Tick-host ecology in the southeastern U.S. and its implications for Lyme disease

Background/Question/Methods

Throughout the United States, the incidence of human Lyme disease cases varies on a latitudinal cline along the eastern seaboard, with higher incidence of disease in the north. However, the Lyme disease vector Ixodes scapularis, and reservoir hosts for the Lyme etiological agent Borrelia burgdorferi, occur sympatrically throughout the eastern U.S. making it unclear why prevalence of disease differs between locations. In association with a larger NSF funded study, the goal of this project was to determine species composition in the area, the tick burdens of potential hosts (particularly mice (Peromyscus sp.) and skinks (Plestiodon sp.) and how they may influence disease transmission. We examined the distribution of larval and nymphal I. scapularis on hosts at the Savannah River Site (SRS) in South Carolina from spring 2010 - spring 2012 and in the New Jersey Pine Barrens (NJ) from June - September 2011. Three replicated arrays were at each site where a wide range of methods in capturing animals was utilized, including traditional methods such as Sherman traps, pitfall arrays, and novel techniques like burlap bands that targeted certain lizard species. Questing ticks were collected with traditional flagging and dragging techniques.

Results/Conclusions

During this study, there were defined nymphal and larval peaks with emergence at different times with nymphs preceding larvae both in NJ and SRS. Plestiodon species were parasitized by I. scapularis significantly more often than mice at SRS (P<.0001). Tick burdens found on Peromyscus species in NJ and SRS were significantly different (P<.0001) with a significant difference in where ticks were located on animals (P<.0001). Flagging and dragging produced low numbers of juvenile I. scapularis at SRS which is congruent with past studies in the southeast. The difference in host utilization by I. scapularis in NJ and SRS, the difficulties in flagging/dragging questing juvenile ticks in the south, and the high occurrence of ticks on Plestiodon species suggests possible behavioral differences in I. scapularis found in the southeast compared to the northern U.S. Behavioral differences may account for the lower human Lyme disease cases in the south even if ticks, pathogens, and reservoir hosts are present in an area. If juvenile I.scapularis are questing in leaf litter and not on vegetation as in the north, human encounters with ticks would be lowered. Other institutions associated with this project are conducting studies that may further support these findings.