Dual infection of Ixodes ricinus ticks with two viruses of the tick-borne encephalitis complex.

Ixodes ricinus female ticks were inoculated with Skalica (SK) virus (non-pathogenic for adult albino mice by subcutaneous route) and 14 days later they were challenged with strain 198 of Tick-borne Encephalitis (TBE) virus (highly pathogenic for adult albino mice by subcutaneous route). After additional 14 days of incubation, 42.9 to 65.0% of the adult (10-12 g) albino mice infested with these double infected ticks developed antibodies to TBE without signs of sickness (transmission of SK virus), while paralysis or death was registered in 35.0 to 57.1% of infested mice (transmission of strain 198) depending on the concentration of strain 198 used for inoculation of ticks. However, a low degree of interference to superinfection with strain 198 was observed, when the dissected tick salivary glands were examined by subcutaneous inoculation of adult albino mice (more than 90% of examined salivary glands contained strain 198 virus).