Host specialization is a key issue in infectious disease research because patterns of cross-species transmission affect parasite dispersal.

In the northeastern United States, the Lyme disease agent, Borrelia burgdorferi sensu stricto, is maintained by enzoonotic transmission, cycling between white-footed mice (Peromyscus leucopus) and black-legged ticks (Ixodes scapularis). B. burgdorferi sensu stricto is genetically variable and has been divided into three major genotypes based on 16S-23S ribosomal DNA spacer (RST) analysis. To better understand how genetic differences in B. burgdorferi sensu stricto may influence transmission dynamics in nature, we investigated the interaction between an RST1 and an RST3 strain in a laboratory system with P. leucopus mice and I. scapularis ticks. Two groups of mice were infected with either BL206 (RST1) or B348 (RST3). Two weeks later, experimental mice were challenged with the opposite strain, while control mice were challenged with the same strain as that used for the primary infection. The transmission of BL206 and B348 from infected mice was then determined by xenodiagnosis with uninfected larval ticks at weekly intervals for 42 days. Mice in both experimental groups were permissive for infection with the second strain and were able to transmit both strains to the xenodiagnostic ticks. However, the overall transmission efficiencies of BL206 and B348 were significantly different. BL206 was more efficiently transmitted than B348 to xenodiagnostic ticks. Significantly fewer double infections than expected were detected in xenodiagnostic ticks. The results suggest that some B. burgdorferi sensu stricto strains, such as BL206, may be preferentially maintained in transmission cycles between ticks and white-footed mice. Other strains, such as B348, may be more effectively maintained in different tick-vertebrate transmission cycles.

Borrelia burgdorferi gene expression within the guts of engorging Ixodes scapularis ticks was examined by use of differential immunoscreening and differential expression with a customized amplified library. Fourteen chromosomal genes involved in energy metabolism, substrate transport, and signal transduction and 10 (4 chromosomal and 6 plasmid) genes encoding putative lipoproteins and periplasmic proteins were preferentially expressed in engorging ticks. These data demonstrate a new approach to the global analysis of B. burgdorferi genes that are preferentially expressed within the vector during feeding.Borrelia burgdorferi, the agent of Lyme disease, is transmitted when Ixodes ticks feed on mammals (5, 17). While the tick is engorging, the antigenic composition of B. burgdorferi changes dramatically (1,8,9,20,21). Analysis of differentially expressed genes will provide insights into the molecular changes that occur in spirochetes during tick feeding. Recent studies have focused on the expression profiles of only a few genes, such as ospA and ospC (12,15,20), erpT (10), bbk32 and bbk50 (11), and more recently rev, mlpA, erpa/i/n, and erpb/j/o (14), that are expressed in the tick vector. In order to systematically identify B. burgdorferi antigens that are differentially expressed during tick feeding, we have used an antibody-based approach, differential immunoscreening (24), and differential expression with a customized amplification library (DECAL), a new technique to examine the transcriptomes of prokaryotic genomes. DECAL was first developed and utilized for the global analysis of gene expression in Mycobacterium tuberculosis grown in vitro (2). The rationale for exploiting DECAL is based on the following factors: (i) the analysis can be performed with as little as 10 ng of total bacterial RNA and can detect differences in levels of gene expression that are as small as fourfold and (ii) the technique is ideally suited for investigations where contaminating host material is present.Differential immunoscreening of B. burgdorferi. Ixodes scapularis nymphs infected with B. burgdorferi strain N40 and either fed to repletion on C3H/HeN mice (9) or left unfed were dissected. The isolated guts were suspended in phosphate-buffered saline (10 l/tick gut) and homogenized. The number of spirochetes in each preparation was measured by direct immunofluorescence (9). Equivalent doses of B. burgdorferi (10 6 organisms) in complete Freund's adjuvant were used to immunize C3H/HeN mice after heat inactivating the spirochetes (1 h at 60°C). Control mice were immunized with gut extracts from uninfected I. scapularis nymphs. Ten days after the final booster injection, antisera against spirochetes from unfed and fed ticks were collected. A ZAP II-B. burgdorferi N40 expression library (10,000 plaques) was screened with antisera from unfed and fed ticks. Hybridizing plaques were visualized with a picoBlue immunoscreening kit (Stratagene, La Jolla, Calif.). About 100 clones hybridized to sera from both unfed and fed ticks. Seven positi...

The density of spirochetes in field-collected or experimentally infected ticks is estimated mainly by assays based on microscopy. In this study, A high degree of spirochete aggregation among infected ticks (variance-to-mean ratio of 24,877; moment estimate of k ‫؍‬ 0.279) was observed. From the frequency distribution data and previously published transmission studies, we estimated that a minimum of 300 organisms may be required in a host-seeking nymphal tick to be able to transmit infection to mice while feeding on mice. These data indicate that real-time qPCR is a reliable approach for simultaneous detection and quantification of B. burgdorferi infection in field-collected ticks and can be used for ecological and epidemiological surveillance of Lyme disease spirochetes.Hard ticks (Ixodidae) in the Ixodes persulcatus complex, such as Ixodes scapularis and Ixodes pacificus in North America, Ixodes ricinus in Europe, and Ixodes persulcatus in far eastern Russia and Asia, are the principal vectors of the Lyme disease spirochete, Borrelia burgdorferi, and several other tick-borne pathogens (2, 25). The incidence of human Lyme disease in areas where it is endemic is correlated with the abundance and prevalence of Ixodes ticks infected with B. burgdorferi (34). Moreover, studies of laboratory animals have suggested that the efficiency of host infection is determined in part by the number of spirochetes inoculated using a needle or deposited by the tick at the time of feeding (21, 27). Thus, monitoring B. burgdorferi density in host-seeking ticks will provide more accurate data for assessment of population risk of Lyme disease and the potential variability of disease manifestations after tick bites.Currently, the number of spirochetes in field-collected or experimentally infected Ixodes ticks is estimated mainly by microscopy-based assays in which the spirochetes are counted directly on tick midgut smears stained with fluorescently labeled specific antibodies (8, 9, 27) or on silver-stained histological sections of ticks (11,14). For specific detection of B. burgdorferi in field-collected adult I. scapularis ticks and monitoring of the spirochete kinetics during the tick life cycle, an OspA antigen-capture enzyme-linked immunosorbent assay (ELISA) was also developed (3-5). These methods are laborintensive, which limits the number of ticks that can be analyzed. Moreover, the sensitivities of these methods are relatively low, e.g., a lower detection limit of approximately 150 spirochetes was reported for the antigen-capture ELISA (5).Real-time PCR has features that allow for rapid detection of infectious pathogens in environmental or experimentally infected animal tissues and clinical specimens (38). The technique has recently been employed to detect the presence of B. burgdorferi DNA in I. ricinus ticks from Switzerland (15), to quantify the spirochete loads in experimentally infected animal tissues (23,24,35), and to differentiate the three B. burgdorferi sensu lato species that are pathogenic to humans in Europe (22,2...

As part of the Northeast Area-wide Tick Control Project (NEATCP), meta-analyses were performed using pooled data on the extent of tick-vector control achieved through seven concurrent studies, conducted within five states, using U.S. Department of Agriculture ''4-Poster'' devices to deliver targeted-acaricide to white-tailed deer. Although reductions in the abundance of all life-stages of Ixodes scapularis were the measured outcomes, this study focused on metrics associated with I. scapularis nymphal tick densities as this measure has consistently proven to directly correlate with human risk of acquiring Lyme disease. Since independent tick sampling schemes were undertaken at each of the five environmentally distinct study locations, a meta-analytic approach permitted estimation of a single true control-effect size for each treatment year of the NEATCP. The control-effect is expressed as the annual percent I. scapularis nymphal control most consistent with meta-analysis data for each treatment year. Our meta-analyses indicate that by the sixth treatment year, the NEATCP effectively reduced the relative density of I. scapularis nymphs by 71% on the 5.14 km 2 treatment sites, corresponding to a 71% lower relative entomologic risk index for acquiring Lyme disease.