Order No: AAC 9637106    ProQuest - Dissertation Abstracts
Title:ECOLOGICAL STUDY OF THE LYME DISEASE SPIROCHETE, BORRELIA BURGDORFERI, IN SOUTH CAROLINA
Author:CLARK, KERRY LEE
School:UNIVERSITY OF SOUTH CAROLINA (0202) Degree: PHD
Date:1996 pp: 132
Advisor: WILLIAMS, DWIGHT C.
Source: DAI-B 57/07, p. 4168, Jan 1997
Subject: BIOLOGY, ENTOMOLOGY (0353); BIOLOGY, ECOLOGY (0329); HEALTH SCIENCES, PUBLIC HEALTH (0573)

Abstract: Rodents and ticks were collected in four regions of South Carolina during May 1994 through December 1995. A total of 237 rodents representing eight species was captured.

The most common species were cotton mouse, Peromyscus gossypinus (Le Conte) (n = 97), hispid cotton rat, Sigmodon hispidus Say & Ord (n = 60), and eastern woodrat, Neotoma floridana (Ord) (n = 49).

Of the 1,514 ticks recovered from these hosts, Ixodes minor Neumann (n = 818) was the most abundant, representing 54% of all host-attached ticks.

Other species parasitizing rodents were Dermacentor variabilis (Say) (n =346), Amblyomma maculatum Koch (n = 209), Ixodes affinis Neumann (n =89), and Ixodes scapularis Say (n = 52).

All five tick species parasitized cotton mice, cotton rats, and woodrats, which were found to be the most important small mammal hosts for ticks at the localities studied.

Of 3,535 host-seeking adult ticks collected from vegetation, I. scapularis (n = 1,627), Amblyomma americanum (L.) (n =1,052), and D. variabilis (n = 649) were most common.

Tissues of rodents and host-seeking adult ticks were cultured in an attempt to isolate the Lyme disease spirochete, Borrelia burgdorferi Johnson, Schmid, Hyde, Steigerwalt & Brenner.

Spirochetes were isolated from tissues of 71 rodents, revealing that 22 (68.7%) of 32 woodrats, 38 (51.3%) of 74 cotton mice, and 11 (25.0%) of 44 cotton rats tested were infected.

Rodent infection levels were significantly higher in the Coastal Zone than in other regions. Spirochetes were cultured from 31 (2.6%) of 1,192 questing ticks. Prevalence of spirochetes in I. affinis (19/73, 26%) was significantly higher than in I. scapularis (12/864, 1.3%) and other species (0/255, 0%) of ticks tested.

Two (8.6%) of 23 adult I. minor removed from woodrats also contained spirochetes.

Samples of isolates from rodents and ticks were confirmed as B. burgdorferi by polymerase chain reaction (PCR) and indirect flourescent antibody (IFA) assays.

These isolates are the first obtained from rodents and ticks in South Carolina, and the first recovered from the eastern woodrat, I. affinis, and I. minor. Ixodes minor was the only tick species which showed a significant positive association with spirochetal infection in rodents, and, among spirochete-infected hosts, was present in significantly greater numbers than other tick species.

More I. affinis parasitized spirochete-infected hosts than I. scapularis. Geographic distribution and seasonal activities of most stages and species of ticks, including the first detailed description of the seasonal activities for all motile stages of I. minor in the United States, is presented and discussed in relation to enzootic transmission of the Lyme disease spirochete.

Results of this study confirm that B. burgdorferi is endemic in South Carolina, and that an intense enzootic transmission cycle exists at sites in the Coastal Zone.

They also implicate I. minor as the primary enzootic vector of the spirochete in the Coastal Zone, and indicate that the high level of spirochetal infection in rodents from this region is a function of the combined involvement of I. minor, I. affinis, and I. scapularis in the enzootic transmission of B. burgdorferi.

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