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The incidence of spotted fever group (SFG) rickettsioses in the United States has tripled since 2010. Rocky Mountain spotted fever, the most severe SFG rickettsiosis, is caused by Rickettsia rickettsii. The lack of species-specific confirmatory testing obfuscates the relative contribution of R. rickettsii and other SFG Rickettsia to this increase. We report a newly recognized rickettsial pathogen, Rickettsia sp. CA6269, as the cause of severe Rocky Mountain spotted fever-like illness in 2 case-patients residing in northern California. Multilocus sequence typing supported the recognition of this pathogen as a novel Rickettsia genotype most closely related to R. rickettsii. Cross-reactivity observed for an established molecular diagnostic test indicated that Rickettsia sp. CA6269 might be misidentified as R. rickettsii. We developed a Rickettsia sp. CA6269-specific real-time PCR to help resolve this diagnostic challenge and better characterize the spectrum of clinical disease and ecologic epidemiology of this pathogen.

We report a case-series study of 5 patients with Japanese spotted fever from the Three Gorges Area in China, including 1 fatal case. Seroprevalence of Rickettsia japonica was ≈21% among the local population. Our report highlights the emerging potential threat to human health of Japanese spotted fever in the area.

In 2020, a novel spotted fever group Rickettsia was described in 3 clinically ill dogs in the United States. Using naturally infected canine blood, the novel Rickettsia sp. was isolated in epithelial (Vero E6) and mononuclear (DH82 and 030D) cell lines. The sequenced whole genome revealed a 1.27 Mb circular chromosome with 96.87% identity to Rickettsia raoultii on the basis of average nucleotide identity analysis. A maximum-likelihood phylogeny tree placed the novel Rickettsia in its own branch within the spotted fever group. Immunofluorescence revealed single rods localized along the membrane in epithelial cells and randomly distributed in the cytoplasm of mononuclear cells. We propose the name Rickettsia finnyi sp. nov., strain 2024-CO-Wats, which is available from national and international Rickettsial isolate reference collections. Fever and thrombocytopenia were among abnormalities in the 17 naturally infected dogs we describe, underscoring the pathogenic importance of R. finnyi sp. nov. and its potential public health relevance.

Testing for spotted fever group rickettsioses (SFGR) and the criteria for identifying suspected patients are not routinely used in Kazakhstan. In 2019, we performed a cross-sectional study in 6 sentinel hospitals in the Pavlodar region. We tested 105 hospitalized patients with SFGR-like symptoms by using PCR or indirect immunofluorescence antibody assay and identified 62 cases of SFGR. Most (78%) cases of disease were caused by Rickettsia sibirica and R. raoultii. Cutaneous signs (eschar or rash) were found in 87% of SFGR patients; 79% had a rash, 48% had an eschar, and 13% had neither. Testing of suspected rickettsia cases resulted in a 27% increase in laboratory-detected SFGR over the mean of the previous 3 years (62 vs. 49). Broadening the case definition by including fever, headache, or myalgia and expanding routine testing for suspected cases of SFGR could contribute to improved case detection and earlier treatment.

We found serologic evidence of spotted fever group Rickettsia in humans and dogs and typhus group Rickettsia in dogs in Reynosa, Mexico. Our investigation revealed serologic samples reactive to spotted fever group Rickettsia in 5 community members, which highlights a potential rickettsial transmission scenario in this region.

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

Rickettsial infections are a common cause of hospitalization in tropical settings, although early diagnosis is challenging in the rural locations where these infections are usually seen. This retrospective, clinical audit of microbiologically-confirmed cases of scrub typhus or spotted fever group (SFG) rickettsial infection between 1997 and 2016 was performed a tertiary referral hospital in tropical Australia. Clinical, laboratory and radiological findings at presentation were correlated with the patients' subsequent clinical course. There were 135 locally-acquired cases (95 scrub typhus, 37 SFG, 3 undifferentiated). There were nine hospitalizations during the first 5 years of the study period and 81 in the last 5 years (p for trend = 0.003). Eighteen (13%) of the 135 cases required ICU admission, all of whom were adults. A greater proportion of patients with SFG infection required ICU support (8/37 (22%) compared with 10/95 (11%) scrub typhus cases), although this difference did not reach statistical significance (p = 0.10). Three (8%) of the 37 patients with SFG infection had severe disease (1 died, 2 developed permanent disability) versus 0/95 scrub typhus patients (p = 0.02). Adults with a high admission qSOFA score (≥2) had an odds ratio (OR) of 19 (95% CI:4.8-74.5) for subsequent ICU admission (p<0.001); adults with a high NEWS2 score (≥7) had an OR of 14.3 (95% CI:4.5-45.32) for ICU admission (p<0.001). A patient's respiratory rate at presentation had strong prognostic utility: if an adult had an admission respiratory rate <22 breaths/minute, the negative predictive value for subsequent ICU admission was 95% (95% CI 88-99). In the well-resourced Australian health system outcomes are excellent, but the local burden of rickettsial disease appears to be increasing and the clinical phenotype of SFG infections may be more severe than previously believed. Simple, clinical assessment on admission has prognostic utility and may be used to guide management.

Tick-borne spotted fever group (SFG) rickettsioses are considered emerging vector-borne infectious diseases with potentially severe consequences for public health, particularly in the temperate regions of Europe. The aim of the study was to determine the prevalence and the diversity of Rickettsia spp. in questing Ixodes ricinus ticks in north-eastern Poland, evaluate the serological evidence of exposure to SFG rickettsiae among adult residents of this region, as well as to determine the level of SFG rickettsiae co-infection with Borrelia spirochaetes in ticks and humans. In a total of 4090 ticks, the presence of Rickettsia spp. was detected by PCR and confirmed by sequencing. IgG antibodies against SFG Rickettsia and Borrelia were detected using ELISA. Rickettsial DNA was revealed in 11.3% of females, 11.8% of males and nymphs of 6.5% (MIR, minimum infection rate). Based on DNA sequencing, R. helvetica and R. monacensis were identified. IgG antibodies against SFG rickettsiae were confirmed in 38.7% of adult residents of north-eastern Poland. The co-infection rate of SFG rickettsiae with Borrelia spirochaetes in questing adult I. ricinus ticks was low (2.6%), compared to the co-infection rate (16.1%) observed based on the presence of immunological responses in the study group of residents from northeastern Poland. These findings provide important evidence filling the gap between the environmental detection of SFG rickettsiae in vector populations and the limited number of diagnosed clinical cases in humans.

Spotted fever group and related rickettsia (SFGR) are a neglected group of pathogens that belong to the genus Rickettsia. SFGR are zoonotic and are transmitted by arthropod vectors, primarily ticks, fleas and mites to accidental hosts. These emerging and re-emerging infections are widely distributed throughout the world. Land-use change and increasing human–wildlife conflict compound the risk of SFGR infection to local people in endemic areas and travelers to these regions. In this article, we discuss the rickettsial organisms causing spotted fever and related diseases, their arthropod vectors in Asia and the impact of land-use change on their spread.

Since 1996, the incidence of rickettsiosis has been increasing in Yucatán, Mexico, but recent prevalence data are lacking. This study aimed to determine exposure to the Spotted Fever Group (SFG) and Typhus Group (TG) in human serum samples suspected of tick-borne diseases (TBD) between 2015 and 2022. A total of 620 samples were analysed using indirect immunofluorescence assay (IFA) to detect IgG antibodies against SFG (Rickettsia rickettsii) and TG (Rickettsia typhi), considering a titer of ≥64 as positive. Results showed that 103 samples (17%) were positive for R. rickettsii and 145 (24%) for R. typhi, while 256 (41%) and 229 (37%) were negative, respectively. There was a cross-reaction in 244 samples (39%). Individuals with contact with vectors, such as ticks, showed significant exposure to fleas (p = 0.0010). The study suggests a high prevalence of rickettsiosis and recommends prospective studies to assess the disease burden and strengthen surveillance and prevention in Yucatán, considering factors like temperature and ecological changes.