Orthoflavivirus Lammi in Russia: Possible Transovarial Transmission and Trans-Stadial Survival in Aedes cinereus (Diptera, Culicidae)

In the last few years, there has been a dramatic increase in the number of discovered viruses that are transmitted by arthropods. Some of them are pathogenic for humans and mammals, and the pathogenic potential of others is unknown. The genus Orthoflavivirus belongs to the family Flaviviridae and includes arboviruses that cause severe human diseases with damage to the central nervous system and hemorrhagic fevers, as well as viruses with unknown vectors and viruses specific only to insects. The latter group includes Lammi virus, first isolated from a mosquito pool in Finland. It is known that Lammi virus successfully replicates in mosquito cell lines but not in mammalian cell cultures or mice. Lammi virus reduces the reproduction of West Nile virus during superinfection and thus has the potential to reduce the spread of West Nile virus in areas where Lammi virus is already circulating. In this work, we isolated Lammi virus from a pool of adult Aedes cinereus mosquitoes that hatched from larvae/pupae collected in Saint Petersburg, Russia. This fact may indicate transovarial transmission and trans-stadial survival of the virus.

Distribution and Characterisation of Tick-Borne Flavi-, Flavi-like, and Phenuiviruses in the Chelyabinsk Region of Russia

In this work, we presented data from a two-year study of flavi-, flavi-like, and phenuiviruses circulation in the population of ixodid ticks in the Chelyabinsk region. We isolated three tick-borne encephalitis virus (TBEV) strains from I. persulcatus, which was not detected in the ticks of the genus Dermacentor. The virus prevalence ranged from 0.66% to 2.28%. The Yanggou tick virus (YGTV) is widespread in steppe and forest-steppe zones and is mainly associated with ticks of the genus Dermacentor. We isolated 26 strains from D. reticulatus, D. marginatus, and I. persulcatus ticks in the HAE/CTVM8 tick cell line. The virus prevalence ranged from 1.58% to 4.18% in D. reticulatus, ranged from 0.78% to 3.93% in D. marginatus, and was 0.66% in I. persulcatus. There was combined focus of TBEV and YGTV in the territory of the Chelyabinsk region. The Alongshan virus (ALSV) was found to be associated with I. persulcatus ticks and is spread in forest zone. We detected 12 amplicons and isolated 7 strains of ALSV in tick cells. The virus prevalence ranged from 1.13% to 6.00%. The phlebovirus Gomselga and unclassified phenuivirus Stavropol were associated with I. persulcatus and D. reticulatus ticks, respectively. Virus prevalence of the unclassified phenuivirus Stavropol in the Chelyabinsk region is lower than that in neighbouring regions.

Pathogens in Ixodes persulcatus and Ixodes ricinus ticks (Acari, Ixodidae) in Karelia (Russia)

Ixodid ticks (Acarina, Ixodidae) are vectors of dangerous human infections. The main tick species that determine the epidemiological situation for tick-borne diseases in northern Europe are Ixodes ricinus and Ixodes persulcatus. In recent years, significant changes in the number and distribution of these species have been observed, accompanied by an expansion of the sympatric range. This work summarizes the data of long-term studies carried out in Karelia since 2007 on the infection of I. persulcatus and I. ricinus ticks with various pathogens, including new viruses with unclear pathogenic potential. As a result, tick-borne encephalitis virus (TBEV, Siberian genotype), Alongshan virus, several representatives of the family Phenuiviridae, Borrelia afzelii, Borrelia garinii, Ehrlichia muris, Candidatus Rickettsia tarasevichiae and Candidatus Lariskella arthropodarum were identified. Data were obtained on the geographical and temporal variability of tick infection rates with these main pathogens. The average infection rates of I. persulcatus with TBEV and Borrelia burgdorferi sensu lato were 4.4% and 23.4% and those of I. ricinus were 1.1% and 11.9%, respectively. We did not find a correlation between the infection rate of ticks with TBEV, B. burgdorferi s.l. and Ehrlichia muris/chaffeensis with the sex of the vector. In general, the peculiarities of the epidemiological situation in Karelia are determined by the wide distribution and high abundance of I. persulcatus ticks and by their relatively high infection rate with TBEV and B. burgdorferi s.l. in most of the territory, including the periphery of the range.

Geographical and Tick-Dependent Distribution of Flavi-Like Alongshan and Yanggou Tick Viruses in Russia

The genus Flavivirus includes related, unclassified segmented flavi-like viruses, two segments of which have homology with flavivirus RNA-dependent RNA polymerase NS5 and RNA helicase-protease NS3. This group includes such viruses as Jingmen tick virus, Alongshan virus, Yanggou tick virus and others. We detected the Yanggou tick virus in Dermacentor nuttalli and Dermacentor marginatus ticks in two neighbouring regions of Russia. The virus prevalence ranged from 0.5% to 8.0%. We detected RNA of the Alongshan virus in 44 individuals or pools of various tick species in eight regions of Russia. The virus prevalence ranged from 0.6% to 7.8%. We demonstrated the successful replication of the Yanggou tick virus and Alongshan virus in IRE/CTVM19 and HAE/CTVM8 tick cell lines without a cytopathic effect. According to the phylogenetic analysis, we divided the Alongshan virus into two groups: an Ixodes persulcatus group and an Ixodes ricinus group. In addition, the I. persulcatus group can be divided into European and Asian subgroups. We found amino acid signatures specific to the I. ricinus and I. persulcatus groups and also distinguished between the European and Asian subgroups of the I. persulcatus group.

Phlebovirus sequences detected in ticks collected in Russia: Novel phleboviruses, distinguishing criteria and high tick specificity

Phlebovirus is an abundant and rather heterogeneous genus within the Phenuiviridae family (order Bunyavirales). The genus Phlebovirus is divided into two antigenic complexes, which also correspond to the main vector: sandflies/mosquitoes and ticks. Previously, only sandfly/mosquito-borne phleboviruses were associated with human disease, such as Rift Valley fever virus, Toscana virus, Sicilian and Naples Sandfly fever viruses and others. Until recently, tick-borne phleboviruses were not considered as human pathogens. After the discovery of severe fever with thrombocytopenia syndrome, interest to tick-borne phleboviruses has increased dramatically. In the last decade, many novel phleboviruses have been reported in different regions. Despite this, the diversity, ecology and pathogenicity of these viruses still remain obscure. The aim of this work was to study the diversity of phleboviruses in ticks collected in several regions of Russia. We used pan-phlebovirus RT-PCR assays based on multiple degenerate primers targeting the polymerase gene fragment. Arthropod specimens were collected from 2005 to 2018. A total of 5901 Ixodidae ticks combined into 1116 pools were screened. A total of 160 specific amplicons were produced. In three cases RT-PCR assays amplified two distinct viruses from same tick pools. Direct sequencing of amplicons and subsequent phylogenetic analysis revealed twelve representatives of divergent phlebovirus groups. Based on the distribution of pairwise nucleotide sequence identity values, a cut-off (88%) was suggested to distinguish tick-borne phleboviruses. According to this provisional criterion, two viruses found here could be termed novel, while ten viruses have been described in previous studies. Detected phleboviruses demonstrated almost perfect specificity to a tick species or, at least, a genus. The same pattern was observed for tick-borne phleboviruses found in different studies around the world. Viruses that grouped together on a phylogenetic tree and differed less than this sequence identity threshold suggested above were hosted by ticks from the same genus.

Isolation and Characterisation of Alongshan Virus in Russia

In recent decades, many new flavi-like viruses have been discovered predominantly in different invertebrates and, as was recently shown, some of them may cause disease in humans. The Jingmenvirus (JMV) group holds a special place among flaviviruses and flavi-like viruses because they have a segmented ssRNA(+) genome. We detected Alongshan virus (ALSV), which is a representative of the JMV group, in ten pools of adult Ixodes persulcatus ticks collected in two geographically-separated Russian regions. Three of the ten strains were isolated in the tick cell line IRE/CTVM19. One of the strains persisted in the IRE/CTVM19 cells without cytopathic effect for three years. Most ALSV virions purified from tick cells were spherical with a diameter of approximately 40.5 nm. In addition, we found smaller particles of approximately 13.1 nm in diameter. We obtained full genome sequences of all four segments of two of the isolated ALSV strains, and partial sequences of one segment from the third strain. Phylogenetic analysis on genome segment 2 of the JMV group clustered our novel strains with other ALSV strains. We found evidence for the existence of a novel upstream open reading frame in the glycoprotein-coding segment of ALSV and other members of the JMV group.

Phylogeography of Crimean Congo Hemorrhagic Fever Virus

Crimean Congo hemorrhagic fever virus (CCHFV) is one of the most severe viral zoonozes. It is prevalent throughout Africa, Asia and southern Europe. Limited availability of sequence data has hindered phylogeographic studies. The complete genomic sequence of all three segments of 14 Crimean Congo hemorrhagic fever virus strains isolated from 1958–2000 in Russia, Central Asia and Africa was identified. Each genomic segment was independently subjected to continuous Bayesian phylogeographic analysis. The origin of each genomic segment was traced to Africa about 1,000–5,000 years ago. The virus was first introduced to South and Central Asia in the Middle Ages, and then spread to China, India and Russia. Reverse transfers of genomic segments from Asia to Africa were also observed. The European CCHFV genotype V was introduced to Europe via the Astrakhan region in South Russia 280–400 years ago and subsequently gradually spread westward in Russia, to Turkey and the Balkans less than 150 years ago. Only a few recombination events could be suggested in S and L genomic segments, while segment reassortment was very common. The median height of a non-reassortant phylogenetic tree node was 68–156 years. There were reassortment events within the European CCHFV lineage, but not with viruses from other locations. Therefore, CCHFV in Europe is a recently emerged zoonosis that represents a spillover from the global gene pool.

Development of pan-phlebovirus RT-PCR assay

This study reports the pan-phlebovirus assay capable of detecting both sandfly/mosquito- and tick-borne phleboviruses. Sensitivity and specificity of the assay was verified using a panel of arboviruses. The RT-PCR assay is simple and sensitive, and thus well suited for screening of field samples.