Studies On The Relationship Between The Genetic Characteristics And Pathogenicity Of Schistosoma Japonicum

Objective: Schistosomiasis is a prevalent zoonotic parasitic disease, which is severely harmful to human health. China, as one of the most affected countries, has the most prevailing epidemic disease of schistosomiasis japonica. Schistosome life cycle is complex, asexual proliferation in the middle host(snail), while sexual reproduction in the definitive host(mammal). Studies concerned about genetic dissimilarity and heterozygosity of schistosome individual influencing its mate choice in the definitive host, had been reported. However, whether schistosome individual genetic differences influence their final host’s pathogenicity, yet rarely studied. Therefore, this study use microsatellite loci markers for S.japonicum DNA genotyping, to calculate the genetic dissimilarity and heterozygosity difference between mates and observe them relationship with pathogenicity of S.japonicum in the definitive host. Our work will contribute to understanding the pathogenicity and epidemic of S. japonicum characteristics, as well as providing new ideas to control schistosomiasis.Methods: The snails infected with single miracidia and the sex of cercariae shedding from the snails were predetermined before infection of vertebrate hosts. A group of two BALB/c mice were individually infected by using 5 female cercariae shedding from one snail and 10 male cercariae shedding from another snail randomly paired. The excess of males can ensure that all females would have been mated. After five weeks’ infection, we first collected schistosomiasis individual and counted the number, then calculated liver weight/body weight/worm pair and spleen weight/body weight/worm pair, the mean number of eggs per worm pair in the liver and intestinal tissue, the hatching rate of deposited eggs and the average diameter of granuloma in the liver.Extracted DNA from male and female worms, multiplex PCRed by applying microsatellite loci, the amplified fragment length product was detected by the Shanghai Biological Engineering(Sangon) Limited testing. Used software SPAGe DI 1.4 to estimate r coefficient to get gene similarity for pairs of schitosomes. Heterozygosity was calculated as the number of heterozygous loci divided by the total number of loci. We defined △H as the difference in heterozygosity between the male and the female worms, △H =male heterozygosity―female heterozygosity.Results:1. There was a significant correlation between the genetic similarity of S.japonicum mates and the mean number of eggs per worm pair in the liver(r=0.5016, P=0.0478) and the mean number of eggs per worm pair in the intestinal tissue(r=0.7965, P=0.0002) and the hatching rate of deposited eggs in the liver(r=0.5083, P=0.0444); there was no correlation between the genetic similarity of mates and liver weight/body weight/worm pair(r=0.1095, P=0.6865) and spleen weight/body weight/worm pair(r=0.2653, P=0.3206) and the average diameter of granuloma in the liver(r=-0.2727, P=0.3069).2. The heterozygosity difference of mates(△H) influenced the pathogenicity of S.japonicum in the definitive host. The mean number of eggs per worm pair in the intestinal tissue and the hatching rate of deposited eggs in the liver of △H<0(the male heterozygosity less than the female) were significantly higher(P=0.0023, P=0.0102, respectively) than △H=0(the heterozygosity of mates were equal). The mean number of eggs per worm pair in the intestinal tissue and the hatching rate of deposited eggs in the liver of △H>0(the male heterozygosity more than the female) were significantly higher(P=0.0069, P=0.0161, respectively) than △H=0(the heterozygosity of mates were equal). Liver weight/body weight/worm pair and spleen weight/body weight/worm pair of △H=0 were significantly higher(P=0.0164, P=0.0153, respectively) than △H<0; Liver weight/body weight/worm pair and spleen weight/body weight/worm pair of △H=0 were significantly higher(P=0.0040, P=0.0105, respectively) than △H>0; The mean number of eggs per worm pair in the liver and the average diameter of granuloma in the liver were no significant difference(P> 0.05) among the groups of △H<0, △H=0, △H>0; But these all indicators were no significant difference between △H<0 and △H>0(P> 0.05).Conclusions:1. There is correlation between genetic dissimilarity of mates and pathogenicity of S.japonicum in the definitive host, the genetic dissimilarity is greater while the pathogenicity in the definitive host is weaker; one potential explanation for such negative correlation may be “trade-offs”, a trade-off in pathogenicity and transmission, negative correlation between parasite reproductive success in definitive and intermediate hosts may also be relevant.2. Effects on pathogenicity and transmission in the definitive host infected with heterozygosity difference of the S. japonicum mates.Compare to the mates with equal heterozygosity, the mates with different heterozygosity has higher transmission in the definitive host. However, The mates with equal heterozygosity has higher pathogenicity in the definitive host.3. Analysis of genetic dissimilarity and heterozygosity difference help us to understand the pathogenicity and transmission characteristics of Schistosoma japonicum in the definitive host, meanwhile contribute to providing more effective new ideas to control schistosomiasis.