Experimental Infection of Amblyomma americanum (Acari: Ixodidae) With Bourbon Virus (Orthomyxoviridae: Thogotovirus)

Widespread Circulation of Tick-Borne Viruses in Virginia-Evidence of Exposure to Heartland, Bourbon, and Powassan Viruses in Wildlife and Livestock

Emerging tick-borne viruses such as Powassan virus (POWV), Bourbon virus (BRBV), and Heartland virus (HRTV), whilst rare, can cause severe health problems in humans. While limited clinical cases have been reported thus far in Virginia, the presence of tick-borne viruses poses a serious health threat, and the extent of their prevalence in Virginia is unknown. Here, we sought evidence of POWV, BRBV, and HRTV exposure in Virginia via a serological assessment of wildlife and livestock. Wildlife in Virginia were found to be seropositive against POWV (18%), BRBV (8%), and HRTV (5%), with western and northern regions of the state having a higher prevalence. Multiple wildlife species were shown to have been exposed to each virus examined. To a lesser extent, cattle also showed exposure to tick-borne viruses, with seroprevalences of 1%, 1.2%, and 8% detected in cattle against POWV, BRBV, and HRTV, respectively. Cross-reactivity against other known circulating mosquito-borne flaviviruses was ruled out. In conclusion, there is widespread exposure to tick-borne viruses in western and northern Virginia, with exposure to a diverse range of animal populations. Our study provides the first confirmation that HRTV is circulating in the Commonwealth. These findings strengthen the existing evidence of emerging tick-borne viruses in Virginia and highlight the need for public health vigilance to avoid tick bites.

Emerging tickborne viruses vectored by Amblyomma americanum (Ixodida: Ixodidae): Heartland and Bourbon viruses

Heartland (HRTV) and Bourbon (BRBV) viruses are newly identified tick-borne viruses, isolated from serious clinical cases in 2009 and 2014, respectively. Both viruses originated in the lower Midwest United States near the border of Missouri and Kansas, cause similar disease manifestations, and are presumably vectored by the same tick species, Amblyomma americanum Linnaeus (Ixodida: Ixodidae). In this article, we provide a current review of HRTV and BRBV, including the virology, epidemiology, and ecology of the viruses with an emphasis on the tick vector. We touch on current challenges of vector control and surveillance, and we discuss future directions in the study of these emergent pathogens.

Bourbon virus, a newly discovered zoonotic thogotovirus

The recent discovery of Bourbon virus (BRBV) put a new focus on the genus of thogotoviruses as zoonotic, tick-transmitted pathogens within the orthomyxovirus family. Since 2014, BRBV has been linked to several human cases in the Midwest United States with severe acute febrile illness and a history of tick bites. The detection of the virus in the Lone Star tick, Amblyomma americanum, and a high sero-prevalence in wild animals suggest widespread circulation of BRBV. Phylogenetic analysis of the viral RNA genome classified BRBV into the subgroup of Dhori-like thogotoviruses. Strikingly, BRBV is apathogenic in mice, contrasting not only with the fatal disease in affected patients but also with the severe disease in mice caused by other members of the thogotovirus genus. To gain insights into this intriguing discrepancy, we will review the molecular biology and pathology of BRBV and its unique position within the thogotovirus genus. Lastly, we will discuss the zoonotic threat posed by this newly discovered pathogen.

Non-target effects of chemical malaria vector control on other biological and mechanical infectious disease vectors

Public health insecticides play a crucial role in malaria control and elimination programmes. Many other arthropods, including mechanical and biological vectors of infectious diseases, have similar indoor feeding or resting behaviours, or both, as malaria mosquitoes, and could be exposed to the same insecticides. In this Personal View, we show that little is known about the insecticide susceptibility status and the extent of exposure to malaria interventions of other arthropod species. We highlight that there is an urgent need to better understand the selection pressure for insecticide resistance in those vectors, to ensure current and future active ingredients remain effective in targeting a broad range of arthropod species, allowing us to prevent and control future outbreaks of infectious diseases other than malaria.

Diversification of Bourbon Virus in New York State

Bourbon virus (BRBV, family Orthomyxoviridae) is a tickborne virus recently detected in the United States (US). BRBV was first identified from a fatal human case in 2014 in Bourbon County, Kansas. Enhanced surveillance in Kansas and Missouri implicated Amblyomma americanum as the primary vector for BRBV. Historically, BRBV was only detected in the lower midwestern US, but since 2020 it has been reported in North Carolina, Virginia, New Jersey, and New York State (NYS). This study aimed to elucidate genetic and phenotypic characteristics of BRBV strains from NYS through whole genome sequencing and the assessment of replication kinetics in mammalian cultures and A. americanum nymphs. Sequence analysis revealed the existence of two divergent BRBV clades circulating in NYS. BRBV NY21-2143 is closely related to the midwestern BRBV strains but has unique substitutions in the glycoprotein. Two other NYS BRBV strains, BRBV NY21-1814 and BRBV NY21-2666, form a distinct clade unique from previously sequenced BRBV strains. Phenotypic diversification was also detected in NYS BRBV strains compared to each other and midwestern BRBV strains, with BRBV NY21-2143 displaying attenuation in rodent-derived cell culture and a fitness advantage in experimentally infected A. americanum. These data suggest genetic and phenotypic diversification of emergent BRBV strains circulating in NYS that could contribute to increased spread of BRBV in the northeastern US.

Zebrafish-based platform for emerging bio-contaminants and virus inactivation research

Emerging bio-contaminants such as viruses have affected health and environment settings of every country. Viruses are the minuscule entities resulting in severe contagious diseases like SARS, MERS, Ebola, and avian influenza. Recent epidemic like the SARS-CoV-2, the virus has undergone mutations strengthen them and allowing to escape from the remedies. Comprehensive knowledge of viruses is essential for the development of targeted therapeutic and vaccination treatments. Animal models mimicking human biology like non-human primates, rats, mice, and rabbits offer competitive advantage to assess risk of viral infections, chemical toxins, nanoparticles, and microbes. However, their economic maintenance has always been an issue. Furthermore, the redundancy of experimental results due to aforementioned aspects is also in examine. Hence, exploration for the alternative animal models is crucial for risk assessments. The current review examines zebrafish traits and explores the possibilities to monitor emerging bio-contaminants. Additionally, a comprehensive picture of the bio contaminant and virus particle invasion and abatement mechanisms in zebrafish and human cells is presented. Moreover, a zebrafish model to investigate the emerging viruses such as coronaviridae and poxviridae has been suggested.

Comprehensive Review of Emergence and Virology of Tickborne Bourbon Virus in the United States

This novel human pathogenic tickborne thogotovirus is found in the eastern and central regions of the country.

The emergence of SARS-CoV-2 and the worldwide COVID-19 pandemic triggered considerable attention to the emergence and evolution of novel human pathogens. Bourbon virus (BRBV) was first discovered in 2014 in Bourbon County, Kansas, USA. Since its initial discovery, several cases of BRBV infection in humans have been identified in Kansas, Oklahoma, and Missouri. BRBV is classified within the Thogotovirus genus; these negative-strand RNA viruses appear to be transmitted by ticks, and much of their biology remains unknown. In this review, we describe the emergence, virology, geographic range and ecology, and human disease caused by BRBV and discuss potential treatments for active BRBV infections. This virus and other emerging viral pathogens remain key public health concerns and require continued surveillance and study to mitigate human exposure and disease.

Modeling of historical and current distributions of lone star tick, Amblyomma americanum (Acari: Ixodidae), is consistent with ancestral range recovery

The lone star tick, Amblyomma americanum L., is a three-host hard tick notorious for aggressive feeding behavior. In the early to mid-20th century, this species' range was mostly limited to the southern USA. Since the 1950s, A. americanum has been detected in many new localities in the western, northcentral, and northeastern regions of the country. To examine the influence of climate on this apparent expansion, we used historical (1748-1950) lone star locations from the literature and museum records to model areas suitable for this species based on past environmental conditions in the late 1800s - early 1900s. We then projected this model forward using present (2011-2020) climatic conditions and compared the two for evidence of climate-associated distributional shifts. A maximum entropy distribution or Maxent model was generated by using a priori selected climatic variables including temperature, precipitation, and vapor pressure deficit. Temperature and vapor pressure deficit were selected as the most important factors in creating a sensitive and specific model (success rate = 82.6 ± 6.1%) that had a good fit to the existing data and was significantly better than a random model [partial ROC (receiver operating characteristic) to AUC (area under the ROC curve) ratio = 1.97 ± 0.07, P < 0.001]. The present projected model was tested with an independent dataset of curated museum records (1952-2020) and found to be 95.6% accurate. Comparison of past and present models revealed > 98% A. americanum niche overlap. The model suggests that some areas along the western fringe are becoming less suitable for A. americanum, whereas areas in some Great Lakes and coastal northeastern regions are becoming more suitable, results that are compatible with possible effects of climate change. However, these changes are minor, and overall climate in North America does not appear to have changed in ways significant to A. americanum's distribution. These findings are consistent with an alternative hypothesis that recent changes in A. americanum's distribution are a result of this species re-occupying its historical range, driven predominantly by factors other than climate, such as shifts in land use and population densities of major hosts.

Bourbon Virus Transmission, New York, USA

In July 2019, Bourbon virus RNA was detected in an Amblyomma americanum tick removed from a resident of Long Island, New York, USA. Tick infection and white-tailed deer (Odocoileus virginianus) serosurvey results demonstrate active transmission in New York, especially Suffolk County, emphasizing a need for surveillance anywhere A. americanum ticks are reported.

Prevalence of Bourbon and Heartland viruses in field collected ticks at an environmental field station in St. Louis County, Missouri, USA

Heartland and Bourbon viruses are pathogenic tick-borne viruses putatively transmitted by Amblyomma americanum, an abundant tick species in Missouri. To assess the prevalence of these viruses in ticks, we collected 2778 ticks from eight sampling sites at Tyson Research Center, an environmental field station within St. Louis County and close to the City of St. Louis, from May - July in 2019 and 2021. Ticks were pooled according to life stage and sex, grouped by year and sampling site to create 355 pools and screened by RT-qPCR for Bourbon and Heartland viruses. Overall, 14 (3.9%) and 27 (7.6%) of the pools were positive for Bourbon virus and Heartland virus respectively. In 2019, 11 and 23 pools were positive for Bourbon and Heartland viruses respectively. These positives pools were of males, females and nymphs. In 2021, there were 4 virus positive pools out of which 3 were positive for both viruses and were comprised of females and nymphs. Five out of the 8 sampling sites were positive for at least one virus. This included a site that was positive for both viruses in both years. Detection of these viruses in an area close to a relatively large metropolis presents a greater public health threat than previously thought.

Tick Species Composition, Collection Rates, and Phenology Provide Insights into Tick-Borne Disease Ecology in Virginia

To better understand tick ecology in Virginia and the increasing Lyme disease incidence in western Virginia, a comparative phenological study was conducted in which monthly collections were performed at twelve sampling locations in southwestern Virginia (high Lyme disease incidence) and 18 equivalent sampling locations in southeastern Virginia (low Lyme disease incidence) for one year. In western Virginia, we also explored the effect of elevation on collection rates of Ixodes scapularis Say (Acari: Ixodidae) and Amblyomma americanum (L.) (Acari: Ixodidae). In total, 35,438 ticks were collected (33,106 A. americanum; 2,052 I. scapularis; 134 Ixodes affinis Neumann [Acari: Ixodidae]; 84 Dermacentor variabilis [Say] [Acari: Ixodidae]; 49 Dermacentor albipictus [Packard] [Acari: Ixodidae]; 10 Haemaphysalis leporispalustris [Packard] [Acari: Ixodidae]; 2 Ixodes brunneus Koch [Acari: Ixodidae]; 1 Haemaphysalis longicornis Neumann [Acari: Ixodidae]). Within southwestern Virginia, Ixodes scapularis collection rates were not influenced by elevation, unlike A. americanum which were collected more frequently at lower elevations (e.g., below 500 m). Notably, I. scapularis larvae and nymphs were commonly collected in southwestern Virginia (indicating that they were questing on or above the leaf litter) but not in southeastern Virginia. Questing on or above the leaf litter is primarily associated with northern populations of I. scapularis. These findings may support the hypothesis that I. scapularis from the northeastern United States are migrating into western Virginia and contributing to the higher incidence of Lyme disease in this region. This comparative phenological study underscores the value of these types of studies and the need for additional research to further understand the rapidly changing tick-borne disease dynamics in Virginia.

Tick species infesting humans in the United States

The data for human tick encounters in the United States (US) presented in this paper were compiled with the goals of: (i) presenting quantitative data across the full range of native or recently established human biting ixodid (hard) and argasid (soft) tick species with regards to their frequency of infesting humans, based on published records of ticks collected while biting humans or crawling on clothing or skin; and (ii) providing a guide to publications on human tick encounters. Summary data are presented in table format, and the detailed data these summaries were based on are included in a set of Supplementary Tables. To date, totals of 36 ixodid species (234,722 specimens) and 13 argasid species (230 specimens) have been recorded in the published literature to infest humans in the US. Nationally, the top five ixodid species recorded from humans were the blacklegged tick, Ixodes scapularis (n=158,008 specimens); the lone star tick, Amblyomma americanum (n=36,004); the American dog tick, Dermacentor variabilis (n=26,624); the western blacklegged tick, Ixodes pacificus (n=4,158); and the Rocky Mountain wood tick, Dermacentor andersoni (n=3,518). Additional species with more than 250 ticks recorded from humans included Ixodes cookei (n=2,494); the Pacific Coast tick, Dermacentor occidentalis (n=809); the brown dog tick, Rhipicephalus sanguineus sensu lato (n=714); the winter tick, Dermacentor albipictus (n=465); and the Gulf Coast tick, Amblyomma maculatum (n=335). The spinose ear tick, Otobius megnini (n=69), and the pajaroello tick, Ornithodoros coriaceus (n=55) were the argasid species most commonly recorded from humans. Additional information presented for each of the 49 tick species include a breakdown of life stages recorded from humans, broad geographical distribution in the US, host preference, and associated human pathogens or medical conditions. The paper also provides a history of publications on human tick encounters in the US, with tables outlining publications containing quantitative data on human tick encounters as well as other notable publications on human-tick interactions. Data limitations are discussed. Researchers and public health professionals in possession of unpublished human tick encounter data are strongly encouraged to publish this information in peer-reviewed scientific journals. In future papers, it would be beneficial if data consistently were broken down by tick species and life stage as well as host species and ticks found biting versus crawling on clothing or skin.

Seasonal changes in questing efficiency of wild Amblyomma americanum (Acari: Ixodidae) nymphs

Understanding the factors which influence host-seeking behavior of ticks is essential to determine the risk they pose as a vector of pathogens. While many studies have evaluated the impact of environmental variables on tick behavior, few have examined how seasonal changes in physiological status may further modify patterns of activity. In this study, we measured differences in questing behavior of mid spring- and early summer-caught Amblyomma americanum nymphs held under standardized laboratory conditions. As both groups represent the same cohort of overwintered nymphs, we hypothesized that age-related changes in the older summer ticks may influence questing behavior. In each season, we collected nymphs from field and forest habitats in northeast Missouri, after which we placed each nymph individually in a desiccating vertical questing apparatus with a hydrating microenvironment at the base. On the day following collection, we recorded the height of each nymph in the apparatus bi-hourly from 04:00 to 22:00 and calculated the vertical displacement between consecutive observations. Despite displaying no differences in mean questing height throughout the experiment, active ticks collected in the summer group (n = 89) travelled greater cumulative distances between desiccating and hydrating microenvironments than those collected in the spring (n = 119). This suggests that questing efficiency decreases in summer nymphs to accommodate increased time allocation towards rehydration. While we observed no direct association between body size and distance travelled, body size of the nymphal population also decreased significantly from spring to summer. Overall, our results demonstrate that there are seasonal changes in how A. americanum responds to environmental conditions. To more accurately predict host-seeking behavior of ticks across seasons, models should incorporate physiological parameters of the active ticks in a given population.

Detection of Bourbon Virus-Specific Serum Neutralizing Antibodies in Human Serum in Missouri, USA

Bourbon virus (BRBV) was first discovered in 2014 in a fatal human case. Since then it has been detected in the tick Amblyomma americanum in the states of Missouri and Kansas in the United States. Despite the high prevalence of BRBV in ticks in these states, very few human cases have been reported, and the true infection burden of BRBV in the community is unknown. Here, we developed two virus neutralization assays, a vesicular stomatitis virus (VSV)-BRBV pseudotyped rapid assay and a BRBV focus reduction neutralization assay, to assess the seroprevalence of BRBV neutralizing antibodies in human sera collected in 2020 in St. Louis, MO. Of 440 human serum samples tested, three (0.7%) were able to potently neutralize both VSV-BRBV and wild-type BRBV. These findings suggest that human infections with BRBV are more common than previously recognized. IMPORTANCE Since the discovery of the Bourbon virus (BRBV) in 2014, a total of five human cases have been identified, including two fatal cases. BRBV is thought to be transmitted by the lone star tick, which is prevalent in the eastern, southeastern, and midwestern United States. BRBV has been detected in ticks in Missouri and Kansas, and serological evidence suggests that it is also present in North Carolina. However, the true infection burden of BRBV in humans is not known. In the present study, we developed two virus neutralization assays to assess the seroprevalence of BRBV-specific antibodies in human sera collected in 2020 in St. Louis, MO. We found that a small subset of individuals are seropositive for neutralizing antibodies against BRBV. Our data suggest that BRBV infection in humans is more common than previously thought.

Potential Mechanisms of Transmission of Tick-Borne Viruses at the Virus-Tick Interface

Ticks (Acari; Ixodidae) are the second most important vector for transmission of pathogens to humans, livestock, and wildlife. Ticks as vectors for viruses have been reported many times over the last 100 years. Tick-borne viruses (TBVs) belong to two orders (Bunyavirales and Mononegavirales) containing nine families (Bunyaviridae, Rhabdoviridae, Asfarviridae, Orthomyxovirida, Reoviridae, Flaviviridae, Phenuviridae, Nyamiviridae, and Nairoviridae). Among these TBVs, some are very pathogenic, causing huge mortality, and hence, deserve to be covered under the umbrella of one health. About 38 viral species are being transmitted by <10% of the tick species of the families Ixodidae and Argasidae. All TBVs are RNA viruses except for the African swine fever virus from the family Asfarviridae. Tick-borne viral diseases have also been classified as an emerging threat to public health and animals, especially in resource-poor communities of the developing world. Tick-host interaction plays an important role in the successful transmission of pathogens. The ticks' salivary glands are the main cellular machinery involved in the uptake, settlement, and multiplication of viruses, which are required for successful transmission into the final host. Furthermore, tick saliva also participates as an augmenting tool during the physiological process of transmission. Tick saliva is an important key element in the successful transmission of pathogens and contains different antimicrobial proteins, e.g., defensin, serine, proteases, and cement protein, which are key players in tick-virus interaction. While tick-virus interaction is a crucial factor in the propagation of tick-borne viral diseases, other factors (physiological, immunological, and gut flora) are also involved. Some immunological factors, e.g., toll-like receptors, scavenger receptors, Janus-kinase (JAK-STAT) pathway, and immunodeficiency (IMD) pathway are involved in tick-virus interaction by helping in virus assembly and acting to increase transmission. Ticks also harbor some endogenous viruses as internal microbial faunas, which also play a significant role in tick-virus interaction. Studies focusing on tick saliva and its role in pathogen transmission, tick feeding, and control of ticks using functional genomics all point toward solutions to this emerging threat. Information regarding tick-virus interaction is somewhat lacking; however, this information is necessary for a complete understanding of transmission TBVs and their persistence in nature. This review encompasses insight into the ecology and vectorial capacity of tick vectors, as well as our current understanding of the predisposing, enabling, precipitating, and reinforcing factors that influence TBV epidemics. The review explores the cellular, biochemical, and immunological tools which ensure and augment successful evading of the ticks' defense systems and transmission of the viruses to the final hosts at the virus-vector interface. The role of functional genomics, proteomics, and metabolomics in profiling tick-virus interaction is also discussed. This review is an initial attempt to comprehensively elaborate on the epidemiological determinants of TBVs with a focus on intra-vector physiological processes involved in the successful execution of the docking, uptake, settlement, replication, and transmission processes of arboviruses. This adds valuable data to the existing bank of knowledge for global stakeholders, policymakers, and the scientific community working to devise appropriate strategies to control ticks and TBVs.

Pathogen Spillover to an Invasive Tick Species: First Detection of Bourbon Virus in Haemaphysalis longicornis in the United States

Haemaphysalis longicornis (Neumann, 1901) (Acari: Ixodidae), the Asian longhorned tick, is an invasive tick species present in the USA since at least 2017 and has been detected in one-third of Virginia counties. While this species is associated with the transmission of multiple pathogens in its native geographical range of eastern Asia, little is known about its ability to acquire and transmit pathogens in the USA, specifically those that are transmissible to humans, although from an animal health perspective, it has already been shown to vector Theileria orientalis Ikeda strains. Emerging tick-borne viruses such as Bourbon virus (genus: Thogotovirus) are of concern, as these newly discovered pathogenic agents have caused fatal clinical cases, and little is known about their distribution or enzootic maintenance. This study examined H. longicornis collected within Virginia (from ten counties) for Bourbon and Heartland viruses using PCR methods. All ticks tested negative for Heartland virus via qRT-PCR (S segment target). Bourbon-virus-positive samples were confirmed on two different gene targets and with Sanger sequencing of the PB2 (segment 1) gene. Bourbon virus RNA was detected in one nymphal stage H. longicornis from Patrick County, one nymph from Staunton City, and one larval pool and one adult female tick from Wythe County, Virginia. An additional 100 Amblyomma americanum (Linnaeus 1758; lone star tick) collected at the same Patrick County site revealed one positive nymphal pool, suggesting that Bourbon virus may have spilled over from the native vector, potentially by co-feeding on a shared Bourbon-virus-infected vertebrate host. Blood tested from local harvested deer revealed a 11.1% antibody seroprevalence against Bourbon virus, exposure which further corroborates that this tick-borne virus is circulating in the southwest Virginia region. Through these results, it can be concluded that H. longicornis can carry Bourbon virus and that pathogen spillover may occur from native to invasive tick species.

The Original Scientific Description of the Lone Star Tick (Amblyomma americanum, Acari: Ixodidae) and Implications for the Species' Past and Future Geographic Distributions

Amblyomma americanum L. is an important vector in North America originally described by Linnaeus based on Pehr Kalm's 1754 report. While Kalm's 'Travels into North America' is well known, his 1754 report remains obscure. Some authors were skeptical that Kalm referred to A. americanum because he encountered them at sites farther north outside of the species' range. However, the details in 1754 report leave no doubt that Kalm described lone star ticks. In this historical review, we provide support for Kalm's identification using a modern translation of his 1754 report and other sources. We also delineate distributional changes of lone star ticks from the pre-colonization era to the present and interpret them in the context of large-scale anthropogenic changes in the landscape. In this framework, the lone star tick's current northward expansion is a recolonization of their former range. Extensive deforestation and extirpation of their principal host species, white-tailed deer, led to A. americanum's disappearance from the northern parts of its range by the 20th century. Subsequent recolonization by second-growth forest and increases in white-tailed deer populations by the mid-20th century is now allowing A. americanum to reclaim its former range. These changes in the land appear to be the driving force behind A. americanum's present expansion. Understanding this species' history and the factors contributing to its current expansion will enable better predictions about its future distribution and potential to transmit human pathogens.

Development of accelerated high-throughput antiviral screening systems for emerging orthomyxoviruses

Bourbon virus (BRBV) is an emerging tick-borne orthomyxovirus that causes severe febrile illness in humans. There are no specific treatments for BRBV disease currently available. Here, we developed a highly accessible and robust, quantitative fluorescence-based BRBV minigenome (MG) system and applied it to high-throughput antiviral drug screening. We demonstrated that human dihydroorotate dehydrogenase (DHODH) inhibitors, hDHODH-IN-4 and brequinar, efficiently reduced BRBV RNA synthesis, and validated these findings using infectious BRBV in vitro. The DHODH inhibitors also exhibited high potency in inhibiting MG activities of other orthomyxoviruses with emerging zoonotic potential, including bat influenza A virus, swine influenza D virus, and Thogoto virus. Our newly developed MG system is a powerful platform for antiviral drug screening across the Orthomyxoviridae family, enabling rapid development and deployment of antivirals against future emerging orthomyxoviruses.

Comparative study of ten thogotovirus isolates and their distinct in vivo characteristics

Thogotoviruses are tick-borne arboviruses that comprise a unique genus within the Orthomyxoviridae family. Infections with thogotoviruses primarily cause disease in livestock with occasional reports of human infections suggesting a zoonotic potential. In the past, multiple genetically distinct thogotoviruses were isolated mostly from collected ticks. However, many aspects regarding their phylogenetic relationships, morphological characteristics and virulence in mammals remain unclear. For the present comparative study, we used a collection of ten different thogotovirus isolates from different geographic areas. Next generation sequencing and subsequent phylogenetic analyses revealed a distinct separation of these viruses into two major clades - the Thogoto-like and Dhori-like viruses. Electron microscopy demonstrated a heterogeneous morphology with spherical and filamentous particles being present in virus preparations. To study their pathogenicity, we analyzed the viruses in a small animal model system. In intraperitoneally infected C57BL/6 mice, all isolates showed a tropism for liver, lung and spleen. Importantly, we did not observe horizontal transmission to uninfected, highly susceptible contact mice. The isolates enormously differed in their capacity to induce disease, ranging from subclinical to fatal outcomes. In vivo multi-step passaging experiments of two low-pathogenic isolates showed no increased virulence and sequence analyses of the passaged viruses indicated a high stability of the viral genomes after ten mouse passages. In summary, our analysis demonstrates the broad genetic and phenotypic variability within the thogotovirus genus. Moreover, thogotoviruses are well adapted to mammals but their horizontal transmission seems to depend on ticks as their vectors. Importance Since their discovery over sixty years ago, fifteen genetically distinct members of the thogotovirus genus have been isolated. These arboviruses belong to the Orthomyxovirus family and share many features with influenza viruses. However, numerous of these isolates have not been characterized in depth. In the present study, we comparatively analyzed a collection of ten different thogotovirus isolates to answer basic questions about their phylogenetic relationships, morphology and pathogenicity in mice. Our results highlight shared and unique characteristics of this diverse genus. Taken together, these observations provide a framework for the phylogenic classification and phenotypic characterization of newly identified thogotovirus isolates that could potentially cause severe human infections as exemplified by the recently reported, fatal Bourbon virus cases in the United States.

Eight years' advances on Bourbon virus, a tick-born Thogotovirus of the Orthomyxovirus family

Bourbon virus (BRBV) was first isolated from a blood sample collected from a male patient living in Bourbon county, Kansas, during the spring of 2014. The patient later died due to complications associated with multiorgan failure. Currently, several BRBV infection-caused deaths have been reported in the United States, and misdiagnosed cases are often undercounted. BRBV is a member of the genus Thogotovirus of the Orthomyxoviridae family, and is transmitted through the Lone Star tick, Amblyomma Americanum, in North America. Currently, there are no specific antivirals or vaccinations available to treat or prevent BRBV infection. Several small molecular compounds have been identified to effectively inhibit BRBV infection of in vitro cell cultures at a single- or sub-micromolar level. Favipiravir, an RNA-dependent RNA polymerase inhibitor, prevented the death of Type I interferon receptor knockout mice infected with BRBV infection.

The expanding spectrum of disease caused by the Lone Star Tick, Amblyomma americanum

Ticks are remarkable vectors of a diverse and growing list of infectious agents of importance to both medical and veterinary disciplines. The tick Amblyomma americanum is one of the most frequently identified ticks in the United States with an expanding spectrum of human disease given its vast geographic range. The recently described Bourbon and Heartland viruses are likely transmitted by the Lone Star tick and are just two of the several novel tick-borne pathogens discovered in recent decades. The review will focus on these two viruses that can cause illness with similar characteristics to other diseases transmitted by the Lone Star tick. Healthcare professionals should consider these viruses in patients presenting with an ailment suggestive of a tick-born rickettsial disease that fails to improve with treatment with doxycycline. Additionally, some individuals may develop life-threatening allergic reactions triggered by the bite of the Lone Star tick.