Survival dynamics of tick-borne encephalitis virus in Ixodes ricinus ticks.

Biotic factors contributing to the survival of tick-borne viruses in nature are poorly understood. Using tick-borne encephalitis virus (TBEV) and its principal European vector, Ixodes ricinus, we examined the relative roles of salivary gland infection, co-feeding transmission, and moulting in virus survival. Virus titres in the salivary glands increased after blood-feeding in a time- and dose-dependent manner. This was observed in ticks infected by inoculation but not in ticks infected by the natural route of co-feeding. Amplification of infection prevalence occurred via co-feeding. However, when larvae or nymphs subsequently moulted, the infection prevalence dramatically declined although this was not observed when ticks were infected by inoculation. Trans-stadial survival is a hitherto overlooked parameter that may contribute to the low incidence of TBEV infection in field-collected I. ricinus ticks.