Molecular hybridization with cloned fragments of tick-borne encephalitis (TBE) virus cDNA in acute and chronic TBE infection.

Recombinant plasmid DNA was used as a probe to detect tick-borne encephalitis (TBE) virus RNA during incubation period, acute disease and persistent infection of syrian hamsters. Within the first three weeks post-infection the results of direct virus isolation and RNA detection in the brain agreed by a rate of 100%, the virus titre ranging between 10(1.9) to 10(10.5) LD50/ml and viral RNA concentration at 1-1000 pg. At the same time TBE virus RNA was detected in the spleen when the virus titre was greater than or equal to 10(6.5) LD50/ml. By 8 months post infection (p.i.) viral RNA was found in the brain, liver, and spleen in the absence of infectious TBE virus. No viral RNA was present in the thymus. In addition, electron microscopic findings in hamster brain confirmed the hypothesis that TBE virus persistence was accompanied by formation of virus-specific structures but impaired virion maturation.