The effects of long-term prescribed burning on ticks and tick-borne pathogen prevalence

Abstract

Identifying methods for control of tick populations and reducing risk of tick-borne disease is critical. One promising method is prescribed fire. To determine the impacts of long-term prescribed burning on tick and pathogen dynamics, 21 sites in southwestern Georgia with varying burn regimes (burned surrounded by burned [BB], burned surrounded by unburned [BUB], unburned surrounded by burned [UBB], and unburned surrounded by unburned [UBUB]) were sampled monthly for 2 years. Simultaneously, data on other variables known to affect tick abundance (e.g. host abundance, vegetation structure, and micro- and macroclimate) were collected. In total, 47,184 ticks were collected, of which, 99% were Amblyomma americanum followed by Ixodes scapularis (0.7%) and fewer numbers of A. maculatum, Dermacentor variabilis, and 1 I. brunneus. Long-term prescribed burning significantly reduced tick abundance regardless of other variables and burn regimes. Furthermore, tick species composition differed with A. americanum dominating in UBUB sites and A. maculatum dominating in BB sites. To determine whether Solenopsis invicta (red imported fire ants [RIFA]) (typically associated with burned areas) and/or habitat type were driving tick dynamics in burned areas, an experimental field study in which A. americanum and A. maculatum nymphs were placed in enclosures assigned to three treatments (burned, RIFA present; burned, RIFA absent; and unburned, RIFA absent) was performed. A. maculatum survival was significantly greater than A. americanum survival in burned habitats (regardless of RIFA) and A. americanum survival was significantly greater in unburned habitat as compared to burned habitat. To further investigate impacts of burning on tick dynamics, all ticks collected during the field study were tested for pathogens including Rickettsia spp., Borrelia spp., Anaplasma phagocytophilum, and Ehrlichia spp. Prevalences of each organism (Rickettsia 6.7-66.7%, Borrelia 0-2.2%, E. chaffeensis 0-1.1%, E. ewingii 0-7.2%, and Panola Mountain Ehrlichia 0-3.8%) were similar to other studies in the Southeast. While long-term prescribed burning did not alter pathogen prevalence, the reduction in tick counts resulted in the density of infected ticks being 35 times lower in burned sites as compared to UBUB sites. Thus, long-term prescribed burning is an effective tool for controlling tick populations and ultimately reducing risk of tick-borne disease.