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Tính sẵn có của mô hình tinh tinh cho phép xác định titres lây nhiễm của huyết thanh có chứa NANBH.26, 33 điểm Cuối titres lây nhiễm, quy định như pha loãng lớn nhất của inocula mà tại đó 50% các loài động vật bị nhiễm, được xác định cho một số lâm sàng mẫu liên quan trong việc truyền tải của bệnh | The availability of the chimpanzee model permitted the determination of infectivity titres of sera containing NANBH.26 33 End-point titres of infectivity defined as the greatest dilution of the inocula at which 50 of the animals became infected were determined for several clinical samples implicated in the transmission of the disease. The results of these titration studies showed that the end-point infectivity titre of NANBH is generally very low ranging from 100 to 102.5 50 chimpanzee infectious doses CID50 per mL. Only two inocula among those reported to date had a high infectivity titre 106.5 mL each .33 34 Thus the infectivity of NANBH viruses in serum is markedly lower than that commonly observed in HBV 108 26 and HDV infection 1011 .38 This feature of NANBH may help to explain the difficulties initially encountered in transmission studies before the introduction of pedigreed inocula as well as the difficulty encountered in attempting to identify the causative agent. Physico-chemical properties of the NANB agent Most of the physico-chemical properties of the putative agent of NANBH have been determined in experiments utilizing the chimpanzee. Both in humans and in experimentally infected chimpanzees studies of serum and liver biopsies by electron microscopy EM failed to identify virus-like particles specific for NANBH. This failure most probably stemmed from the low infectivity titres of virus in clinical materials. The absence of any serological assays and the inability to grow the virus in vitro further hampered the characterization of the causative agent. Infectivity studies in chimpanzees demonstrated that the agent was stable at pH 8.0 but could be inactivated by formalin at a concentration of 1 1000 at 37 C for 96 hours39 or 1 2000 at 37 C for 72 hours.40 Infectivity could be abolished by heating at 100 C for 5 minutes40 or at 60 C for 10 hours.39 Complete inactivation of the agent was also achieved by heating at 60 C for 30 hours after lyophilization 41
