.Both results of trial 1 and trial 2 revealed that the water baffaloes have strong resistance against the second reinfection.Compared with group 4,a 97.3%-98.0% worm reduction(P <0.05)and a 91.1%-100% egg count reduction(P < 0.05)in liver and rectum were obtained.Shortening of adult male and female worms,and reduced lesion were also observed in group 3.However,the worm burdens in group 1 of both trials were more than group 2,mainly because of the short interval(18 days)between PZQ administration and infection in trial 1,and the incomplete treatment for the first infection caused by the low purity of PZQ of the powder used in trial 2.Thus,the results obtained here can’t illustrate if there is resistance for the first reinfection.We also investigated the content of immunoregulatory cytokines(L-4,IL-5,IL-7,IL-10,IFN-γ)and antibodies(IgG,IgG1)in peripheral serum of each animals in trial 1 and the results showed that group 1 and group 3 were higher than their controls at most survey point.2.Preventive results of S.japonicum infection in water buffalos induced by PZQThe preventive effect of PZQ against S.japonicum infection in water buffalo was evaluated in 2trials.The PZQ powder used in the first trial was purchased from Nanjing Pharmaceutical Co.Ltd while that used in the second trial was purchased from Suzhou Qinqiang Co.Ltd [The purity of PZQ was only19.5%,compared with PZQ from Nanjing Pharmaceutical Co.Ltd,analyzed by High PerformanceLiquid Chromatography(HPLC)].The two experimental groups of the first trial,D18 and D34,were the two controls used in the trial 1 for “Study on the degree and mechanism of resistance to S.japonicum reinfection in water buffaloes” in which the animals were respectively treated with two oral doses[25mg/kg body weight(with a maximum of 10 g)] of PZQ on days 19,18(D18)and on days 35,34(D34)before infection.The animals in experimental group D8 of the second trial were equally treated with PZQ(actual effective dose 5 mg/Kg)on days 9 and 8 before infection.Animals in blank group of both trials were not treated with PZQ.In the first trial,the developmental rate of parasites in the D18 group was reduced by 91.1% compared with the control group,but not in the D34 group.Compared with D34 group,a 94.6% worm reduction,a 95.7% of liver egg reduction and a 97.9% rectum egg reductions were obtained in D18 group.In the second trial,the worm reduction rate was 31% in the D8 group compared with the control group,and the reduction rate of liver eggs was 100%.However,no reduction in the number of eggs of the rectum was observed.At the same time,morphological observations revealed that the matured worms from D18 in the first trial and D8 in the second trial were significantly shorter(D18 compared with D34 group,D8 group compared with blank control).We also measured the level of cytokines(IL-4,IL-5,IL-7,IL-10,IFN-γ)and antibody(IgG)in peripheral blood at different time points in the two trials.The results showed that the buffalos treated with PZQ had higher level of antibody and cytokines from 8 to 18 days after administration(before infection)and early infection with Schistosoma(28 days).The results of this study revealed that oral administration of PZQ can induce water buffalos to prevent S.japonicum infection for at least 18 days.In summary,our studies clarified that buffalos can effectively prevent reinfection after two infections & treatments and oral administration of PZQ can induce buffalo to prevent Schistosoma japonicum infection for at least 18 days,both were the first reportd. |
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