Coyotes, Red Foxes, and the Prevalence of Lyme Disease

Lyme disease is the most prevalent vector-borne disease in north temperate areas worldwide, with the majority of cases reported in the northeastern United States. The transmission cycle involves ticks, deer, small mammalian hosts such as mice, and numerous other species. Levi et al. (2012) suggested that Canis latrans (Coyote) abundance and Vulpes vulpes (Red Fox) scarcity are strong predictors of Lyme disease cases in eastern North America, with Odocoileus virginianus (White-tailed Deer) abundance being less important. This suggestion was based on correlations of disease dynamics with human harvests of canids, as it has been suggested that Red Foxes occur at a lower abundance because of Coyote predation. Because Red Foxes are more effective predators of small mammals, the authors of that work contend that the lower Red Fox abundance results in an increase in the incidence of Lyme disease. This paper re-examines the evidence used by Levi at al. (2012) to reach their conclusions. We address the following points: 1) Levi et al. did not provide data on rodent populations or Lyme disease incidence; 2) Coyotes eat rodents, so a Coyoteinduced reduction of Red Fox populations might not result in increased rodent populations; 3) Coyote harvests are poor indicators of Coyote abundance; 4) both Red Fox numbers and rodent numbers fluctuate dramatically due to factors such as disease and weather; 5) some of the data used by Levi et al. (2012) were from regions with western Coyotes, while other data were from areas with hybrid eastern Coyotes, thus confounding the situation; and 6) Levi et al. did not consider important alternative hypotheses, such as habitat fragmentation and climate change. Additionally, the historical dynamics of the Lyme disease system are unknown given that Canis lupus lycaon (= Canis lycaon) (Eastern Wolf) and Urocyon cinereoargenteus (Gray Foxes) originally lived in most of the northeast, while Red Foxes and Coyotes were historically absent from most of the area. We suggest proceeding with caution before concluding that the presence of Coyotes (or the reduction of Red Foxes) is the primary cause of increased incidence of Lyme disease cases in the eastern United States.