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1.  The Eco-epidemiology of Pacific Coast Tick Fever in California 
PLoS Neglected Tropical Diseases  2016;10(10):e0005020.
Rickettsia philipii (type strain “Rickettsia 364D”), the etiologic agent of Pacific Coast tick fever (PCTF), is transmitted to people by the Pacific Coast tick, Dermacentor occidentalis. Following the first confirmed human case of PCTF in 2008, 13 additional human cases have been reported in California, more than half of which were pediatric cases. The most common features of PCTF are the presence of at least one necrotic lesion known as an eschar (100%), fever (85%), and headache (79%); four case-patients required hospitalization and four had multiple eschars. Findings presented here implicate the nymphal or larval stages of D. occidentalis as the primary vectors of R. philipii to people. Peak transmission risk from ticks to people occurs in late summer. Rickettsia philipii DNA was detected in D. occidentalis ticks from 15 of 37 California counties. Similarly, non-pathogenic Rickettsia rhipicephali DNA was detected in D. occidentalis in 29 of 38 counties with an average prevalence of 12.0% in adult ticks. In total, 5,601 ticks tested from 2009 through 2015 yielded an overall R. philipii infection prevalence of 2.1% in adults, 0.9% in nymphs and a minimum infection prevalence of 0.4% in larval pools. Although most human cases of PCTF have been reported from northern California, acarological surveillance suggests that R. philipii may occur throughout the distribution range of D. occidentalis.
Author Summary
Rickettsia philipii, a spotted fever group rickettsia, is the etiologic agent of Pacific Coast tick fever, an emerging tick-borne disease transmitted by the Pacific Coast tick (Dermacentor occidentalis). The Pacific Coast tick’s range, and thus potential for exposure to R. philipii, includes most of California, southern Oregon, and northern Baja California, Mexico. This study describes the clinical manifestations of the 14 human cases reported to date in California and the known acarological risk factors for encountering PCTF. While Rickettsia rickettsii, the agent of Rocky Mountain spotted fever (RMSF) is genetically similar to R. philipii, PCTF is a milder disease than RMSF; the two diseases share key clinical features such as headache and fever but differ in that PCTF presents with a localized eschar (necrotic wound) but without a petechial rash. Most case-patients have illness onset dates in the summer (peak: July and August) which is coincident with the activity period of immature D. occidentalis. Results from this study support the premise that larval and nymphal D. occidentalis are the vectors of PCTF to humans in California. While only three ticks have tested positive for R. rickettsii over decades of surveillance in California, the prevalence of R. philipii in D. occidentalis ticks averages 0.4% in larvae, 0.9% in nymphs, and 2.1% in adult ticks, indicating a higher risk of acquiring PCTF than RMSF statewide.
PMCID: PMC5051964  PMID: 27706171
2.  Rickettsia africae and Candidatus Rickettsia barbariae in Ticks in Israel 
DNA of several spotted fever group rickettsiae was found in ticks in Israel. The findings include evidence for the existence of Rickettsia africae and Candidatus Rickettsia barbariae in ticks in Israel. The DNA of R. africae was detected in a Hyalomma detritum tick from a wild boar and DNA of C. Rickettsia barbariae was detected in Rhipicephalus turanicus and Rhipicephalus sanguineus collected from vegetation. The DNA of Rickettsia massiliae was found in Rh. sanguineus and Haemaphysalis erinacei, whereas DNA of Rickettsia sibirica mongolitimonae was detected in a Rhipicephalus (Boophilus) annulatus. Clinicians should be aware that diseases caused by a variety of rickettsiae previously thought to be present only in other countries outside of the Middle East may infect residents of Israel who have not necessarily traveled overseas. Furthermore, this study reveals again that the epidemiology of the spotted fever group rickettsiae may not only involve Rickettsia conorii but may include other rickettsiae.
PMCID: PMC4015588  PMID: 24615133
3.  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.
PMCID: PMC3029176  PMID: 21292893
4.  Challenges Posed by Tick-Borne Rickettsiae: Eco-Epidemiology and Public Health Implications 
Rickettsiae are obligately intracellular bacteria that are transmitted to vertebrates by a variety of arthropod vectors, primarily by fleas and ticks. Once transmitted or experimentally inoculated into susceptible mammals, some rickettsiae may cause febrile illness of different morbidity and mortality, and which can manifest with different types of exhanthems in humans. However, most rickettsiae circulate in diverse sylvatic or peridomestic reservoirs without having obvious impacts on their vertebrate hosts or affecting humans. We have analyzed the key features of tick-borne maintenance of rickettsiae, which may provide a deeper basis for understanding those complex invertebrate interactions and strategies that have permitted survival and circulation of divergent rickettsiae in nature. Rickettsiae are found in association with a wide range of hard and soft ticks, which feed on very different species of large and small animals. Maintenance of rickettsiae in these vector systems is driven by both vertical and horizontal transmission strategies, but some species of Rickettsia are also known to cause detrimental effects on their arthropod vectors. Contrary to common belief, the role of vertebrate animal hosts in maintenance of rickettsiae is very incompletely understood. Some clearly play only the essential role of providing a blood meal to the tick while other hosts may supply crucial supplemental functions for effective agent transmission by the vectors. This review summarizes the importance of some recent findings with known and new vectors that afford an improved understanding of the eco-epidemiology of rickettsiae; the public health implications of that information for rickettsial diseases are also described. Special attention is paid to the co-circulation of different species and genotypes of rickettsiae within the same endemic areas and how these observations may influence, correctly or incorrectly, trends, and conclusions drawn from the surveillance of rickettsial diseases in humans.
PMCID: PMC4404743  PMID: 25954738
Rickettsia; spotted fever rickettsioses; ticks; co-feeding transmission; transovarial maintenance; acquisition feeding; eco-epidemiology; molecular epidemiology
5.  New Spotted Fever Group Rickettsia in a Rhipicephalus turanicus Tick Removed from a Child in Eastern Sicily, Italy 
A new genotype of spotted fever group Rickettsia (SFGR) was identified in Rhipicephalus turanicus from eastern Sicily. On the basis of current molecular criteria, the genetic characteristics obtained from multiple locus sequence typing satisfy the requirements for Candidatus status of this SFGR. Further detection and identification of this SFGR during entomological and clinical surveys will be required to establish the prevalence of this Rickettsia and its potential pathogenicity for humans.
PMCID: PMC3005513  PMID: 21212209
6.  High Prevalence and Genetic Heterogeneity of Rodent-Borne Bartonella Species on Heixiazi Island, China 
Applied and Environmental Microbiology  2015;81(23):7981-7992.
We performed genetic analysis of Bartonella isolates from rodent populations from Heixiazi Island in northeast China. Animals were captured at four sites representing grassland and brushwood habitats in 2011 and examined for the prevalence and genetic diversity of Bartonella species, their relationship to their hosts, and geographic distribution. A high prevalence (57.7%) and a high diversity (14 unique genotypes which belonged to 8 clades) of Bartonella spp. were detected from 71 rodents comprising 5 species and 4 genera from 3 rodent families. Forty-one Bartonella isolates were recovered and identified, including B. taylorii, B. japonica, B. coopersplainsensis, B. grahamii, B. washoensis subsp. cynomysii, B. doshiae, and two novel Bartonella species, by sequencing of four genes (gltA, the 16S rRNA gene, ftsZ, and rpoB). The isolates of B. taylorii and B. grahamii were the most prevalent and exhibited genetic difference from isolates identified elsewhere. Several isolates clustered with strains from Japan and far-eastern Russia; strains isolated from the same host typically were found within the same cluster. Species descriptions are provided for Bartonella heixiaziensis sp. nov. and B. fuyuanensis sp. nov.
PMCID: PMC4651081  PMID: 26362983
7.  Rickettsia felis in Ctenocephalides felis from Guatemala and Costa Rica 
Rickettsia felis is an emerging human pathogen associated primarily with the cat flea Ctenocephalides felis. In this study, we investigated the presence of Rickettsia felis in C. felis from Guatemala and Costa Rica. Ctenocephalides felis were collected directly from dogs and cats, and analyzed by polymerase chain reaction for Rickettsia-specific fragments of 17-kDa protein, OmpA, and citrate synthase genes. Rickettsia DNA was detected in 64% (55 of 86) and 58% (47 of 81) of flea pools in Guatemala and Costa Rica, respectively. Sequencing of gltA fragments identified R. felis genotype URRWXCal2 in samples from both countries, and genotype Rf2125 in Costa Rica. This is the first report of R. felis in Guatemala and of genotype Rf2125 in Costa Rica. The extensive presence of this pathogen in countries of Central America stresses the need for increased awareness and diagnosis.
PMCID: PMC3366522  PMID: 22665618
8.  Spotted Fever Group Rickettsiae in Ticks Collected from Wild Animals in Israel 
We report molecular evidence for the presence of spotted fever group rickettsiae (SFGR) in ticks collected from roe deer, addax, red foxes, and wild boars in Israel. Rickettsia aeschlimannii was detected in Hyalomma marginatum and Hyalomma detritum while Rickettsia massiliae was present in Rhipicephalus turanicus ticks. Furthermore, a novel uncultured SFGR was detected in Haemaphysalis adleri and Haemaphysalis parva ticks from golden jackals. The pathogenicity of the novel SFGR for humans is unknown; however, the presence of multiple SFGR agents should be considered when serological surveillance data from Israel are interpreted because of significant antigenic cross-reactivity among Rickettsia. The epidemiology and ecology of SFGR in Israel appear to be more complicated than was previously believed.
PMCID: PMC3205642  PMID: 22049050
9.  Rickettsia typhi and R. felis in Rat Fleas (Xenopsylla cheopis), Oahu, Hawaii  
Emerging Infectious Diseases  2008;14(10):1613-1615.
Rickettsia typhi (prevalence 1.9%) and R. felis (prevalence 24.8%) DNA were detected in rat fleas (Xenopsylla cheopis) collected from mice on Oahu Island, Hawaii. The low prevalence of R. typhi on Oahu suggests that R. felis may be a more common cause of rickettsiosis than R. typhi in Hawaii.
PMCID: PMC2609893  PMID: 18826827
Murine typhus; Rickettsia felis; Rickettsia typhi; molecular assays; Hawaii; dispatch
10.  Rocky Mountain Spotted Fever, Panama 
Emerging Infectious Diseases  2007;13(11):1763-1765.
We describe a fatal pediatric case of Rocky Mountain spotted fever in Panama, the first, to our knowledge, since the 1950s. Diagnosis was established by immunohistochemistry, PCR, and isolation of Rickettsia rickettsii from postmortem tissues. Molecular typing demonstrated strong relatedness of the isolate to strains of R. rickettsii from Central and South America.
PMCID: PMC3375809  PMID: 18217566
Rickettsia rickettsii; RMSF; Panama; immunohistochemistry; PCR; molecular typing; dispatch
12.  Emergence of a New Pathogenic Ehrlichia Species, Wisconsin and Minnesota, 2009 
The New England Journal of Medicine  2011;365(5):422-429.
Ehrlichiosis is a clinically important, emerging zoonosis. Only Ehrlichia chaffeensis and E. ewingii have been thought to cause ehrlichiosis in humans in the United States. Patients with suspected ehrlichiosis routinely undergo testing to ensure proper diagnosis and to ascertain the cause.
We used molecular methods, culturing, and serologic testing to diagnose and ascertain the cause of cases of ehrlichiosis.
On testing, four cases of ehrlichiosis in Minnesota or Wisconsin were found not to be from E. chaffeensis or E. ewingii and instead to be caused by a newly discovered ehrlichia species. All patients had fever, malaise, headache, and lymphopenia; three had thrombocytopenia; and two had elevated liver-enzyme levels. All recovered after receiving doxycycline treatment. At least 17 of 697 Ixodes scapularis ticks collected in Minnesota or Wisconsin were positive for the same ehrlichia species on polymerase-chain-reaction testing. Genetic analyses revealed that this new ehrlichia species is closely related to E. muris.
We report a new ehrlichia species in Minnesota and Wisconsin and provide supportive clinical, epidemiologic, culture, DNA-sequence, and vector data. Physicians need to be aware of this newly discovered close relative of E. muris to ensure appropriate testing, treatment, and regional surveillance. (Funded by the National Institutes of Health and the Centers for Disease Control and Prevention.)
PMCID: PMC3319926  PMID: 21812671
13.  Beta Interferon-Mediated Activation of Signal Transducer and Activator of Transcription Protein 1 Interferes with Rickettsia conorii Replication in Human Endothelial Cells ▿  
Infection and Immunity  2011;79(9):3733-3743.
Infection of the endothelial cell lining of blood vessels with Rickettsia conorii, the causative agent of Mediterranean spotted fever, results in endothelial activation. We investigated the effects of R. conorii infection on the status of the Janus kinase (JAK)-signal transducer and activator of transcription protein (STAT) signaling pathway in human microvascular endothelial cells (HMECs), the most relevant host cell type, in light of rickettsial tropism for microvascular endothelium in vivo. R. conorii infection induced phosphorylation of STAT1 on tyrosine 701 and serine 727 at 24, 48, and 72 h postinfection in HMECs. Employing transcription profile analysis and neutralizing antibodies, we further determined that beta interferon (IFN-β) production and secretion are critical for STAT1 activation. Secreted IFN-β further amplified its own expression via a positive-feedback mechanism, while expression of transcription factors interferon regulatory factor 7 (IRF7) and IRF9, implicated in the IFN-β–STAT1 feedback loop, was also induced. Metabolic activity of rickettsiae was essential for the IFN-β-mediated response(s) because tetracycline treatment inhibited R. conorii replication, IFN-β expression, and STAT1 phosphorylation. Inclusion of IFN-β-neutralizing antibody during infection resulted in significantly enhanced R. conorii replication, whereas addition of exogenous IFN-β had the opposite inhibitory effect. Finally, small interfering RNA-mediated knockdown further confirmed a protective role for STAT1 against intracellular R. conorii replication. In concert, these findings implicate an important role for IFN-β-mediated STAT1 activation in innate immune responses of vascular endothelium to R. conorii infection.
PMCID: PMC3165482  PMID: 21690236
14.  Eschar-associated Spotted Fever Rickettsiosis, Bahia, Brazil 
Emerging Infectious Diseases  2011;17(2):275-278.
In Brazil, Brazilian spotted fever was once considered the only tick-borne rickettsial disease. We report eschar-associated rickettsial disease that occurred after a tick bite. The etiologic agent is most related to Rickettsia parkeri, R. africae, and R. sibirica and probably widely distributed from São Paulo to Bahia in the Atlantic Forest.
PMCID: PMC3204763  PMID: 21291605
Spotted fever group rickettsiosis; rickettsia; eschar; multiple-locus sequence analysis; ticks; molecular diagnosis; dispatch
15.  Murine Typhus in Austin, Texas, USA, 2008 
Emerging Infectious Diseases  2010;16(3):412-417.
Physicians should be alert for possible cases in this area.
In August 2008, Texas authorities and the Centers for Disease Control and Prevention investigated reports of increased numbers of febrile rash illnesses in Austin to confirm the causative agent as Rickettsia typhi, to assess the outbreak magnitude and illness severity, and to identify potential animal reservoirs and peridomestic factors that may have contributed to disease emergence. Thirty-three human cases of confirmed murine typhus were identified. Illness onset was reported from March to October. No patients died, but 23 (70%) were hospitalized. The case-patients clustered geographically in central Austin; 12 (36%) resided in a single ZIP code area. Specimens from wildlife and domestic animals near case-patient homes were assessed; 18% of cats, 44% of dogs, and 71% of opossums had antibodies reactive to R. typhi. No evidence of R. typhi was detected in the whole blood, tissue, or arthropod specimens tested. These findings suggest that an R. typhi cycle involving opossums and domestic animals may be present in Austin.
PMCID: PMC3322020  PMID: 20202415
Murine typhus; Rickettsia typhi; emergence; opossums; fleas; zoonoses; bacteria; Texas; research
16.  Rickettsia felis, West Indies 
Emerging Infectious Diseases  2010;16(3):570-571.
PMCID: PMC3322037  PMID: 20202452
Rickettsia felis; West Indies; St. Kitts; Dominica; rickettsia; letter
17.  Cluster of Sylvatic Epidemic Typhus Cases Associated with Flying Squirrels, 2004–2006 
Emerging Infectious Diseases  2009;15(7):1005-1011.
Infected persons had slept in an infested cabin.
In February 2006, a diagnosis of sylvatic epidemic typhus in a counselor at a wilderness camp in Pennsylvania prompted a retrospective investigation. From January 2004 through January 2006, 3 more cases were identified. All had been counselors at the camp and had experienced febrile illness with myalgia, chills, and sweats; 2 had been hospitalized. All patients had slept in the same cabin and reported having seen and heard flying squirrels inside the wall adjacent to their bed. Serum from each patient had evidence of infection with Rickettsia prowazekii. Analysis of blood and tissue from 14 southern flying squirrels trapped in the woodlands around the cabin indicated that 71% were infected with R. prowazekii. Education and control measures to exclude flying squirrels from housing are essential to reduce the likelihood of sylvatic epidemic typhus.
PMCID: PMC2744229  PMID: 19624912
Sylvatic typhus; epidemic typhus; flying squirrel; Rickettsia prowazekii; rickettsia; zoonoses; CME; podcast; Pennsylvania; research
18.  Rickettsia parkeri in Argentina 
Emerging Infectious Diseases  2008;14(12):1894-1897.
Clinical reports of an eschar-associated rickettsiosis in the Paraná River Delta of Argentina prompted an evaluation of Amblyomma triste ticks in this region. When evaluated by PCR, 17 (7.6%) of 223 questing adult A. triste ticks, collected from 2 sites in the lower Paraná River Delta, contained DNA of Rickettsia parkeri.
PMCID: PMC2634642  PMID: 19046514
Rickettsia parkeri; Amblyomma triste; rickettsiosis; Argentina; dispatch
19.  Bartonella spp. and Rickettsia felis in Fleas, Democratic Republic of Congo 
Emerging Infectious Diseases  2008;14(12):1972-1974.
PMCID: PMC2634628  PMID: 19046544
Bartonella; Rickettsia; flea-borne diseases; Democratic Republic of Congo; letter
20.  Isolation and Characterization of Bartonella bacilliformis from an Expatriate Ecuadorian▿  
Journal of Clinical Microbiology  2007;46(2):627-637.
Carrion's disease is typically biphasic with acute febrile illness characterized by bacteremia and severe hemolytic anemia (Oroya fever), followed by benign, chronic cutaneous lesions (verruga peruana). The causative agent, Bartonella bacilliformis, is endemic in specific regions of Peru and Ecuador. We describe atypical infection in an expatriate patient who presented with acute splenomegaly and anemia 3 years after visiting Ecuador. Initial serology and PCR of the patient's blood and serum were negative for Bartonella henselae, Bartonella quintana, and B. bacilliformis. Histology of splenic biopsy was suggestive of bacillary angiomatosis, but immunohistochemistry ruled out B. henselae and B. quintana. Bacilli (isolate EC-01) were subsequently cultured from the patient's blood and analyzed using multilocus sequence typing, protein gel electrophoresis with Western blotting, and an immunofluorescence assay (IFA) against a panel of sera from patients with Oroya fever in Peru. The EC-01 nucleotide sequences (gltA and internal transcribed spacer) and protein band banding pattern were most similar to a subset of B. bacilliformis isolates from the region of Caraz, Ancash, in Peru, where B. bacilliformis is endemic. By IFA, the patient's serum reacted strongly to two out of the three Peruvian B. bacilliformis isolates tested, and EC-01 antigen reacted with 13/20 Oroya fever sera. Bacilliary angiomatosis-like lesions were also detected in the spleen of the patient, who was inapparently infected with B. bacilliformis and who presumably acquired infection in a region of Ecuador where B. bacilliformis was not thought to be endemic. This study suggests that the range of B. bacilliformis may be expanding from areas of endemicity in Ecuador and that infection may present as atypical clinical disease.
PMCID: PMC2238110  PMID: 18094131
21.  Fatal Rickettsia conorii subsp. israelensis Infection, Israel 
Emerging Infectious Diseases  2008;14(5):821-824.
Fatal Rickettsia conorii subsp. israelensis Infection, Israel
Underdiagnosis of fatal spotted fever may be attributed to nonspecific clinical features and insensitive acute-phase serologic studies. We describe the importance of molecular and immunohistochemical methods in establishing the postmortem diagnosis of locally acquired Israeli spotted fever due to Rickettsia conorii subsp. israelensis in a traveler returning to Israel from India.
PMCID: PMC2600240  PMID: 18439372
PCR; Israel; epidemiology; Rickettsia infections; Rickettsia conorii; genetics; pathogenicity; travel; dispatch
22.  On Rickettsia Nomenclature 
Emerging Infectious Diseases  2008;14(3):528-9.
On Rickettsia Nomenclature
PMCID: PMC2570829  PMID: 18325277
rickettsia; bacterial nomenclature; taxonomy; commentary
23.  Molecular Typing of Isolates of Rickettsia rickettsii by Use of DNA Sequencing of Variable Intergenic Regions▿  
Journal of Clinical Microbiology  2007;45(8):2545-2553.
Rickettsia rickettsii, the causative agent of Rocky Mountain spotted fever, is found throughout the Americas, where it is associated with different animal reservoirs and tick vectors. No molecular typing system currently exists to allow for the robust differentiation of isolates of R. rickettsii. Analysis of eight completed genome sequences of rickettsial species revealed a high degree of sequence conservation within the coding regions of chromosomes in the genus. Intergenic regions between coding sequences should be under less selective pressure to maintain this conservation and thus should exhibit greater nucleotide polymorphisms. Utilizing these polymorphisms, we developed a molecular typing system that allows for the genetic differentiation of isolates of R. rickettsii. This typing system was applied to a collection of 38 different isolates collected from humans, animals, and tick vectors from different geographic locations. Serotypes 364D, from Dermacentor occidentalis ticks, and Hlp, from Haemaphysalis leporispalustris ticks, appear to be distinct genotypes that may not belong to the species R. rickettsii. We were also able to differentiate 36 historical isolates of R. rickettsii into three different phylogenetic clades containing seven different genotypes. This differentiation correlated well, but not perfectly, with the geographic origin and likely tick vectors associated with the isolates. The few apparent typing discrepancies found suggest that the molecular ecology of R. rickettsii needs more investigation.
PMCID: PMC1951237  PMID: 17553977
24.  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.
PMCID: PMC1538723  PMID: 16885311
25.  Evaluation of a PCR Assay for Quantitation of Rickettsia rickettsii and Closely Related Spotted Fever Group Rickettsiae 
Journal of Clinical Microbiology  2003;41(12):5466-5472.
A spotted fever rickettsia quantitative PCR assay (SQ-PCR) was developed for the detection and enumeration of Rickettsia rickettsii and other closely related spotted fever group rickettsiae. The assay is based on fluorescence detection of SYBR Green dye intercalation in a 154-bp fragment of the rOmpA gene during amplification by PCR. As few as 5 copies of the rOmpA gene of R. rickettsii can be detected. SQ-PCR is suitable for quantitation of R. rickettsii and 10 other genotypes of spotted fever group rickettsiae but not for R. akari, R. australis, R. bellii, or typhus group rickettsiae. The sensitivity of SQ-PCR was comparable to that of a plaque assay using centrifugation for inoculation. The SQ-PCR assay was applied successfully to the characterization of rickettsial stock cultures, the replication of rickettsiae in cell culture, the recovery of rickettsial DNA following different methods of extraction, and the quantitation of rickettsial loads in infected animal tissues, clinical samples, and ticks.
PMCID: PMC308968  PMID: 14662926

Results 1-25 (28)