Antigenic polypeptides of Israeli spotted fever isolates compared with other spotted fever group rickettsiae

The presence of foci of Rickettsia conorii infection in China

China is not considered as an endemic area of Rickettsia conorii, so there is no routine clinical way to diagnose this infection. This study aims to determine whether 2 febrile patients who had a tick bite in East China were indeed infected with R. conorii. The citrate synthase gene (gltA) was amplified with universal rickettsial primers by real-time fluorescent PCR from the patients' blood samples. Nested PCR was used to amplify the outer membrane protein A gene (ompA) for positive specimens. PCR products were further identified and analyzed through nucleic acid sequencing. Positive amplification of the gltA and ompA genes was found in both patients. The nucleotide sequences (303 bp) of the ompA gene of the 2 patients had high homology (99%) with the R. conorii Indian tick typhus strain in GenBank. A more than 4-fold increase in IgG against R. conorii provided supportive evidence of SFG Rickettsia infection. And the rapid recovery after doxycycline treatment also supported a rickettsial cause for the disease. Physicians in East China should be aware of human infections with R. conorii. PCR-based diagnostic methods offer a rapid and precise way to diagnose rickettsiosis, improving patient identification and management.

Spotted Fever Group Rickettsioses in Israel, 2010-2019

In a multicenter, nationwide, retrospective study of patients hospitalized with spotted fever group rickettsiosis in Israel during 2010-2019, we identified 42 cases, of which 36 were autochthonous. The most prevalent species was the Rickettsia conorii Israeli tick typhus strain (n = 33, 79%); infection with this species necessitated intensive care for 52% of patients and was associated with a 30% fatality rate. A history of tick bite was rare, found for only 5% of patients; eschar was found in 12%; and leukocytosis was more common than leukopenia. Most (72%) patients resided along the Mediterranean shoreline. For 3 patients, a new Rickettsia variant was identified and had been acquired in eastern, mountainous parts of Israel. One patient had prolonged fever before admission and clinical signs resembling tickborne lymphadenopathy. Our findings suggest that a broad range of Rickettsia species cause spotted fever group rickettsiosis in Israel.

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.

Host- and microbe-related risk factors for and pathophysiology of fatal Rickettsia conorii infection in Portuguese patients

BACKGROUND

The pathophysiologic mechanisms that determine the severity of Mediterranean spotted fever (MSF) and the host-related and microbe-related risk factors for a fatal outcome are incompletely understood.

METHODS

This prospective study used univariate and multivariate analyses to determine the risk factors for a fatal outcome for 140 patients with Rickettsia conorii infection admitted to 13 Portuguese hospitals during 1994-2006 with documented identification of the rickettsial strain causing their infection.

RESULTS

A total of 71 patients (51%) were infected with the Malish strain of Rickettsia conorii, and 69 (49%) were infected with the Israeli spotted fever (ISF) strain. Patients were admitted to the intensive care unit (40 [29%]), hospitalized as routine inpatients (95[67%]), or managed as outpatients (5[4%]). Death occurred in 29 adults (21%). A fatal outcome was significantly more likely for patients infected with the ISF strain, and alcoholism was a risk factor. The pathophysiology of a fatal outcome involved significantly greater incidence of petechial rash, gastrointestinal symptoms, obtundation and/or confusion, dehydration, tachypnea, hepatomegaly, leukocytosis, coagulopathy, azotemia, hyperbilirubinemia, and elevated levels of hepatic enzymes and creatine kinase. Some, but not all, of these findings were observed more often in ISF strain-infected patients.

CONCLUSIONS

Although fatalities and similar clinical manifestations occurred among both groups of patients, the ISF strain was more virulent than the Malish strain. Multivariate analysis revealed that acute renal failure and hyperbilirubinemia were most strongly associated with a fatal outcome.

Proposal to create subspecies of Rickettsia conorii based on multi-locus sequence typing and an emended description of Rickettsia conorii

BACKGROUND

Rickettsiae closely related to the Malish strain, the reference Rickettsia conorii strain, include Indian tick typhus rickettsia (ITTR), Israeli spotted fever rickettsia (ISFR), and Astrakhan fever rickettsia (AFR). Although closely related genotypically, they are distinct serotypically. Using multilocus sequence typing (MLST), we have recently found that distinct serotypes may not always represent distinct species within the Rickettsia genus. We investigated the possibility of classifying rickettsiae closely related to R. conorii as R. conorii subspecies as proposed by the ad hoc committee on reconciliation of approaches to bacterial systematics. For this, we first estimated their genotypic variability by using MLST including the sequencing of 5 genes, of 31 rickettsial isolates closely related to R. conorii strain Malish, 1 ITTR isolate, 2 isolates and 3 tick amplicons of AFR, and 2 ISFR isolates. Then, we selected a representative of each MLST genotype and used multi-spacer typing (MST) and mouse serotyping to estimate their degree of taxonomic relatedness.

RESULTS

Among the 39 isolates or tick amplicons studied, four MLST genotypes were identified: i) the Malish type; ii) the ITTR type; iii) the AFR type; and iv) the ISFR type. Among these four MLST genotypes, the pairwise similarity in nucleotide sequence varied from 99.8 to 100%, 99.4 to 100%, 98.2 to 99.8%, 98.4 to 99.8%, and 99.2 to 99.9% for 16S rDNA, gltA, ompA, ompB, and sca4 genes, respectively. Representatives of the 4 MLST types were also classified within four types using MST genotyping as well as mouse serotyping.

CONCLUSION

Although homogeneous genotypically, strains within the R. conorii species show MST genotypic, serotypic, and epidemio-clinical dissimilarities. We, therefore, propose to modify the nomenclature of the R. conorii species through the creation of subspecies. We propose the names R. conorii subsp. conorii subsp. nov. (type strain = Malish, ATCC VR-613), R. conorii subspecies indica subsp. nov. (type strain = ATCC VR-597), R. conorii subspecies caspia subsp. nov. (type strain = A-167), and R. conorii subspecies israelensis subsp. nov. (type strain = ISTT CDC1). The description of R. conorii is emended to accomodate the four subspecies.

Report of eight cases of fatal and severe Mediterranean spotted fever in Portugal

Mediterranean spotted fever (MSF), endemically present, is associated with a low mortality and morbidity in Portugal. Etiological agents are Malish and Israeli tick typhus strains of Rickettsia conorii. In the last few years severe forms of MSF have emerged, with patients presenting atypical symptoms, major neurological manifestations, and multiorgan involvement, who have required intensive care facilities. Advanced age, underlying chronic disease, and delay of appropriate treatment are bad prognostic factors. In the acute phase of diagnosis, serological studies are delayed, inconclusive, and often unhelpful. A definitive diagnosis can only be made using isolation or molecular biology which can establish and clearly identify agents. Using evidence-based case reports, clinical and laboratory data were evaluated from patients with severe or fatal MSF observed in Garcia da Orta Hospital-Almada. Of the eight reference cases, four died, three in an acute fulminant stage. Of the survivors, four presented atypical involvement: ocular inoculation, massive gastric hemorrhage, acute respiratory disease (ARDS), and necrotizing vasculitis. Diagnosis by isolation of the agent was made in two cases, by immunohistochemistry in three, and by the indirect fluorescent antibody test (IFA) in three others. Israeli tick typhus and Malish R. conorii strains were isolated once each in fatal cases. In early stages, diagnosis continues to be clinical and patients should start appropriate therapy without delay if clinical suspicion of rickettsiosis arises to prevent poor outcome. Patients ranged in age from 39 to 71 years (mean 60), APACHE II ranged from 15 to 38 points and TISS 28 was between 24 and 46 points. In reported cases severity of disease was not obviously related to the usual comorbidities. Accelerated clinical course may not suggest classical MSF. Another relevant factor was prior prescription of an inappropriate antibiotic that contributed to misleading clinical features. The reported complications and atypical manifestations illustrate well the diversity of this disease.

Genetic analysis of isolates of the spotted fever group of rickettsiae belonging to the R. conorii complex

The cytoplasmic 120 kDa antigen genes of 9 isolates of Rickettsia conorii (RC), 12 isolates of R. africae (RA), and 3 isolates of Israeli tick typhus rickettsiae (ISTT) were compared for restriction fragment length polymorphisms (RFLP) present in portions of the open reading frame amplified by polymerase chain reaction (PCR). Initially, DNAs from 13 species or serotypes of spotted fever group rickettsiae were used to select restriction enzymes (RE) that detected RFLP in gene fragments amplified with primer pairs 483WF/1514R and 764F/3409R. Among the R. conorii complex isolates, Dpn II gave RFLP differentiating all three serotypes. Unique RE patterns were obtained for RC with Bsr I and Hinf I, for RA with Mwo I, Pst I and Ssp I, and for ISTT with Hpa II. While RFLP typing of the 120 kDa gene permitted rapid separation of R. conorii complex isolates into three groups corresponding to the RC, RA, and ISTT rOmp serotypes, additional intragroup genetic variation was also detected in all three serotypes.

Taxonomic relationships among spotted fever group rickettsiae as revealed by antigenic analysis with monoclonal antibodies

The spotted fever group (SFG) is made up of more than 20 different rickettsial species and strains. Study of the taxonomic relationships among the group has been attempted by phenotypic, genotypic, and phylogenetic analyses. In this study, we determined taxonomic relationships among the SFG rickettsiae by comparative analysis of immunogenic epitopes reactive against a panel of monoclonal antibodies. A total of 98 monoclonal antibodies, which were directed against epitopes on the major immunodominant proteins or on the lipopolysaccharide-like antigens of strains of Rickettsia africae, Rickettsia conorii, Rickettsia massiliae, Rickettsia akari, Rickettsia sibirica, and Rickettsia slovaca, were used in the study. The distribution and expression of the epitopes among 29 SFG rickettsiae and Rickettsia bellii were assessed by determination of reaction titers in a microimmunofluorescence assay. The results were scored as numerical taxonomic data, and cluster analysis was used to construct a dendrogram. The architecture of this dendrogram was consistent with previous taxonomic studies, and the implications of this and other findings are discussed.

Human and tick spotted fever group Rickettsia isolates from Israel: a genotypic analysis

The genomes of spotted fever group rickettsiae isolated in different geographical areas of Israel (two from ticks and four from humans, obtained over a span of 20 years) were studied by polymerase chain reaction (PCR) and restriction endonuclease fragment length polymorphism (RFLP) analysis. The human isolates were obtained from patients suffering from rickettsial disease of different degrees of severity. The PCR products obtained with five pairs of oligonucleotide primers (two primer sets derived from the 190-kDa polypeptide gene and three from the 120-kDa polypeptide gene) and cleaved with restriction endonucleases were used to study the Israeli isolates and reference Rickettsia conorii isolates. Subtle differences between the PCR-RFLP patterns of Israeli isolates and the two R. conorii reference strains (Moroccan and no. 7) were seen when the PCR products derived from the 190-kDa gene-derived primer sets were digested. All of the Israeli isolates were identical by RFLP analysis using all of the primer sets. This study showed that the Israeli spotted fever group isolates (from both ticks and humans) were genetically homogeneous by the criteria used in this study, despite the time and location differences in their original isolation, and different as a group from R. conorii.

Western blot analysis of immune response to Legionella bozemanii antigens

The immune response to individual major antigens of Legionella bozemanii was studied in 67 sera from 26 inpatients with febrile disease using immunoblotting techniques. All the patients had fever of unknown origin and showed strong serological reactions to L bozemanii that cross-reacted with Rickettsia typhi, as determined by a standard indirect microimmunofluorescence assay. Sera analysed by western blotting reacted with 12-14 molecular components of L bozemanii with apparent molecular weights ranging from 14,000 to 94,000 daltons. These reactions compared well with a reference system using antisera of rabbits immunised with the same strain of Legionella. The three major cross-reactive components of R typhi were polypeptide antigens of 94,000, 67,000 and 43,000 daltons. It is concluded that western blotting can help in the differential diagnosis of patients with fever of unknown origin whose sera cross-react to L bozemanii and R typhi.