The Research Platform Of Mice Model For Fasciola Gigantica Experimental Infection: Preliminary Study

Fascioliasis, which mainly invade the hepatobiliary system, is always difficult to give an instant diagnosis, even if the pathogenic parasites have been eliminated by chemical treatment, the hepatic tissue injury caused by fluke parasitism is too extensive to be repaired. Therefore, a clearer understanding of the mechanism about liver injury by Fasciola gigantica infectionhas extremely important implications for the mechanism of interplay between F.gigantica and experimental animal host,as well as the therapy and functional recovery of host hepatobiliary system post parasiticinfection. With these aims, this study has successfully improvedand optimizedan in-laboratorial culture system for F.gigantica metacercariae, established the Kuming mice (KM mice) model for F.gigantica infection, and some preliminary research of hepatic pathology on infected KM mice, which together allows to make a solid foundation for the further works, i.e. hepatic immunity against F.gigantica, and enovation of damaged tissue.To improve and optimize the previous methodology of F.gigantica metacercariae cultural in laboratory, and to observe the fluke development in the specific intermediate host Galba pervia (Gastropoda:Mollusca). In this experiment, snails with two different shell size were used as the snail hosts: 2-3mm shell-length snails, and 5-7mm shell-length snails.Both the large and small snails were infected with different miracidia doses (1,3, and 7). The results showed that:the miracidia developed into mother rediawithin 10 to 17 days post-infection (DPI) under room temperature (26℃). A rapid production of the longtail-larve form, cercaria, was observed fulfilled the daughter redia, and became metacercaria as early as 30 to 33 DPI. From the comparative analysis of the number of metacercaria liberated from one individual snail of each group, the optimal breeding condition of F.gigantica metacercariae is different from the condition of F.hepatica metacercariae, for the best F.gigantica metacercaria production, Gpervia snail with 3-5mm of shell length,infected by 3 miracidium at room temperature 26℃.To preliminarily establish the KM mice model for F.gigantica infection, mice were orally infected with 5,15,30 and 50 metacercariae, respectively, and non-infected KM mice were served as controls. The KM mice were sacrificed by stages,and parasite development and distribution, as well as the lesson and pathological changes in the liver were all highly concerned during the observation. The results showed that some flukes had found migrating into the liver parenchyma after 5 DPI, and in the common bile duct during 35～42 DPI, however, none adult-stage fluke was found.The aberrant migration cases were observed frequently,and some individuals were recovered from non-hepatic sites, lung tissue, oral cavity, diaphragm, or forelimb subcutaneous i.e.The pathological changes of the liver,caused by F.gigantica,could be summarized as disseminated bleeding, purulent, steatosis, fibrosis, necrosis, cirrhosis, and the size of lesions was increased with the dosage of infection.This experiment indicates:KM mice has the capability tobe infected by F.gigantica and used as the small animal infection model for the relevant studies. Fifteen-metacercariae dosage is the optimal infection dose for dynamically observatory of the host infection status.Observations of the pathological changes in liver of KM mice infected with F.gigantica showed:on 7 DPI, slight tissue damage was found in the liver parenchyma, and disorder of hepatic cells were observed by microscope as well. After that, the liver damage was gradually increased, and the typical pathological changes of the liver tissuewere observed, including liver cell necrosis, connective tissue hyperplasia, and inflammatory cell infiltration.Tests of ALP, AST, ALT, TP, ALB and GLOB levels in serum samples showed:the AST level in serum began to rise on 3 DPI,elevated significantly on 21～56 DPI (P<0.01), and reached the peak on 49 DPI.ALT began to rise on 14 DPI, elevated on 21～56 DPI (P<0.01), peaked on 49 DPI. ALP elevated obviously on 14～21 DPI, decreaseon 35～49 DPI, and rose again on 56 DPI.GLOB showed a general upward trend on 21～56 DPI, whereas ALB showed a downward trend since the infection begun, then reached the lowest value on 49 DPI. It was evident that the serological factors associated liver pathological changes were consistent with the progress of liver injury,and the serological aminotransferase changes occurred earlier than histopathological characterization. Moreover, AST and ALT can be used as indicators of the acute phase of infection, while the range values of ALB, GLOB and A/G ratio can be intended to assess the degree of hepatic tissue inflammation and fibrosis caused by parasitic Egigantica.These results suggests that joint application of these serological indexes above is of great significance during the diagnosis and prognosis of fascioliasis.