Mediterranean Spotted Fever

Coxiella-like endosymbionts

In the past two decades, many Coxiella-like bacteria have been found in hard ticks and soft ticks as well as in vertebrate hosts. It is interesting to note that many ticks harbor Coxiella-like bacteria with high prevalence. Coxiella-like bacteria and virulent Coxiella burnetii have high homology to each other; they form a monophyletic clade based on 16S rRNA sequence data and subsequent phylogenetic tree analyses. In this chapter, methods of detection, phylogeny, prevalence and density, distribution in tick organs, transmission routes, bacteria-host interactions, and putative functions of the Coxiella-like bacteria are reviewed.

Matrix-assisted laser desorption ionization-time of flight mass spectrometry for rapid identification of tick vectors

A method for rapid species identification of ticks may help clinicians predict the disease outcomes of patients with tick bites and may inform the decision as to whether to administer postexposure prophylactic antibiotic treatment. We aimed to establish a matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) spectrum database based on the analysis of the legs of six tick vectors: Amblyomma variegatum, Rhipicephalus sanguineus, Hyalomma marginatum rufipes, Ixodes ricinus, Dermacentor marginatus, and Dermacentor reticulatus. A blind test was performed on a trial set of ticks to identify specimens of each species. Subsequently, we used MALDI-TOF MS to identify ticks obtained from the wild or removed from patients. The latter tick samples were also identified by 12S ribosomal DNA (rDNA) sequencing and were tested for bacterial infections. Ticks obtained from the wild or removed from patients (R. sanguineus, I. ricinus, and D. marginatus) were accurately identified using MALDI-TOF MS, with the exception of those ticks for which no spectra were available in the database. Furthermore, one damaged specimen was correctly identified as I. ricinus, a vector of Lyme disease, using MALDI-TOF MS only. Six of the 14 ticks removed from patients were found to be infected by pathogens that included Rickettsia, Anaplasma, and Borrelia spp. MALDI-TOF MS appears to be an effective tool for the rapid identification of tick vectors that requires no previous expertise in tick identification. The benefits for clinicians include the more targeted surveillance of patients for symptoms of potentially transmitted diseases and the ability to make more informed decisions as to whether to administer postexposure prophylactic treatment.

Vectors of rickettsiae in Africa

Vector-borne diseases are caused by parasites, bacteria, or viruses transmitted by the bites of hematophagous arthropods. In Africa, there has been a recent emergence of new diseases and the re-emergence of existing diseases, usually with changes in disease epidemiology (e.g., geographical distribution, prevalence, and pathogenicity). In Africa, rickettsioses are recognized as important emerging vector-borne infections in humans. Rickettsial diseases are transmitted by different types of arthropods, ticks, fleas, lice, and mites. This review will examine the roles of these different arthropod vectors and their geographical distributions.

Unusual bacterial infections and the pleura

Rickettsiosis, Q fever, tularemia, and anthrax are all bacterial diseases that can affect the pleura. Rocky Mountain Spotted Fever (RMSF) and Mediterranean Spotted Fever (MSF) are caused by Rickettsia rickettsii and Rickettsia conorii, respectively. Pleural fluid from a patient with MSF had a neutrophil-predominant exudate. Coxiellaburnetii is the causative agent of Q fever. Of the two cases described in the literature, one was an exudate with a marked eosinophilia while the other case was a transudate due to a constrictive pericarditis. Francisella tularensis is the causative agent of tularemia. Pleural fluid from three tularemia patients showed a lymphocyte predominant exudate. Bacillusanthracis is the causative agent of anthrax. Cases of inhalational anthrax from a recent bioterrorist attack evidenced the presence of a serosanguineous exudative pleural effusion. These four bacterial microorganisms should be suspected in patients presenting with a clinical history, exposure to known risk factors and an unexplained pleural effusion.

Regulation of inducible heme oxygenase and cyclooxygenase isozymes in a mouse model of spotted fever group rickettsiosis

Vascular endothelial cells (ECs) lining the blood vessels are the preferred primary targets of pathogenic Rickettsia species in the host. In response to oxidative stress triggered by infection, ECs launch defense mechanisms such as expression of heme oxygenase-1 (HO-1). Previous evidence from an established animal model of Rocky Mountain spotted fever also suggests selective modulation of anti-oxidant enzyme activities in the target host tissues. In this study, we have examined the expression profiles of HO-1 and COX-2 in different tissues during Rickettsia conorii infection of susceptible C3H/HeN mice. RNA hybridization with murine HO-1 and COX-2-specific complementary DNA probes revealed increased HO-1 expression in the liver and brain of mice infected with three different doses of R. conorii ranging from 2.25×10(3) to 2.25×10(5) pfu, relatively non-remarkable changes in the lungs, and a trend for down-regulation in the spleen. The most prominent HO-1 response was evident in the liver with ∼4-fold increase on day 4 post-infection, followed by a decline on day 7. HO-1 expression in the brain, however, peaked with significantly higher levels on day 7. Following infection with both sub-lethal as well as lethal doses of infection, the transcript encoding COX-2 also displayed a pattern of increased expression in the liver and brain. Although immunohistochemical staining revealed increased abundance of HO-1 protein in the liver of infected mice, adjoining serial sections did not exhibit positive staining for COX-2 in infected tissues. The levels of monocyte chemoattractant protein-1 (MCP-1) and keratinocyte-derived cytokine (KC) were significantly higher in the sera of infected mice and corresponded with the onset and severity of the disease. Treatment of infected animals with anti-oxidants α-lipoic acid and N-acetylcysteine and HO inhibitor stannous protoporphyrin (SnPPIX) showed only selective beneficial effects on HO-1 and COX-2 expression in the liver and spleen and serum levels of KC and MCP-1. R. conorii infection of susceptible mice, therefore, results in selective regulation of the expression of HO-1 and COX-2 in a manner dependent on the target host tissue's cellular environment and the propensity of infection with rickettsiae.

Deleterious effect of ciprofloxacin on Rickettsia conorii-infected cells is linked to toxin-antitoxin module up-regulation

OBJECTIVES

To confirm and better understand the deleterious effect of fluoroquinolones reported during Rickettsia conorii infection in humans.

METHODS

We used a new plaque assay to test the effect of ciprofloxacin on cells infected by R. conorii. Controls were mock-treated infected cells and infected cells treated with doxycycline. We used real-time quantitative RT-PCR to quantify vapC and vapB transcripts in cells infected by R. conorii treated with ciprofloxacin or mock treated.

RESULTS

By plaque assay, at baseline (0 h) there is no difference in lytic area between cells treated with ciprofloxacin (whatever concentration used) and controls. Ciprofloxacin at 0.5 and 50 mg/L induced a significant increase in lytic areas compared with the control at 2 h, 4 h, 6 h (P<0.0001) and 24 h (P<0.0001 and P=0.035, respectively) when not induced with doxycycline. By real-time quantitative RT-PCR, ciprofloxacin was found to cause an up-regulation of toxin-antitoxin (TA) module transcription. Indeed, the mRNA levels of vapC and vapB were significantly increased at 2 h and 4 h in cells treated with 50 mg/L ciprofloxacin (not with 0.5 mg/L ciprofloxacin) compared with control levels (fold change >2.9).

CONCLUSIONS

These in vitro findings correlated with our previous clinical findings: fluoroquinolones have a deleterious effect during R. conorii infection, not found with doxycycline. We speculate that the toxic effect of fluoroquinolones on R. conorii-infected cells is mediated by the overexpression of TA, possibly followed by their release into the host cytoplasm as described in Rickettsia felis.

Spotted fever group Rickettsiae in ticks in Cyprus

In two surveys conducted from March 1999 to March 2001 and from January 2004 to December 2006, a total of 3,950 ticks (belonging to ten different species) were collected from seven domestic and wild animals (goat, sheep, cattle, dog, fox, hare, and mouflon) from different localities throughout Cyprus. In order to establish their infection rate with Spotted Fever Rickettsiae (SFG), ticks were pooled and tested by polymerase chain reaction targeting gltA and ompA genes, followed by sequencing analysis. When tick pools tested positive, individual ticks were then tested one by one, and of the 3,950 ticks screened, rickettsial DNA was identified in 315 ticks (infection rate, 8%). Five SFG Rickettsiae were identified: Rickettsia aeschlimannii in Hyalomma marginatum marginatum, Rickettsia massiliae in Rhipicephalus turanicus and Rhipicephalus sanguineus, Rickettsia sibirica mongolotimonae in Hyalomma anatolicum excavatum, and a Rickettsia endosymbiont of Haemaphysalis sulcata (later described as Rickettsia hoogstraalii) in Haemaphysalis punctata. Two additional genes, 17 kDa and ompB, were targeted to characterize a new genotype of "Candidatus Rickettsia barbariae" genotype in R. turanicus, designated here as "Candidatus Rickettsia barbariae" Cretocypriensis. These results confirm the presence of a spectrum of SFG Rickettsiae on the island. Further studies are necessary to gain better knowledge on the epidemiology of SFG Rickettsiae in Cyprus.

Rickettsia conorii infection stimulates the expression of ISG15 and ISG15 protease UBP43 in human microvascular endothelial cells

Rickettsia conorii, an obligate intracellular bacterium and the causative agent of Mediterranean spotted fever, preferentially infects microvascular endothelial cells of the mammalian hosts leading to onset of innate immune responses, characterized by the activation of intracellular signaling mechanisms, release of pro-inflammatory cytokines and chemokines, and killing of intracellular rickettsiae. Our recent studies have shown that interferon (IFN)-β, a cytokine traditionally considered to be involved in antiviral immunity, plays an important role in the autocrine/paracrine regulation of host defense mechanisms and control of R. conorii growth in the host endothelial cells. Here, we show that R. conorii infection induces the expression of ISG15 (an interferon-stimulated gene coding a protein of 17kD) and UBP43 (an ISG15-specific protease) at the levels of mRNA and protein and report the evidence of ISGylation of as yet unidentified target proteins in cultured human microvascular endothelium. Infection-induced expression of ISG15 and UBP43 requires intracellular replication of rickettsiae and production of IFN-β, because treatment with tetracycline and presence of an antibody capable of neutralizing IFN-β activity resulted in near complete attenuation of both responses. Inhibition of R. conorii-induced ISG15 by RNA interference results in significant increase in the extent of rickettsial replication, whereas UBP43 knockdown yields a reciprocal inhibitory effect. In tandem, these results demonstrate the stimulation of interferon-β-mediated innate immune mechanisms capable of perturbing the growth and replication of pathogenic rickettsiae and provide first evidence for ISG15-mediated post-translational modification of host cellular proteins during infection with an intracellular bacterium.

Effect of rickettsial toxin VapC on its eukaryotic host

Rickettsia are intracellular bacteria typically associated with arthropods that can be transmitted to humans by infected vectors. Rickettsia spp. can cause mild to severe human disease with a possible protection effect of corticosteroids when antibiotic treatments are initiated. We identified laterally transferred toxin-antitoxin (TA) genetic elements, including vapB/C, in several Rickettsia genomes and showed that they are functional in bacteria and eukaryotic cells. We also generated a plaque assay to monitor the formation of lytic plaques over time and demonstrated that chloramphenicol accelerates host cell lysis of vapB/C-containing Rickettsia. Whole-genome expression, TUNEL and FISH assays on the infected cells following exposure to the antibiotic revealed early apoptosis of host cells, which was linked to over-transcription of bacterial vapB/C operons and subsequent cytoplasmic VapC toxin release. VapC that is expressed in Escherichia coli and Saccharomyces cerevisiae or microinjected into mammalian cells is toxic through RNase activity and is prevented by dexamethasone. This study provides the first biological evidence that toxin-antitoxin elements act as pathogenic factors in bacterial host cells, confirming comparative genomic evidence of their role in bacterial pathogenicity. Our results suggest that early mortality following antibiotic treatment of some bacterial infections can be prevented by administration of dexamethasone.

Tick-borne rickettsioses, neglected emerging diseases in rural Senegal

BACKGROUND

Rickettsioses are one of the most important causes of systemic febrile illness among travelers from developed countries, but little is known about their incidence in indigenous populations, especially in West Africa.

METHODOLOGY/PRINCIPAL FINDINGS

Overall seroprevalence evaluated by immunofluorescence using six rickettsial antigens (spotted fever and typhus group) in rural populations of two villages of the Sine-Saloum region of Senegal was found to be 21.4% and 51% for spotted fever group rickettsiae for Dielmo and Ndiop villages, respectively. We investigated the role of tick-borne rickettsiae as the cause of acute non-malarial febrile diseases in the same villages. The incidence of rickettsial DNA in 204 blood samples from 134 (62M and 72F) febrile patients negative for malaria was studied. DNA extracted from whole blood was tested by two qPCR systems. Rickettsial DNA was found in nine patients, eight with Rickettsia felis (separately reported). For the first time in West Africa, Rickettsia conorii was diagnosed in one patient. We also tested 2,767 Ixodid ticks collected in two regions of Senegal (Niakhar and Sine-Saloum) from domestic animals (cows, sheep, goats, donkeys and horses) by qPCR and identified five different pathogenic rickettsiae. We found the following: Rickettsia aeschlimannii in Hyalomma marginatum rufipes (51.3% and 44.8% in Niakhar and Sine-Saloum region, respectively), in Hyalomma truncatum (6% and 6.8%) and in Rhipicephalus evertsi evertsi (0.5%, only in Niakhar); R. c. conorii in Rh. e. evertsi (0.4%, only in Sine-Saloum); Rickettsia massiliae in Rhipicephalus guilhoni (22.4%, only in Niakhar); Rickettsia sibirica mongolitimonae in Hyalomma truncatum (13.5%, only in Sine-Saloum); and Rickettsia africae in Rhipicephalus evertsi evertsi (0.7% and 0.4% in Niakhar and Sine-Saloum region, respectively) as well as in Rhipicephalus annulatus (20%, only in Sine-Saloum). We isolated two rickettsial strains from H. truncatum: R. s. mongolitimonae and R. aeschlimannii.

CONCLUSIONS/SIGNIFICANCE

We believe that together with our previous data on the high prevalence of R. africae in Amblyomma ticks and R. felis infection in patients, the presented results on the distribution of pathogenic rickettsiae in ticks and the first R. conorii case in West Africa show that the rural population of Senegal is at risk for other tick-borne rickettsioses, which are significant causes of febrile disease in this area.

Diversity of life-threatening complications due to Mediterranean spotted fever in returning travelers

BACKGROUND

Mediterranean spotted fever (MSF) is a tick-borne infection caused by Rickettsia conorii conorii mainly endemic in the Mediterranean Basin. Although usually considered as a benign disease, severe forms of MSF have been sporadically reported.

METHODS

We report on three patients who developed severe MSF complications after a stay in Morocco. Literature was reviewed to assess the frequency and pattern of MSF complications in the largest reported case series in endemic countries.

RESULTS

Each of our three patients diagnosed with MSF presented with a different complicated course: one with meningoencephalitis, one with lung embolism and one with septic shock and multi organ failure. In published series, rate of complications (defined as severe organ involvement) ranged from 1% to 20%. However, study designs and settings were highly variable and did not allow for relevant comparisons. Meningoencephalitis and shock with multi organ failure were the most frequently observed complications. Mortality of severe course was up to 20% in some series.

CONCLUSION

Severe organ involvement is not infrequent in patients with Mediterranean spotted fever and fatal outcome is regularly reported. Because presentations of complicated course may be extremely diverse, a high index of suspicion is required in febrile patients with potential exposure, in particular if skin rash and/or eschar are found. Early appropriate antibiotherapy is crucial to improve outcome.

Review of microarray studies for host-intracellular pathogen interactions

Obligate intracellular bacteria are privileged soldiers on the battlefield that represent host-pathogen interactions. Microarrays are a powerful technology that can increase our knowledge about how bacteria respond to and interact with their hosts. This review summarizes the limitations inherent to host-pathogen interaction studies and essential strategies to improve microarray investigations of intracellular bacteria. We have compiled the comparative genomic and gene expression analyses of obligate intracellular bacteria currently available from microarrays. In this review we explore ways in which microarrays can be used to identify polymorphisms in different obligate intracellular bacteria such as Coxiella burnetii, Chlamydia trachomatis, Ehrlichia chaffeensis, Rickettsia prowazekii and Tropheryma whipplei. These microarray studies reveal that, while genomic content is highly conserved in obligate intracellular bacteria, genetic polymorphisms can potentially occur to increase bacterial pathogenesis. Additionally, changes in the gene expression of C. trachomatis throughout its life cycle, as well as changes in the gene expression profile of the pathogens R. prowazekii, Rickettsia rickettsii, Rickettsia typhi, T. whipplei and C. trachomatis following environmental changes, are discussed. Finally, an in vivo model of Rickettsia conorii within the skin is discussed. The gene expression analyses highlight the capacity of obligate intracellular bacteria to adapt to environmental changes and potentially to thwart the host response.

Diagnosis and treatment of tick infestation and tick-borne diseases with cutaneous manifestations

Hard and soft ticks may be associated directly or indirectly with a number of dermatoses, both infectious and inflammatory in origin. Morbidity may occur as a result of tick bites, tick toxicosis, and even infestation. These arthropod vectors may transmit life-threatening protozoan, bacterial, rickettsial, and viral diseases with systemic and cutaneous findings. Additionally, ticks may transmit more than one pathogen with subsequent human coinfection. This article reviews the presentation of tick-borne illnesses and the medical management of these diseases. Among others, diseases such as ehrlichiosis, anaplasmosis, babesiosis, tularemia, borrelioses, tick-borne encephalitides, rickettsial spotted fevers, and tick typhus are discussed in this article. The recognition of skin manifestations associated with these diseases is paramount to early diagnosis and treatment initiation.

Host-cell interactions with pathogenic Rickettsia species

Pathogenic Rickettsia species are Gram-negative, obligate intracellular bacteria responsible for the spotted fever and typhus groups of diseases around the world. It is now well established that a majority of sequelae associated with human rickettsioses are the outcome of the pathogen's affinity for endothelium lining the blood vessels, the consequences of which are vascular inflammation, insult to vascular integrity and compromised vascular permeability, collectively termed 'Rickettsial vasculitis'. Signaling mechanisms leading to transcriptional activation of target cells in response to Rickettsial adhesion and/or invasion, differential activation of host-cell signaling due to infection with spotted fever versus typhus subgroups of Rickettsiae, and their contributions to the host's immune responses and determination of cell fate are the major subtopics of this review. Also included is a succinct analysis of established in vivo models and their use for understanding Rickettsial interactions with host cells and pathogenesis of vasculotropic rickettsioses. Continued progress in these important but relatively under-explored areas of bacterial pathogenesis research should further highlight unique aspects of Rickettsial interactions with host cells, elucidate the biological basis of endothelial tropism and reveal novel chemotherapeutic and vaccination strategies for debilitating Rickettsial diseases.