Dynamics of Dissemination and Outer Surface Protein Expression of Different European Borrelia burgdorferi Sensu Lato Strains in Artificially Infected Ixodes ricinus Nymphs

Abstract

Unfed Ixodes ricinus nymphs were infected with eight different strains and clones of Borrelia afzelii and B. garinii by capillary feeding. Except one B. afzelii clone, all expressed OspC in culture. Tick midguts and salivary glands were investigated at different time intervals for the presence of borreliae and for OspA and OspC phenotypes by immunofluorescence with simultaneous staining of OspA and OspC with monoclonal antibodies. Both species were transmittable to I. ricinus. All OspC-expressing strains and clones were able to disseminate into the salivary glands. In contrast, the OspC-negative B. afzelii clone was not detectable in the salivary glands, an indication that OspC plays an important role in dissemination. OspA-positive borreliae prevailed in the midgut. OspC positives were more frequent in the salivary glands than in the midgut. Notably, simultaneously OspA-and OspC-negative borreliae were detected in both organs. Kinetics of dissemination varied with the strains. The OspC-positive B. afzelii clone and all B. garinii OspA type 4 strains were detectable in the salivary glands right after feeding, while one B. garinii OspA type 6 strain invaded the salivary glands with a delay of 24 h. These findings support the hypothesis that OspA is abundantly expressed in unfed ticks while upregulation of OspC is also a prerequisite for dissemination in the vector for the Eurasian species B. afzelii and B. garinii. However, we found strain-specific dynamics of Osp expression and strain-specific kinetics of systemic infection in the vector tick and it appears that additional factors are involved in the initiation and regulation of the dissemination process.The Borrelia burgdorferi sensu lato complex comprises at least three human-pathogenic species, all of which are present in Europe: B. burgdorferi sensu stricto, the only species causing Lyme borreliosis in the United States; B. afzelii; and B. garinii (1, 3). These spirochetes alternate in nature between endothermic hosts (mammals) and poikilothermic vectors (hard ticks within the genus Ixodes). In the vector, the spirochetes restart replication during the feeding process, migrate through the gut wall, and invade various tissues, including the salivary glands, wherefrom they are transmitted to the host via saliva (2,7,11,25,27,36). The borreliae are confronted with abrupt environmental changes during this cycling, such as differences in temperature, pH, the immune system, or osmotic pressure. To cope with these rapid changes, effective regulatory mechanisms for adaptation are required. Alteration of the outer surface protein (Osp) expression pattern-especially that of OspA and OspC-seems to be crucial for this adaptation process; expression of these two proteins varies even under routine culture conditions and seems to be inversely correlated (5,29,30,31). Elevated temperature and cocultivation with tick cells have been shown to induce OspC expression (10,20,26,28). OspA is abundantly expressed in unfed ticks, possibly mediating adherence to midgut cells and thu...

Complementation of a Borrelia afzelii OspC mutant highlights the crucial role of OspC for dissemination of Borrelia afzelii in Ixodes ricinus

“…ospCÀ and the transformed cPKo345 ospC+ by the capillary feeding method as previously described (Fingerle et al, 2002;Gern et al, 1990). In short, the ticks were adapted to room temperature 1 h before start of the experiments and allowed to feed for 3-4 h at room temperature in a humid chamber on capillaries containing MKP with 10 7 -10 8 borreliae/ml.…”

“…During tick feeding, B. burgdorferi migrates through the gut wall, disseminates and invades various tissues, including the salivary glands wherefrom they are transmitted to the host by saliva. During borrelial dissemination from vector to host, the spirochetes have been shown to differentially regulate several lipoproteins possibly in response to the rapid environmental changes (Fingerle et al, 1998(Fingerle et al, , 2002LeubaGarcia et al, 1998;Schwan and Piesman, 2000). In particular the outer surface protein (Osp) C is upregulated with rising temperature and decrease of pH (Carroll et al, 1999;Schwan and Piesman, 2000) and seems to be a crucial factor in the initial events of the infection process.…”

“…We previously have described a B. afzelii clone lacking the OspC protein because of a frameshift mutation in the corresponding gene, which had lost its ability to disseminate from the midgut to the salivary glands of I. ricinus (Fingerle et al, 2000(Fingerle et al, , 2002. After a positive preliminary test to transform B. afzelii with green fluorescent protein (GFP) as a confirmatory marker, we succeeded to complement the ospC B. afzelii mutant to subsequently investigate the borrelial dissemination behavior in capillary-fed I. ricinus.…”

Artificial feeding of Amblyomma cajennense (Acari: Ixodidae) fasting females through capillary tube technique

“…This process was consider so important, that use it as the only method for evaluating their results (INDEST et al, 2001;FINGERLE et al 2002). In the present work, ticks excreted a whitish or sometimes reddish substance through the anal opening.…”

“…At the same time, it is advantageous when compared to other methods, because it permits experimental manipulations. Apart from this, it is possible to infect the ticks with clones of pathogens or with different strains at the same time (FINGERLE et al, 2002).…”