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BackgroundIn Brazil, spotted fever (SF) is caused by the bacteria Rickettsia parkeri and Rickettsia rickettsii. Seroepidemiological data on Rickettsia spp. in humans are rare in Brazil and nonexistent in the Amazon biome. We sought to quantify antibodies reactive to Rickettsia spp. in serum samples collected from humans in the Amazonia biome, and to detect Rickettsia spp. in ticks parasitizing these hosts.MethodsHuman blood samples were collected from three different locations within the eastern Amazon in Maranhão State, northeastern Brazil between 2010 and 2018. Sera generated from those samples were tested for the presence of antibodies reactive to Rickettsia by immunofluorescence assay (IFA) using crude antigens from five Rickettsia isolates from Brazil: R. rickettsii strain Taiaçu, R. amblyommatis strain Ac37, Rickettsia rhipicephali strain HJ5, R. parkeri strain At24, and Rickettsia bellii strain Mogi. Between 2020 and 2025, ticks were manually collected while attached to the skin of humans in seven municipalities in Maranhão State. Adult ticks were randomly selected and individually processed for DNA extraction and examined using a real-time PCR (qPCR) assay targeting a fragment of the rickettsial gltA gene. The qPCR-positive samples were subsequently examined by conventional PCR (cPCR) targeting the ompA gene of SFG rickettsiae. The cPCR amplicons were purified and sequenced bidirectionally using the amplification primers. The resulting sequences were compared with those in GenBank using BLASTn to identify related Rickettsia spp.ResultsA total of 341 human serum samples were analyzed, and 145 (42.5%) were recorded as reactive with at least one species of Rickettsia. Among the reactive samples, 68 (47%) were from Imperatriz, 45 (31%) from Açailândia, and 32 (22%) from the municipality of São Luís. Rickettsia rhipicephali was recorded as the possible antigen involved in a homologous reaction (PAIHR) in one individual, R. amblyommatis in five, and R. bellii in three. A total of 187 ticks were collected parasitizing humans in the Amazon biome. Molecular analyses revealed that Rickettsia DNA was present in 44.4% (4/9) of A. cajennense s.s. from Açailândia, 52.4% (22/42) from Centro Novo do Maranhão, and 0% (0/8) from Imperatriz. Among the adults of A. coelebs from Centro Novo do Maranhão, 36.8% (7/19) tested positive. In contrast, all adults of A. oblongoguttatum from the same location tested negative (0/20).ConclusionsThis is the first study to detect anti-Rickettsia antibodies in humans and to identify R. amblyommatis in ticks parasitizing humans in the Amazon biome. The detection of R. amblyommatis in human-biting ticks, together with concurrent seropositivity in human sera from the same region, supports the hypothesis that this agent is actively circulating in the Amazon biome and may be responsible for undiagnosed cases of nonlethal spotted fever in the area.

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

Due to a resurgence of flea-borne rickettsioses in Orange County, California, we investigated the etiologies of rickettsial infections of Ctenocephalides felis, the predominant fleas species obtained from opossums (Didelphis virginiana) and domestic cats (Felis catus), collected from case exposure sites and other areas in Orange County. In addition, we assessed the prevalence of IgG antibodies against spotted fever group (SFGR) and typhus group (TGR) rickettsiae in opossum sera. Of the 597 flea specimens collected from opossums and cats, 37.2% tested positive for Rickettsia. PCR and sequencing of rickettsial genes obtained from C. felis flea DNA preparations revealed the presence of R. typhi (1.3%), R. felis (28.0%) and R. felis-like organisms (7.5%). Sera from opossums contained TGR-specific (40.84%), but not SFGR-specific antibodies. The detection of R. felis and R. typhi in the C. felis fleas in Orange County highlights the potential risk for human infection with either of these pathogens, and underscores the need for further investigations incorporating specimens from humans, animal hosts, and invertebrate vectors in endemic areas. Such studies will be essential for establishing a link in the ongoing flea-borne rickettsioses outbreaks.

Background. Rickettsia rickettsii, Rickettsia parkeri, and Rickettsia akari are the most common causes of spotted fever group rickettsioses indigenous to the United States. Infected patients characteristically present with a maculopapular rash, often accompanied by an inoculation eschar. Skin biopsy specimens are often obtained from these lesions for diagnostic evaluation. However, a species-specific diagnosis is achieved infrequently from pathologic specimens because immunohistochemical stains do not differentiate among the causative agents of spotted fever group rickettsiae, and existing polymerase chain reaction (PCR) assays generally target large gene segments that may be difficult or impossible to obtain from formalin-fixed tissues. Methods. This work described the development and evaluation of a multiplex real-time PCR assay for the detection of these 3 Rickettsia species from formalin-fixed, paraffin-embedded (FFPE) skin biopsy specimens. Results. The multiplex PCR assay was specific at discriminating each species from FFPE controls of unrelated bacterial, viral, protozoan, and fungal pathogens that cause skin lesions, as well as other closely related spotted fever group Rickettsia species. Conclusions. This multiplex real-time PCR demonstrates greater sensitivity than nested PCR assays in FFPE tissues and provides an effective method to specifically identify cases of Rocky Mountain spotted fever, rickettsialpox, and R. parkeri rickettsiosis by using skin biopsy specimens.

Rickettsia occurs worldwide and rickettsiosis is recognized as an emerging infection in several parts of the world. Ticks are reservoir hosts for pathogenic Rickettsia species in humans and domestic animals. Most pathogenic Rickettsia species belong to the spotted Fever Group (SFG). This study aimed to identify and diagnose tick fauna and investigate the prevalence of Rickettsia spp. in ticks collected from domestic animals and dogs in the rural regions of Kerman Province, Southeast Iran. In this study, tick species (fauna) were identified and 2100 ticks (350 pooled samples) from two genera and species including Rhipicephalus linnaei (1128) and Hyalomma deteritum (972) were tested to detect Rickettsia genus using Real-time PCR. The presence of the Rickettsia genus was observed in 24.9% (95%CI 20.28–29.52) of the pooled samples. Sequencing and phylogenetic analyses revealed the presence of Rickettsia aeschlimannii (48.98%), Rickettsia conorii israelensis (28.57%), Rickettsia sibirica (20.41%), and Rickettsia helvetica (2.04%) in the positive samples. The results showed a significant association between county variables and the following variables: tick spp. ( p  < 0.001), Rickettsia genus infection in ticks ( p  < 0.001) and Rickettsia spp. ( p  < 0.001). In addition, there was a significant association between tick species and host animals (dogs and domestic animals) ( p  < 0.001), Rickettsia spp infection in ticks ( p  < 0.001), and Rickettsia spp. ( p  < 0.001). This study indicates a high prevalence of Rickettsia spp. (SFG) in ticks of domestic animals and dogs in rural areas of Kerman Province. The health system should be informed of the possibility of rickettsiosis and the circulating species of Rickettsia in these areas.

We document a case of Rickettsia parkeri rickettsiosis in a patient in Connecticut, USA, who became ill after a bite from a Gulf Coast tick (Amblyomma maculatum). We used PCR to amplify R. parkeri DNA from the detached tick. The patient showed a 4-fold rise in IgG reactive with R. parkeri antigens.

ABSTRACT Bacterial infection is a highly complex biological process involving a dynamic interaction between the invading microorganism and the host. Specifically, intracellular pathogens seize control over the host cellular processes including membrane dynamics, actin cytoskeleton, phosphoinositide metabolism, intracellular trafficking and immune defense mechanisms to promote their host colonization. To accomplish such challenging tasks, virulent bacteria deploy unique species-specific secreted effectors to evade and/or subvert cellular defense surveillance mechanisms to establish a replication niche. However, despite superficially similar infection strategies, diverse Rickettsia species utilize different effector repertoires to promote host colonization. This review will discuss our current understandings on how different Rickettsia species deploy their effector arsenal to manipulate host cellular processes to promote their intracytosolic life within the mammalian host. Rickettsiae deploy their effector arsenal to manipulate membrane dynamics, actin cytoskeleton, phosphoinositide metabolism, intracellular trafficking and immune defense mechanisms; to gain access, and promote their intracytosolic lifespan to ultimately expedite transmission.

Background. Rickettsia parkeri rickettsiosis, a recently identified spotted fever transmitted by the Gulf Coast tick (Amblyomma maculatum), was first described in 2004. We summarize the clinical and epidemiological features of 12 patients in the United States with confirmed or probable disease attributable to R. parkeri and comment on distinctions between R. parkeri rickettsiosis and other United States rickettsioses. Methods. Clinical specimens from patients in the United States who reside within the range of A. maculatum for whom an eschar or vesicular rash was described were evaluated by ⩾1 laboratory assays at the Centers for Disease Control and Prevention (Atlanta, GA) to identify probable or confirmed infection with R. parkeri. Results. During 1998–2007, clinical samples from 12 patients with illnesses epidemiologically and clinically compatible with R. parkeri rickettsiosis were submitted for diagnostic evaluation. Using indirect immunofluores-cence antibody assays, immunohistochemistry, polymerase chain reaction assays, and cell culture isolation, we identified 6 confirmed and 6 probable cases of infection with R. parkeri. The aggregate clinical characteristics of these patients revealed a disease similar to but less severe than classically described Rocky Mountain spotted fever. Conclusions. Closer attention to the distinct clinical features of the various spotted fever syndromes that exist in the United States and other countries of the Western hemisphere, coupled with more frequent use of specific confirmatory assays, may unveil several unique diseases that have been identified collectively as Rocky Mountain spotted fever during the past century. Accurate assessments of these distinct infections will ultimately provide a more valid description of the currently recognized distribution, incidence, and case-fatality rate of Rocky Mountain spotted fever. An unnamed, apparently new rickettsia has been repeatedly isolated at the Rocky Mountain Laboratory during the past nine years from specimens of Amblyomma maculatum, a tick of wide distribution in the Southern States…the presumptive evidence from animal experimentation suggests that human infection might be confusingly similar to spotted fever. Parker Ralph R. 1948 [1, p. 146]

Although flea-borne rickettsiosis is endemic in Los Angeles County, outbreaks are rare. In the spring of 2015 three human cases of flea-borne rickettsiosis among residents of a mobile home community (MHC) prompted an investigation. Fleas were ubiquitous in common areas due to presence of flea-infested opossums and overabundant outdoor cats and dogs. The MHC was summarily abated in June 2015, and within five months, flea control and removal of animals significantly reduced the flea population. Two additional epidemiologically-linked human cases of flea-borne rickettsiosis detected at the MHC were suspected to have occurred before control efforts began. Molecular testing of 106 individual and 85 pooled cat fleas, blood and ear tissue samples from three opossums and thirteen feral cats using PCR amplification and DNA sequencing detected rickettsial DNA in 18.8% of the fleas. Seventeen percent of these cat fleas tested positive for R. felis-specific DNA compared to under two (<2) percent for Candidatus R. senegalensis-specific DNA. In addition, serological testing of 13 cats using a group-specific IgG-ELISA detected antibodies against typhus group rickettsiae and spotted fever group rickettsiae in six (46.2%) and one (7.7%) cat, respectively. These results indicate that cats and their fleas may have played an active role in the epidemiology of the typhus group and/or spotted fever group rickettsial disease(s) in this outbreak.

Leptotrombidium scutellare mites, the vector of Orientia tsutsugamushi, have rarely been reported to associate with Rickettsia species. Three hundred nineteen chiggers were collected from the ears of 32 rodents captured in Huangdao District of Qingdao City, China, in October 2015. The chigger samples were tested for Rickettsia, severe fever with thrombocytopenia syndrome virus, and hantavirus by PCR or RT-PCR amplification. All mites were classified morphologically and molecularly as L. scutellare chiggers. Rickettsial DNA sequences were amplified for four genes including 16S rRNA, ompB, gltA, and 17 kD protein genes. The minimum infection rate (MIR; number of positive pools/total specimens tested) of the Rickettsia species in the chiggers were 2.8% (9/319). Phylogenetic analysis indicated that individual genes were closely related to different Rickettsia species including R. felis (with 16S rRNA gene), R. australis (with gltA gene), an unnamed Rickettsia sp. TwKM02 (with ompB gene), and Rickettsia endosymbiont of soft tick Ornithodoros erraticus (with 17 kD protein gene). Phylogenic analysis of the concatenated sequence of 16S rRNA, gltA, ompB, and 17 kD protein genes indicated that the Rickettsia species from L. scutellare chigger was most closely related to R. australis and R. akari. These results indicated that the Rickettsia species in chiggers was unique; it was named Candidatus Rickettsia leptotrombidium. Severe fever with thrombocytopenia syndrome virus and hantavirus were not amplified from the chiggers, suggesting lack of infection of these pathogens in the chiggers. A unique Rickettsia species was detected in L. scutellare, which expanded the knowledge on the vector distribution of Rickettsia.