Colorado tick fever in the United States, 2002-2012

Colorado Tick Fever in the United States, 2013-2022

Colorado tick fever (CTF) virus is an arbovirus maintained in an enzootic cycle between Rocky Mountain wood ticks (Dermacentor andersoni) and rodent species in the western United States. Individuals with CTF typically present with symptoms including fever, headache, myalgia, and lethargy, with a biphasic illness frequently occurring. We reviewed data on CTF cases reported to the national U.S. arboviral disease surveillance system and identified through testing at the CDC to characterize the epidemiology of CTF from 2013-2022. During this period, 148 CTF cases were identified, all likely infected in an endemic area in one of six states (Montana, Wyoming, Oregon, Colorado, Utah, Idaho). A median of 11 cases (range: 5-37) were identified per year, with an average annual national incidence of 0.04 cases per million population. The median age of cases was 55 years (range: 1-84 years), and 96 (65%) were male. Most (n = 145; 98%) cases acquired infection from April through July. The hospitalization rate was 16% (16 of 102 cases with data), and no deaths were reported. These findings substantiate the continued circulation of CTF virus in the western United States, highlighting the importance of implementing approaches to ensure CTF awareness for medical providers and providing education on tick bite prevention strategies for residents and visitors to risk areas.

Square the Circle: Diversity of Viral Pathogens Causing Neuro-Infectious Diseases

Neuroinfections rank among the top ten leading causes of child mortality globally, even in high-income countries. The crucial determinants for successful treatment lie in the timing and swiftness of diagnosis. Although viruses constitute the majority of infectious neuropathologies, diagnosing and treating viral neuroinfections remains challenging. Despite technological advancements, the etiology of the disease remains undetermined in over half of cases. The identification of the pathogen becomes more difficult when the infection is caused by atypical pathogens or multiple pathogens simultaneously. Furthermore, the modern surge in global passenger traffic has led to an increase in cases of infections caused by pathogens not endemic to local areas. This review aims to systematize and summarize information on neuroinvasive viral pathogens, encompassing their geographic distribution and transmission routes. Emphasis is placed on rare pathogens and cases involving atypical pathogens, aiming to offer a comprehensive and structured catalog of viral agents with neurovirulence potential.

Colorado tick fever virus: a review of historical literature and research emphasis for a modern era

Colorado tick fever virus is an understudied tick-borne virus of medical importance that is primarily transmitted in the western United States and southwestern Canada. The virus is the type species of the genus Coltivirus (Spinareoviridae) and consists of 12 segments that remain largely uncharacterized. Patterns of viral distribution are driven by the presence of the primary vector, the Rocky Mountain wood tick, Dermacentor andersoni. Infection prevalence in D. andersoni can range from 3% to 58% across the geographic distribution of the tick. Infection in humans can be severe and often presents with fever relapses but is rarely fatal. Here, we review the literature from primary characterizations in the early 20th century to current virus/vector research being conducted and identify vacancies in current research.

From Tick to Test: A Comprehensive Review of Tick-Borne Disease Diagnostics and Surveillance Methods in the United States

Tick-borne diseases (TBDs) have become a significant public health concern in the United States over the past few decades. The increasing incidence and geographical spread of these diseases have prompted the implementation of robust surveillance systems to monitor their prevalence, distribution, and impact on human health. This comprehensive review describes key disease features with the geographical distribution of all known tick-borne pathogens in the United States, along with examining disease surveillance efforts, focusing on strategies, challenges, and advancements. Surveillance methods include passive and active surveillance, laboratory-based surveillance, sentinel surveillance, and a One Health approach. Key surveillance systems, such as the National Notifiable Diseases Surveillance System (NNDSS), TickNET, and the Tick-Borne Disease Laboratory Network (TBDLN), are discussed. Data collection and reporting challenges, such as underreporting and misdiagnosis, are highlighted. The review addresses challenges, including lack of standardization, surveillance in non-human hosts, and data integration. Innovations encompass molecular techniques, syndromic surveillance, and tick surveillance programs. Implications for public health cover prevention strategies, early detection, treatment, and public education. Future directions emphasize enhanced surveillance networks, integrated vector management, research priorities, and policy implications. This review enhances understanding of TBD surveillance, aiding in informed decision-making for effective disease prevention and control. By understanding the current surveillance landscape, public health officials, researchers, and policymakers can make informed decisions to mitigate the burden of (TBDs).

Geographical distribution and pathogenesis of ticks and tick-borne viral diseases

Ticks are obligatory hematophagous arthropods that harbor and transmit infectious pathogens to humans and animals. Tick species belonging to Amblyomma, Ixodes, Dermacentor, and Hyalomma genera may transmit certain viruses such as Bourbon virus (BRBV), Dhori virus (DHOV), Powassan virus (POWV), Omsk hemorrhagic fever virus (OHFV), Colorado tick fever virus (CTFV), Crimean-Congo hemorrhagic fever virus (CCHFV), Heartland virus (HRTV), Kyasanur forest disease virus (KFDV), etc. that affect humans and certain wildlife. The tick vectors may become infected through feeding on viraemic hosts before transmitting the pathogen to humans and animals. Therefore, it is vital to understand the eco-epidemiology of tick-borne viruses and their pathogenesis to optimize preventive measures. Thus this review summarizes knowledge on some medically important ticks and tick-borne viruses, including BRBV, POWV, OHFV, CTFV, CCHFV, HRTV, and KFDV. Further, we discuss these viruses' epidemiology, pathogenesis, and disease manifestations during infection.

Increase in Colorado Tick Fever Virus Disease Cases and Effect of COVID-19 Pandemic on Behaviors and Testing Practices, Montana, 2020

In 2020, Montana, USA, reported a large increase in Colorado tick fever (CTF) cases. To investigate potential causes of the increase, we conducted a case-control study of Montana residents who tested positive or negative for CTF during 2020, assessed healthcare providers' CTF awareness and testing practices, and reviewed CTF testing methods. Case-patients reported more time recreating outdoors on weekends, and all reported finding a tick on themselves before illness. No consistent changes were identified in provider practices. Previously, only CTF serologic testing was used in Montana. In 2020, because of SARS-CoV-2 testing needs, the state laboratory sent specimens for CTF testing to the Centers for Disease Control and Prevention, where more sensitive molecular methods are used. This change in testing probably increased the number of CTF cases detected. Molecular testing is optimal for CTF diagnosis during acute illness. Tick bite prevention measures should continue to be advised for persons doing outdoor activities.

Climate Crises and Developing Vector-Borne Diseases: A Narrative Review

Background

Climate change based on temperature, humidity and wind can improve many characteristics of the arthropod carrier life cycle, including survival, arthropod population, pathogen communication, and the spread of infectious agents from vectors. This study aimed to find association between content of disease followed climate change we demonstrate in humans.

Methods

All the articles from 2016 to 2021 associated with global climate change and the effect of vector-borne disease were selected form databases including PubMed and the Global Biodiversity information facility database. All the articles selected for this short review were English.

Results

Due to the high burden of infectious diseases and the growing evidence of the possible effects of climate change on the incidence of these diseases, these climate changes can potentially be involved with the COVID-19 epidemic. We highlighted the evidence of vector-borne diseases and the possible effects of climate change on these communicable diseases.

Conclusion

Climate change, specifically in rising temperature system is one of the world's greatest concerns already affected pathogen-vector and host relation. Lice parasitic, fleas, mites, ticks, and mosquitos are the prime public health importance in the transmission of virus to human hosts.

Dermatological manifestations of tick-borne viral infections found in the United States

Tick-borne diseases (TBDs) are bacterial, viral, and parasitic diseases transmitted by ticks. Viral TBDs have increased in prevalence over the last decade with many new pathogenic viruses being discovered. Doxycycline is often empirically prescribed by clinicians to treat symptomatic patients following tick bites due to suspicions of bacterial TBDs such as Rocky Mountain spotted fever, anaplasmosis, and ehrlichiosis. However, viral TBDs are included in the differential diagnosis if patients do not clinically improve following antibiotic therapy. Several viral TBDs present with dermatological manifestations. Recognizing the differences in clinical presentations of TBDs, particularly of newly emerging viral TBDs in the United States, can help physicians identify the viral TBD, and possibly rule out viral illnesses with different clinical presentations. Therefore, this review discusses clinical manifestations, with an emphasis on dermatologic manifestations of Heartland Virus, Bourbon Virus, Powassan Virus, Deer Tick Virus and Colorado Tick Fever Virus. KEY POINTS: Viral tick-borne diseases have increased in prevalence over the last decade and often have similar clinical manifestations to other tick-borne diseases, including bacterial infections. Here, we review the dermatologic manifestations of Heartland Virus (HRTV), Bourbon Virus (BRBV), Powassan Virus (POWV), Deer Tick Virus (DTV) and Colorado Tick Fever Virus (CTFV) that are important for clinicians.

Colorado Tick Fever Virus in the Far West: Forgotten, but Not Gone

In the past few decades, reported human cases of Colorado tick fever in the western United States have decreased dramatically. The goal of this study was to conduct surveillance for Colorado tick fever virus (CTFV) in Dermacentor ticks in recreational sites in Colorado, Wyoming, and California to determine whether the virus is still present in Dermacentor ticks from these states. Surveillance focused on regions where surveys had been conducted in the 1950s, 1960s, and 1970s. Adult Rocky Mountain wood ticks (Dermacentor andersoni), Pacific Coast ticks (Dermacentor occidentalis), and winter ticks (Dermacentor albipictus) were tested by PCR. A subset of PCR-positive D. andersoni ticks (n = 7) were cultured in Vero cells. CTFV-positive Rocky Mountain wood ticks were found in all states: Colorado (58% prevalence), Wyoming (21%), and California (4%). Although no winter ticks tested positive, Pacific Coast ticks tested positive in one county (Siskiyou County, 15% prevalence) and were positive only in a location that also maintained Rocky Mountain wood ticks and golden mantled ground squirrels, a known CTFV host. In summary, CTFV is prevalent in D. andersoni and D. occidentalis in regions where they are sympatric in California and in D. andersoni in Colorado and Wyoming. Although the number of human CTFV cases has declined dramatically, this decrease in reported disease does not appear to be due to the disappearance or even the decline in prevalence of this virus in ticks in historically endemic regions of the country.

Genomic Evaluation of the Genus Coltivirus Indicates Genetic Diversity among Colorado Tick Fever Virus Strains and Demarcation of a New Species

The type species of the genus Coltivirus, Colorado tick fever virus (CTFV), was discovered in 1943 and is the most common tick-borne viral infection in the Western US. Despite its long history, very little is known about the molecular diversity of viruses classified within the species Colorado tick fever coltivirus. Previous studies have suggested genetic variants and potential serotypes of CTFV, but limited genetic sequence information is available for CTFV strains. To address this knowledge gap, we report herein the full-length genomes of five strains of CTFV, including Salmon River virus and California hare coltivirus (CTFV-Ca). The sequence from the full-length genome of Salmon River virus identified a high genetic identity to the CTFV prototype strain with >90% amino acid identity in all the segments except segment four, suggesting Salmon River virus is a strain of the species Colorado tick fever coltivirus. Additionally, analysis suggests that segment four has been associated with reassortment in at least one strain. The CTFV-Ca full-length genomic sequence was highly variable from the prototype CTFV in all the segments. The genome of CTFV-Ca was most similar to the Eyach virus, including similar segments six and seven. These data suggest that CTFV-Ca is not a strain of CTFV but a unique species. Additional sequence information of CTFV strains will improve the molecular surveillance tools and provide additional taxonomic resolution to this understudied virus.

Discovery and Surveillance of Tick-Borne Pathogens

Within the past 30 yr molecular assays have largely supplanted classical methods for detection of tick-borne agents. Enhancements provided by molecular assays, including speed, throughput, sensitivity, and specificity, have resulted in a rapid increase in the number of newly characterized tick-borne agents. The use of unbiased high throughput sequencing has enabled the prompt identification of new pathogens and the examination of tick microbiomes. These efforts have led to the identification of hundreds of new tick-borne agents in the last decade alone. However, little is currently known about the majority of these agents beyond their phylogenetic classification. Our article outlines the primary methods involved in tick-borne agent discovery and the current status of our understanding of tick-borne agent diversity.

Colorado tick fever virus induces apoptosis in human endothelial cells to facilitate viral replication

Colorado tick fever virus (CTFV) belongs to the genus Coltivirus of the Reoviridae family, and it is the causative agent of Colorado tick fever. Symptoms of the infection are characterized by sudden biphasic fever, headache, and petechial rash, while severe forms of the disease can include meningoencephalitis, hemorrhagic fever, and death in children. However, the mechanisms underlying CTFV induced pathology and severe complications remain unknown. As CTFV is spread by tick bites and disseminates systemically via hematogenous routes, we performed in vitro analysis examining the interactions between endothelial cells (ECs) and CTFV. Our findings indicate that dermal microvascular ECs, HMEC-1, are susceptible and permissive to CTFV infection. To investigate the role of CTFV infection on endothelial barrier function, we assessed transendothelial electrical resistance (TEER) by xCELLigence and observed a dose-dependent decrease in cell index, indicating increased vascular permeability starting at approximately hour 18 (MOI=1) and hour 26 (MOI=0.1). Since CTFV induced cytopathic effect and increased vascular permeability in HMEC-1 cells, we hypothesized that CTFV causes apoptotic cell death. Our results showed that HMEC-1 cells infected with CTFV at 48 h caused a significant increase in Annexin V staining with reduced viability compared to uninfected cells suggesting CTFV induces apoptotic cell death in human ECs. Electron microscopy also was consistent with apoptotic features, including chromatin condensation and cell blebbing. Furthermore, CTFV induced caspase-3/7 activation at 24 and 48 h post-infection (hpi). The inhibition of caspase activity using Z-VAD-FMK reduced CTFV induced cell death and significantly reduced viral titer. These results indicated that CTFV can infect ECs, exerting direct adverse effects, leading to vascular permeability and cell death. Overall, our data suggest that caspase-mediated apoptosis is a critical mechanism by which CTFV induces disease in the host and enhances viral replication. Future studies will examine the viral and cellular determinants involved in CTFV induced apoptosis in human ECs.

Ticks and Tick-Borne Diseases of Colorado, Including New State Records for Argas radiatus (Ixodida: Argasidae) and Ixodes brunneus (Ixodida: Ixodidae)

We report 28 species of ticks (Acari: Ixodida) from Colorado (CO). We include the soft ticks (Argasidae) Argas (Argas) cooleyi Kohls and Hoogstraal, Argas (Persicargas) radiatus Railliet, Carios (Alectorobius) concanensis (Cooley and Kohls), Carios (Alectorobius) kelleyi (Cooley and Kohls), Ornithodoros (Pavlovskyella) hermsi Wheeler et al., Ornithodoros (Pavlovskyella) parkeri Cooley, Ornithodoros (Pavlovskyella) turicata (Dugès), Otobius (Otobius) lagophilus Cooley and Kohls, and Otobius (Otobius) megnini (Dugès). We include the metastriate hard ticks (Ixodidae) Dermacentor (Americentor) albipictus (Packard), Dermacentor (Dermacentor) andersoni Stiles, Dermacentor (Dermacentor) parumapertus Neumann, Dermacentor (Dermacentor) variabilis (Say), Haemaphysalis (Aboimisalis) chordeilis (Packard), Haemaphysalis (Gonixodes) leporispalustris (Packard), and Rhipicephalus (Rhipicephalus) sanguineus Latreille. Prostriate hard ticks include Ixodes (Ixodiopsis) angustus Neumann, Ixodes (Phoeloioxdes) baergi Cooley and Kohls, Ixodes (Trichotoixodes) brunneus Koch, Ixodes (Scaphixodes) howelli Cooley and Kohls, Ixodes (Phoeloioxdes) kingi Bishopp, Ixodes (Phoeloioxdes) marmotae Cooley and Kohls, Ixodes (Ixodiopsis) ochotonae Gregson, Ixodes (Phoeloioxdes) sculptus Neumann, Ixodes (Ixodiopsis) soricis Gregson, Ixodes (Ixodes) spinipalpis Hadwen and Nuttall, Ixodes (Phoeloioxdes) texanus Banks, and Ixodes (Ixodiopsis) woodi Bishopp. Argas radiatus and Ixodes brunneus represent new state records. Review of collection reports revealed that inclusion of Ixodes (Multidentatus) auritulus (Neumann), Ixodes (Phoeloioxdes) cookei Packard, Ixodes (Phoeloioxdes) marxi Banks, and Ixodes (Ixodes) pacificus Cooley and Kohls is dubious or unconfirmed and, conversely, that C. concanensis and H. chordeilis have distributions that include CO. We list an additional five species occasionally detected and 13 exotic species intercepted in CO. Tick-host associations, geographical distributions, and medical/veterinary importance are included.

Diagnostic Approach for Arboviral Infections in the United States

Domestic arthropod-borne viruses (arboviruses) are single-stranded RNA viruses, the most common of which include the mosquito-borne West Nile virus, St. Louis encephalitis virus, La Crosse virus, Jamestown Canyon virus, and eastern equine encephalitis virus, as well as the tick-borne Powassan virus. Previously considered rare infections, they have been detected with increasing frequency over the past 2 decades. Here, we present an overview of the domestic arboviruses listed above and describe the modalities employed to diagnose infection. Global arboviruses, including dengue virus, Zika virus, and chikungunya virus, have also been increasingly detected in the United States within the last 5 years but are not a focus of this minireview. Typical manifestations of arbovirus infection range from no symptoms, to meningitis or encephalitis, to death. Serologies are the standard means of diagnosis in the laboratory, since most viruses have a short period of replication, limiting the utility of molecular tests. The interpretation of serologies is confounded by antibody cross-reactivity with viruses belonging to the same serogroup and by long-lasting antibodies from prior infections. Next-generation assays have improved performance by increasing antigen purity, selecting optimal epitopes, and improving interpretive algorithms, but challenges remain. Due to cross-reactivity, a positive first-line serology test requires confirmation by either a plaque reduction neutralization test or detection of seroconversion or a 4-fold rise in virus-specific IgM or IgG antibody titers from acute- and convalescent-phase sera. The use of molecular diagnostics, such as reverse transcription PCR or unbiased metagenomic sequencing, is limited to the minority of patients who present with ongoing viremia or central nervous system replication. With the continued expansion of vector range, the diagnosis of domestic arboviruses will become an increasingly important task for generalists and specialists alike.

The Ecology of New Constituents of the Tick Virome and Their Relevance to Public Health

Ticks are vectors of several pathogens that can be transmitted to humans and their geographic ranges are expanding. The exposure of ticks to new hosts in a rapidly changing environment is likely to further increase the prevalence and diversity of tick-borne diseases. Although ticks are known to transmit bacteria and viruses, most studies of tick-borne disease have focused upon Lyme disease, which is caused by infection with Borrelia burgdorferi. Until recently, ticks were considered as the vectors of a few viruses that can infect humans and animals, such as Powassan, Tick-Borne Encephalitis and Crimean–Congo hemorrhagic fever viruses. Interestingly, however, several new studies undertaken to reveal the etiology of unknown human febrile illnesses, or to describe the virome of ticks collected in different countries, have uncovered a plethora of novel viruses in ticks. Here, we compared the virome compositions of ticks from different countries and our analysis indicates that the global tick virome is dominated by RNA viruses. Comparative phylogenetic analyses of tick viruses from these different countries reveals distinct geographical clustering of the new tick viruses. Some of these new tick RNA viruses (notably severe fever with thrombocytopenia syndrome virus and Heartland virus) were found to be associated with serious human diseases. Their relevance to public health remains unknown. It is plausible that most of these newly identified tick viruses are of endogenous origin or are restricted in their transmission potential, but the efforts to identify new tick viruses should continue. Indeed, future research aimed at defining the origin, the ecology and the spillover potential of this novel viral biodiversity will be critical to understand the relevance to public health.

Prevalence and Strains of Colorado Tick Fever Virus in Rocky Mountain Wood Ticks in the Bitterroot Valley, Montana

The Rocky Mountain wood tick, Dermacentor andersoni, has long been known to transmit human pathogens. Within the Bitterroot Valley, Ravalli County, Montana, these agents include Rickettsia rickettsii, Francisella tularensis, and Colorado tick fever virus (CTFV). Found in the western United States where wood ticks occur, CTFV causes a biphasic, febrile illness in humans and persists in enzootic cycles involving the ticks and small mammals. CTFV belongs to the genus Coltivirus, family Reoviridae, whose genome consists of 12 double-stranded RNA segments. Previous studies revealed the presence of CTFV-infected ticks and rodents in select locations within the valley in the 1960s and 1970s, using animal and cell culture methods for detection. We aimed to determine the range and prevalence of the virus in adult questing ticks throughout the valley using molecular tools and to examine the genomic variation between virus strains. Adult D. andersoni ticks were collected during 2002-2003 and 2009-2013. RNA extractions and reverse transcription-polymerase chain reaction were performed on 921 ticks, of which 61 ticks were positive for CTFV, resulting in a 6.6% prevalence of infection. Four genetic loci, one from each of the segments 9, 10, 11, and 12, within the viral genome were sequenced. Reassortment was detected between CTFV sequence strains within the valley. This study confirmed the prevalence of CTFV in D. andersoni ticks within the Bitterroot Valley, which has remained at levels found in the 1950s and 60s. Additional CTFV sequences were obtained and evidence of reassortment was observed between strains within the valley.

Case Report: A Case of Colorado Tick Fever Acquired in Southwestern Saskatchewan

Colorado tick fever virus is transmitted by Dermacentor andersoni ticks. In Canada, these ticks are found in the southern regions of British Columbia (Rocky Mountains) and Alberta, as well as southwestern Saskatchewan. Colorado tick fever should be clinically suspected in patients presenting with a biphasic febrile illness and leukopenia following tick exposure in the appropriate geographic area.

Tick-Borne Zoonoses in the United States: Persistent and Emerging Threats to Human Health

In the United States, ticks transmit the greatest diversity of arthropod-borne pathogens and are responsible for the most cases of all vector-borne diseases. In recent decades, the number of reported cases of notifiable tick-borne diseases has steadily increased, geographic distributions of many ticks and tick-borne diseases have expanded, and new tick-borne disease agents have been recognized. In this review, we (1) describe the known disease agents associated with the most commonly human-biting ixodid ticks, (2) review the natural histories of these ticks and their associated pathogens, (3) highlight spatial and temporal changes in vector tick distributions and tick-borne disease occurrence in recent decades, and (4) identify knowledge gaps and barriers to more effective prevention of tick-borne diseases. We describe 12 major tick-borne diseases caused by 15 distinct disease agents that are transmitted by the 8 most commonly human-biting ixodid ticks in the United States. Notably, 40% of these pathogens were described within the last two decades. Our assessment highlights the importance of animal studies to elucidate how tick-borne pathogens are maintained in nature, as well as advances in molecular detection of pathogens which has led to the discovery of several new tick-borne disease agents.

Summary of Notifiable Infectious Diseases and Conditions - United States, 2015

The Summary of Notifiable Infectious Diseases and Conditions - United States, 2015 (hereafter referred to as the summary) contains the official statistics, in tabular and graphical form, for the reported occurrence of nationally notifiable infectious diseases and conditions in the United States for 2015. Unless otherwise noted, data are final totals for 2015 reported as of June 30, 2016. These statistics are collected and compiled from reports sent by U.S. state and territories, New York City, and District of Columbia health departments to the National Notifiable Diseases Surveillance System (NNDSS), which is operated by CDC in collaboration with the Council of State and Territorial Epidemiologists (CSTE). This summary is available at https://www.cdc.gov/MMWR/MMWR_nd/index.html. This site also includes summary publications from previous years.

Encephalitic Arboviruses: Emergence, Clinical Presentation, and Neuropathogenesis

Arboviruses are arthropod-borne viruses that exhibit worldwide distribution, contributing to systemic and neurologic infections in a variety of geographical locations. Arboviruses are transmitted to vertebral hosts during blood feedings by mosquitoes, ticks, biting flies, mites, and nits. While the majority of arboviral infections do not lead to neuroinvasive forms of disease, they are among the most severe infectious risks to the health of the human central nervous system. The neurologic diseases caused by arboviruses include meningitis, encephalitis, myelitis, encephalomyelitis, neuritis, and myositis in which virus- and immune-mediated injury may lead to severe, persisting neurologic deficits or death. Here we will review the major families of emerging arboviruses that cause neurologic infections, their neuropathogenesis and host neuroimmunologic responses, and current strategies for treatment and prevention of neurologic infections they cause.