Comparison of serologic typing, sodium dodecyl sulfate-polyacrylamide gel electrophoresis protein analysis, and genetic restriction fragment length polymorphism analysis for identification of rickettsiae: characterization of two new rickettsial strains

Association of SFG Rickettsia massiliae and Candidatus Rickettsia shennongii with Different Hard Ticks Infesting Livestock Hosts

Ixodid ticks are responsible for the transmission of various intracellular bacteria, such as the Rickettsia species. Little Information is available about the genetic characterization and epidemiology of Rickettsia spp. The current study was designed to assess the tick species infesting various livestock hosts and the associated Rickettsia spp. in Pakistan. Ticks were collected from different livestock hosts (equids, cattle, buffaloes, sheep, goats, and camels); morphologically identified; and screened for the genetic characterization of Rickettsia spp. by the amplification of partial fragments of the gltA, ompA and ompB genes. Altogether, 707 ticks were collected from 373 infested hosts out of 575 observed hosts. The infested hosts comprised 105 cattle, 71 buffaloes, 70 sheep, 60 goats, 34 camels, and 33 equids. The overall occurrence of Rickettsia spp. was 7.6% (25/330) in the tested ticks. Rickettsia DNA was detected in Rhipicephalus haemaphysaloides (9/50, 18.0%), followed by Rhipicephalus turanicus (13/99, 13.1%), Haemaphysalis cornupunctata (1/18, 5.5%), and Rhipicephalus microplus (2/49, 4.1%); however, no rickettsial DNA was detected in Hyalomma anatolicum (71), Hyalomma dromedarii (35), and Haemaphysalis sulcata (8). Two Rickettsia agents were identified based on partial gltA, ompA, and ompB DNA sequences. The Rickettsia species detected in Rh. haemaphysaloides, Rh. turanicus, and Rh. microplus showed 99-100% identity with Rickettsia sp. and Candidatus Rickettsia shennongii, and in the phylogenetic trees clustered with the corresponding Rickettsia spp. The Rickettsia species detected in Rh. haemaphysaloides, Rh. turanicus, Rh. microplus, and Ha. cornupunctata showed 100% identity with R. massiliae, and in the phylogenetic trees it was clustered with the same species. Candidatus R. shennongii was characterized for the first time in Rh. haemaphysaloides, Rh. turanicus, and Rh. microplus. The presence of SFG Rickettsia spp., including the human pathogen R. massiliae, indicates a zoonotic risk in the study region, thus stressing the need for regular surveillance.

Molecular Detection of Tick-Borne Bacteria from Amblyomma (Acari: Ixodidae) Ticks Collected from Reptiles in South Africa

Reptiles are hosts for various tick species and tick-associated organisms, many of which are zoonotic. However, little is known about the presence and diversity of tick-borne bacteria infecting reptiles and their ticks in South Africa. Amblyomma ticks (n = 253) collected from reptiles were screened for the presence of Coxiella, Anaplasma, Rickettsia, and Borrelia species by amplification, sequencing and phylogenetic analysis of the 16S rRNA, 23S rRNA, gltA, OmpA, and Flagellin genes, respectively. This study recorded the presence of reptile associated Borrelia species and Coxiella-like endosymbiont in South Africa for the first time. Furthermore, a spotted fever group Rickettsia species was observed in 7 Amblyomma marmoreum and 14 Amblyomma sylvaticum from tortoises of genera Kinixys and Chersina. Francisella-like endosymbiont was observed from 2 Amblyomma latum collected from the Mozambique spitting cobra, Naja mossambica. Coxiella burnetii and Anaplasma spp., were not detected from the current samples. Although the direct evidence that reptiles can act as reservoir hosts remains to be determined, observations from this study provide indications that reptilian ticks may play a role in the transmission of pathogenic bacteria to homothermic animals. Furthermore, the absence of Anaplasma spp., and C. burnetii does not mean that these pathogens should be completely neglected.

The role of Rhipicephalus sanguineus ticks parasitizing dogs in the spread of tick-borne rickettsial pathogens in the city of Sevastopol

The occurrence of Mediterranean fever with periods of increase and decrease has been recorded in the Crimean peninsula. The city of Sevastopol and its vicinity are known endemic areas for this disease. Some of the most active agents in the spread of this rickettsiosis are feral and abandoned dogs. The aim of this study was to test ticks parasitizing dogs in Sevastopol for the presence of Rickettsia using molecular methods. The testing of ticks was carried out using real-time PCR and the 'Real Best DNA Rickettsia species' kit (AO 'Vector-Best') followed by sequence identification of the rickettsial DNA detected. The DNA marker for Rickettsia species (a conservative area of citrate synthase gene, gltA) was detected in 16 of 84 (19.1%) samples of Rhipicephalus sanguineus ticks tested. Larger fragments of gltA, ompA and sca4 were amplified and sequenced for 10 of 16 PCR-positive samples. Rickettsia DNA amplified from eight of the samples matched the sequence of Rickettsia conorii conorii Malish, the causative agent of Mediterranean fever. The sequences of Rickettsia DNA from two other ticks had the closest match to homologous fragments of Rickettsia massiliae, a pathogenic spotted fever rickettsia that was identified in the Crimean Peninsula for the first time as part of this study. The detection of two pathogenic species of Rickettsia in the studied ticks suggests the potential for two rickettsial diseases in the region and warrants further epidemiological and clinical studies.

Molecular investigation of Rickettsia spp. and Francisella tularensis in ticks from three provinces of Turkey

Ticks are obligate hematophagous ectoparasites as well as mechanical and biological vectors of a wide variety of microbial pathogens. To date, 19 tick-borne diseases have been reported from Turkey. In this study, ticks collected from Aydın, İzmir and Şanlıurfa provinces of Turkey were identified using morphological and molecular methods. After the presence of bacterial DNA was checked, Rickettsia spp. and Francisella tularensis were investigated in bacterial DNA-positive tick specimens by PCR. Furthermore, amplicons belonging to tick specimens and positive bacterial samples were sequenced and processed for BLAST, alignment and phylogenetic analysis. As a result, seven tick species were identified: Rhipicephalus sanguineus, Rh. bursa, Rh. turanicus, Hyalomma marginatum, Hy. aegyptium, Hy. anatolicum and Haemaphysalis erinacei. Fifty-five tick specimens tested positive for bacterial DNA and among them, rickettsial DNA was found in five ticks (infection rate = 9.1%) belonging to Hy. marginatum, Hy. aegyptium, Rh. bursa and Rh. turanicus. Of the five Rickettsia-positive ticks, three contained Rickettsia aeschlimannii, one Ri. massiliae and one an unidentified Rickettsia sp. No Francisella tularensis DNA was detected. Sequence analysis of the ompB gene indicated two novel single nucleotide polymorphisms (SNP) in two different Ri. aeschlimannii strains and two novel SNPs as well as a novel insertion (GACGGT) were found in Rickettsia sp. This study indicated the presence of polymorphic Rickettsia species in ticks from Turkey.

Molecular confirmation & characterization of Rickettsia conorii in north India: A report of three cases

Background & objectives

In India, spotted fever group rickettsiae (SFGR) are an underdiagnosed cause of acute febrile illness (AFI). The non-specific Weil-Felix test is the first diagnostic modality for the diagnosis of SFGR in many laboratories due to the lack of advanced diagnostic facilities in developing countries. The aim of this study was to detect SFGR using molecular methods in the patients, presenting with AFI in a tertiary care centre in north India.

Methods

Consecutive patients (>14 yr of age) with AFI were enrolled over a six month period. Standard investigations for common pathogens causing AFI in India (malaria, dengue, scrub typhus, leptospirosis and enteric fever) were carried out. In patients who were negative for all of the above investigations, blood was subjected to polymerase chain reaction (PCR) targeting outer membrane protein A (ompA) gene of Rickettsia.

Results

Of the 51 patients with an undiagnosed aetiology, three were positive by ompA PCR. Two of the PCR products produced good sequences and BLAST identification confirmed them as Rickettsia conorii. The sequences of R. conorii reported from south India clustered with two previously reported novel rickettsial genotypes. The study sequences clustered in a group different from that of Rickettsia spp. of the south Indian sequences reported earlier.

Interpretation & conclusions

This study showed the existence of R. conorii in north India. Testing for SFGR may be included in the diagnostic workup of AFI for better disease management.

Seasonal distribution of Rickettsia spp. in ticks in northeast Algeria

This article discusses research conducted on the sampling of two tick species: Ixodes ricinus and Rhipicephalus bursa. Ticks were collected in northern Algeria (El Tarf) in 2014 and studied for differences in abundance and seasonal distribution of population dynamics, as well as tested by PCR for the presence of Rickettsia spp. By molecular tools, four Rickettsia pathogens agents were detected: R. helvetica, R. monacensis, R. raoultii and R. massiliae.

Suspected and Confirmed Vector-Borne Rickettsioses of North America Associated with Human Diseases

The identification of pathogenic rickettsial agents has expanded over the last two decades. In North America, the majority of human cases are caused by tick-borne rickettsioses but rickettsiae transmitted by lice, fleas, mites and other arthropods are also responsible for clinical disease. Symptoms are generally nonspecific or mimic other infectious diseases; therefore, diagnosis and treatment may be delayed. While infection with most rickettsioses is relatively mild, delayed diagnosis and treatment may lead to increased morbidity and mortality. This review will discuss the ecology, epidemiology and public health importance of suspected and confirmed vector-transmitted Rickettsia species of North America associated with human diseases.

Detection of Rickettsia massiliae in Rhipicephalus sanguineus from the eastern United States

We report the first evidence of Rickettsia massiliae in the brown dog tick, Rhipicephalus sanguineus, from the East Coast of the United States. As part of routine pathogen surveillance, DNA samples from ixodid ticks were tested for spotted fever group rickettsiae by nested PCR. A R. massiliae-positive tick was collected off a beagle mix recently rescued from North Carolina. Infection was confirmed by partial sequence analysis of the htrA, gltA, ompB, ompA, and sca4 genes, which had 100% identity to a R. massiliae isolate from Arizona.

Genome sequence of Rickettsia conorii subsp. indica, the agent of Indian tick typhus

Rickettsia conorii subsp. indica is the agent of Indian tick typhus. The present study reports the draft genome of Rickettsia conorii subsp. indica strain ITTR (ATCC VR-597).

A focus of dogs and Rickettsia massiliae-infected Rhipicephalus sanguineus in California

A recurrent focus of Rhipicephalus sanguineus infestation was investigated in a suburban area of southern California after reports of suspected Rocky Mountain spotted fever in two dogs on the same property. Abundant quantities of Rh. sanguineus were collected on the property and repeatedly from each dog, and Rickettsia massiliae DNA was detected by polymerase chain reaction (PCR). Whole blood and serum samples from four dogs were tested by using PCR and microimmunofluorescent assay for antibodies against spotted fever group rickettsiae. Serum samples from all four dogs contained antibodies reactive with R. massiliae, R. rhipicephali, R. rickettsii, and 364D Rickettsia but no rickettsial DNA was detected by PCR of blood samples. Serum cross-absorption and Western blot assays implicated R. massiliae as the most likely spotted fever group rickettsiae responsible for seropositivity. To our knowledge, this is the first detection of R. massiliae in ticks in California.

The science and fiction of emerging rickettsioses

As newly recognized rickettsial diseases and rickettsial pathogens increase in scope and magnitude, several elements related to the concept of emerging rickettsioses deserve consideration. Newly identified rickettsiae may be mildly pathogenic, or perhaps even nonpathogenic, and have little direct impact on human or animal health, yet nonetheless wield considerable influence on the epidemiology and ecology of historically recognized diseases. In this context "new" rickettsioses provide a lens through which "old" rickettsioses are more accurately represented. Predicting pathogen from nonpathogen is not an exact science, particularly as so few rickettsiae have been broadly accepted as nonpathogenic by contemporary rickettsiologists. However, various factors relating to specific physiologic requirements and molecular machinery of the particular rickettsia, as well as characteristics of its invertebrate host that either position or exclude the rickettsia from infecting a human host, must be considered. Close inspection of mild or atypical forms of historically recognized rickettsioses and a greater emphasis on culture- and molecular-based diagnostic techniques are the keys to identifying future rickettsial agents of disease.

Isolation and identification of Rickettsia massiliae from Rhipicephalus sanguineus ticks collected in Arizona

Twenty Rhipicephalus sanguineus ticks collected in eastern Arizona were tested by PCR assay to establish their infection rate with spotted fever group rickettsiae. With a nested PCR assay which detects a fragment of the Rickettsia genus-specific 17-kDa antigen gene (htrA), five ticks (25%) were found to contain rickettsial DNA. One rickettsial isolate was obtained from these ticks by inoculating a suspension of a triturated tick into monolayers of Vero E6 monkey kidney cells and XTC-2 clawed toad cells, and its cell culture and genotypic characteristics were determined. Fragments of the 16S rRNA, GltA, rOmpA, rOmpB, and Sca4 genes had 100%, 100%, 99%, 99%, and 99%, respectively, nucleotide similarity to Rickettsia massiliae strain Bar29, previously isolated from R. sanguineus in Catalonia, Spain (L. Beati et al., J. Clin. Microbiol. 34:2688-2694, 1996). The new isolate, AZT80, does not elicit cytotoxic effects in Vero cells and causes a persistent infection in XTC-2 cells. The AZT80 strain is susceptible to doxycycline but resistant to rifampin and erythromycin. Whether R. massiliae AZT80 is pathogenic or infectious for dogs and humans or can cause seroconversion to spotted fever group antigens in the United States is unknown.

Tick-borne rickettsioses around the world: emerging diseases challenging old concepts

During most of the 20th century, the epidemiology of tick-borne rickettsioses could be summarized as the occurrence of a single pathogenic rickettsia on each continent. An element of this paradigm suggested that the many other characterized and noncharacterized rickettsiae isolated from ticks were not pathogenic to humans. In this context, it was considered that relatively few tick-borne rickettsiae caused human disease. This concept was modified extensively from 1984 through 2005 by the identification of at least 11 additional rickettsial species or subspecies that cause tick-borne rickettsioses around the world. Of these agents, seven were initially isolated from ticks, often years or decades before a definitive association with human disease was established. We present here the tick-borne rickettsioses described through 2005 and focus on the epidemiological circumstances that have played a role in the emergence of the newly recognized diseases.

Transmission of Rickettsia massiliae in the tick, Rhipicephalus turanicus

Rickettsia massiliae, strain Bar29, was detected in engorged female ticks of the Rhiphicephalus sanguineus group collected in Corsica, a French Mediterranean island. Ticks were identified by molecular analysis as Rhipicephalus turanicus (Pomerantsev) (Acari: Ixodidae). Twenty larvae of the second generation obtained from a R. massiliae-infected, engorged female were tested by polymerase chain reaction (PCR) and all were positive for R. massiliae. Larvae of the same cohort were fed on rabbits and specimens of subsequent stages of the second and third generation of ticks were tested by PCR. Both transovarial and transstadial transmission were demonstrated; the transovarial transmission rate was estimated at 100%. A high filial infection rate was demonstrated; 132 out of 134 larvae obtained from five infected females of the fourth generation were infected. When saliva samples from half-engorged Rh. turanicus of the second generation were tested by PCR, four out of five were positive. Rickettsia massiliae was detected in faeces of infected ticks by PCR and immunofluorescence assay, although no rickettsiae could be maintained in culture. Co-feeding/transsexual transmission of R. massiliae Bar29 was demonstrated by feeding male Rh. turanicus on a rabbit with Rhipicephalus sanguineus (Latreille) (Acari: Ixodidae) females (the latter were the only uninfected ticks available). Infection was subsequently detected in nine out of the thirteen females (69.2%). These results suggest that Rh. turanicus ticks are potential vectors and reservoirs for R. massiliae Bar29.

Phylogenetic analysis of spotted fever group Rickettsiae isolated from ticks in Japan

Eight spotted fever group (SFG) rickettsiae isolated from ticks in Japan were classified by phylogenetic analysis based on the nucleotide sequences of both the citrate synthase-encoding gene (gltA) and 190-kDa antigen-encoding gene (rOmpA). In the phylogenetic tree of gltA, strains DT-1 and FLA-1 isolated from the Dermacentor taiwanensis and Haemaphysalis frava ticks, respectively, were placed as Rickettsia japonica, and strains IO-1, IO-2, IO-25, IM-1 and IP-2 from genus Ixodes ticks were placed as Rickettsia helvetica. Strain AT-1 isolated from the Amblyomma testudinarium belonged to the cluster including Rickettsia akari, Rickettsia australis and Rickettsia felis. In the phylogenetic tree of the rOmpA, strains DT-1 and FLA-1 were placed as R. japonica, and strain AT-1 belonged to the cluster including Rickettsia cooleyi and the symbiont of Ixodes scapularis. The rOmpA fragments of 5 Ixodes isolates could not be amplified by PCR. The present study showed that strains DT-1 and FLA-1 were genotypically identical to R. japonica, and 5 Ixodes isolates were associated with the R. helvetica. Based on previous genotypic and antigenic data, and the phylogenetic analysis presented here, strain AT-1 should be considered as a new species among SFG rickettsiae.

Antigenic classification of Rickettsia felis by using monoclonal and polyclonal antibodies

Rickettsia felis is a flea-transmitted rickettsia. There is a discrepancy between its reported phylogenic and phenotypic identifications. Following the first report of R. felis, it was considered by tests with serologic reagents to be closely related to another recognized flea-transmitted rickettia, R. typhi. Subsequently, it appeared to be more closely related to spotted fever group (SFG) rickettsiae by genetic analysis. In the present work, R. felis was studied by microimmunofluorescence (MIF) serologic typing and with monoclonal antibodies (MAbs). Mouse polyclonal antisera to R. felis cross-reacted only with SFG rickettsiae. A neighbor-joining analysis based on MIF indicated that R. felis is actually related to SFG rickettsiae antigenically, clustering with R. australis, R. akari, and R. montanensis. A panel of 21 MAbs was raised against a 120-kDa protein antigen or a 17-kDa polypeptide of R. felis. They cross-reacted with most members of the SFG rickettsiae but not with R. prowazekii, R. typhi, or R. canadensis of the typhus group (TG) rickettsiae. Sixty-four MAbs previously generated to seven other ricketttsial species were tested with R. felis. Three MAbs reacted with the 120-kDa antigen and were generated by R. africae, R. conorii, and R. akari, respectively. They exhibited cross-reactivities with R. felis. All our data show that R. felis harbors the antigenic profile of an SFG rickettsia.

Antibodies against rickettsia in humans and potential vector ticks from Dhofar, Oman

OBJECTIVE

To determine the extent of rickettsial infections prevalence of potential vector ticks in the rural population of Dhofar, Oman.

METHOD

Human sera (n = 347) were obtained from six rural localities (school children, farmers, outpatients) in Dhofar, Sultanate of Oman. Sera were tested by immunofluorescence for the presence of antibodies reacting with Rickettsia conorii antigen.

RESULTS

More than half the samples (59%) gave positive reactions (titres of at least 1:64). Ticks (n=707) were collected from cattle, camels and goats (n=102) and included Amblyomma variegatum, Hyalomma a. anatolicum, H. dromedarii, H. rufipes and Rhipicephalus spp., all of which can potentially transmit rickettsiae to humans.

CONCLUSION

The results suggest that rickettsial infections are common among the rural population of Dhofar.

Molecular detection of pathogen DNA in ticks (Acari: Ixodidae): a review

Ticks play an important role in human and veterinary medicine, in particular due to their ability to transmit a wide spectrum of pathogenic micro-organisms of protozoal, rickettsial, bacterial and viral origin. Pathogens in ticks can be identified by conventional methods such as indirect immunofluorescence, isolation in cell culture or by using histological staining techniques. However, the advent of the polymerase chain reaction (PCR) has resulted in tremendous improvements in the specific and sensitive detection of pathogen DNA in ticks. In this paper, literature on DNA extraction methods, PCR protocols, primers and probes, which are in use for the successful detection and identification of pathogens in ticks, are critically reviewed. Some recommendations are also given towards the end of this review.

Ticks feeding on humans: a review of records on human-biting Ixodoidea with special reference to pathogen transmission

In this article, literature records of argasid and ixodid ticks feeding on humans worldwide are provided in view of increased awareness of risks associated with tick bites. Ticks can cause paralyses, toxicoses, allergic reactions and are vectors of a broad range of viral, rickettsial, bacterial and protozoan pathogens. Approximately 12 argasid species (Argas and Ornithodos) are frequently found attached to humans who intrude into tick-infested caves and burrows. Over 20 ixodid tick species are often found on humans exposed to infested vegetation: four of these are Amblyomma species, 7 Dermacentor spp., 3 Haemaphysalis spp., 2 Hyalomma spp. and 6 Ixodes species. Personal protection methods, such as repellents and acaricide-impregnated clothing are advised to minimize contact with infected ticks. Acaricidal control of ixodid ticks is impractical because of their wide distribution in forested areas, but houses infested with soft ticks can be sprayed with acaricidal formulations. Attached ticks should be removed without delay. The best way is to grasp the tick as close to the skin as possible with fine tweezers and pull firmly and steadily without twisting. Finally, despite the fact that most people who are bitten destroy the offending tick in disgust, it is recommended that they preserve specimens in ethanol for taxonomic identification and detection of pathogens by molecular methods.

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.

First isolation of Rickettsia helvetica from Ixodes ricinus ticks in France

Two rickettsial isolates recovered from Ixodes ricinus ticks in Puy-de-Dôme (Central France) were characterized by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, Western blot immunoassay, restriction fragment length polymorphism analysis, and sequencing of a portion of the citrate-synthase gene. By these methods, the isolates appeared to be identical to a member of the spotted fever group rickettsiae, Rickettsia helvetica. This first isolation of Rickettsia helvetica in France has epidemiologic importance; a serosurvey on Mediterranean spotted fever conducted previously in Puy-de-Dôme, where the infection is not endemic, demonstrated a high seroprevalence of nonspecific antibodies directed against spotted fever group rickettsiae lipopolysaccharides, and thus the possibility of infection due to a rickettsia different from Rickettsia conorii was suggested. The isolation of Rickettsia helvetica in anthropophilic ticks in the same area further supports this hypothesis.

Rickettsioses as paradigms of new or emerging infectious diseases

Rickettsioses are caused by species of Rickettsia, a genus comprising organisms characterized by their strictly intracellular location and their association with arthropods. Rickettsia species are difficult to cultivate in vitro and exhibit strong serological cross-reactions with each other. These technical difficulties long prohibited a detailed study of the rickettsiae, and it is only following the recent introduction of novel laboratory methods that progress in this field has been possible. In this review, we discuss the impact that these practical innovations have had on the study of rickettsiae. Prior to 1986, only eight rickettsioses were clinically recognized; however, in the last 10 years, an additional six have been discovered. We describe the different steps that resulted in the description of each new rickettsiosis and discuss the influence of factors as diverse as physicians' curiosity and the adoption of molecular biology-based identification in helping to recognize these new infections. We also assess the pathogenic potential of rickettsial strains that to date have been associated only with arthropods, and we discuss diseases of unknown etiology that may be rickettsioses.

Production of monoclonal antibodies against Rickettsia massiliae and their use in antigenic and epidemiological studies

Rickettsiae are gram-negative, obligate intracellular bacteria which have historically been divided into three groups: the typhus group, the scrub typhus group, and the spotted fever group (SFG). Recently, several new SFG rickettsiae have been characterized, and most of these species are associated with ticks and have, as yet, no known pathogenicity toward humans. Rickettsia massiliae, which is widely distributed in Europe and Africa, is one such rickettsia. In order to investigate the antigenic relationships between R. massiliae and other rickettsial species and to develop a more convenient methodology for identifying R. massiliae, we produced monoclonal antibodies against the type strain (Mtu1T) of R. massiliae by fusing immunized splenocytes with SP2/0-Ag14 myeloma cells. A panel of 16 representatives were selected from the 163 positive hybridomas identified on initial screening, and their secreted monoclonal antibodies were further characterized. The reactivities of these 16 monoclonal antibodies with a large panel of rickettsial species were assessed by the microimmunofluorescence assay. All species of the SFG rickettsiae reacted with the monoclonal antibodies directed against epitopes on lipopolysaccharide, which is the common antigen among the SFG rickettsiae. Some closely related species of the SFG, such as Bar29, "R. aeschlimanni," and R. rhipicephali, showed strong cross-reactivities with the monoclonal antibodies directed against epitopes on the two major high-molecular-mass heat-labile proteins (106 and 120 kDa). In addition, species-specific monoclonal antibodies demonstrated that R. massiliae is antigenically different from other rickettsial species. Moreover, these species-specific monoclonal antibodies were successfully used for identifying R. massiliae in the ticks collected from southern France, and are therefore potentially useful tools in the identification and investigation of R. massiliae in ticks in large-scale field work.

Characterization of and application of monoclonal antibodies against Rickettsia africae, a newly recognized species of spotted fever group rickettsia

Rickettsia africae is a newly described species which causes African tick bite fever. Mediterranean spotted fever caused by R. conorii is endemic in the same regions of Africa as tick bite fever, and differentiation of the two syndromes by characterization of their etiological agents is important for epidemiological studies. R. africae and R. conorii are, however, difficult to distinguish, and therefore, our aim was to produce monoclonal antibodies to address this problem. Monoclonal antibodies were produced against R. africae by fusing splenocytes from BALB/C mice immunized with purified rickettsial organisms and SP2/0-Ag14 myeloma cells. A total of 355 hybridomas producing monoclonal antibodies to R. africae were identified by initial screening with six different antigens by microimmunofluorescence assay. A panel of 23 representative monoclonal antibodies were selected and subcloned. This panel was screened with a further 17 different spotted fever group (SFG) rickettsial reference antigens. Of these 23 monoclonal antibodies, 1 cross-reacted with only R. parkeri, whereas the others cross-reacted with more than two different antigens. Immunoblotting indicated that all the monoclonal antibodies were directed against the epitopes on two major high-molecular-mass heat-labile proteins, of which the molecular masses were 128 and 135 kDa, respectively. This monoclonal antibody panel was used successfully to identify R. africae in the blood culture of an infected patient, in infected cells within shell vials, and in infected ticks collected from Africa. Furthermore, the cross-reactivity of each SFG rickettsia with each of these 23 monoclonal antibodies was scored and was used to build a dendrogram of taxonomic relatedness between R. africae and the other SFG rickettsiae on the basis of Jaccard coefficients and unweighted pair group method with arithmetic mean analysis. The relatedness was generally consistent with that obtained by other methods of comparison.

Phenotypic and genotypic characterization of spotted fever group Rickettsiae isolated from Catalan Rhipicephalus sanguineus ticks

Eighty-nine Rhipicephalus sanguineus ticks and 21 Rhipicephalus bursa ticks collected in Catalonia were tested by the hemolymph test to establish their infection rate with spotted fever group rickettsiae. By Giménez staining, 11.2% of the R. sanguineus isolates and 0% of the R. bursa isolates were found to contain rickettsia-like organisms. Six spotted fever group rickettsial strains (Bar29, Bar31, Gir4, Tar1, Tar2, and Tar3) were isolated from these ticks and were characterized by phenotypic and genotypic analyses. PCR followed by restriction fragment length polymorphism analysis showed that the six strains were identical and were characterized by the same restriction profiles as a strain, Mtu5, previously isolated from Rhipicephalus turanicus ticks in the South of France. Microimmunofluorescence serotyping, sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the purified organisms, and Western blot (immunoblot) assay with mouse polyclonal sera confirmed this observation. Pulsed field gel electrophoresis of the whole genome of three of the strains showed that, although closely related, the profile of Tar1 was slightly different from that of the Bar strains. Phylogenetic analysis showed that this new rickettsial sero- and genotype, which will be named the "Catalan strain," is closely related to Rickettsia massiliae. This strain shows an unexpected resistance to rifampin. The epidemiological implications of these findings are considered.

Differentiation of spotted fever group rickettsiae by sequencing and analysis of restriction fragment length polymorphism of PCR-amplified DNA of the gene encoding the protein rOmpA

Currently, the genotypic identification of the spotted fever group (SFG) rickettsiae is based on restriction fragment length polymorphism analysis of PCR-amplified genes coding for the enzyme citrate synthase and the surface proteins rOmpA and rOmpB. A set of useful restriction endonucleases was found following comparison of Rickettsia rickettsii and R. prowazekii sequences. However, by using three PCR amplifications and four enzyme digestions with this set, it was impossible to differentiate between all of the known serotypes of the SFG rickettsiae. We amplified by PCR and sequenced using an automated laser fluorescent DNA sequencer a fragment of the gene encoding the protein rOmpA from 21 serotypes of the SFG rickettsiae. A 632-bp amplification product was obtained for most of the strains, although no product could be obtained by using R. akari, R. australis, R. helvetica, and R. bellii DNAs. We found a characteristic sequence for all strains studied except the two isolates of R. massiliae, isolates GS and Mtul. Using the software package BISANCE, we determined the restriction map of this fragment and identified five potentially useful endonucleases, RsaI, AluI, PstI, XbaI, and AvaII. We confirmed the computer analysis-derived profiles by PCR-restriction fragment length polymorphism analysis. The combination of the profiles obtained after digestion of the PCR product by RsaI and PstI allowed for the differentiation of 16 strains. The use of AluI and XbaI allowed for the characterization of R. parkeri and strain HA-91, respectively. R. africae and strain S were differentiated by AvaII digestion. Thus, using a single PCR amplification, we were able to differentiate all of the SFG rickettsiae whose ompA gene was amplified by PCR.

Isolation, cultivation, and partial characterization of the ELB agent associated with cat fleas

ELB rickettsiae from cat flea homogenates were recovered in tissue culture cells following sequential passage through laboratory rats and the yolk sacs of embryonated chicken eggs. Seven days after inoculation of ELB from the infected yolk sacs, Vero cells and L929 cells were observed to contain intracellular bacteria as demonstrated by Diff Quik and indirect immunofluorescence assay staining. The rickettsial and ELB identity of the cultured agent was confirmed by PCR detection of the 16S rRNA and citrate synthase genes and PCR-restriction fragment length polymorphism analysis of the 17-kDa conserved rickettsial antigen gene. The ELB rickettsiae induced plaques in Vero cells on day 11 postinfection. Rat anti-ELB serum reacted at 1:4,096 to cultured ELB and had lower reactivity to Rickettsia typhi Wilmington (1:1,024), Rickettsia akari Kaplan (1:512), and Rickettsia australis JC (1:64). Spotted fever group polyclonal sera also exhibited lower reactivity to ELB than to the homologous antigen. Coomassie blue-stained sodium dodecyl sulfate-polyacrylamide gel electrophoresis profiles of the ELB isolate and two R. typhi strains were identical.

Genomic and proteinic characterization of strain S, a rickettsia isolated from Rhipicephalus sanguineus ticks in Armenia

Strain S, a spotted fever group (SFG) rickettsia isolated from Rhipicephalus sanguineus ticks collected in Armenia, was identified. Microimmunofluorescence, sodium dodecyl sulfate-polyacrylamide gel protein electrophoresis and Western immunoblotting, PCR and then restriction fragment length polymorphism analysis, pulsed-field gel electrophoresis, and 16S rRNA gene sequencing were used to compare strain S with reference isolates. Strain S was found to possess proteinic, antigenic, and genomic patterns which were unique among SFG rickettsiae. Strain S is characterized by its high degree of pathogenicity for experimental animals, but its role as a potential human pathogen should be determined. The role of R. sanguineus ticks in the epidemiology of SFG rickettsiae is discussed.

Genotype characterization of the bacterium expressing the male-killing trait in the ladybird beetle Adalia bipunctata with specific rickettsial molecular tools

The male-killing ladybird beetle (LB) bacterium (AB bacterium) was analyzed with specific rickettsial molecular biology tools in the LB Adalia bipunctata strains. Eight phenotype-positive LB strains showing mortality of male embryos were amplified with rickettsial genus-specific primers from the gene for citrate synthase (CS) and the gene for a 17-kDa protein and spotted fever group-specific primers from the gene for the 120-kDa outer membrane protein (ompB). The specificity of amplification was confirmed by Southern hybridization and the absence of the above-listed gene products in three phenotype-negative LB strains. Restriction polymorphism patterns of three examined amplicons from the CS gene, 17-kDa-protein gene, and ompB gene were identical among the eight phenotype-positive LB strains and were unique among all known rickettsiae of the spotted fever and typhus groups. Amplified fragments of the CS genes of the AB bacterium, Rickettsia prowazekii Breinl, Rickettsia typhi Wilmington, Rickettsia canada 2678, and Rickettsia conorii 7 (Malish) were sequenced. The greatest differences among the above-listed rickettsial and AB bacterium CS gene sequences were between bp 1078 and 1110. Numerical analysis based on CS gene fragment sequences shows the close relationships of the AB bacterium to the genus Rickettsia. Expanding of knowledge about rickettsial arthropod vectors and participation of rickettsiae in the cytoplasmic maternal inheritance of arthropods is discussed.

Genotypic evaluation of rickettsial isolates recovered from various species of ticks in Portugal

Twelve rickettsial isolates, from Rhipicephalus sanguineus, R. turanicus, Dermacentor marginatus and Hyalomma marginatus, were subjected to genotypic analysis. Amplification of specific DNA sequences, restriction endonuclease digestion of amplified DNA products, and gel electrophoresis were used to identify specific DNA fragment-banding patterns. Five patterns were resolved. Four were homologous with those of previously described rickettsial genotypes, R. conorii, R. slovaca, R. rhipicephali and R. massiliae. The fifth pattern differed by only a single altered restriction endonuclease cleavage site. For the first time in Portugal a widely distributed spectrum of spotted fever group rickettsia was found among potential vector species stressing the need to determine their potential for human and domestic animals infection.

Typing Neisseria meningitidis by analysis of restriction fragment length polymorphisms in the gene encoding the class 1 outer membrane protein: application to assessment of epidemics throughout the last 4 decades in China

A typing method was developed for Neisseria meningitidis serogroup A by analysis of restriction fragment length polymorphisms (RFLP) of the class 1 outer membrane protein gene (porA). By using appropriate primers, an approximately 1,116-bp fragment of the porA gene was amplified by PCR and then was digested with the restriction endonuclease MspI. The digestion products were separated on 10% polyacrylamide gels and were stained with silver. One hundred three clinical isolates of group A N. meningitidis from 17 provinces of China collected over a 26-year period were analyzed. Results of MspI-generated RFLP profiles of PCR-amplified porA genes were compared with those obtained by conventional serosubtyping. There was a band of about 400 bp common to all strains examined, and the 103 strains of serogroup A resulted in 22 unique RFLP patterns. The differences in bands could be observed mainly in the range of 120 to 280 bp. The smaller fragments were useful in distinguishing meningococci with the same serosubtype. Three epidemic periods were characterized by the presence of three distinct genotypes (a1, a2, and a3), accounting for 74.5% of the strains examined (3.88, 26.21, and 44.66%, respectively). Three predominant RFLP patterns were correlated epidemiologically with cycles of epidemic meningococcal meningitis and were well-matched to the predominant serosubtypes (P1.9, P1.7, 10, and P1.9) that presented at the same prevalence cycles. The genotyping yielded information that allowed strains from one epidemic to be distinguished from those from another that would have been indistinguishable if only serotyping and serosubtyping were available. Therefore, the PCR-RFLP typing method was very useful in the epidemiologic investigation of group A meningococcal meningitis.

Species-specific BALB/c mouse antibodies to rickettsiae studied by western blotting

BALB/c mice were inoculated intraperitoneally either once only, or up to four times at weekly intervals, with viable Rickettsia rickettsii, Rickettsia conorii or the Israeli spotted fever group rickettsia. Sera collected one week after the last inoculation were tested for the presence of antibodies reactive with the above organisms by indirect fluorescent antibody testing and Western blot. With repeated inoculations there was a general progressive rise in homologous and heterologous immunofluorescence titers although the increase after the first inoculation was always the greatest. For each rickettsia, the homologous titers were higher than the heterologous titers. Western blots showed that the reactive antibodies were against rickettsial high molecular mass species specific protein antigens and homologous species-specific antibody reactions were detectable earlier than heterologous cross-reacting antibody reactions. Antibodies in mice sera did not react with the group specific lipopolysaccharide-like antigens of the rickettsiae although such reactivity was strong in Western blots with sera from patients suffering from acute Rickettsia conorii infections. Our findings suggest that the intraperitoneal route of inoculation of BALB/c mice can be used for the differentiation of spotted fever group rickettsiae.

Differentiation among spotted fever group rickettsiae species by analysis of restriction fragment length polymorphism of PCR-amplified DNA

Restriction fragment length polymorphism (RFLP) analysis of PCR-amplified genes was used to study spotted fever group (SFG) rickettsiae, extending the previous work of Regnery et al. (R.L. Regnery, C.L. Spruill, and B.D. Plikaytis, J. Bacteriol. 173:1576-1589, 1991). Twenty-six strains of SFG rickettsia were studied, including several recognized species which have never been studied (R. parkeri, R. helvetica, and R. japonica) as well as strains which are not currently classified. Two previously used primer pairs derived from the R. prowazekii citrate syntase gene and the R. rickettsii 190-kDa protein antigen gene were studied, as were primer pairs obtained from the R. rickettsii 120-kDa protein antigen gene. By using three amplifications and three enzyme digestions, it was possible to differentiate between almost all of the known SFG rickettsia species and to differentiate between several strains of the R. conorii complex. Two human pathogens, "R. africae" and the Israeli tick typhus rickettsia, were first separated by using BG-12 pair primer amplification and then RsaI restriction endonuclease digestion. The proposed simplified model of identification may be useful in studying the geographical distributions of SFG rickettsiae.

Proteinic and genomic identification of spotted fever group rickettsiae isolated in the former USSR

Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), restriction fragment length polymorphism of polymerase chain reaction-amplified genes (RFLP-PCR), and pulsed-field gel electrophoresis (PFGE) were used to identify 25 isolates of spotted fever group rickettsia collected in the former USSR. Six Rickettsia akari isolates which were identical to the MK reference strain from the American Type Culture Collection were found. Also, 14 isolates were found to be Rickettsia sibirica and identical to reference strain 246. Two of three isolates previously considered as atypical, low-pathogenic strains of R. sibirica, were found to be strains of Rickettsia slovaca. The third, strain S, was similar in its RFLP-PCR profile to "R. africae" sp. nov. (proposed name for a rickettsia pathogenic for human beings in southern Africa) but in its SDS-PAGE and PFGE profiles was unique among spotted fever group rickettsiae. Strain M-1 was confirmed as a genetic variant of Rickettsia conorii. The Astrachan isolate, the causative agent of a tick-bite rickettsiosis at the North of the Caspian Sea, showed a previously described RFLP-PCR profile identical to that of the Israeli tick typhus rickettsia, but its SDS-PAGE and PFGE profiles different from those of the other strains tested.

Prevalence of antibodies to spotted fever group rickettsiae along the eastern coast of the Adriatic sea

A seroepidemiological survey in coastal Croatia detected antibodies reactive with Rickettsia conorii in 4.2% of sera by immunofluorescence assay and in 5.0% of sera by enzyme immunoassay. Western immunoblotting demonstrated antibodies to the 120-kDa surface protein in all 20 positive serum samples examined and to rickettsial lipopolysaccharide in 3 of these serum samples. Humans in this area are clearly being exposed to spotted fever rickettsiae.

Genotypic identification and phylogenetic analysis of the spotted fever group rickettsiae by pulsed-field gel electrophoresis

Using pulsed-field gel electrophoresis, we studied the chromosomes of spotted fever group rickettsiae. We digested the DNA of 16 species currently known to belong to this group with SmaI, EagI, and BssHII. The genome size of 13 rickettsiae was between 1,200 and 1,300 kb. "Rickettsia massiliae" and "R. helvetica" genome sizes were 1,370 and 1,397 kb, respectively, and that of R. bellii was 1,660 kb. It was possible to obtain distinctive patterns for each species, but in R. conorii, 10 isolates exhibited the same profiles, showing that pulsed-field gel electrophoresis is a good interspecies identification tool. We achieved a phylogenetic analysis of these bacteria by using the Dice coefficient and UPGMA and Package Philip programming. We established a dendrogram of the genetic relationships between the different species showing the existence of a cluster in the spotted fever group rickettsiae including R. conorii, R. rickettsii, R. parkeri, R. sibirica, "R. africae," "R. slovaca," Thai tick typhus rickettsia, and Israeli tick typhus rickettsia. We located three genes previously cloned and sequenced (genes encoding the R. rickettsii surface proteins of 120 and 190 kDa and the R. prowazekii citrate synthase gene), using Southern hybridization. The genes encoding citrate synthase and the surface protein of 190 kDa were usually located on the same band, and it is hypothesized that they are relatively close on the chromosome.

Differentiation of Rickettsia japonica by restriction endonuclease fragment length polymorphism using products of polymerase chain reaction amplification with Rickettsia rickettsii 190-kilodalton surface antigen gene primers

Restriction fragment length polymorphism of polymerase chain reaction (PCR) amplification products differentiated Rickettsia japonica, a causative agent of Oriental spotted fever, from other spotted fever group (SFG) rickettsiae. Primer pair Rr190. 70p and Rr190. 602n of R. rickettsii 190-kDa antigen gene sequence primed genomic DNAs obtained from R. japonica, type strain YH and strains NT, NK, YKI, and TKN. The products were cleaved by PstI but not by AfaI restriction endonuclease. The PstI digestion pattern of PCR-products amplified from all strains of R. japonica was identical and easily differentiated from that of other SFG rickettsiae. The present study demonstrated a genotypic difference between R. japonica and other pathogenic SFG rickettsiae.