Role of topographic corridors and small mammals in facilitating the spread of Lyme disease from southwestern Virginia to northwestern North Carolina

UNCG Author/Contributor (non-UNCG co-authors, if there are any, appear on document)
Reuben Akwei Garshong (Creator)
The University of North Carolina at Greensboro (UNCG )
Web Site:
Gideon Wasserberg

Abstract: Lyme disease is the most important vector-borne disease in the United States. It is caused by the bacterium, Borrelia burgdorferi and transmitted by blacklegged ticks, Ixodes scapularis. An estimated 30,000 cases are reported to the CDC yearly from across the United States. Lyme disease cases in the Appalachian and western Piedmont foothills in northwestern North Carolina are rising, suggesting that there is an invasion of the disease in northwestern North Carolina. This study therefore set out to (1) evaluate if there are evidence for an invasion, and (2) understand how the invasion works and if northwestern North Carolina is a permissive area for Lyme disease establishment. Specifically, we do not know (1) how certain geographic features along the route of invasion may be influencing the spread of the disease, (2) whether the host community structure, and (3) seasonal tick lifecycle, are suitable for the establishment of Lyme disease enzootic cycle in northwestern NC. Hence, my specific goals were to: (1) determine the role of the New River as a potential route facilitating the spread of the pathogen and vector. (2) characterize the local and regional rodent community within northwestern North Carolina region, and (3) investigate the phenology of the life stages of the blacklegged tick vector within the region. For aim 1, I determined the role of the New River as a putative corridor for the spread of I. scapularis and B. burgdorferi by sampling ticks along a north-to-south gradient from southwestern Virginia to northwestern North Carolina using two 10-12 site flagging transects: one along the New River and a parallel one in the western NC Piedmont. My results showed (1) about thrice more I. scapularis density and 8% higher B. burgdorferi infection along the New River compared with the western Piedmont, (2) a more southern extent of the tick and pathogen along the New River compared with the western Piedmont, although the tick extended further southern than the pathogen in both the New River and western Piedmont. These results suggested that the New River is acting as a corridor that is facilitating the spread of Lyme disease from southwestern Virginia into northwestern North Carolina. The mechanism of invasion can be (1) tick-first (when the tick precedes the pathogen), (2) dual-invasion (when the tick and pathogen invade simultaneously), or (3) spirochete-first (when the pathogen already exists, awaiting the invasion of the tick). My result was indicative of the tick-first hypothesis. In aim 2, I trapped rodents in selected sites along the New River and the Western Piedmont, inspected them for attached ticks, and collected ear tissue samples for B. burgdorferi screening. Out of the 174 rodents captured, 89.14% of them were P. leucopus, the competent reservoir host of B. burgdorferi, with 74% more individuals in the western Piedmont than the New River. Out of the 172 rodents tested, 38 of them were positive for B. burgdorferi of which 63.2% were from the New River. Of the 38 rodents that tested positive, two were not P. leucopus (one eastern gray squirrel and one pine vole) All the 98 I. scapularis ticks on rodents were collected from P. leucopus with 91.8% of them from the New River. Ninety-two of the I. scapularis ticks from the rodents were tested with 26 out of the 30 of them that tested positive for B. burgdorferi coming from the New River sites. These results provide a further support for the role of the New River as a potential spread corridor and showed that the rodent community structure in the mountains and western Piedmont area is suitable for the establishment of an effective enzootic transmission system of B. burgdorferi. To evaluate the phenology of the tick and of the transmission cycles, in aim 3, I flagged the two sites that showed highest tick densities in my first aim (i.e., the Alleghany and Ashe County sites), each month for 12 months to obtain seasonal information on the life cycle of the I. scapularis ticks. The results showed a phenology pattern that was typical to that of the Lyme disease hyper-endemic regions in northeastern US. In this phenology pattern, the adults have two peaks (a lower one in early spring and a higher one in fall), and nymphs emerge in early spring before the emergence of larvae in mid-summer. Such a phenology is suited for an effective transmission of the pathogen among the wild rodents and humans, indicating that northwestern North Carolina is a suitable geographic region for the establishment of Lyme disease. Put together, these findings indicated that western North Carolina, specifically the New River valley area, is a hotspot for the establishment of Lyme disease and could serve as a focus from where the disease can further spread to neighboring counties. To control the spread of the B. burgdorferi from wild animals to susceptible hosts such as humans, there is the need for state regulated programs that will ensure that regular monitoring through enhanced active surveillance for I. scapularis within the region (and possibly statewide) and their control using acaricides, and periodic P. leucopus vaccinations in the northwestern North Carolina area. This control measure will ensure that the prevalence of the pathogen in wild rodents is kept low to reduce Lyme disease risk. Public health officials also need to educate people who live and visit areas in and around northwestern North Carolina on proper tick control such as the wearing of permethrin treated clothes when conducting outdoor activities, frequent checking of self for attached ticks when out in the woods and staying on demarcated paths when hiking in the woods. Information on what the early symptoms of Lyme disease are may also help to reduce the risk of Lyme disease becoming chronic in affected individuals. Future studies should include sampling ticks on hunter-harvested deer since this approach is the easier way to locate the ticks and usually show high I. scapularis detectability rate even when their densities are low. Also, other adjoining counties around the New River and its tributaries require investigation. It may also be important to aim at identifying other possible natural and artificial events around the northwestern North Carolina that may be influencing the disease invasion.

Additional Information

Language: English
Date: 2022
Lyme disease, North Carolina, Phenology, River corridor, Southeast, White-footed mouse
Lyme disease $x Environmental aspects $z New River (N.C.-W. Va.)
Lyme disease $z New River (N.C.-W. Va.) $x Epidemiology

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