Sequence determination and analysis of the full-length genome of colorado tick fever virus, the type species of genus Coltivirus (Family Reoviridae)

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.

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.

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.

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.

Dengue Virus

Dengue virus (DENV) belongs to the family Flaviviridae, genus Flavivirus. It is a single-stranded positive-sense ribonucleic acid virus with 10,700 bases. The genus Flavivirus includes other arthropod borne viruses such as yellow fever virus, West Nile virus, Zika virus, tick-borne encephalitis virus. It infects ~50–200 million people annually, putting over 3.6 billion people living in tropical regions at risk and causing ~20,000 deaths annually. The expansion of dengue is attributed to factors such as the modern dynamics of climate change, globalization, travel, trade, socioeconomics, settlement, and also viral evolution. There are four antigenically different serotypes of DENV based on the differences in their viral structural and nonstructural proteins. DENV infection causes a spectrum of illness ranging from asymptomatic to dengue fever to severe dengue shock syndrome. Infection with one serotype confers lifelong immunity against that serotype, but heterologus infection leads to severe dengue hemorrhagic fever due to antibody-dependent enhancement. Diagnosis of dengue infections is based mainly on serological detection of either antigen in acute cases or antibodies in both acute and chronic infection. Viral detection and real-time PCR detection though helpful is not feasible in resource poor setup. Treatment of dengue depends on symptomatic management along with fluid resuscitation and may require platelet transfusion. Although vaccine development is in late stages of development, developing a single vaccine against four serotypes often causes serious challenges to researchers; hence, the main stay of prevention is vector control and management.

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.

Isolation and characterization of Tarumizu tick virus: A new coltivirus from Haemaphysalis flava ticks in Japan

During the course of tick-borne virus surveillance in Japan, three independent isolates of probably the same virus were obtained from three geographically distant populations of the hard tick Haemaphysalis flava. Genome analyses of the three isolates demonstrated that they were closely related but distinct strains of a novel virus, designated Tarumizu tick virus (TarTV), which has a genome of 12 double-stranded RNA segments. The development of the virus-induced cytopathic effects on BHK cells significantly varied according to virus strains. Ten out of 12 segments of TarTV appeared to encode putative orthologs or functional equivalents of viral proteins of Colorado tick fever virus (CTFV) and Eyach virus, suggesting that TarTV is the third member of the genus Coltivirus in the family Reoviridae. This was supported by the facts that the 5'- and 3'-terminal consensus sequences of coltivirus genomes were found also in TarTV genome, and segment 9 of TarTV had sequence and structural features that may mediate a stop codon read-through as observed in that of CTFV. However, segment 7 and 10 of TarTV had no significant sequence similarities to any other proteins of known coltiviruses. Electron microscopic analysis demonstrated that TarTV particle had a non-enveloped bilayer icosahedral structure, and viral inclusion bodies were formed in infected cells. TarTV could infect and replicate in several mammalian cell lines tested, but show no clinical symptoms in intracerebrally inoculated mice. Taken together, our findings provide new insights into genetic diversity and evolution of the genus Coltivirus.

A novel Coltivirus-related virus isolated from free-tailed bats from Côte d'Ivoire is able to infect human cells in vitro

BACKGROUND

Zoonotic transmission events play a major role in the emergence of novel diseases. While such events are virtually impossible to predict, wildlife screening for potential emerging pathogens can be a first step. Driven by recent disease epidemics like severe acute respiratory syndrome (SARS), Middle East respiratory syndrome (MERS), and Ebola, bats have gained special interest as reservoirs of emerging viruses.

METHODS

As part of a bigger study investigating pathogens in African bats we screened animals for the presence of known and unknown viruses.

RESULTS

We isolated and characterised a novel reovirus from blood of free-tailed bats (Chaereophon aloysiisabaudiae) captured in 2006 in Côte d'Ivoire. The virus showed closest relationship with two human pathogenic viruses, Colorado tick fever virus and Eyach virus, and was able to infect various human cell lines in vitro.

CONCLUSION

The study shows the presence of a coltivirus-related virus in bats from Sub-Sahara Africa. Serological studies could help to assess its impact on humans or wildlife health.

Identification and genomic characterization of a novel fish reovirus, Hubei grass carp disease reovirus, isolated in 2009 in China

A novel fish reovirus, Hubei grass carp disease reovirus (HGDRV; formerly grass carp reovirus strain 104, GCRV104), was isolated from diseased grass carp in China in 2009 and the full genome sequence was determined. This reovirus was propagated in a grass carp kidney cell line with a typical cytopathic effect. The total size of the genome was 23 706 bp with a 51 mol% G+C content, and the 11 dsRNA segments encoded 12 proteins (two proteins encoded by segment 11). A nucleotide sequence similarity search using blastn found no significant matches except for segment 2, which partially matched that of the RNA-dependent RNA polymerase (RdRp) from several viruses in the genera Aquareovirus and Orthoreovirus of the family Reoviridae. At the amino acid level, seven segments (Seg-1 to Seg-6, and Seg-8) matched with species in the genera Aquareovirus (15-46 % identities) and Orthoreovirus (12-44 % identities), while for four segments (Seg-7, Seg-9, Seg-10 and Seg-11) no similarities in these genera were found. Conserved terminal sequences, 5'-GAAUU----UCAUC-3', were found in each HGDRV segment at the 5' and 3' ends, and the 5'-terminal nucleotides were different from any known species in the genus Aquareovirus. Phylogenetic analysis based on RdRp amino acid sequences from members of the family Reoviridae showed that HGDRV clustered with aquareoviruses prior to joining a branch common with orthoreoviruses. Based on these observations, we propose that HGDRV is a new species in the genus Aquareovirus that is distantly related to any known species within this genus.

Molecular characterization of genome segment 2 encoding RNA dependent RNA polymerase of Antheraea mylitta cytoplasmic polyhedrosis virus

Genome segment 2 (S2) from Antheraea mylitta cypovirus (AmCPV) was converted into cDNA, cloned and sequenced. S2 consisted of 3798 nucleotides with a long ORF encoding a 1116 amino acid long protein (123 kDa). BLAST and phylogenetic analysis showed 29% sequence identity and close relatedness of AmCPV S2 with RNA dependent RNA polymerase (RdRp) of other insect cypoviruses, suggesting a common origin of all insect cypoviruses. The ORF of S2 was expressed as 123 kDa soluble His-tagged fusion protein in insect cells via baculovirus recombinants which exhibited RdRp activity in an in vitro RNA polymerase assay without any intrinsic terminal transferase activity. Maximum activity was observed at 37 °C at pH 6.0 in the presence of 3 mM MgCl_2. Site directed mutagenesis confirmed the importance of the conserved GDD motif. This is the first report of functional characterization of a cypoviral RdRp which may lead to the development of anti-viral agents.

Powassan encephalitis and Colorado tick fever

This article discusses two tick-borne illnesses: Powassan encephalitis, a rare cause of central nervous system infection caused by the Powassan virus, and Colorado tick fever, an acute febrile illness caused by the Colorado tick fever virus common to the Rocky Mountain region of North America.

Complete characterisation of the American grass carp reovirus genome (genus Aquareovirus: family Reoviridae) reveals an evolutionary link between aquareoviruses and coltiviruses

An aquareovirus was isolated from several fish species in the USA (including healthy golden shiners) that is not closely related to members of species Aquareovirus A, B and C. The virus, which is atypical (does not cause syncytia in cell cultures at neutral pH), was implicated in a winter die-off of grass carp fingerlings and has therefore been called 'American grass carp reovirus' (AGCRV). Complete nucleotide sequence analysis of the AGCRV genome and comparisons to the other aquareoviruses showed that it is closely related to golden ide reovirus (GIRV) (>92% amino acid [aa] identity in VP5(NTPase) and VP2(Pol)). However, comparisons with grass carp reovirus (Aquareovirus C) and chum salmon reovirus (Aquareovirus A) showed only 22% to 76% aa identity in different viral proteins. These findings have formed the basis for the recognition of AGCRV and GIRV as members of a new Aquareovirus species 'Aquareovirus G' by ICTV. Further sequence comparisons to other members of the family Reoviridae suggest that there has been an 'evolutionary jump,' involving a change in the number of genome segments, between the aquareoviruses (11 segments) and coltiviruses (12 segments). Segment 7 of AGRCV encodes two proteins, from two distinct ORFs, which are homologues of two Coltivirus proteins encoded by genome segments 9 and 12. A similar model has previously been reported for the rotaviruses and seadornaviruses.

Molecular cloning, sequence analysis and expression of genome segment 7 (S7) of Antheraea mylitta cypovirus (AmCPV) that encodes a viral structural protein

The Genome segment 7 (S7) of the 11 double stranded RNA genomes from Antheraea mylitta cypovirus (AmCPV) was converted to cDNA, cloned and sequenced. The nucleotide sequence showed that segment 7 consisted of 1789 nucleotides with an ORF of 530 amino acids and could encode a protein of approximately 61 kDa, termed P61. The 5' terminal sequence, AGTAAT and the 3' terminal sequence, AGAGC of the plus strand was found to be the same as genome segment 10 of AmCPV encoding polyhedrin. No sequence similarity was found by searching nucleic acid and protein sequence databases using BLAST. The secondary structure prediction showed the presence of 17 alpha-helices, 18 extended beta-sheets along the entire length of P61. The ORF of segment 7 was expressed in E. coli as His-tagged fusion protein, purified through Ni-NTA chromatography, and polyclonal antibody was raised in rabbit indicating that P61 is immunogenic. Immunoblot analysis using this antibody on viral infected cells as well as purified polyhedra showed that P61 is a viral structural protein. Motif scan search showed some similarity of P61 with Inosine monophosphate dehydrogenase (IMPDH) cystathionine-beta-synthase (CBS) domain at the C-terminus and it was hypothesized that by binding to single stranded viral RNA through its CBS domain P61 may help in virus replication or transcription.

Micromonas pusilla reovirus: a new member of the family Reoviridae assigned to a novel proposed genus (Mimoreovirus)

Micromonas pusilla reovirus (MpRV) is an 11-segmented, double-stranded RNA virus isolated from the marine protist Micromonas pusilla. Sequence analysis (including conserved termini and presence of core motifs of reovirus polymerase), morphology and physicochemical properties confirmed the status of MpRV as a member of the family Reoviridae. Electron microscopy showed that intact virus particles are unusually larger (90–95 nm) than the known size of particles of viruses belonging to the family Reoviridae. Particles that were purified on caesium chloride gradients had a mean size of 75 nm (a size similar to the size of intact particles of members of the family Reoviridae), indicating that they lost outer-coat components. The subcore particles had a mean size of 50 nm and a smooth surface, indicating that MpRV belongs to the non-turreted Reoviridae. The maximum amino acid identity with other reovirus proteins was 21 %, which is compatible with values existing between distinct genera. Based on morphological and sequence findings, this virus should be classified as the representative of a novel genus within the family Reoviridae, designated Mimoreovirus (from Micromonas pusilla reovirus). The topology of the phylogenetic tree built with putative polymerase sequences of the family Reoviridae suggested that the branch of MpRV could be ancestral. Further analysis showed that segment 1 of MpRV was much longer (5792 bp) than any other reovirus segment and encoded a protein of 200 kDa (VP1). This protein exhibited significant similarities to O-glycosylated proteins, including viral envelope proteins, and is likely to represent the additional outer coat of MpRV.

Coltiviruses and seadornaviruses in North America, Europe, and Asia

Coltiviruses are tickborne viruses of the genus Coltivirus. The type species, Colorado tick fever virus (from North America), has been isolated from patients with flulike syndromes, meningitis, encephalitis, and other severe complications. Another coltivirus, Eyach virus, has been isolated from ticks in France and Germany and incriminated in febrile illnesses and neurologic syndromes. Seadornaviruses are endemic in Southeast Asia, particularly Indonesia and China. The prototype virus of the genus, Banna virus (BAV), has been isolated from many mosquito species, humans with encephalitis, pigs, and cattle. Two other seadornaviruses, Kadipiro and Liao Ning, were isolated only from mosquitoes. The epidemiology of seadornaviruses remains poorly documented. Evidence suggests that BAV is responsible for encephalitis in humans. Infection with BAV may be underreported because it circulates in regions with a high incidence of Japanese encephalitis and could be misdiagnosed as this disease.

Molecular characterization of dsRNA segments 2 and 5 and electron microscopy of a novel reovirus from a hypovirulent isolate, W370, of the plant pathogen Rosellinia necatrix

A hypovirulent isolate, W370, of the white root rot fungus Rosellinia necatrix has previously been shown to harbour 12 dsRNA segments. In this study, complete nucleotide sequences of segments 2 and 5 of W370 dsRNAs were determined. The nucleotide sequence of genome segment 2 was 3773 bases long with a single long open reading frame (ORF) encoding 1226 amino acid residues with a predicted molecular mass of approximately 138.5 kDa. The nucleotide sequence of segment 5 was 2089 bases long with a single long ORF, whose deduced polypeptide contained 646 amino acid residues with a predicted molecular mass of about 72 kDa. Comparative analysis showed that the deduced protein sequence of segment 2 had significant homology with the putative VP2 of Colorado tick fever virus (CTFV) and European Eyach virus (EYAV) in the genus Coltivirus, but the deduced protein sequence of segment 5 had no similarity with other virus proteins. Double-shelled spherical particles approximately 80 nm in diameter associated with W370 dsRNAs were observed in a preparation from the mycelial tissue of isolate W370. The results demonstrated that the virus associated with W370 dsRNAs is a novel reovirus of the family Reoviridae. The virus was named Rosellinia anti-rot virus (RArV).

Recombinant VP7-based enzyme-linked immunosorbent assay for detection of immunoglobulin G antibodies to Colorado tick fever virus

VP6, VP7, VP9, VP10, VP11, and VP12 of Colorado tick fever virus (CTF virus), a virus member of the genus Coltivirus, family Reoviridae, were expressed in bacteria with the pGEX-4T-2 vector. A partial sequence of VP7 (designated pVP7) was chosen to elaborate an enzyme-linked immunosorbent assay (ELISA) for detecting anti-CTF virus immunoglobulin G (IgG) antibodies in humans. This was based on two observations: (i) among all expressed proteins, pVP7 showed the highest immunoreactivity to an anti-CTF virus hyperimmune ascitic fluid; (ii) to provide the highest selectivity of antibody detection, the expressed sequence was chosen within a region which is highly divergent (49% amino acid identity) from the homologous sequence of another coltivirus, the Eyach virus. The pVP7 ELISA was evaluated with 368 serum samples from French blood donors and found to provide 98.1% specificity. Assays with the Calisher set of human serum samples, positive for anti-CTF virus antibodies (C. H. Calisher, J. D. Poland, S. B. Calisher, and L. A Warmoth, J. Clin. Microbiol. 22:84-88, 1985), showed that the pVP7 ELISA provided 100% sensitivity for the tested population. After elaboration of recombinant-protein-based ELISAs for diagnosis of infections with members of the viral genera Orbivirus, Orthoreovirus, and Rotavirus, it was shown that a recombinant protein could be used to detect antibodies to the human pathogen Colorado tick fever virus.

Nucleotide sequences of double-stranded RNA segments from a hypovirulent strain of the white root rot fungus Rosellinia necatrix: possibility of the first member of the Reoviridae from fungus

Twelve double-stranded (ds) RNA segments were detected from a hypovirulent strain W370 of the white root rot fungus Rosellinia necatrix. The estimated molecular weights ranged from 0.41 x 10(6) to 2.95 x 10(6). Full length cDNA clones for eight segments were obtained. Northern blot analysis suggested that each segment was genetically unique. The nucleotide sequences of eight full length dsRNA segments were determined. One long open reading frame was found in each segment. Conserved sequences at the 5'-end (5'-ACAAUUU-3') and at the 3'-end (5'-UGCAGAC-3') were identified in all eight segments. Segment-specific panhandle structures, formed by inverted terminal repeats, were also found in all segments. Comparative analyses of the predicted translational products of eight dsRNA segments showed that the deduced amino acid sequence partially matched those of the Reoviridae family members: Colorado tick fever virus, Nilaparvata lugens reovirus, and rice black streaked dwarf virus. The results suggested that W370 dsRNA is derived from a new member of the family Reoviridae detected in fungus.

Colorado tick fever

Colorado tick fever, also known as mountain fever and mountain tick fever, is a well-described, viral, tick-borne disease common to the Rocky Mountain region of the United States and Canada. The Rocky Mountain wood tick, Dermacentor andersoni, is the primary vector. The triad of high fever, severe myalgia, and headache is typical, but not specific. Although a self-limited disease in most cases, severe complications may occur. PCR techniques have been developed that allow the diagnosis to be established from the first day of symptoms. Ribavirin may merit consideration in the appropriate clinical setting.