ABSTRACT
Free-living Ixodes ricinus ticks were collected from 12 different sites of canton Ticino, south of the Alps (Switzerland). Each tick was examined for the presence of Borrelia burgdorferi sensu lato (sl), the etiologic agent of Lyme borreliosis using direct fluorescent antibody assay, and isolation of the bacteria. Borreliae were characterized by PCR followed by RFLP. The abundance and infection rates of I. ricinus ticks varied greatly between the areas. Two localities were found free of Borrelia. The prevalence of infected ticks ranged from 5 to 19%. Most ticks (96%) were found infected by < 50 spirochetes. Three B. burgdorferi sl species were successfully isolated: B. garinii dominated, followed by B. lusitaniae and B. valaisiana. Additionally, a mixed infection with B. garinii and B. valaisiana was observed. The distribution of the various Borrelia species in the different areas was heterogeneous. This is the first report of the presence of B. lusitaniae in I. ricinus in Switzerland.
Subject(s)
Borrelia burgdorferi Group/isolation & purification , DNA, Bacterial/analysis , Ixodes/parasitology , Tick Infestations/microbiology , Altitude , Animals , Arachnid Vectors/microbiology , Borrelia burgdorferi Group/classification , Borrelia burgdorferi Group/genetics , Female , Fluorescent Antibody Technique , Humans , Ixodes/microbiology , Lyme Disease/parasitology , Lyme Disease/transmission , Male , Polymerase Chain Reaction , Polymorphism, Restriction Fragment Length , Prevalence , Sex Factors , Switzerland , TimeABSTRACT
In tick salivary glands, several genes are induced during the feeding process, leading to the expression of new proteins. These proteins are typically secreted in tick saliva and are potentially involved in the modulation of the host immune and hemostatic responses. In a previous study, the construction and the analysis of a subtractive library led to the identification of Ixodes ricinus immunosuppressor (Iris), a novel protein, differentially expressed in I. ricinus salivary glands during the blood meal. In the present study, the data strongly suggest that this protein is secreted by tick salivary glands into the saliva. In addition, Iris is also found to modulate T lymphocyte and macrophage responsiveness by inducing a Th2 type response and by inhibiting the production of pro-inflammatory cytokines. In conclusion, these results suggest that Iris is an immunosuppressor, which might play an important role in the modulation of host immune response.
Subject(s)
Immunosuppressive Agents/pharmacology , Saliva/metabolism , Salivary Proteins and Peptides/biosynthesis , Salivary Proteins and Peptides/chemistry , Animals , CD28 Antigens/biosynthesis , CD3 Complex/biosynthesis , CHO Cells , Cell Division , Cells, Cultured , Cricetinae , Cytokines/biosynthesis , DNA, Complementary/metabolism , Dose-Response Relationship, Drug , Humans , Interferon-gamma/biosynthesis , Interleukin-10/biosynthesis , Interleukin-5/biosynthesis , Ixodes , Macrophages/metabolism , Mice , Mice, Inbred BALB C , Microscopy, Confocal , Protein Binding , Protein Structure, Tertiary , Salivary Glands/metabolism , Spleen/cytology , T-Lymphocytes/metabolism , Th2 Cells/metabolismABSTRACT
Borrelia burgdorferi sensu lato (sl), the agent of Lyme disease, is transmitted to the host during the blood meal of Ixodes ticks. In most unfed ticks, spirochetes are present in the midgut and migrate during blood feeding to the salivary glands, from which they are transmitted to the host via saliva. In the present study, the efficiency of Ixodes ricinus ticks to transmit B. afzelii and B. burgdorferi sensu stricto (ss) and their infectivity for mice were examined in relation to the duration of the blood meal. In addition, we investigated whether these two Borrelia species can penetrate intact skin. Three modes of infection of mice were studied: tick-bite infection, inoculation of tick homogenates, and transcutaneous infection by topical application of tick homogenates on mouse skin. Transmission of B. burgdorferi sl from I. ricinus nymphs to mouse increased with duration of tick attachment. B. afzelii-infected ticks start to transmit infection earlier (< or = 48 h) than B. burgdorferi ss-infected ticks. As previously shown for B. burgdorferi ss in Ixodes scapularis, B. burgdorferi ss and B. afzelii in unfed I. ricinus were noninfectious for mice when tick homogenates were inoculated. However, the inoculation of homogenates of ticks fed for 24 h readily produced infection in mice. Therefore, B. burgdorferi ss and B. afzelii spirochetes are potentially infectious in the tick before natural transmission can occur. None of the mice (n = 33) became infected by transcutaneous transmission when tick homogenates were applied on mouse skin, showing that B. burgdorferi ss and B. afzelii are unable to penetrate intact skin, in contrast to relapsing fever spirochetes. This study also shows that B. afzelii is transmitted by I. ricinus to the host earlier than B. burgdorferi ss and that I. ricinus seems to be a more efficient vector of B. afzelii than B. burgdorferi ss.
