The basic reproductive number of tick-borne encephalitis virus. An empirical approach

Tick-borne encephalitis virus (TBEV) is reciprocally transmitted between Ixodes ricinus ticks and small mammals. Recently, transmission between co-feeding ticks has been postulated as an epidemiological by important mechanism of perpetuating the agent. To empirically examine the question whether the "traditional" mode of transmission is sufficient to maintain enzootic TBEV transmission, the basic reproductive number R(0) of TBEV could be estimated under this model for sites in which TBEV is enzootic. I propose an empirical estimator of R(0) for TBEV which is based on longitudinal stage-specific local tick infestation densities assessed by live trapping of small mammals. A Gibbs sampler-based 95%-credibility interval is presented. When applied to published field data from TBEV enzootic sites sub-critical R(0) estimates are obtained for both sites. I discuss potential shortcomings of this method and possible implications of these findings on the discussion of supplemental mechanisms of transmission.