Deer, predators, and the emergence of Lyme disease

Background/Question/Methods ]

Lyme disease is the most prevalent vector-borne disease in North America and both the annual incidence and geographic range are still increasing. The emergence of Lyme disease was initially attributed to a century-long recovery of deer, an important reproductive host for adult ticks, but an incompetent host for the bacterial pathogen. However, a growing body of evidence suggests that Lyme disease risk is now more dynamically linked to fluctuations in the abundance of several species of disease amplifying small mammals that are responsible for infecting the vast majority of ticks. This evidence and the rapid increase in Lyme disease over the last decade, long after the recolonization of deer, suggests that changes in the ecology of small mammal hosts may be responsible for the continuing emergence of Lyme disease. 

Results/Conclusions

We show that small reductions in the density of small mammal predators can sharply increase Lyme disease risk. We then show that increases in Lyme disease in the northeastern and midwestern USA over the past few decades coincide with a range-wide decline of a key small mammal predator, the red fox, likely due to expansion of coyote populations. Further, we find that coyote abundance and fox rarity predict the spatial distribution of Lyme disease in New York, but that deer density is uncorrelated with Lyme disease incidence across states. These results suggest that changes in predator communities can have cascading impacts that facilitate the emergence of zoonotic diseases-the vast majority of which rely on hosts that occupy low trophic levels.