Conspicuous impacts of inconspicuous hosts on the Lyme disease epidemic

Abstract

Emerging zoonotic pathogens are a constant threat to human health throughout the world. Control strategies to protect public health regularly fail, due in part to the tendency to focus on a single host species assumed to be the primary reservoir for a pathogen. Here, we present evidence that a diverse set of species can play an important role in determining disease risk to humans using Lyme disease as a model. Host-targeted public health strategies to control the Lyme disease epidemic in North America have focused on interrupting Borrelia burgdorferi sensu stricto (ss) transmission between blacklegged ticks and the putative dominant reservoir species, white-footed mice. However, B. burgdorferi ss infects more than a dozen vertebrate species, any of which could transmit the pathogen to feeding ticks and increase the density of infected ticks and Lyme disease risk. Using genetic and ecological data, we demonstrate that mice are neither the primary host for ticks nor the primary reservoir for B. burgdorferi ss, feeding 10% of all ticks and 25% of B. burgdorferi-infected ticks. Inconspicuous shrews feed 35% of all ticks and 55% of infected ticks. Because several important host species influence Lyme disease risk, interventions directed at a multiple host species will be required to control this epidemic.

Figure 1

Distribution of larval blood meals across host species. Estimate of the blood meals taken from each species using molecular data (box and whiskers) matches the estimate using independent ecological data (line). More than 50% of ticks take their larval blood meal from species with low reservoir competence (LRC). 1, estimates from signature matching analyses; 2, estimates from inverse model including category LRC; 3, estimates from inverse model including squirrels; 4, empirical estimates from traditional trapping methods.