Decline of foxes, not increases in deer, mirrors rise in Lyme disease cases

A rise in Lyme disease cases in some parts of the United States might be partly explained by declining populations of red foxes, according to a study. Taal Levi and colleagues performed mathematical modeling to determine why the incidence of Lyme disease continues to rise across parts of North America despite stabilized numbers of deer, long known to act as reproductive hosts for adult ticks that carry Lyme disease bacteria, in those regions. The authors’ analysis revealed that increases in Lyme disease across the northeastern and midwestern United States over the past three decades coincide with shrinking populations of a mammalian predator – the red fox, which feeds on small mammals, such as white-footed mice, short-tailed shrews, and Eastern chipmunks, all of which transmit Lyme disease bacteria to ticks. Dwindling numbers of red foxes, the authors suggest, might be attributed to expanding populations of coyotes, top predators whose ranks are swelling in regions previously occupied by wolves. Spatial analyses also revealed that regional differences in Lyme disease risk are related to regional differences in coyote and fox abundance. According to the authors, the findings suggest that population fluctuations among top predators might influence the emergence of vector-borne diseases.

Article #12-04536: “Deer, predators, and the emergence of Lyme disease,” by Taal Levi, A. Marm Kilpatrick, Marc Mangel, and Christopher C. Wilmers

MEDIA CONTACT: Taal Levi, Department of Environmental Studies, University of California, Santa Cruz, CA; tel: 831-332-7873; e-mail: thetaaltree@gmail.com