Land use change is widely documented as a driver of vector-borne disease (VBD) distribution and frequency. As land use is altered by expansion of urban and peri-urban development, fragmentation and expanded interfaces of human habitation with vector and host environments is common. Although resultant spatial patterns of human exposure have been documented and land use designs have been suggested to moderate human exposure to disease vectors, expanding urban/suburban areas in the southeastern United States (US) generally do not consider effects of rampant development on human risk of VBDs. The Charlotte, NC, metropolitan area of Mecklenburg and surrounding counties, is one of the fastest growing in the US. In Mecklenburg, three different tick species, each potentially infected with a different Rickettsia bacterium, occur. Field surveys, from the urban parks of Charlotte to the rural areas of the county, examined the distribution and habitat use of these ticks and their pathogen infection rates. Subsequently, seasonal phenology of Amblyomma americanum, a species believed to be expanding its range, was surveyed. Circuit theory and resistance surface modeling were applied to examine spatial patterns of local expansion by A. americanum from established populations.
Results/Conclusions
Mecklenburg field surveys show that: A. americanum is a relatively uncommon forest species with a high (75%) rate of R. amblyommii infection. A. maculatum is a common old field/edge species also with a 61% rate of R. parkeri infection; and Dermacentor variabilis is a relatively rare habitat generalist with a modest (14%) infection rate for R. rickettsii. Based on A. maculatum abundance and widespread habitat distribution, R. parkeri is likely the most common cause of human rickettsiosis cases in Mecklenburg. Monthly sampling for A. americanum revealed the presence of several locally established populations, the transient appearance of propagules, and no detection in most forest stands. Modeling indicated little resistance to A. americanum dispersal from current localized populations, suggesting the patchy distribution of this species results from habitat-specific microclimate conditions for tick survival. Collectively, these results suggest land use will expand risk of human exposure to A. maculatum while perhaps decreasing exposure to A. americanum. Control of human exposure to tick-borne diseases should thus focus on edge habitat expansion and management in the peri-urban fringe surrounding the intensive urban development of Charlotte, while continued development of wooded nature preserves would have little effect on tick-borne disease.