Louping ill virus (LIV) in the Far East.

This study focused on finding, culturing, and identifying the biological and genetic characteristics of three louping ill virus (LIV) strains in the south of the Russian Far East. The Primorye-155-77 and Primorye-20-79 virus strains were isolated from Ixodes persulcatus ticks, and the Primorye-185-91 strain was isolated from the blood of a person after a tick bite. According to the hemagglutination and neutralization tests, Primorye-155-77, Primorye-20-79 and Primorye-185-91 had weak reactivity with antibodies in an antiserum against tick-borne encephalitis virus. In Primorye-155-77 and Primorye-20-79, the sequences of the 5' ends of the 2456-nucleotide-long viral RNA including the 5' untranslated region (UTR) and genes of the capsid protein, prM protein and envelope E protein were determined. The complete genome sequence of Primorye-185-91 was determined. The E protein gene of the Negishi strain differed from those of three analyzed strains, as there were mutations resulting in the replacement of three amino acids: Ala163Thr, Asp193Asn and Ala313Thr. The homology of Primorye-185-91 to LIV 369/T2 was 97.57 %, and to the Penrith strain, it was 98.36 %. Phylogenetic analysis showed that Primorye-155-77, Primorye-20-79 and Primorye-185-91 are related to LI/A and LI/K strains isolated in England and Scotland and to the Negishi strain; these strains have a common progenitor. Negishi-like strains were represented by one subtype of louping ill virus, i.e. the British subtype (LIV-Brit). The possibility is discussed of a single introduction of the virus to the Far Eastern region (Japan and Primorsky Krai) from a single natural locus more than 50 years ago.

The nature of replication of tick-borne encephalitis virus strains isolated from residents of the Russian Far East with inapparent and clinical forms of infection.

We describe the biological properties and molecular characteristics of complete genomes of 33 tick-borne encephalitis virus (TBEV) strains that induced different forms of infection, from inapparent to severe focal ones resulting in fatal outcome. Hemagglutinating activity of Oshima-like strains was higher at pH 5.8, while activity of Sofjin- and Senhzang-like strains were higher at pH 6.2 and 6.8, respectively. We determined susceptibility of porcine kidney (PK) cell cultures to these TBEV strains by cytopathic effect (CPE), plaque formation, and size of plaques. The clinical TBEV strains had higher virus titers both in tissue culture infectious dose 50(TCID50) and in plaque-forming unit (PFU) titers and larger plaques than the inapparent strains. A comparison of virus multiplication kinetics by PFU in culture fluid with kinetics of ELISA antigen and hemagglutinin accumulation suggested a different mechanism of interaction between these virus strains and PK cells at the initial stage of cell infection.