The incidence and emergence of tick-borne diseases, such as Lyme disease and ehrlichioses, has increased dramatically in the past several decades. Although this increase appears to be due to numerous factors, including enhanced diagnostics and increased reporting, one of the primary drivers is thought to be changing land use and management. This hypothesis underscores the importance of understanding land management impacts on tick populations as well as identifying how to control tick populations to reduce human disease risk.
Perhaps one of the most promising methods for controlling tick populations is prescribed burning, because it can be applied on a landscape level and is relatively time and cost efficient. Additionally, prescribed burning is a well- accepted form of ecosystem management and wildfire prevention. Several past studies have been conducted on the impacts of prescribed burns on tick populations, and the results have varied. However, these studies often did not simulate real-world land management practices and/or account for other variables known to affect tick populations such as host abundance and vegetation structure.
To investigate impacts of long-term prescribed burning on tick population dynamics and human disease risk, we performed a two-year study in southwestern Georgia at multiple locations with variable histories of more than ten years of operational burn management. Additionally, other factors known to potentially affect tick abundance (e.g., host abundance, vegetation structure, and microclimate) were evaluated at each plot. Collectively, these data provided insights into the efficacy of long-term prescribed burning for tick control and also revealed seasonality for numerous tick species in southwestern Georgia and northwestern Florida, an area for which there currently is little or no information on ticks or tick-borne pathogens.
Ultimately, we found that over the long-term, prescribed fires significantly reduced tick populations regardless of burn interval, host abundance, vegetation, or climate, with a 98% reduction in ticks observed in sites that were managed with any type of burning. Interestingly, we did not observe the recovery of tick populations after burns that previous studies reported. Instead, ticks simply were not present (or were present at very low numbers) in these sites for the duration of our study. Furthermore, these reductions also were observed in unburned sites immediately adjacent to burned sites, indicating that burning may be impacting tick dynamics beyond the area actually being burned. Burning also affected tick species composition, with unburned areas primarily harboring the lone star tick (Amblyomma americanum) and burned areas primarily harboring the Gulf coast tick (A. maculatum). Through follow-up studies, it was determined that the forest structure and resulting harsh microclimate achieved through long-term prescribed burning (minimal to no mid-story forest types, and semi-open pine canopy leading to hotter, drier conditions) was driving these trends. Thus, in order to achieve a healthy ecosystem and/or a reduction in ticks, the need for regular prescribed fires, not singular burns, has been underscored. Results from this part of the study recently were published in the journal Plos One (http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0112174).
Finally, all ticks collected during this study were tested for common, human, tick-borne pathogens including Ehrlichia spp., Borrelia spp., and Anaplasma phagocytophilum. Burning did not significantly affect tick-borne pathogen prevalence in the remaining ticks. However, taking into account the significant reductions in tick populations, burning does reduce the density of infected ticks in an area. On average, we calculated that an individual would encounter 0.02 infected ticks per hour in areas that were burned regularly as well as in immediately adjacent areas. However, an individual would encounter 0.70 infected ticks per hour in an unburned habitat. Thus, long-term prescribed burning can significantly reduce human tick- borne disease risk. (Prepared by Elizabeth Gleim, Oxford College, and Michael Yabsley)