Persistence and transmission of tick-borne viruses: Ixodes ricinus and louping-ill virus in red grouse populations

Transmission of louping ill virus between infected and uninfected ticks co-feeding on mountain hares

Most of the data on oral infection of ticks by louping ill virus have been obtained from experiments in which animals were infected by syringe inoculation with infectious material. Using infected ticks to mimic the natural situation, we have demonstrated that louping ill (LI) virus transmission can occur from infected to uninfected Ixodes ricinus feeding in close proximity on mountain hares (Lepus timidus). Under these conditions the hares developed either low or undetectable viraemias. Highest prevalence of LI virus infection was observed in recipient nymphs which had fed to repletion between days 3 and 7 post-attachment of virus-infected adults; following engorgement, 56% of nymphs acquired virus. These results demonstrate the efficient transmission of LI virus between co-feeding ticks on naive mountain hares. However, when ticks were allowed to co-feed on virus-immune hares a significant reduction in the frequency of infection was observed. Neither red deer (Cervus elaphus) nor New Zealand White rabbits supported transmission of LI virus. The significance of virus transmission between cofeeding ticks on LI virus epidemiology is discussed.

Co-feeding ticks: Epidemiological significance for tick-borne pathogen transmission

Until recently, the transmission of tick-borne pathogens via vertebrates was thought to depend on the development of a systemic infection in the vertebrate hosts. Pathogen transmission has now been shown to occur between infected and uninfected ticks co-feeding in time or space in the absence of a systemic infection, originally for viruses, but now also for bacteria. The epidemiological consequences of this new non-systemic transmission pathway necessitate a major reassessment of the components and dynamics of tick-borne pathogen enzootic cycles. Here Sarah Randolph, Lise Gern and Pat Nuttall show that a much wider range of natural hosts than was previously recognized may contribute significantly to the transmission of tick-borne diseases, and compare quantitatively the relative contributions made by the systemic and non-systemic transmission pathways.