Isolation, Cultivation, and Characterization of Borrelia burgdorferi from Rodents and Ticks in the Charleston Area of South Carolina

ABSTRACT

Twenty-eight Borrelia burgdorferi isolates from the Charleston, S.C., area are described. This represents the first report and characterization of the Lyme disease spirochete from that state. The isolates were obtained from December 1994 through December 1995 from the tick Ixodes scapularis, collected from vegetation, and from the rodents Peromyscus gossypinus (cotton mouse), Neotoma floridana (eastern wood rat), and Sigmodon hispidus (cotton rat). All isolates were screened immunologically by indirect immunofluorescence with monoclonal antibodies to B. burgdorferi-specific outer surface protein A (OspA) (antibodies H5332 and H3TS) and B. burgdorferi-specific OspB (antibodies H6831 and H614), a Borrelia (genus)-specific antiflagellin antibody (H9724), Borrelia hermsii-specific antibodies (H9826 and H4825), and two polyclonal antibodies (one to Borrelia species and another to B. burgdorferi). Six of the isolates were analyzed by exposing Western blots to monoclonal antibodies H5332, H3TS, H6831, and H9724. All isolates were also analyzed by PCR with five pairs of primers known to amplify selected DNA target sequences specifically reported to be present in the reference strain, B. burgdorferi B-31. The protein profiles of six of the isolates (two from ticks, one from a cotton mouse, two from wood rats, and one from a cotton rat) also were compared by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. We conclude that the 28 Charleston isolates are B. burgdorferi sensu stricto based on their similarities to the B. burgdorferi B-31 reference strain.

Human cases of Lyme disease (LD) have been reported in 46 of the 48 contiguous states of the United States, with most cases recorded in the mid-Atlantic and northeastern areas, followed by the north central and northern California coastal regions. More than 13,000 cases of LD in 43 states were reported to the Centers for Disease Control and Prevention (CDC) in 1994; more than 15,000 cases were reported in 1998 (CDC, personal communication). Nevertheless, controversy as to whether LD occurs in the southern United States exists.

Clinical cases of LD in South Carolina have been reported, but there is disagreement as to whether they were true LD cases. In the absence of isolates of Borrelia burgdorferi, the etiologic agent of LD, from humans in South Carolina, epidemiologic evidence assumes great importance. Ixodes scapularis, the main tick vector of B. burgdorferi in most regions of the United States, is widely distributed in South Carolina and infests various vertebrates there, including humans. Serologic surveys for antibodies against B. burgdorferi in South Carolina rodents indicated a prevalence of 38% in cotton mice (Peromyscus gossypinus) in the eastern counties of Marion and Dillon. Moreover, putative B. burgdorferi isolates have been cultured from birds, rodents, and ticks in South Carolina. If these isolates are definitively confirmed to be B. burgdorferi, it would indicate that this pathogen is endemic and cycling enzootically in South Carolina. This would greatly strengthen the epidemiologic arguments for the likely presence of human cases of LD in that state.

Here we report the first isolation, cultivation, and characterization of 28 isolates of B. burgdorferi from ticks and rodents in the area of Charleston, S.C. These 28 spirochetal isolates are among 146 that we have obtained from ticks, rodents, and birds from seven geographic areas within five counties in South Carolina, encompassing sites in the Piedmont, Sandhills, Coastal Plain, and Coastal Zone regions of the state.

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