Vector-Borne and Zoonotic Diseases

The cat flea (Ctenocephalides felis) is the primary arthropod vector responsible for the transmission of Bartonella henselae, the etiologic agent of cat scratch disease. Although domestic cats serve as the principal reservoir host, maintaining long-term intraerythrocytic bacteremia, the spread of B. henselae within feline populations relies entirely on flea-mediated acquisition and transmission. Early work demonstrated that fleas readily acquire the bacterium while feeding on bacteremic cats and can subsequently infect naïve hosts; however, the underlying biological mechanisms remain only partially understood.

This review synthesizes current knowledge of how B. henselae interacts with its flea vector, tracing the process from acquisition through midgut colonization, persistence, and transmission via contaminated feces.

By integrating findings from artificial feeding systems, natural infection models, and recent advances in bacterial and vector biology, this review provides an updated assessment of the field and identifies key knowledge gaps that must be addressed to fully elucidate this vector–pathogen relationship.

Small mammals can carry and transmit various virulent pathogens. Xinjiang Uygur Autonomous Region (Xinjiang), with its rich diversity of small mammal species, represents a high-risk region for pathogen transmission. Epidemiological analysis and genetic sequencing of these pathogens are crucial for strengthening public health interventions.

Methods: This study examined the analysis of effects of region, habitat, host genus, and climatic factors on pathogen infection rates in small mammals using spleen and lung tissue samples collected between May and September 2024. Categorical variables were assessed using Pearson χ 2 test/Monte Carlo χ 2 test, while continuous variables were analyzed with the Wilcoxon rank-sum test. Principal component analysis was applied to extract key influence factors, followed by binary logistic regression modeling. Pathogens were detected in 43 host animals, including Anaplasma phagocytophilum (n = 27) and Spotted fever group rickettsiae (SFGR; n = 15), with infection rate comparisons conducted under different conditions (α = 0.05). Positive samples were sequenced and subjected to phylogenetic analysis.

The overall pathogen infection rate in small mammals from Xinjiang border ports was 40.19%, comprising A. phagocytophilum (25.23%) and SFGR (14.02%). High temperature, low relative humidity, the Huoerguosi Port, and grassland habitats were associated with a reduced infection rate of pathogenic microorganisms (odds ratio = 0.71, 95% confidence interval = 0.51–0.93, p = 0.021). Spatially, A. phagocytophilum showed the highest infection rate in the Dulata Port, desert habitats, and Meriones spp., whereas SFGR predominated in the Takeshiken Port, alpine meadow steppes, and Marmota spp. Genetic homology analysis revealed maximum sequence similarities of 99.15% for A. phagocytophilum and 98.35% for SFGR.

Xinjiang border ports have a high diversity of small mammal species with elevated pathogen infection rates. These findings underscore the necessity for sustained and enhanced surveillance of small mammal-borne diseases in this region.

Tick-borne diseases caused by spotted fever group (SFG) Rickettsia and members of the family Anaplasmataceae are important public health concerns. Given that previous studies on SFG in Hokkaido, the northernmost prefecture of Japan, have been limited by small sample sizes or limited to specific pathogens or tick species, the epidemiology of tick-borne bacteria remains unclear. This study investigated the prevalence of SFG Rickettsia and Anaplasmataceae bacteria in multiple tick species in Hokkaido.

DNA was extracted from 1,115 questing ticks representing six species (548 Ixodes ovatus, 368 Ixodes persulcatus, 95 Haemaphysalis concinna, 74 Haemaphysalis japonica, 28 Haemaphysalis megaspinosa, and 2 Haemaphysalis longicornis) collected from six districts in Hokkaido. Samples were screened using PCR assays targeting the gltA gene of SFG Rickettsia species and the groEL gene of Anaplasmataceae. Amplicons were sequenced for species identification.

SFG Rickettsia DNA was found only in I. persulcatus (48.9%, 180/368), including R. helvetica (32.1%) and Candidatus R. tarasevichiae (16.8%). Anaplasmataceae DNA was detected in 3.9% (44/1,115) of ticks, including I. persulcatus, I. ovatus, H. japonica, and H. megaspinosa. In I. persulcatus, Ehrlichia muris, Candidatus Neoehrlichia mikurensis, and Anaplasma phagocytophilum were detected in 4.6%, 3.3%, and 0.3%, respectively. Ehrlichia japonica was found in I. ovatus (0.9%), while unclassified Ehrlichia spp. were detected in H. japonica (1.4%) and H. megaspinosa (3.6%). Seventeen I. persulcatus (4.6%) carried both SFG Rickettsia and Anaplasmataceae.

The findings showed that questing ticks in Hokkaido harbor zoonotic bacteria. While I. persulcatus appears to be the principal vector, the detection of pathogens in I. ovatus, H. japonica, and H. megaspinosa suggests the potential for additional vectors in the region. These findings underscore the importance of continuous surveillance and heightened clinical awareness of tick-borne diseases in northern Japan.

Leptospirosis is a globally important zoonosis maintained by chronically infected animal reservoirs, yet its long-term eco-epidemiological dynamics remain poorly understood. Southeast China has historically been an endemic region, but changing climate and land use may be reshaping Leptospira transmission.

We conducted 15-year longitudinal surveillance (2009–2024) in Pan’an County, Zhejiang Province, integrating field sampling of rodents and other hosts, serogroup identification, multilocus sequence typing, and experimental mouse infection. Annual rainfall, host data, and molecular analyses were combined to assess temporal trends, serogroup turnover, and virulence differences between classical and emerging lineages.

Rodent Leptospira positivity persisted annually (1.2–18%) with peaks during heavy-rainfall years, while human cases declined after 2015. The host range narrowed from multispecies detection to rodent dominance after 2020. Serological and phylogenetic analyses revealed a post-2020 emergence of serogroup 56601, which replaced historical O1/O6 lineages and formed a genetically compact cluster, suggesting recent clonal expansion. In mice, the 56601 strain caused higher renal bacterial loads, more severe tubular injury, and stronger cytokine responses than O1.

Long-term surveillance demonstrates rapid ecological and genetic turnover of Leptospira and identifies 56601 as an emerging lineage with increased pathogenic potential in endemic regions.

This study explores the application of long-read sequencing technologies for genotyping, epigenetic profiling, and epidemiological monitoring of Yersinia pestis isolates obtained from natural foci in Central Asia and previous zoonotic outbreaks.

Computational tools for genome assembly and genotyping were developed, enabling high-precision identification of both chromosomal and plasmid sequences, including the small plasmid pCKF.

Genotyping based on genetic polymorphisms distinguished the major Y. pestis biovars and lineages, and revealed cluster-specific diversity among Medievalis (2.MED) isolates, including groups of strains associated with different plague foci and disease outbreaks in domestic animals and humans. These specific genomic polymorphisms identified in subclades of 2.MED isolates allow their high-precision identification. The distribution of pCKF-positive strains in the region and the potential involvement of these pathogens in disease outbreaks are discussed. Additionally, comparative epigenomic analysis uncovered strain-specific cytosine methylation patterns at cgGATCG motifs. Further studies involving more sequenced strains are needed to determine whether this cytosine methylation specificity is linked to genome function regulation and adaptation to different hosts and environments.

These findings demonstrate the effectiveness of long-read sequencing technologies in revealing both genetic and epigenetic features of bacterial pathogens, contributing to our understanding of the evolutionary mechanisms underlying the emergence and spread of this especially dangerous infection.

There is limited understanding of the replication and transmission of bandaviruses and the influence of host genotype in successful infection. An in vitro Bandavirus model, such as Lone Star virus (LSV, Bandavirus amblyommae), capable of propagating in standard cell lines, could provide some of this critical information. In this study, we sequenced the genome of LSV and profiled its relationship with a key host viral-interacting protein, Synaptogyrin-2 (SYNGR2), known to influence the replication of another Bandavirus, Bandavirus dabieense.

The genome of the LSV TMA 1381 strain was sequenced and assembled using Oxford Nanopore Technology. The expression of SYNGR2 was profiled and annotated in Vero cells. SYNGR2 knockout (KO) Vero clones were obtained via CRISPR-Cas9 gene editing of the first exon, present in all SYNGR2 isoforms. Following LSV infection, expression of SYNGR2 and LSV titer was measured in SYNGR2-KO and wild-type cell lines.

Sequence variation and evidence of viral heterogeneity were detected across all segments of the LSV TMA 1381 strain (4 missense substitutions out of 7 single-nucleotide polymorphisms identified, q > 16). Important amino acid sequence differences for the nonstructural protein, known to directly interact with host SYNGR2, were observed between LSV and other bandaviruses (15.5–47.4%). The change in SYNGR2 expression in wild-type Vero cells was limited following LSV infection (1.77-fold). No difference in estimated LSV titer was detected between wild-type and SYNGR2-KO Vero cells (p > 0.16). Our data illustrate key distinctions from previous Bandavirus reports and underline the need for future studies to explore the mechanisms of LSV replication and pathogenesis.

Vesicular stomatitis is endemic in southern Mexico, Central America, and northern South America. The causative agent, vesicular stomatitis virus (VSV; Rhabdoviridae: Vesiculovirus), includes two serotypes—New Jersey (VSNJV) and Indiana (VSIV)—both present in Costa Rica. Transmission occurs via direct contact, fomites, and insect vectors. Occupational exposure, particularly in livestock workers, is a known risk, and high human seroprevalence has been reported elsewhere in Central America. Some cases present with a self-limited febrile illness, occasionally with vesicular lesions. No studies have assessed human VSV seropositivity in Costa Rica.

A cross-sectional survey was conducted in two dairy cantons of Costa Rica: Poás (n = 174) and Tilarán (n = 84). Serum samples were tested for neutralizing antibodies against VSNJV and VSIV using microseroneutralization in Vero-E6 cells. The seroprevalence with 95% confidence intervals was estimated. Associations with occupation and cattle contact were evaluated using chi-square tests and relative risk (RR). No clinical data were collected, as the study was focused solely on serological evidence of exposure.

In Poás, VSNJV seroprevalence was 40.8% and VSIV 16.7%. Agricultural work was associated with higher VSNJV (RR = 2.28, p = 0.0001) and VSIV seropositivity (RR = 4.78, p = 0.0004). Direct cattle contact correlated with VSIV seropositivity (RR = 4.22, p = 0.0050). In Tilarán, VSNJV seroprevalence was 26.2% and VSIV 3.6%; only direct cattle contact was significantly associated with VSNJV (RR = 6.14, p = 0.0191). Prevalence was higher in Poás for both VSNJV (RR = 1.56, p = 0.022) and VSIV (RR = 4.67, p = 0.0028).

This first report of human VSV seropositivity in Costa Rica shows a predominance of VSNJV. Higher prevalence among agricultural workers and those with cattle contact highlights occupational risk. Findings align with bovine seroprevalence and historical Central American human data, underscoring the need to consider VSV in febrile illnesses and to strengthen integrated “One Health” surveillance.