this Discover article based on Richard Ostfeld's research. The article doesn't have much detail; the ScienceDaily report has a little more detail.
Lyme disease is big news in the North East and Mid West. Here's a very recent story from the detroit Free Press: Increase in Lyme disease cases might have a coyote connection
This report is based on this paper in PNAS: Deer, predators, and the emergence of Lyme disease.
The emergence of Lyme disease has been attributed to a century-long recovery of deer, an important reproductive host for adult ticks. However, a growing body of evidence suggests that Lyme disease risk may now be more dynamically linked to fluctuations in the abundance of small-mammal hosts that are thought to infect the majority of ticks. The continuing and rapid increase in Lyme disease over the past two decades, long after the recolonization of deer, suggests that other factors, including changes in the ecology of small-mammal hosts may be responsible for the continuing emergence of Lyme disease. We present a theoretical model that illustrates how reductions in small-mammal predators can sharply increase Lyme disease risk.