High-throughput sequencing methods have made it possible to identify numerous novel tick-borne viruses that are potentially pathogenic to humans. Among these, Songling virus (Orthonairovirus songlingense, SGLV) has been associated with febrile illness in patients following tick bites in China, but its geographic distribution outside China remains largely unexplored. In this study, we aimed to detect SGLV circulation in ticks across Asian Russia, focusing on regions bordering China. A total of 3444 adult ticks representing six species were collected from 170 locations across 11 regions during the summer of 2024. SGLV RNA was detected in Haemaphysalis concinna ticks, with 11 positive specimens yielding an SGLV RNA prevalence rate of 2.2%. Positive ticks were found in four regions, with the highest positivity rate (5.8%) recorded in Amur Oblast, which directly borders China. The detection of SGLV in the Republic of Altai represents the westernmost record of this virus to date. Full-length nucleoprotein-coding sequences obtained for all Russian isolates revealed up to 1.2% nucleotide divergence. Phylogenetic analysis confirmed that all Russian SGLV isolates belong to Orthonairovirus songlingense, with the Altai SGLV isolate showing genetic similarity to a human-derived Chinese SGLV isolate. Co-infections with Rickettsia heilongjiangensis were detected in four SGLV-positive ticks, highlighting the potential for simultaneous pathogen transmission. These findings establish the first evidence of SGLV circulation in Russia across a wide geographic range and underscore the need for differential diagnosis of febrile illnesses following tick bites in this region.

Spotted fever group (SFG) rickettsioses are emerging zoonotic diseases of increasing relevance in Latin America, yet the specific species involved in human infections remain poorly defined in many endemic regions. This study aimed to determine the most probable antigen among SFG-seroreactive febrile patients from Villeta, Colombia. A panel of 25 convalescent-phase serum samples previously identified as positive for SFG Rickettsia spp. antibodies was analyzed by indirect immunofluorescence assay using antigens of Rickettsia rickettsii, R. amblyommatis and R. parkeri. Antibody titers were compared to identify differential seroreactivity patterns. Overall, 44% (11/25) of the samples showed differential antibody titers against one of the tested antigens. Among these, nine (36%) exhibited higher titers to R. parkeri and two (8%) to R. amblyommatis, while none showed exclusive reactivity to R. rickettsii. The remaining 56% (14/25) presented similar titers across antigens, consistent with indeterminate or cross-reactive SFG responses. Antibody titers ranged from 1:128 to 1:4096, with R. parkeri showing the strongest reactivity. These findings suggest R. parkeri or a highly related Rickettsia species as the predominant probable antigen in Villeta, highlighting its potential role in mild rickettsial infections and emphasizing the need for eco-epidemiological studies to identify local vectors and reservoirs.

Typhus (FBT), caused by Rickettsia typhi, rarely causes neurological disease. Herein, we describe neurological involvement in two cases of FBT. In the first case, an adult presented with persistent fever which deteriorated into status epilepticus. He was successfully treated with doxycycline and made a complete recovery. In the second case, a patient suffered an ischemic stroke and had a protracted clinical course but ultimately made a near complete recovery. In addition to these cases, we conducted a comprehensive narrative review of 43 cases of neurologic involvement in FBT reported from 1989 to 2025. Cases were excluded if there were pathologic discrepancies with typical cases of FBT. Presentations ranged from cranial nerve palsies to meningitis and fulminant encephalitis. This review highlights the spectrum of CNS complications associated with FBT and underscores the importance of early recognition and treatment with doxycycline to improve outcomes. Given the potential severity of neurologic involvement, clinicians in endemic areas should maintain a high index of suspicion for FBT in patients presenting with a febrile illness and neurologic symptoms.

Rocky Mountain spotted fever (RMSF) is one of the most common tick-borne rickettsial diseases in the USA. It is caused by the bacterium Rickettsia rickettsii, which is found in most states. It tends to be fatal even in otherwise healthy people. The diagnosis of RMSF is difficult because of the non-specific, wide-ranging presentations of the disease, especially early in its course, when symptoms may begin with a mild fever, headache, and rash after three or more days of illness, and may progress to fulminant disease. Prompt empirical antimicrobial therapy and aggressive supportive care are mandatory to avoid life-threatening complications, and treatment should not be delayed while awaiting diagnostic confirmation. We present a case of a 62-year-old male who presented with confusion and multiple falls, later developing a maculopapular rash. The initial non-specific symptoms contributed to a delay in diagnosis. Complicating management further, the patient has a documented allergy to doxycycline, the first-line treatment for RMSF. This case underscores the importance of early clinical suspicion and the unique challenges in managing RMSF in patients with a contraindication to standard therapy.

Group testing protocols physically combine biomaterial from multiple individuals into a single 'pooled' specimen, which is then tested for markers of infection. Group testing offers a cost-effective approach for surveillance of low-prevalence infections because it greatly reduces the number of tests required relative to individual testing protocols. However, group testing poses challenges for detecting spatial clusters of disease because only pooled test results are observed. This article introduces a spatial scan statistic tailored to group testing data with variable pool sizes, using a likelihood ratio test to compare homogeneous and heterogeneous infection probability models across candidate zones. A simulation study is performed to evaluate the power and type I error rate of the spatial scan statistic test across multiple sample sizes, pooling strategies, and infection prevalences. The results demonstrate that geographically homogeneous pooling improves power relative to heterogeneous pooling. After validating the method, we apply the spatial scan statistic test to pooled testing data from ticks collected across South Carolina as part of spotted fever group Rickettsia surveillance. We detect a cluster of Rickettsia infection in Amblyomma americanum ticks along the southeast coast of South Carolina.

Dogs are common companion animals, often infested by fleas that can transmit zoonotic pathogens in rural tropical areas. In Colombia, studies on flea-borne agents in dogs are limited. Understanding the presence of these ectoparasites and associated microorganisms is crucial. To assess flea infestation and detect and identify Rickettsia and Bartonella spp. in fleas collected from dogs in Cundinamarca, Colombia. Between 2019 and 2020, fleas were collected from rural domestic dogs in 24 municipalities of western Cundinamarca. Fleas were morphologically identified and pooled for DNA extraction. Molecular screening of Rickettsia and Bartonella spp. was performed by qPCR. Positive samples underwent further characterization by conventional PCR. Rickettsia was additionally analyzed using RFLP, while Bartonella was evaluated through phylogenetic analysis. Of the 116 dogs examined across 24 municipalities, 39.7% were infested with fleas. A total of 138 fleas were collected and grouped into 46 pools, with Ctenocephalides felis felis identified in 94% of them. Rickettsia was detected in 83% of pools, with Rickettsia asembonensis and Rickettsia felis identified in most positive samples. Bartonella was found in 28% of pools; however, sequencing success was limited, and no species-level identification could be achieved. This study documents flea infestation in domestic dogs in Cundinamarca, predominantly by C. felis felis. High detection of R. asembonensis and presence of R. felis confirm widespread rickettsial circulation in fleas. Bartonella was detected less frequently, but species-level identification was not achieved.

Rickettsioses is a zoonotic disease caused by an intracellular bacterium transmitted through the bites of hematophagous arthropods. While antibiotics can effectively treat this disease, overuse may lead to the development of antibiotic resistance. To combat this issue, vaccine development has been pursued to address this bacterial infection. The types of vaccines formulated against Rickettsia include inactivated, live-attenuated, subunit, DNA, and nanovaccines, all of which induced immune responses, and some demonstrated protective efficacy against infectious challenges. These outcomes have encouraged new scientific efforts to develop vaccines against rickettsiosis. Therefore, this review focuses on describing Rickettsia classification, transmission, pathogenesis, and immune evasion, followed by a discussion of advancements in vaccine development against Rickettsia, detailing the antigens, synthesis and production, formulations, immunization, delivery strategies, and protective efficacy. Additionally, challenges for Rickettsia vaccines were identified and placed in perspective as future opportunities.

Bovine anaplasmosis is a tick-borne rickettsial disease of significant sanitary and economic importance to livestock, particularly in tropical and subtropical regions, and is associated with high morbidity and reduced productivity. However, data on its molecular prevalence in cattle from semiarid and transitional areas of the Northeast region of Brazil remain scarce. This study aimed to determine the prevalence of Anaplasma spp. in cattle from smallholder farms located in the Sertão and Agreste mesoregions of the states of Paraíba and Pernambuco, Brazil. A total of 380 whole blood samples from cattle were analyzed by conventional PCR targeting the msp4 gene, following confirmation of DNA extraction by amplification of the endogenous GAPDH gene. Anaplasma spp. was detected in 92.1% of the cattle, with no significant association with sex, age group, breed, production system, or level of tick infestation. Positive cattle exhibited significantly lower hematocrit values compared to negative animals (p = 0.0087). These results represent the first report of molecular detection of Anaplasma spp. in cattle from the states of Pernambuco and Paraíba and suggest the presence of enzootic stability microregions in the Sertão and Agreste mesoregions of Northeast Brazil.

Murine typhus is a reemerging infectious disease with the potential for severe manifestations. We conducted a retrospective study to examine severe illness in those hospitalized with murine typhus in Galveston, Texas. We identified 149 cases, of which 119 (79.8%) were hospitalized and 33 (28%) required admission to the intensive care unit (ICU). ICU patients were older than non-ICU patients (54.9 vs. 47.2 years; p<0.02). Thrombocytopenia was more severe in the ICU group (101 × 10[3] µ/L) compared to the non-ICU group (137 × 10[3] µ/L) (p<0.01). The median time from healthcare contact in the emergency department to initiation of appropriate antibiotics was similar for the ICU group (1 day) and non-ICU group (2 days) (p = 0.26). Two deaths (1.7%) in the ICU group were attributed to multiorgan failure and hemophagocytic lymphohistiocytosis. In murine typhus-endemic regions, early recognition and prompt treatment is imperative to mitigate adverse outcomes.

Rickettsial diseases present ongoing diagnostic challenges due to antigenic diversity, serological cross-reactivity, and the lack of reliable standardised control reagents. Current serodiagnostic assays frequently rely on convalescent human sera as positive controls, which are inherently variable, limited in supply, and poorly suited to assay standardisation and quality assurance. In this study, we developed and validated human-mouse chimeric monoclonal antibodies targeting the conserved outer membrane protein B (OmpB) of Rickettsia typhi as defined, renewable, positive-control calibrators for existing rickettsial serological platforms. Murine monoclonal antibodies were generated and engineered into chimeric IgG antibodies, which were expressed in HEK293T cells. The chimeric antibodies demonstrated high antigen specificity, bound native OmpB on the surface of R. typhi, and showed no detectable cross-reactivity within the tested antigen panel when evaluated using dot blot, immunofluorescence microscopy, and Luminex-based multiplex assays. Compared with patient-derived positive control sera, the chimeric antibodies demonstrated improved specificity and consistent performance within the evaluated assay conditions. These findings support the potential use of chimeric monoclonal antibodies as standardised positive controls for rickettsial serodiagnostics, with potential applications in assay validation, quality assurance, and inter-laboratory harmonisation.