Mutations in the NS3 gene and 3 '-NCR of Japanese encephalitis virus isolated from an unconventional ecosystem and implications for natural attenuation of the virus

The T1P1 strain of Japanese encephalitis (JE) virus was recently isolated f rom paddy-free Liu-Chiu Islet in which natural JE antibody has been prevale nt. In mouse neuroblastoma-derived Neuro-2a cells, T1P1 appeared significan tly lower in virus productivity than another local isolate, CH1392. It impl ied that this new isolate possesses a characteristic viral replication patt ern other than that of CH1392. T1P1 has also shown lower neurovirulence, wh ich was reflected by a significantly higher LD50 (2.44 X 10(6) PFU) than CH 1392 (2.87 X 10(2) PFU). In comparison of the full-length RNA sequences bet ween T1P1 and CH1392, a total of 7 nucleotides, including 1 in preM/M and 2 each in NS3, NS5, and the 3'-end noncoding region (NCR), appeared differen t. Of them, only the changes in NS3 (position 325, T for CH1392, A for T1P1 ; and position 364, G for CH1392 and A for T1P1) resulted in substitutions of deduced amino acids. There were two additional nucleotide changes appear ing in the 3'-NCR. The amino acids 109 Phe and 122 Glu in NS3 of CH1392 wer e substituted by Ile and Lys, respectively, in T1P1, The unique growth prop erties and low virulence of T1P1 presented in this report were likely relat ed to abnormal enzymatic activity due to mutations of the NS3 gene (especia lly position 364) and possibly to the mutations in the 3'-NCR. The natural attenuation of T1P1 that has been circulating in paddy-free Liu-Chiu Islet may account for the absence of clinical JE cases in past years. (C) 2001 Ac ademic Press.