COS 96-2 - The dual role of lizards in Lyme disease ecology in the far-western United States

Thursday, August 11, 2011: 8:20 AM
10B, Austin Convention Center
Andrea Swei, Biology, San Francisco State University, San Francisco, CA, Cheryl J. Briggs, Dept. of Ecology, Evolution & Marine Biology, University of California, Santa Barbara, Santa Barbara, CA, Robert S. Lane, Environmental Science, Policy, and Management, University of California - Berkeley, Berkeley, CA and Richard S. Ostfeld, Cary Institute of Ecosystem Studies, Millbrook, NY
Background/Question/Methods The distribution of vector meals in the host community is an important element of understanding and predicting vector-borne disease risk. Lizards (such as the western fence lizard; Sceloporus occidentalis) play a unique role in Lyme disease ecology in the far-western United States. Lizards rather than mammals serve as the blood meal hosts for a large fraction of larval and nymphal western black-legged ticks (Ixodes pacificus – the vector for Lyme disease in that region) but are not competent reservoirs for the pathogen, Borrelia burgdorferi.  Prior studies have suggested that the net effect of lizards is to reduce risk of human exposure to Lyme disease, a hypothesis that we tested experimentally. 

Results/Conclusions Following experimental removal of lizards, we documented incomplete host-switching by ticks (5.19%) of larvae switched from lizards to other hosts. Larval tick burdens increased on woodrats, a competent reservoir, but not on deer mice, a less competent pathogen reservoir. However, most larvae failed to find an alternate host. This resulted in significantly lower densities of nymphal ticks the following year. Unexpectedly, the removal of reservoir-incompetent lizards did not cause an increase in tick infection prevalence.  The net result of lizard removal was a decrease in the density of infected nymphal ticks, and therefore a decreased risk to humans of Lyme disease. Our results indicate that an incompetent reservoir for a pathogen may, in fact, increase disease risk though the maintenance of higher vector density and therefore, higher density of infected vectors.

Copyright © . All rights reserved.
Banner photo by Flickr user greg westfall.