The origin and insecticide resistance of Aedes albopictus mosquitoes established in southern Mozambique.

BACKGROUND: The Aedes albopictus mosquito is of medical concern due to its ability to transmit viral diseases, such as dengue and chikungunya. Aedes albopictus originated in Asia and is now present on all continents, with the exception of Antarctica. In Mozambique, Ae. albopictus was first reported in 2015 within the capital city of Maputo, and by 2019, it had become established in the surrounding area. It was suspected that the mosquito population originated in Madagascar or islands of the Western Indian Ocean (IWIO). The aim of this study was to determine its origin. Given the risk of spreading insecticide resistance, we also examined relevant mutations in the voltage-sensitive sodium channel (VSSC). METHODS: Eggs of Ae. albopictus were collected in Matola-Rio, a municipality adjacent to Maputo, and reared to adults in the laboratory. Cytochrome c oxidase subunit I (COI) sequences and microsatellite loci were analyzed to estimate origins. The presence of knockdown resistance (kdr) mutations within domain II and III of the VSSC were examined using Sanger sequencing. RESULTS: The COI network analysis denied the hypothesis that the Ae. albopictus population originated in Madagascar or IWIO; rather both the COI network and microsatellites analyses showed that the population was genetically similar to those in continental Southeast Asia and Hangzhou, China. Sanger sequencing determined the presence of the F1534C knockdown mutation, which is widely distributed among Asian populations, with a high allele frequency (46%). CONCLUSIONS: These results do not support the hypothesis that the Mozambique Ae. albopictus population originated in Madagascar or IWIO. Instead, they suggest that the origin is continental Southeast Asia or a coastal town in China.

Tiger prowling: Distribution modelling for northward-expanding Aedes albopictus (Diptera: Culicidae) in Japan.

The Asian tiger mosquito, Aedes albopictus, is a significant public health concern owing to its expanding habitat and vector competence. Disease outbreaks attributed to this species have been reported in areas under its invasion, and its northward expansion in Japan has caused concern because of the potential for dengue virus infection in newly populated areas. Accurate prediction of Ae. albopictus distribution is crucial to prevent the spread of the disease. However, limited studies have focused on the prediction of Ae. albopictus distribution in Japan. Herein, we used the random forest model, a machine learning approach, to predict the current and potential future habitat ranges of Ae. albopictus in Japan. The model revealed that these mosquitoes prefer urban areas over forests in Japan on the current map. Under predictions for the future, the species will expand its range to the surrounding areas and eventually reach many areas of northeastern Kanto, Tohoku District, and Hokkaido, with a few variations in different scenarios. However, the affected human population is predicted to decrease owing to the declining birth rate. Anthropogenic and climatic factors contribute to range expansion, and urban size and population have profound impacts. This prediction map can guide responses to the introduction of this species in new areas, advance the spatial knowledge of diseases vectored by it, and mitigate the possible disease burden. To our knowledge, this is the first distribution-modelling prediction for Ae. albopictus with a focus on Japan.

Blowflies are potential vector for avian influenza virus at enzootic area in Japan.

High pathogenicity avian influenza (HPAI) poses a significant threat to both domestic and wild birds globally. The avian influenza virus, known for environmental contamination and subsequent oral infection in birds, necessitates careful consideration of alternative introduction routes during HPAI outbreaks. This study focuses on blowflies (genus Calliphora), in particular Calliphora nigribarbis, attracted to decaying animals and feces, which migrate to lowland areas of Japan from northern or mountainous regions in early winter, coinciding with HPAI season. Our investigation aims to delineate the role of blowflies as HPAI vectors by conducting a virus prevalence survey in a wild bird HPAI-enzootic area. In December 2022, 648 Calliphora nigribarbis were collected. Influenza virus RT-PCR testing identified 14 virus-positive samples (2.2% prevalence), with the highest occurrence observed near the crane colony (14.9%). Subtyping revealed the presence of H5N1 and HxN1 in some samples. Subsequent collections in December 2023 identified one HPAI virus-positive specimen from 608 collected flies in total, underscoring the potential involvement of blowflies in HPAI transmission. Our observations suggest C. nigribarbis may acquire the HPAI virus from deceased wild birds directly or from fecal materials from infected birds, highlighting the need to add blowflies as a target of HPAI vector control.

Identification and epidemiological study of an uncultured flavivirus from ticks using viral metagenomics and pseudoinfectious viral particles.

During their blood-feeding process, ticks are known to transmit various viruses to vertebrates, including humans. Recent viral metagenomic analyses using next-generation sequencing (NGS) have revealed that blood-feeding arthropods like ticks harbor a large diversity of viruses. However, many of these viruses have not been isolated or cultured, and their basic characteristics remain unknown. This study aimed to present the identification of a difficult-to-culture virus in ticks using NGS and to understand its epidemic dynamics using molecular biology techniques. During routine tick-borne virus surveillance in Japan, an unknown flaviviral sequence was detected via virome analysis of host-questing ticks. Similar viral sequences have been detected in the sera of sika deer and wild boars in Japan, and this virus was tentatively named the Saruyama virus (SAYAV). Because SAYAV did not propagate in any cultured cells tested, single-round infectious virus particles (SRIP) were generated based on its structural protein gene sequence utilizing a yellow fever virus-based replicon system to understand its nationwide endemic status. Seroepidemiological studies using SRIP as antigens have demonstrated the presence of neutralizing antibodies against SAYAV in sika deer and wild boar captured at several locations in Japan, suggesting that SAYAV is endemic throughout Japan. Phylogenetic analyses have revealed that SAYAV forms a sister clade with the Orthoflavivirus genus, which includes important mosquito- and tick-borne pathogenic viruses. This shows that SAYAV evolved into a lineage independent of the known orthoflaviviruses. This study demonstrates a unique approach for understanding the epidemiology of uncultured viruses by combining viral metagenomics and pseudoinfectious viral particles.

Reconsideration of importance of the point mutation L982W in the voltage-sensitive sodium channel of the pyrethroid resistant Aedes aegypti (L.)(Diptera: Culicidae) in Vietnam.

Pyrethroid resistance in Aedes aegypti is widespread in southern Vietnam because the photostable 2nd generation pyrethroids have been used in large amounts over extensive areas for malaria and dengue vector control. In our previous report in 2009, F1534C, one of the point mutations in the voltage-sensitive sodium channel (VSSC) in Ae. aegypti, was widespread at high frequency in south and central area. However, no significant correlation between the frequency of F1534C and pyrethroid susceptibility was detected primarily because the F1534C mutation frequency in the southern highland area was very low, despite that the bioassay indicated high pyrethroid resistance. The point mutation in the VSSC, L982W, which was not the target mutation in our previous study, was recently determined to be an important mutation causing high-pyrethroid resistance in Vietnamese Ae. aegypti. In the present study, a re-investigation of L982W in the mosquito samples collected in 2006-2008 revealed a greater distribution of this mutation (allelic percentage 59.2%) than F1534C (21.7%) and the greater proportion of homozygous L982W as compared to F1534C provided a plausible answer to the question concerning the unknown resistance factor in the southern highland area. L982W frequencies were uniformly higher in the southern part of Vietnam, including the highland area with a significantly high positive correlation with pyrethroid resistance in Ae. aegypti.

Blood meal source identification and RNA virome determination in Japanese encephalitis virus vectors collected in Ishikawa Prefecture, Japan, show distinct avian/mammalian host preference.

In Asia, Culex mosquitoes are of particular interest because of their role in maintaining endemic mosquito-borne viral diseases, including the Japanese encephalitis virus (JEV). Nonetheless, host-feeding preferences, along with naturally infecting RNA viruses in certain Culex species, remain understudied. In this study, selected blood-fed mosquitoes were processed for avian and mammalian blood meal source identification. Concurrently, cell culture propagation and high-throughput sequencing (HTS) approaches were used to determine the RNA virome of Culex mosquitoes collected in Ishikawa Prefecture, Japan. The identification of blood meal sources from wild-caught Culex spp. revealed that Culex (Culex) tritaeniorhynchus Giles, 1901, has a robust preference toward wild boar (62%, 26/42), followed by heron (21%, 9/42). The other two species, Culex (Oculeomyia) bitaeniorhynchus Giles, 1901, and Culex (Culex) orientalis Edwards, 1921, showed a distinct preference for avian species, including migratory birds. From the HTS results, 34 virus sequences were detected, four of which were newly identified virus sequences of unclassified Aspiviridae, Qinviridae, Iflaviridae, and Picornaviridae. The absence of observable cytopathic effects in mammalian cells and phylogenetic analysis suggested that all identified virus sequences were insect-specific. Further investigations involving other mosquito populations collected in different areas are warranted to explore previously unknown vertebrate hosts that may be linked to JEV dispersal in nature.

Evaluating the mosquito host range of Getah virus and the vector competence of selected medically important mosquitoes in Getah virus transmission.

BACKGROUND: The Getah virus (GETV) is a mosquito-borne Alphavirus (family Togaviridae) that is of significant importance in veterinary medicine. It has been associated with major polyarthritis outbreaks in animals, but there are insufficient data on its clinical symptoms in humans. Serological evidence of GETV exposure and the risk of zoonotic transmission makes GETV a potentially medically relevant arbovirus. However, minimal emphasis has been placed on investigating GETV vector transmission, which limits current knowledge of the factors facilitating the spread and outbreaks of GETV. METHODS: To examine the range of the mosquito hosts of GETV, we selected medically important mosquitoes, assessed them in vitro and in vivo and determined their relative competence in virus transmission. The susceptibility and growth kinetics of GETVs in various mosquito-derived cell lines were also determined and quantified using plaque assays. Vector competency assays were also conducted, and quantitative reverse transcription-PCR and plaque assays were used to determine the susceptibility and transmission capacity of each mosquito species evaluated in this study. RESULTS: GETV infection in all of the investigated mosquito cell lines resulted in detectable cytopathic effects. GETV reproduced the fastest in Culex tritaeniorhynchus- and Aedes albopictus-derived cell lines, as evidenced by the highest exponential titers we observed. Regarding viral RNA copy numbers, mosquito susceptibility to infection, spread, and transmission varied significantly between species. The highest vector competency indices for infection, dissemination and transmission were obtained for Cx. tritaeniorhynchus. This is the first study to investigate the ability of Ae. albopictus and Anopheles stephensi to transmit GETV, and the results emphasize the role and capacity of other mosquito species to transmit GETV upon exposure to GETV, in addition to the perceived vectors from which GETV has been isolated in nature. CONCLUSIONS: This study highlights the importance of GETV vector competency studies to determine all possible transmission vectors, especially in endemic regions.

Correction: Evaluating the competence of the primary vector, Culex tritaeniorhynchus, and the invasive mosquito species, Aedes japonicus japonicus, in transmitting three Japanese encephalitis virus genotypes.

[This corrects the article DOI: 10.1371/journal.pntd.0008986.].

Discovery of super-insecticide-resistant dengue mosquitoes in Asia: Threats of concomitant knockdown resistance mutations.

Aedes aegypti (Linnaeus, 1762) is the main mosquito vector for dengue and other arboviral infectious diseases. Control of this important vector highly relies on the use of insecticides, especially pyrethroids. The high frequency (>78%) of the L982W substitution was detected at the target site of the pyrethroid insecticide, the voltage-gated sodium channel (Vgsc) of A. aegypti collected from Vietnam and Cambodia. Alleles having concomitant mutations L982W + F1534C and V1016G + F1534C were also confirmed in both countries, and their frequency was high (>90%) in Phnom Penh, Cambodia. Strains having these alleles exhibited substantially higher levels of pyrethroid resistance than any other field population ever reported. The L982W substitution has never been detected in any country of the Indochina Peninsula except Vietnam and Cambodia, but it may be spreading to other areas of Asia, which can cause an unprecedentedly serious threat to the control of dengue fever as well as other Aedes-borne infectious diseases.

A long-term field study on mosquito vectors of avian malaria parasites in Japan.

Avian malaria is a mosquito-borne disease of birds caused by avian Plasmodium spp. in worldwide scale. Some naïve birds show serious symptoms which can result in death. Surveillance of vectors and parasites are important to understand and control this disease. Although avian malaria has been found in Japan, detailed prevalence and dynamics remained understudied. We aimed to observe annual changes in the abundance of mosquitoes and the prevalence of avian Plasmodium parasites in Japan. Mosquitoes were collected using dry ice traps over a 10-year period, at a fixed research area located in Kanagawa prefecture. Collected mosquitoes were investigated for the species composition, population size and prevalence of avian Plasmodium by PCR. Mosquitoes belonging to 13 species in 7 genera were collected (n=8,965). The dominant species were Aedes (Ae.) albopictus and Culex (Cx.) pipiens group (gr.). Seven avian Plasmodium lineages, all of which were previously known, were detected from Cx. pipiens gr., Ae. albopictus, and Tripteroides bambusa. Three genetic lineages were dominant and were probably transmitted by Cx. pipiens gr. whose could be the primary vector of these parasites. Annual variations in the seasonal prevalence of mosquitoes and avian Plasmodium were revealed for the first time during recent 10 years in Japan. Namely, avian Plasmodium occurrence in the vector population peaked often in June to July and September to October when the density of the vector population was presumably high enough for the transmission of avian Plasmodium upon appearance of infected birds.

Two hidden taxa in the Japanese encephalitis vector mosquito, Culex tritaeniorhynchus, and the potential for long-distance migration from overseas to Japan.

The Culex vishnui subgroups, particularly Culex tritaeniorhynchus, are considered the primary vectors of the Japanese encephalitis virus (JEV) in Asia. Recent molecular phylogenetic analyses of JEV isolates from Asian countries have shown that JEVs with diverse genetic variants are present in Asia. Furthermore, some JEV strains have been found to have crossed the East China Sea and been introduced into Japan. In this study, the possibility of overseas migration of the JE vector mosquito, Cx. tritaeniorhynchus was examined from the genetic, physical, and meteorological perspectives. Molecular phylogenetic analysis was performed based on both whole coding sequences and on the barcoding region of the mitochondrial cytochrome c oxidase subunit I (COI) gene of Cx. vishnui subgroups collected from Asian countries. Culex tritaeniorhymchus was classified into two genetically independent taxa by COI sequences: the Japanese type (Ct-J), which inhabits Japan except for the Amami Islands of southern Japan, and the continental type (Ct-C), which inhabits the Asian region except for Japan. It was confirmed that approximately 10% of Cx. tritaeniorhynchus trapped during the summer in western Kyushu were Ct-C, and that they could fly for up to 38 h continuously. The meteorological analysis also confirmed that the atmospheric flow occurring over the continent coincided with the date of Ct-C capture. This is the first report showing the existence of two taxa in Cx. tritaeniorhynchus. Their physical and physiological characteristics suggest the possibility of long-distance migration from overseas regions to Japan across the East China Sea. Future efforts are expected to provide evidence to support the occurrence of long-distance migration of Cx. tritaeniorhynchus with JEV.

Detection of Japanese Encephalitis Virus RNA in Host-Questing Ticks in Japan, 2019-2020.

Japanese encephalitis virus (JEV), a mosquito-borne virus, causes severe clinical symptoms in humans in the Asian-Pacific region, where it circulates in a primary transmission cycle among Culex tritaeniorhynchus mosquitoes, domestic swine (Sus scrofa domesticus), and wading birds. We report here an anomalous result that mosquito-borne JEV was detected in unfed host-questing ticks collected from the field in Japan. JEV genomic RNA was detected in four pools of Haemaphysalis flava nymphs collected in November and December 2019, and March 2020, when Cx. tritaeniorhynchus adults were not presumed to be active. Moreover, JEV antigenomic RNA was detected in some JEV-positive tick samples, suggesting virus replication in ticks. However, taken together with no infectious virus isolated, the possibility that the antigenomic RNA was derived from the undigested bloodmeal source in ticks cannot be ruled out. Thus, the role of the ticks as a natural reservoir for JEV remains to be confirmed.

Rat trade and leptospirosis: Molecular epidemiology of Leptospira species in rats exported from Cambodia to Vietnam.

Rats are an important maintenance host of Leptospira spp., the causative agents of leptospirosis, a zoonotic disease with worldwide distribution. Rats are traded as food in the Mekong Delta, where Cambodia exports tons of rats to Vietnam. Handling wild rats is a potential health risk, but the information on Leptospira spp. carried by rats traded in the region remains limited. In this study, we investigated the carriage of Leptospira spp. in rats exported from Cambodia to Vietnam using bacterial culture, nested PCR and DNA sequencing. Isolates were then assessed using serological analysis and whole-genome sequencing (WGS), and Leptospira DNA detected in rat kidney tissues was also analysed by multilocus sequence typing (MLST). Seventy-two rats (2 Bandicota indica, 57 Rattus argentiventer, 11 R. losea, 1 R. norvegicus and 1 R. rattus) were subjected to bacterial culture, and three L. borgpetersenii serogroup Javanica isolates were obtained from R. argentiventer (5.3%). WGS revealed that although Cambodian isolates were genetically related to L. borgpetersenii serogroup Javanica strains widely distributed in East and South-East Asian countries, they formed a different cluster from other strains. In addition to the three L. borgpetersenii sequences, the flaB sequence of L. interrogans was detected in 18 R. argentiventer and 7 R. losea kidney tissue samples (38.9%) using nested PCR followed by DNA sequencing. The L. interrogans flaB-positive samples were further analysed by MLST, revealing that seven housekeeping genes (glmU, pntA, sucA, tpiA, pfkB, mreA and caiB) contained novel sequences with distinct lineages from other sequence types. This study revealed a high prevalence of Leptospira spp. among rats exported from Cambodia to Vietnam, indicating a potential risk to people engaging in rat trade and demonstrating that a fastidious L. interrogans strain circulates among Cambodian rats.

Detection of Quaranjavirus-Like Sequences from Haemaphysalis hystricis Ticks Collected in Japan.

Viruses belonging to the genus Quaranjavirus in the family Orthomyxoviridae are known as argasid tick-borne viruses. Some viruses in this genus or an unassigned quaranjavirus-like variant can infect humans, although little is known about their pathogenicity. During the surveillance of tick-borne viruses in ixodid ticks in Ehime Prefecture, Japan, novel quaranjavirus-like sequences were detected in 3 pooled samples of Haemaphysalis histricis nymphs. Phylogenetic analysis revealed that the detected viruses formed a cluster with quaranjaviruses and other related viruses. Specifically, the viruses were closely related to Zambezi tick virus 1 and Uumaja virus, which are quaranjavirus-like viruses recently discovered in ixodid ticks in Africa and Europe, respectively. These findings indicate that the viruses detected in this study were probably new members of the Quaranjavirus genus or a related group. The viruses were tentatively named "Ohshima virus" even though only limited sequences of their genomes were available. This is the first report on the detection of a quaranjavirus-like virus in the East Asian region. Further investigations are needed to discern its infectivity and pathogenicity against humans and other animals and to determine the potential risk of an emerging tick-borne viral disease.

Population genetics of an invasive mosquito vector, Aedes albopictus in the Northeastern USA.

The Asian tiger mosquito (Aedes albopictus) arrived in the USA in the 1980's and rapidly spread throughout eastern USA within a decade. The predicted northern edge of its overwintering distribution on the East Coast of the USA roughly falls across New York, Connecticut, and Massachusetts, where the species has been recorded as early as 2000. It is unclear whether Ae. albopictus populations have become established and survive the cold winters in these areas or are recolonized every year. We genotyped and analyzed populations of Ae. albopictus from the northeast USA using 15 microsatellite markers and compared them with other populations across the country and to representatives of the major global genetic clades to investigate their connectivity and stability. Founder effects or bottlenecks were rare at the northern range of the Ae. albopictus distribution in the northeastern USA, with populations displaying high levels of genetic diversity and connectivity along the East Coast. There is no evidence of population turnover in Connecticut during the course of three consecutive years, with consistent genetic structure throughout this period. Overall, these results support the presence of established populations of Ae. albopictus in New York, Connecticut, and Massachusetts, successfully overwintering and migrating in large numbers. Given the stability and interconnectedness of these populations, Ae. albopictus has the potential to continue to proliferate and expand its range northward under mean warming conditions of climate change. Efforts to control Ae. albopictus in these areas should thus focus on vector suppression rather than eradication strategies, as local populations have become firmly established and are expected to reemerge every summer.

Detection of Jingmenviruses in Japan with Evidence of Vertical Transmission in Ticks.

Jingmen tick virus (JMTV) and the related jingmenvirus-termed Alongshan virus are recognized as globally emerging human pathogenic tick-borne viruses. These viruses have been detected in various mammals and invertebrates, although their natural transmission cycles remain unknown. JMTV and a novel jingmenvirus, tentatively named Takachi virus (TAKV), have now been identified during a surveillance of tick-borne viruses in Japan. JMTV was shown to be distributed across extensive areas of Japan and has been detected repeatedly at the same collection sites over several years, suggesting viral circulation in natural transmission cycles in these areas. Interestingly, these jingmenviruses may exist in a host tick species-specific manner. Vertical transmission of the virus in host ticks in nature was also indicated by the presence of JMTV in unfed host-questing Amblyomma testudinarium larvae. Further epidemiological surveillance and etiological studies are necessary to assess the status and risk of jingmenvirus infection in Japan.

Updated distribution of anopheline mosquitoes in Hokkaido, Japan, and the first evidence of Anopheles belenrae in Japan.

BACKGROUND: In Hokkaido, northern island of Japan, at least seven cases of falciparum malaria were reported by 1951. A survey conducted at that time was unsuccessful in implicating any mosquito species as the possible vector. Although active anopheline mosquito surveillance continued until the middle of the 1980s, there is very limited information on their current status and distribution in Japan. Therefore, this study is an update on the current status and distribution of anopheline mosquitoes in Hokkaido based on a 15-year entomological surveillance between 2001 and 2015. METHODS: A survey of mosquitoes was conducted at 22 sites in Hokkaido, Japan, from 2001 to 2015. Adult mosquitoes were collected from cowsheds, lakesides, shrubs, and habitats ranging from open grassland to coniferous forest using a Centers for Disease Control and Prevention (CDC) miniature light trap enhanced with dry ice, aspirators, and sweeping nets. Larvae were collected from lakes, ponds, swamps, stagnant and flowing rivers, and paddy fields. All specimens were morphologically identified and subjected to polymerase chain reaction (PCR)-based sequence analysis of the internal transcribed spacer 2 ( ITS2) region of rDNA. Phylogenetic trees were reconstructed using the neighbor-joining method with the Kimura 2-parameter model on MEGA X version 10.2.2. RESULTS: A total of 46 anopheline specimens were used for the phylogenetic analysis. During the survey, a new member of the Anopheles hyrcanus group, An. belenrae, was discovered in eastern Hokkaido in 2004. Anopheles belenrae has since then been consistently found and confirmed to inhabit only this area of Japan. Four members of the An. hyrcanus group, namely An. belenrae, An. engarensis, An. lesteri, and An. sineroides, have been found in Hokkaido. The results also suggest that An. sinensis, formerly a dominant species throughout Japan, has become a rarely found species, at least currently in Hokkaido. CONCLUSION: The updated distribution of anopheline mosquitoes in Hokkaido, Japan, showed considerable differences from that observed in previous surveys conducted from 1969 to 1984. In particular, areas where An. sinensis was previously distributed may have been greatly reduced in Hokkaido. The phylogenetic analysis revealed a novel An. hyrcanus group member identified as An. belenrae, described in South Korea in 2005. It is interesting that An. belenrae was confirmed to inhabit only eastern Hokkaido, Japan.

Toyo virus, a novel member of the Kaisodi group in the genus Uukuvirus (family Phenuiviridae) found in Haemaphysalis formosensis ticks in Japan.

Ticks are important vector arthropods that transmit various pathogens to humans and other animals. Tick-borne viruses are of particular concern to public health as these are major agents of emerging and re-emerging infectious diseases. The Phenuiviridae family of tick-borne viruses is one of the most diverse groups and includes important human pathogenic viruses such as severe fever with thrombocytopenia syndrome virus. Phenuivirus-like sequences were detected during the surveillance of tick-borne viruses using RNA virome analysis from a pooled sample of Haemaphysalis formosensis ticks collected in Ehime, Japan. RT-PCR amplification and Sanger sequencing revealed the nearly complete viral genome sequence of all three segments. Comparisons of the viral amino acid sequences among phenuiviruses indicated that the detected virus shared 46%-70% sequence identity with known members of the Kaisodi group in the genus Uukuvirus. Furthermore, phylogenetic analysis of the viral proteins showed that the virus formed a cluster with the Kaisodi group viruses, suggesting that this was a novel virus, which was designated "Toyo virus" (TOYOV). Further investigation of TOYOV is needed, and it will contribute to understanding the natural history and the etiological importance of the Kaisodi group viruses.

Discovery of a Novel Flavivirus (Flaviviridae) From the Horse Fly, Tabanus rufidens (Diptera: Tabanidae): The Possible Coevolutionary Relationships Between the Classical Insect-Specific Flaviviruses and Host Dipteran Insects.

Tabanid flies (Tabanidae: Diptera) are common hematophagous insects known to transmit some pathogens mechanically or biologically to animals; they are widely distributed throughout the world. However, no tabanid-borne viruses, except mechanically transmitted viruses, have been reported to date. In this study, we conducted RNA virome analysis of several human-biting tabanid species in Japan, to discover and characterize viruses associated with tabanids. A novel flavivirus was encountered during the study in the Japanese horse fly, Tabanus rufidens (Bigot, 1887). The virus was detected only in T. rufidens, but not in other tabanid species, and as such was designated Tabanus rufidens flavivirus (TrFV). TrFV could not be isolated using a mammalian cell line and showed a closer phylogenetic relationship to the classical insect-specific flaviviruses (cISFs) rather than the vertebrate-infecting flaviviruses (VIFs), suggesting that it is a novel member of the cISFs. The first discovery of a cISF from Brachycera provides new insight into the evolutionary history and dynamics of flaviviruses.