Masters Theses

Date of Award

12-2009

Degree Type

Thesis

Degree Name

Master of Science

Major

Wildlife and Fisheries Science

Major Professor

Graham Hickling

Committee Members

Carl Jones, Reid Gerhardt, Lisa Muller

Abstract

Lyme disease (LD), caused by the bacterium Borrelia burgdorferi and transmitted by blacklegged ticks (Ixodes scapularis), is the most commonly reported vector-borne disease in the United States. Lyme disease is endemic in northeastern states, whereas southern states report far fewer cases. This research evaluated the potential LD health risk to humans associated with blacklegged ticks in Tennessee.

I surveyed 1,018 hunter-harvested deer from 71 counties in fall 2007 and fall 2008. Of these, 160 (15.7%) from 35 counties were infested with I. scapularis — 30 of the counties were new distributional records for this species.

I also evaluated the seasonal phenology of I. scapularis at Henry Horton State Park (HHSP) in middle Tennessee by drag sampling and small mammal trapping from November 2007 to May 2009. Larval I. scapularis numbers per 1000m2 dragged peaked at 4.1 ± 2.9SE in July, nymphs peaked at 5.0 ± 3.5SE in March, and adults at 12.0 ± 1.2SE in November. Overall, 191 mice (Peromyscus spp.) were captured on 355 occasions – I. scapularis ticks were present on 68 (19%) of these occasions. Larval I. scapularis infestation of mice peaked in June (8 of 12 mice; 67%); nymphal infestation peaked in May (3 of 16; 19%).

DNA was extracted from the I. scapularis collected from deer (883 samples), and at HHSP (283 samples) and tested for B. burgdorferi and other Borrelia using PCR targeting the 16s-23s intergenic spacer region of these bacteria. No B. burgdorferi was detected, although four samples tested positive for B. miyamotoi.

I conclude that I. scapularis is far more widespread in Tennessee than previously reported. At HHSP, the abundance of this tick reaches levels that sustain endemic cycles of B. burgdorferi in the Northeast. Moreover, their seasonal phenology in Tennessee – whereby nymphal questing precedes larval questing – should favor B. burgdorferi transmission. Nevertheless, B. burgdorferi was not detected in these Tennessee tick populations, so the LD risk to humans posed by I. scapularis in Tennessee appears to be very low at the present time. Future ecological studies are needed to explain the lack of B. burgdorferi infection in these Tennessee ticks.

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