Rocky Mountain spotted fever (RMSF) resulting from the tick-borne Rickettsia rickettsii infections is a potentially fatal tick-borne disease affecting humans and dogs in the Americas. It is difficult to confirm the diagnosis early in the laboratory on account of low-level and inconsistent rickettsemia in whole blood.

Among the 24 tick species documented in Slovakia, Ixodes ricinus is the most widespread and abundant. In some sites, 2-5 epidemiologically important tick species co-occur. Such sites represent hotspots for studying the co-circulation of tick-borne pathogens. Sympatric occurrence of five exophilic species (I. ricinus, Dermacentor reticulatus, D. marginatus, Haemaphysalis concinna, and H. inermis) was confirmed in the environs of the Žemberovce village (Levice region, south-western Slovakia). Here, the seasonal activity and abundance of questing ticks and the tick infestation of game and sheep were investigated. Questing ticks, spleens of game, and ticks removed from game and sheep were examined for the presence of tick-borne pathogens (Babesia spp., Theileria spp., Anaplasma phagocytophilum, Rickettsia spp., Borrelia burgdorferi s.l., and Borrelia miyamotoi) by molecular methods. Among the questing ticks, I. ricinus prevailed. Presence of Babesia crassa, B. microti, Rickettsia helvetica, R. raoultii, A. phagocytophilum, Borrelia afzelii, B. garinii, B. valaisiana, B. burgdorferi sensu stricto and B. miyamotoi was detected. Dermacentor marginatus, I. ricinus and H. concinna were collected from sheep. They were infected with A. phagocytophilum, A. ovis, R. slovaca, and R. raoultii. Anaplasma phagocytophilum was detected in all examined red deer and roe deer and in 55.6% of wild boar. All cervids were positive for Theileria spp. Infestation of game with all five tick species, with a predominance of I. ricinus, was confirmed. In these ticks, A. phagocytophilum, R. helvetica, R. raoultii, Babesia sp. hc-hlj212, B. crassa, B. microti, Babesia spp. and B. miyamotoi were detected. This study confirmed the presence of B. crassa in Slovakia for the first time. The investigated area, with the co-occurrence of five exophilic tick species and a wide spectrum of tick-borne pathogens, represents an epidemiologically important hotspot with the risk of infections of humans and domestic animals.

Tick-borne diseases are an increasing public health concern in Europe, driven by climate change, landscape transformation, and expanding human activity. Urban green spaces provide suitable habitats for ticks and increase human exposure to tick-borne pathogens (TBPs), yet habitat-specific patterns in urban and suburban environments remain poorly characterized. This study examined tick distribution and TBPs prevalence across 11 urban and suburban sites in Kaunas County, Lithuania. A total of 1539 questing Ixodes ricinus ticks were collected and screened by real-time PCR for Borrelia spp., Anaplasma phagocytophilum, Neoehrlichia mikurensis, Rickettsia spp., and Babesia spp., with further species identification by sequencing. Borrelia spp. were most prevalent (24.43%), followed by Rickettsia spp. (7.60%), N. mikurensis (6.63%), A. phagocytophilum (3.64%), and Babesia spp. (2.53%). Tick density, pathogen prevalence, and species diversity varied among habitats, with higher values in forested and ecotonal areas, but notable infection rates were also observed in managed urban sites. Co-infections occurred in 18.8% of infected ticks. Our findings demonstrate that the circulation of TBPs in urban and suburban landscapes is shaped by local habitat features, host communities, and management intensity, highlighting the need for habitat-specific risk assessment in urban planning and public health.

Venezuelan equine encephalitis virus (VEEV) is a mosquito-borne RNA virus that causes low mortality but high morbidity in humans. In addition to natural outbreaks, there is potential for exposure to VEEV via aerosolized virus particles. Currently there are no FDA-licensed vaccines or antiviral therapies for VEEV. We previously demonstrated that high titer anti-VEEV human antibody preparations derived from the plasma of hyperimmunized transchromosomic (Tc) bovines provided significant protection to mice from subcutaneous and aerosol challenge with virulent VEEV (Gardner et al., J. Virol., 91:e00226-17, 2017). In the current studies we utilized the cynomolgus macaque primate model of VEEV infection, challenging some treatment groups with either a IA/B clade virus or a IC clade virus, each derived from a cDNA clone. Animals were treated with liquid or lyophilized transchromosomic bovine polyclonal antibody (TcpAb) preparations via intravenous (IV) or intranasal (IN) routes. Single dose prophylactic (24 hr before challenge) treatment with the liquid TcpAb given IV yielded significant reduction in the magnitude and/or extent of febrile responses and eliminated or greatly reduced serum infectious viremia versus control after aerosol challenge with VEEV regardless of subtype. Therapeutic (24 hr after challenge) treatment showed similar results with the IA/B virus. However, IN treatment alone with lyophilized TcpAb was ineffective against the IC virus. These results indicate that IV treatment with the TcpAb is effective in reducing VEEV disease severity in non-human primates and may be a useful single treatment strategy for infections with this emerging virus.

Sentinel animals are defined as sensitive indicators of environmental hazards that provide an early warning system for public health interventions. Spotted fever group rickettsioses are zoonotic tick-borne diseases that are considered endemic in different American countries with significant rates of morbidity and lethality, mainly when involving species such as Rickettsia rickettsii and Rickettsia parkeri. Dogs have been recognized as good sentinels for these rickettsioses, since they are hosts to different species and stages of ticks, and they sustain a good immunological response after infection. Data from epidemiological studies conducted on dogs in the Americas are dispersed and have not been integrated. In this paper, we present a systematic review and meta-analysis that aimed to present a pooled seroprevalence of Rickettsia sp. in dogs and summarize other relevant data. Literature was reviewed in three databases (PubMed, Scopus, and Web of Science) by different authors, using specific eligibility criteria, and subsequently submitted for meta-analysis to obtain pooled seroprevalences for Rickettsia spp. and different Rickettsia antigens. The systematic search yielded 700 documents, and 49 were selected for review and analysis (years: 2001-2025). Brazil (59.2%) was the country with the highest number of published studies. The Indirect Immunofluorescence Assay (IFA) was used as the main technique with R. rickettsii and R. parkeri as the main antigens used. The estimated overall seroprevalence for Rickettsia sp. was 26.2% (95% CI: 17.8% - 36.8%), with the highest values for R. rickettsii (16.9%, 95% CI: 9.8% - 27.4%), followed by R. parkeri (13.2%, 95% CI: 6.9% - 23.6%). The most frequent tick species collected on dogs were Amblyomma ovale and Rhipicephalus sanguineus s.l. This study confirms the important eco-epidemiological role of dogs as sentinels of rickettsioses. Although this has been studied in some countries, several American countries have not yet addressed it. This could be improved by strengthening surveillance programs focused on rickettsial pathogens that include dogs as sentinels, prioritizing these diseases as relevant zoonoses within a One Health framework.

Piscirickettsia salmonis is an intracellular bacterium responsible for Salmonid Rickettsial Septicemia (SRS) in Atlantic salmon. This pathogen survives within macrophages, hindering immune clearance. In mammals, CD8+ T lymphocytes represent a crucial component of adaptive immunity, as they specifically recognize and eliminate cells infected by intracellular pathogens. Evidence indicates that an analogous mechanism may also operate in teleost fish. Here, the role of CD8+ T lymphocytes in the immune response against P. salmonis was investigated in Atlantic salmon (Salmo salar). Using autologous dorsal fin-derived target cells and leukocytes from infected donors, an ex vivo model to assess antigen-specific cytotoxicity was established. Fin-derived cells internalized P. salmonis and trafficked the bacteria to lysosomal compartments, supporting antigen processing and MHC-I presentation. Sensitized leukocytes exhibited robust antigen-specific lysis of infected target cells, whereas non-specific lysis was negligible. Depletion of CD8a+ cells from sensitized peripheral blood leukocytes resulted in a loss of cytotoxic activity. These CD8a+ cells expressed CD3ζ and TCRβ transcripts, confirming the T-cell phenotype of the effector population. Together, these results provide the first functional evidence that Atlantic salmon mount CD8+ T cell-mediated cytotoxic responses against P. salmonis, highlighting cell-mediated immunity as a critical component of host defense, being a promising target for next-generation vaccines against SRS.

Rickettsia species are vector-borne bacteria, some of which cause rickettsioses, an underrecognized cause of acute undifferentiated febrile illness. While several regions of Colombia are considered endemic for rickettsial infections, information from other areas such as the Cauca department remains limited. Human serum samples and epidemiological data were collected from 506 rural inhabitants in eight rural localities across four municipalities of Cauca department, Colombia, between August and November 2017. Antibodies against SFG (spotted-fever group) and TG (typhus group) rickettsiae were detected using indirect immunofluorescence assay (IFA), and potential risk factors were evaluated using survey data and simple logistic regression analyses. Overall, 65.6% of individuals showed seropositivity for rickettsiae, including 58.3% for SFG, 22.3% for TG rickettsiae, and 15% for both groups. Cattle ownership was identified as a risk factor associated with rickettsial exposure, whereas some regions and housing conditions were associated with lower seropositivity, suggesting possible protective factors. These findings reveal a high level of exposure to SFG and TG rickettsiae among rural inhabitants of the Cauca department and highlight the need for increased surveillance and public health attention in this region.

We report a case of Japanese spotted fever (JSF) showing marked serological cross-reactivity with Rickettsia typhi, which made serological differentiation difficult. An 80-year-old man presented with fever and disseminated erythematous macules. Laboratory finding suggested a rickettsial infection. Minocycline treatment led to clinical improvement. Real-time polymerase chain reaction screening was positive for spotted fever group rickettsiae. Serological testing using paired sera demonstrated comparable increases in antibody titers against R. japonica and R. typhi in the convalescent phase, precluding differentiation based on serology alone. Sequence-based molecular analysis using DNA extracted from the patient's serum revealed 100% identity with R. japonica strain YH, leading to a definitive diagnosis of JSF. This case highlights the diagnostic challenges posed by serological cross-reactivity and underscores the clinical value of molecular diagnostic approaches when serological findings are inconclusive.

Orientia tsutsugamushi causes scrub typhus (tsutsugamushi disease), an acute febrile disease. The infection has been effectively treated with antibiotics since chloramphenicol was introduced. However, occasional reports of treatment failures or delayed responses occur in scrub typhus, and their underlying causes remain poorly understood. This narrative review assesses whether antibiotic antagonism between β-lactam and anti-rickettsial antibiotics delays the resolution of scrub typhus. To address this, we reviewed historical changes in antibiotic use, pitfalls in interpreting study results, in vitro antagonism data, and relevant clinical reports. In subtropical regions, doxycycline and ceftriaxone are frequently used concurrently for the empirical treatment of severe acute undifferentiated fever, targeting scrub typhus and typhoid fever. However, an in vitro study demonstrated that cefotaxime reduces the effects of anti-rickettsial antibiotics, including doxycycline, by at least 25%. This potential antibiotic antagonism may delay fever resolution by 1-5 days, a minor difference often difficult to detect in individual patients. Even when detected, it is frequently misinterpreted as antibiotic resistance or attributed to severe disease or atypical clinical manifestations. Furthermore, this phenomenon may contribute to mortality in cases with life-threatening complications.

Feline rickettsia pneumonia is a rare lung disease caused by feline R. felis infection, which is mainly transmitted by feline fleas. A 57-year-old male patient was hospitalized with pain in the back of the sternum. Chest CT showed bilateral diffuse interstitial lung disease with multiple nodules. After the empirical anti-infection treatment was ineffective, the second-generation meta-genome sequencing (mNGS) of bronchoalveolar lavage (BALF) was diagnosed as feline rickettsia infection. In terms of treatment, inject tegacycline intravenously and then sequentially take minocycline. The patient's symptoms were relieved quickly, and the imaging improved significantly. This report summarizes the clinical and imaging characteristics and diagnosis and treatment experience of the case, aiming to provide reference for the early identification and treatment of such rare infections.

Arthropod-borne rickettsial pathogens are affecting both human and animal health. Due to the lack of studies on tick-borne rickettsiae in this region, the present study aimed to investigate the molecular identity of Rickettsia spp. in ticks in Northwestern Iran. This cross-sectional study was conducted in Ardabil Province from January to December 2024. A total of 700 ticks were collected from livestock. DNA was extracted from pooled ticks, and PCR assays targeting the gltA and 16S rRNA genes were performed to detect Rickettsia spp.; positive PCR products were sequenced for confirmation (Pishgam, Iran). A total of 700 ticks belonging to nine species were isolated from livestock. Among these, Rhipicephalus bursa was the most common species. PCR detected Rickettsia DNA in 2 of 26 pools (7.7%), according to accession gene code: PV929760 and PV929761. According to our findings, R. aeschlimannii was detected in ticks from northwestern Iran. Livestock-associated ticks, including Rhipicephalus spp., are considered logical candidates for further study. Our study highlighted the need for continued surveillance using a One Health approach.