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.