Seroprevalences of Rickettsia conorii, Ehrlichia canis and Coxiella burnetii in Dogs from Montenegro.

PURPOSE: The incidence of vector-borne zoonoses has been increasing in Europe as a result of global climate change, and rickettsioses are a significant etiologic entity among these infections. The objective of this study was to investigate the seroprevalences of Rickettsia conorii, Ehrlichia canis and Coxiella burnetii in dogs in Montenegro. METHODS: The seroepidemiological study covered 259 dogs, of which 155 were owned dogs suspected of infection with agents of rickettsial aetiology from the continental (Podgorica) or five coastal municipalities of Montenegro (Budva, Herceg Novi, Kotor, Ulcinj and Bar), and 104 dogs were from a public shelter in Podgorica. The presence of specific IgG antibodies against R. conorii was analysed using a commercial indirect enzyme-linked immunosorbent assay (ELISA) test, and the presence of antibodies against E. canis and C. burnetii was analysed using commercial indirect immunofluorescence tests (IFAT). RESULTS: Seroprevalences of 73.36, 19.3 and 1.16% were determined for R. conorii, E. canis and C. burnetii, respectively. R. conorii was significantly more prevalent (χ2 = 14.53; p < 0.001) in owned dogs (81.93%) than in dogs from the public shelter (60.6%), while E. canis was more prevalent (χ2 = 12.31; p < 0.001) in dogs from the public shelter (29.81%) than in owned dogs (12.26%). Coinfection with two pathogens was determined in 40 (15.44%) dogs, and the prevalence of R. conorii/E. canis (χ2 = 4.23; p < 0.05) was greater in dogs from the public shelter (20.19%) than in owned dogs (10.97%). CONCLUSION: The prevailing evidence from this study shows that dogs from Montenegro are exposed to pathogens of veterinary and public health importance. This calls for the One Health approach to sensitise the public on the risks of zoonoses from dogs and to formulate policies and strategies to mitigate their spread and safeguard public health.

Rickettsia conorii is a potent complement activator in vivo and combined inhibition of complement and CD14 is required for attenuation of the cytokine response ex vivo.

Mediterranean spotted fever caused by Rickettsia conorii is a potentially lethal disease characterized by vascular inflammation affecting multiple organs. Studies of R. conorii so far have focused on activation of inflammatory cells and their release of inflammatory cytokines, but complement activation has not been investigated in R. conorii-infected patients. Here, we performed a comprehensive analysis of complement activation markers and the soluble cross-talking co-receptor CD14 (sCD14) in plasma from R. conorii-infected patients. The clinical data were supplemented with ex vivo experiments where the cytokine response was characterized in human whole blood stimulated with R. conorii. Complement activation markers at the level of C3 (C3bc, C3bBbP) and terminal pathway activation (sC5b-9), as well as sCD14, were markedly elevated (p <0.01 for all), and closely correlated (p <0.05 for all), in patients at admission compared with healthy matched controls. All tested markers were significantly reduced to baseline values at time of follow up. Rickettsia conorii incubated in human whole blood was shown to trigger complement activation accompanied by release of the inflammatory cytokines interleukin-1ß (IL-1ß), IL-6, IL-8 and tumour necrosis factor. Whereas inhibition of either C3 or CD14 had only a minor effect on released cytokines, combined inhibition of C3 and CD14 resulted in significant reduction, virtually to baseline levels, of the four cytokines (p <0.05 for all). Our data show that complement is markedly activated upon R. conorii infection and complement activation is, together with CD14, responsible for a major part of the cytokine response induced by R. conorii in human whole blood.

Evaluation of a new serological test for the detection of anti-Coxiella and anti-Rickettsia antibodies.

Coxiella burnetii and members of the genus Rickettsia are obligate intracellular bacteria. Since cultivation of these organisms requires dedicated techniques, their diagnosis usually relies on serological or molecular biology methods. Immunofluorescence is considered the gold standard to detect antibody-reactivity towards these organisms. Here, we assessed the performance of a new automated epifluorescence immunoassay (InoDiag) to detect IgM and IgG against C. burnetii, Rickettsia typhi and Rickettsia conorii. Samples were tested with the InoDiag assay. A total of 213 sera were tested, of which 63 samples from Q fever, 20 from spotted fever rickettsiosis, 6 from murine typhus and 124 controls. InoDiag results were compared to micro-immunofluorescence. For acute Q fever, the sensitivity of phase 2 IgG was only of 30% with a cutoff of 1 arbitrary unit (AU). In patients with acute Q fever with positive IF IgM, sensitivity reached 83% with the same cutoff. Sensitivity for chronic Q fever was 100% whereas sensitivity for past Q fever was 65%. Sensitivity for spotted Mediterranean fever and murine typhus were 91% and 100%, respectively. Both assays exhibited a good specificity in control groups, ranging from 79% in sera from patients with unrelated diseases or EBV positivity to 100% in sera from healthy patients. In conclusion, the InoDiag assay exhibits an excellent performance for the diagnosis of chronic Q fever but a very low IgG sensitivity for acute Q fever likely due to low reactivity of phase 2 antigens present on the glass slide. This defect is partially compensated by the detection of IgM. Because it exhibits a good negative predictive value, the InoDiag assay is valuable to rule out a chronic Q fever. For the diagnosis of rickettsial diseases, the sensitivity of the InoDiag method is similar to conventional immunofluorescence.

T-Lymphocyte Subset Absolute Counts in the Peripheral Blood of Mediterranean Spotted Fever Patients: Relations to Disease Severity.

INTRODUCTION: Mediterranean spotted fever (MSF) in Bulgaria is caused by Rickettsia conorii conorii. AIM: This study aims at investigating the absolute counts of T-lymphocyte subsets in the peripheral blood of patients with MSF in order to establish relationships with disease severity. MATERIALS AND METHODS: The absolute counts of T-lymphocyte subsets were tested in the blood of 62 patients in the acute stage of MSF. They were assigned into three age and sex matched groups, based on the severity of disease - with mild, moderate or severe forms. Controls were 32 age and sex matched healthy individuals. The diagnosis was confirmed by an immunofluorescence assay. Immunophenotyping was performed using Epics XL-MCL Coulter, USA flow-cytometer. RESULTS: The absolute counts of immune competent (CD3+) cells, as well as the counts of helper/inducer (CD3+ CD4+) and suppressor/ cytotoxic (CD3+ CD8+) T-cell subsets decreased in parallel with disease severity. Naïve (CD4+ CD45RA+) and activated memory (CD4+ CD45RO+) T-cell subsets were reduced, particularly in severe MSF. Taken as a whole, the counts of activated (CD3+ HLA-DR+) and that of presenting accessory (CD28+) or stimulatory (CD38+) molecules Т-cell subsets was increased, but in the first two subsets the trend from mild to severe forms of the disease was descending. CONCLUSION: Reduced T-lymphocyte subset counts are likely related to trans-migration into perivascular inflammatory foci. The increased number of T-lymphocytes bearing activation molecules reflects a mobilization of the cell-mediated immune response. An important issue of this study is the possible prognostic value of T-cell subsets counting, predicting the evolution of a clinical condition to clinical forms, according to the disease severity.

Skin lesions and inoculation eschars at the tick bite site in spotted fever group rickettsioses: experience from a patient series in eastern crete, Greece.

The main clinical signs and symptoms caused by a rickettsial infection typically begin 6-10 days after the bite and are accompanied by nonspecific findings such as fever, headache and muscle pain. The diagnosis is mainly based on serological tests, however antibody presentation may be delayed, at least at the early stages of the disease, while seroconversion is usually detected 10-15 days after disease onset. Culture is difficult, requires optimized facilities and often proves negative. Under this scope, the presence of a characteristic inoculation eschar at the bite site may prove a useful clinical tool towards the early suspicion and diagnosis/differential diagnosis of tick-borne rickettsioses, even before the onset of rash and fever or serological confirmation. We describe herein the presence of skin lesions and/or an inoculation eschar at the tick bite site in 17 patients diagnosed, by molecular means, as suffering from spotted fever group rickettsioses. The detection of the pathogen's DNA in biopsy samples proved to be a useful means for early rickettsiae detection and identification. Moreover, the presence of an infiltrated erythema always seemed to precede the appearance of an eschar by 2-5 days and the initiation of fever by 1-10 days; these two signs might also prove useful in the context of the final diagnosis.

Rickettsial meningitis.

Rickettsial infections are common in southern Europe and the most frequent and lethal type is Mediterranean spotted fever, caused by Rickettsia conorii. The disease is usually characterised by the classical triad of fever, eschar and rash, and is generally a mild disease in children. Complications including neurological involvement are rarely described. We report an unusual case of meningitis in an 18-year-old man, presenting during summer with fever and persistent headache. The cerebrospinal fluid analysis revealed increased cellularity (107 cells/µL), hypoglycorrhachia (50% of glycaemia) and hyperproteinorrhachia (284 mg/dL). Rickettsial infection was confirmed by serology and the patient was treated with doxycycline, with a favourable outcome. The patient's pet squirrel and/or associated vectors might be involved in the transmission of Rickettsia spp. This case underlines the importance of a high clinical suspicion and the benefits of early empirical treatment when facing compatible epidemiological contexts.

Rickettsioses in the central hills of Sri Lanka: serological evidence of increasing burden of spotted fever group.

OBJECTIVES: To study the epidemiology, clinical features, and changing pattern of rickettsial infections on the western slopes of the hilly Central Province of Sri Lanka over 6 years. METHODS: All patients with rickettsial infections who presented to the Teaching Hospital, Peradeniya were studied prospectively from January 2002 to December 2007. An immunofluorescent antibody assay (IFA) was used to confirm the diagnosis. RESULTS: Of the 371 clinical cases of rickettsial infection, 122 underwent IFA to confirm the diagnosis. Species-specific IgG antibodies were positive in 105/122 (86.1%) cases: 43/105 (40.9%) to Rickettsia conorii and 6/105 (5.7%) to Orientia tsutsugamushi, with mixed antibody reactivity to more than one antigen in 56/105 (53.3%) cases, including Rickettsia typhi in 27/105 (25.7%). Among those with mixed IgG reactivity, IgM assays were used to detect pathogens responsible for acute infections. Finally, a total of 55 spotted fever group (SFG) infections, seven scrub typhus infections, and one case of murine typhus were identified. Of the 105 positive cases, 53 (50.5%) were male and 52 (49.5%) were female, and the mean age was 40 years (range 11-83 years). In the SFG patients, 13/55 (24%) had severe vasculitis with fern leaf type skin necrosis and 17/55 (31%) had arthritis. Three patients (5%) had an altered level of consciousness. A patient with scrub typhus had transient deafness. None of the 105 patients had an eschar. CONCLUSIONS: It appears that SFG rickettsioses are on the rise in the hilly Central Province of Sri Lanka, whilst murine typhus and scrub typhus are present at a lower rate.

OmpA-mediated rickettsial adherence to and invasion of human endothelial cells is dependent upon interaction with α2ß1 integrin.

Rickettsia conorii, a member of the spotted fever group (SFG) of the genus Rickettsia and causative agent of Mediterranean spotted fever, is an obligate intracellular pathogen capable of infecting various mammalian cell types. SFG rickettsiae express two major immunodominant surface cell antigen (Sca) proteins, OmpB (Sca5) and OmpA (Sca0). While OmpB-mediated entry has been characterized, the contribution of OmpA has not been well defined. Here we show OmpA expression in Escherichia coli is sufficient to mediate adherence to and invasion of non-phagocytic human endothelial cells. A recombinant soluble C-terminal OmpA protein domain (954-1735) with predicted structural homology to the Bordetella pertussis pertactin protein binds mammalian cells and perturbs R. conorii invasion by interacting with several mammalian proteins including ß1 integrin. Using functional blocking antibodies, small interfering RNA transfection, and mouse embryonic fibroblast cell lines, we illustrate the contribution of α2ß1 integrin as a mammalian ligand involved in R. conorii invasion of primary endothelial cells. We further demonstrate that OmpA-mediated attachment to mammalian cells is in part dependent on a conserved non-continuous RGD motif present in a predicted C-terminal 'pertactin' domain in OmpA.Our results demonstrate that multiple adhesin-receptor pairs are sufficient in mediating efficient bacterial invasion of R. conorii.

Levels of certain endothelial biomarkers during the acute phase and convalescence in patients with different severity of Mediterranean spotted fever.

INTRODUCTION: Mediterranean spotted fever (MSF) is a tick-borne disease caused by Rickettsia conorii subspp. conorii. It is transmitted by the bite of the tick Rhipicephalus sanguineus. Modified by the rickettsial invasion, the micro-vascular endothelium acquires an activated inflammatory phenotype and initiates secretion of cytokines and expression of cell adhesion molecules (CAMs) and chemoattractans. AIM: This study aims at investigating the alterations in the soluble cellular adhesion molecules (sCAMs) and chemokine MCP-1 levels in patients with MSF of varying severity in the acute and convalescence stage in order to assess their diagnostic and prognostic value. MATERIALS AND METHODS: The soluble forms of cellular adhesion molecules (sCAMs)--sE-selectin and sP-selectin, the intercellular (sICAM-1) and vascular (sVCAM-1) adhesion molecules as well as the monocyte chemoattractant protein-1 (MCP-1) were studied in the sera of 80 patients with MSF. The presence of MSF was confirmed serologically by indirect fluorescence assay (IFA). In order to study disease dynamics, serum samples from 80 patients were drawn on day 1 following the onset of rash; in 60 patients (part of the surveyed 80) a second sample was taken in the convalescence period--14 days post hospital discharge. The investigation was focused on mild, moderate and severe forms of MSF. Enzyme linked immune-sorbent assay was used for sCAMs determination (Quantikine IVD colorimetric RESULTS: Overall, in the acute stage, patients presented with increased levels of sE-selectin, sICAM-1, sVCAM-1 and MCP-1, whereas sP-selectin level was decreased. The levels of sE-selectin, sICAM-1 and sVCAM-1 were significantly elevated in mild, moderate and severe forms of the disease with sE-selectin level exhibiting a plateau tendency and sICAM and sVCAM levels demonstrating an upward trend from mild towards severe MSF forms. MCP-1 level was elevated only in severe MSF. In all forms of MSF, in the convalescence period, sICAM-1, sVCAM-1 and MCP-1 concentration returned to reference levels whereas sE-selectin level persisted elevated. In the convalescence stage, sP- selectin concentration also showed an upward tendency, which in severe forms of MSF slightly exceeded the level in controls. sP-selectin levels correlated directly with platelet count, whereas sICAM-1 and sVCAM-1 levels showed a reverse correlation, sE-selectin, sICAM-1 and MCP-1 levels directly correlated with aminotransferase activity (ALT and/or AST). CONCLUSION: The soluble forms of CAMs reflect the endothelial inflammatory potential. There is evidence that endothelium activation is more potent in severe forms of MSF. Assessment of the endothelial response in the course of the disease is an important predictor of the outcome, the choice of therapeutic approach and disease prognosis.

Detection of natural killer T cells in mice infected with Rickettsia conorii.

Little information is available regarding the role of natural killer T (NKT) cells during the early stage of Rickettsia conorii infection. Herein, C3H/HeN mice were infected with the Malish 7 strain of R. conorii. Splenocytes from these mice were analysed in the early stage of the infection by flow cytometry and compared with uninfected controls. Our results showed an increase in NKT cells in infected mice. Additionally, NKT interleukin (IL)-17(+) cells increased three days after infection, together with a concurrent decrease in the relative amount of NKT interferon (IFN)-γ(+) cells. We also confirmed a higher amount of NK IFN-γ(+) cells in infected mice. Taken together, our data showed that NKT cells producing Il-17 increased during the early stage of rickettsial infection. These results suggest a connection between IL-17(+) NKT cells and vasculitis, which is the main clinical symptom of rickettsiosis.

Clinically helpful rickettsial disease diagnostic IgG titers in relation to duration of illness in an endemic setting in Sri Lanka.

BACKGROUND: Although an initial IFA-IgG titer greater or equal to 1/64 or 1/128 is considered positive in presumptive diagnosis, in clinical practice in an endemic setting for rickettsioses in Sri Lanka, some patients with IFA-IgG titer of 1/128 for either spotted fever group (SFG) or scrub typhus (ST) did not respond to treatment. FINDINGS: To determine a clinically helpful diagnostic algorithm, IFA-IgG results of serologically confirmed treatment responders were analyzed in relation to duration of illness at sampling. Of 146 suspected SFG, 3 responders of 25 patients had titers ≤1/128 with < 7 days of illness while all 9 with titers ≥1/256 responded (false negative with 1/256 cutoff was 12%, false positive was 0%). For illness > 7 days, the false negative and positive rates were 4.3% (3/59) and 11.3% (6/53). Of 115 suspected ST, false negative and positive rates with ≥1/256 cutoff at <7 days of illness were 14.2% (2/14) and 0% (0/8) respectively while > 7 days, false negative and positive rates were 2% (1/51) and 0% (0/42). CONCLUSIONS: For clinical decision making, duration of illness at sampling is important in interpreting serology results in an endemic setting. If sample is obtained ≤7 day of illness, an IgG titer of ≤1/128 requires a follow up sample in the diagnosis and > 7 days of illness, a single ≥1/256 titer is diagnostic for all ST and 90% of SFG.

A complex interaction between Rickettsia conorii and Dickkopf-1--potential role in immune evasion mechanisms in endothelial cells.

The pathophysiological hallmark of spotted fever group rickettsioses comprises vascular inflammation. Based on the emerging importance of the wingless (Wnt) pathways in inflammation and vascular biology, we hypothesized that Dickkopf-1 (DKK-1), as a major modulator of Wnt signaling, could be involved in the pathogenesis in rickettsial infections. Our major findings were: (i) While baseline concentration of DKK-1 in patients with R. conorii infection (n = 32) were not different from levels in controls (n = 24), DKK-1 rose significantly from presentation to first follow-up sample (median 7 days after baseline). (ii) In vitro experiments in human umbilical vein endothelial cells (HUVECs) showed that while heat-inactivated R. conorii enhanced the release of interleukin-6 (IL-6) and IL-8, it down-regulated the release of endothelial-derived DKK-1 in a time- and dose-dependent manner. (iii) Silencing of DKK-1 attenuated the release of IL-6, IL-8 and growth-related oncogene (GRO)α in R. conorii-exposed HUVECs, suggesting inflammatory effects of DKK-1. (iv) Silencing of DKK-1 attenuated the expression of tissue factor and enhanced the expression of thrombomodulin in R. conorii-exposed HUVECs suggesting pro-thrombotic effects of DKK-1. The capacity of R. conorii to down-regulate endothelial-derived DKK-1 and the ability of silencing DKK-1 to attenuate R. conorii-induced inflammation in endothelial cells could potentially reflect a novel mechanism by which R. conorii escapes the immune response at the site of infection.

Cross-protection among Rickettsia species and subspecies in a guinea pig model of cutaneous infection.

Pathogenic rickettsiae of the spotted fever group (SFG) induce skin lesions called "eschars" at the sites of arthropod bites. We recently described a guinea pig model based on eschar formation to predict the eventual pathogenicity of new Rickettsia species, and in this study, we used the model to study cross-protection among SFG Rickettsia species and subspecies. We showed that the intradermal inoculation of guinea pigs with Rickettsia conorii subsp. conorii significantly reduced, but not completely prevented, the number of eschars after sub-challenges with the same pathogen (P=0.0004). The same effect was also observed for other subspecies of the R. conorii complex. Additionally, the bacterial load in the eschars was significantly lower in immunized animals than in naïve animals. No protection was observed when sub-challenges were performed with other Rickettsia species, such as R. africae, R. sibirica subsp. mongolitimonae, R. aeschlimannii and R. massiliae. Our data suggest that patients may experience several episodes of infection with related or with the same species of Rickettsia. Moreover, the absence of cross-protection between Rickettsia species may explain the co-existence of two or more tick-borne rickettsioses in the same geographic areas.

Contribution of NK cells to the innate phase of host protection against an intracellular bacterium targeting systemic endothelium.

We investigated the mechanisms by which natural killer (NK) cells mediate innate host defense against infection with an endothelium-targeting intracellular bacterium, Rickettsia. We found that a robust Rickettsia-induced innate response in resistant mice cleared the bacteria early in the infection and was associated with significantly higher frequencies of splenic interferon (IFN)-γ (+) CD8(+) T cells and cytotoxic NK cells compared with susceptible mice. More importantly, NK cell-deficient Rag(-/-)γc(-/-) animals displayed significantly increased susceptibility to Rickettsia infection compared with NK cell-sufficient Rag(-/-) mice, as evidenced by impaired bacterial clearance, early development of severe thrombosis in the liver, and a decreased serum level of IFN-γ. Furthermore, the lack of NK cells also impaired host resistance of CB-17 scid mice to Rickettsia, similar to what was observed in Rag(-/-)γc(-/-) mice. Interestingly, perforin deficiency in Rag(-/-)Prf1(-/-) mice resulted in greater thrombosis and insignificantly different systemic levels of IFN-γ compared with Rag(-/-) mice, suggesting that perforin, which is mainly produced by NK cells, is involved in the prevention of vascular damage. Together, these findings reveal that NK cells mediate the innate phase of host protection against infection with rickettsiae, most likely via IFN-γ production. Furthermore, NK cells are involved in preventing rickettsial infection-induced endothelial cell damage, possibly via perforin production.

[Emergence of tick-borne spotted fever group rickettsiosis in Moscow].

AIM: Analysis of clinical cases of tick-borne spotted fever (TSF) group rickettsiosis in 2005 - 2010. MATERIALS AND METHODS: General clinical, biochemical and serological parameters were determined in 10 tick-borne spotted fever group rickettsiosis patients who had visited various geographical regions of the World. RESULTS: TSF group rickettsiosis diagnostic criteria, optimal serological diagnostics timing were determined. Possible diagnostic errors, features of serological diagnostics and antibacterial therapy of this nosologic form are discussed. CONCLUSION: Indication for TSF examination are primarily epidemiologic including tick attachment indication and clinical data. Serological studies are positive only in 3 - 4 weeks after the onset of the infection and thus can not be used for early diagnostics.

Dynamics in serum cytokine responses during acute and convalescent stages of Mediterranean spotted fever.

UNLABELLED: Mediterranean spotted fever (MSF) is a re-emerging rickettsiosis in Bulgaria after 20 years of absence (1972-1992), and it has since been affecting many people annually in the endemic regions of the country. The role of cytokines in MSF is still in the focus of research due to their complex participation in the immune pathogenesis of the disease. AIM: To study the changes in the serum cytokine concentrations in MSF patients. PATIENDS AND METHODS: Eighty patients with MSF and 20 healthy controls were enrolled in the study. The pro-inflammatory and immunoregulatory cytokines IL-1beta, TNF-a, IL-6, IL-8, IL-12, IFN-gamma, IL-2, and IL-10 were studied in the burst of disease, at clinical recovery stage, and two weeks later. The disease etiology was verified by indirect IFA in the Referral Rickettsiosis Laboratory. The cytokine levels were determined by ELISA (BioSource Europe S.A). RESULTS: In the disease flare up patients showed a manifold increase in the activity of IL-1beta (p < 0.01), TNF-alpha (p < 0.001), IL-6 (p < 0.001), and IL-8 (p < 0.001) compared with the controls. Significant elevation in IFN-gamma and IL-12 values (p < 0.001) was also found. The increase in the immunoregulatory IL-10 also reached statistical significance (p < 0.001), while the rise in IL-2 did not (p > 0.05). Followed in dynamics, only IL-1beta and IL-6 measured up the control levels at the time of clinical recovery. Two weeks later, in the early convalescence IL-12 and TNF-alpha further diminished but did not normalize their values. CONCLUSION: Our findings show that MSF is characterized by a Th1 cytokine profile. The patient's immune system responds by proinflammatory and immunoregulatory cytokine production that accompanies the rickettsial vasculitis and contributes to the healing process. The latter is probably not fully achieved in the early convalescent period, according to our data concerning some pro-inflammatory cytokines' elevation at this period.

Molecular basis of immunity to rickettsial infection conferred through outer membrane protein B.

Pathogenic rickettsiae are the causative agents of Rocky Mountain spotted fever, typhus, and other human diseases with high mortality and an important impact on society. Although survivors of rickettsial infections are considered immune to disease, the molecular basis of this immunity or the identification of protective antigens that enable vaccine development was hitherto not known. By exploring the molecular pathogenesis of Rickettsia conorii, the agent of Mediterranean spotted fever, we report here that the autotransporter protein, rickettsial outer membrane protein B (rOmpB), constitutes a protective antigen for this group of pathogens. A recombinant, purified rOmpB passenger domain fragment comprised of amino acids 36 to 1334 is sufficient to elicit humoral immune responses that protect animals against lethal disease. Protective immunity requires folded antigen and production of antibodies that recognize conformational epitopes on the rickettsial surface. Monoclonal antibodies (MAbs) 5C7.27 and 5C7.31, which specifically recognize a conformation present in the folded, intact rOmpB passenger domain, are sufficient to confer immunity in vivo. Analyses in vitro indicate this protection involves a mechanism of complement-mediated killing in mammalian blood, a means of rickettsial clearance that has not been previously described. Considering the evolutionary conservation of rOmpB and its crucial contribution to bacterial invasion of host cells, we propose that rOmpB antibody-mediated killing confers immunity to rickettsial infection.

[Pediatric Mediterranean spotted fever]. / La fièvre boutonneuse méditerranéenne chez l'enfant.

In France, Mediterranean spotted fever due to Rickettsia conorii is mainly observed in the South-east. Rhipicephalus sanguineus, the brown dog tick, is the vector and the reservoir of the disease. Clinical diagnosis relies on the association of fever, rash and inoculation's scar during summertime. Pathological lesion is a diffuse vasculitis. Severity is often explained by a delay in diagnosis, but prognosis is good in pediatrics. Treatment relies on doxycycline and on macrolids in children under eight.