Thursday, August 9, 2007 - 9:50 AM

COS 103-6: Estimating the importance of zoonotic reservoir hosts in pathogen transmission

Jesse Brunner and Richard S Ostfeld. Institute of Ecosystem Studies

By definition, all zoonotic pathogens are multi-host pathogens, infecting at least one, but typically many wildlife species plus humans.  The various host species, however, differ dramatically in their interactions with the pathogen, with some acting as reservoirs and amplifying pathogen populations, and others acting as “dilution hosts” or dead-ends for pathogens.  Determining the roles played by various wildlife species as zoonotic hosts, typically termed their “reservoir competence,” is a major challenge.  With vector-borne zoonoses such as Lyme disease, reservoir competence is often estimated by collecting vector ticks from field-caught vertebrate hosts and determining the proportion of ticks that acquire infection from that species of host (“realized reservoir competence”).  However, species can have low realized reservoir competence by virtue of either low infection prevalence or low transmission efficiency when infected.  Here we demonstrate a probabilistic model and likelihood framework for decomposing realized reservoir competence into its component parts: prevalence and transmission efficiency. To illustrate this method we reanalyze data from LoGiudice et al. (2003 PNAS) on the realized reservoir competence of 10 species (or groups) to estimate the relative contributions of prevalence and transmission efficiency in determining reservoir competence. We find that some host species have low realized reservoir competence because of low transmission efficiency despite high prevalence (raccoons and squirrels), whereas other hosts have low realized reservoir competence due to low prevalence (deer).  This method will allow investigators to distinguish physiological from ecological causes of variation in host-specific contributions to disease risk.

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