The Colorado tick fever virus (CTFV), which has 12-segmented double-stranded RNA genomes, is a pathogenic arbovirus that causes severe diseases in humans. However, little progress has been made in the analysis of replication mechanisms and pathogenicity. This virological constraint is due to the absence of a reverse genetics system for CTFV; therefore, we aimed to establish the system. Initially, the efficacy of CTFV replication was investigated in various cell lines. CTFV was found to grow in many cell types derived from different hosts and organs. Subsequently, BHK-T7 cells stably expressing T7 RNA polymerase were transfected with plasmids encoding each of the 12 CTFV gene segments, expression plasmids encoding all CTFV proteins, and a vaccinia virus RNA-capping enzyme. Following transfection, the cells were co-cultured with Vero or HeLa cells. Using this system, we rescued monoreassortants and recombinant viruses harboring peptide-tagged viral proteins. Furthermore, an improved system using Expi293F cells expressing T7 RNA polymerase was established, which enabled the generation of recombinant reporter CTFVs. In conclusion, these reverse genetics systems for CTFV will greatly contribute to the understanding of viral replication mechanisms, pathogenesis, and transmission, ultimately facilitating the development of rational treatments and candidate vaccines.

The Rocky Mountain wood tick, Dermacentor andersoni Stiles, is the most common human biting tick in the Rocky Mountain region of the USA. Although Rickettsia spp. and Colorado tick fever virus have been studied in D. andersoni in certain areas of their distribution, investigations of most other tickborne pathogens are lacking. Despite the history of Rocky Mountain spotted fever in the Bitterroot Mountains of western Montana, no comprehensive surveys of large numbers of ticks for Rickettsia spp. have been conducted there for >40 years. For the present study, host-seeking adult D. andersoni were collected at multiple sites in canyons on the west side of the Bitterroot Valley in western Montana in spring 2021. Following DNA extraction, ticks were screened by polymerase chain reaction assays for several tick-borne microorganisms. DNA sequence data analysis was conducted to confirm identity and conduct phylogenetic comparisons with reference strain sequences of different organisms. No ticks were found to contain Anaplasma spp., Borrelia spp., or Ehrlichia spp. DNA, and a Babesia sp. was detected in only one tick. However, Bartonella spp. DNA was detected in 2 % of tested ticks. Additionally, five species of Rickettsia, including R. peacockii, R. bellii, R. rhipicephali, R. montanensis, and R. rickettsii, were identified in ticks from different sites. The most prevalent Rickettsia species was R. peacockii and the least common was R. rickettsii (found in only two ticks). The relevance of these findings is discussed in relation to historical and contemporary data on Bartonella spp. and Rickettsia spp.

Tickborne infections have increased significantly over the past 2 decades. There are a number of infections caused by tick bites which have similar clinical presentations and which may mimic other types of infections. Infections can range from mild to serious, and some can be life-threatening if not diagnosed early. Although Lyme disease is the most common of all tickborne infections, there are many others to consider in the differential diagnosis.

Colorado tick fever virus (CTFV) is a double-stranded RNA virus in the family Reoviridae. CTFV is the causative agent of Colorado tick fever (CTF), a febrile illness that can have mild to severe manifestations. CTFV is an underreported and underrecognized virus; similarly, the literature concerning neglected tick-borne viruses lacks standard protocols for viral research. Here we describe protocols and procedures for CTFV studies, including the quantification of the virus through viral plaque assay, generation and storage of CTFV stocks, and detection with reverse transcription-quantitative PCR (RT-qPCR).

To estimate rates of hospitalizations for tick-borne diseases (TBDs) in Canada, retrospective analysis was conducted to determine the incidence of patients diagnosed with TBDs during their hospital stay in Canada, and describe demographic characteristics, temporal trends and geographic distributions, from 2009 through 2021. Codes from the International Classification of Diseases, Tenth Revision (ICD-10-CA) were used to capture diagnoses of TBDs in the Discharge Abstract Database (DAD) in Canadian hospitals. From 2009 through 2021, 1,626 patients were diagnosed with TBDs during their hospital stay. Of these, 1,457 were diagnosed with Lyme disease (LD), 162 with other TBDs, and seven were diagnosed with more than one TBD. Annual hospitalization counts for LD showed a significant increase from 50 in 2009 to 259 in 2021 (incidence rate per 100,000 population of 0.1 and 0.7, respectively). Epidemiologic patterns for hospitalized LD cases, including increases and variation in annual incidences, seasonality, demographics and geographic distribution, are consistent with those elucidated in national LD surveillance data. Amongst 162 patients diagnosed with other tick-borne diseases, discharge diagnoses were: rickettsiosis (32.7%), spotted fever due to rickettsia rickettsii (23.5%), tularemia (21.0%), babesiosis (8.6%), other tick-borne viral encephalitis (6.2%), tick-borne relapsing fever (4.9%), and Colorado tick fever (0.6%). Annual incidence increased only for rickettsiosis from 3 to 12 patients over the study period. Monitoring the data of hospitalizations using the DAD provided insights into the burden of emerging TBDs, the severity of illnesses and the population most at risk.