Arboviruses and their related infections in China: A comprehensive field and laboratory investigation over the last 3 decades

Epidemiological Characterization of Dengue Fever - Yunnan Province, China, 2010-2021

Objective

The goal of this study is to analyze the epidemiological patterns of dengue fever across different districts and counties in Yunnan Province from 2010 to 2021.

Methods

In this study, we employed joinpoint regression analysis, spatial autocorrelation analysis, and space-time scan analysis to illustrate the spatio-temporal propagation and demographic influence of dengue fever, using both graphical and tabular presentations to clearly demonstrate the findings.

Results

Yunnan Province reported 14,098 cases of dengue fever during the period from 2010 to 2021. Of these, 11,513 cases were caused by local transmission, 2,566 were imported internationally, and 19 were inter-provincial imports. Seasonal trends emerged, revealing a surge in incidences during the summer and autumn months. The sex ratio of male to female cases was 1:0.88, with a significant majority of 82.00% of cases involving individuals belonging to the age group of 15-60. Commercial service workers constituted the most impacted occupational group, forming 20.96% of total cases. A spatio-temporal scan identified significant clustering of dengue fever cases across space and time, with the most pronounced cluster observed in southern Yunnan, primarily between 2015 and 2019.

Conclusions

Dengue fever in Yunnan Province manifests as biennial outbreaks, underscoring the necessity for increased surveillance, particularly in counties bordering other regions.

Genome and evolution of Tibet orbivirus, TIBOV (genus Orbivirus, family Reoviridae)

Tibet orbivirus (TIBOV) was first isolated from Anopheles maculatus mosquitoes in Xizang, China, in 2009. In recent years, more TIBOV strains have been isolated in several provinces across China, Japan, East Asia, and Nepal, South Asia. Furthermore, TIBOVs have also been isolated from Culex mosquitoes, and several midge species. Additionally, TIBOV neutralizing antibodies have been detected in serum specimens from several mammals, including cattle, sheep, and pigs. All of the evidence suggests that the geographical distribution of TIBOVs has significantly expanded in recent years, with an increased number of vector species involved in its transmission. Moreover, the virus demonstrated infectivity towards a variety of animals. Although TIBOV is considered an emerging orbivirus, detailed reports on its genome and molecular evolution are currently lacking. Thus, this study performed the whole-genome nucleotide sequencing of three TIBOV isolates from mosquitoes and midges collected in China in 2009, 2011, and 2019. Furthermore, the genome and molecular genetic evolution of TIBOVs isolated from different countries, periods, and hosts (mosquitoes, midges, and cattle) was systematically analyzed. The results revealed no molecular specificity among TIBOVs isolated from different countries, periods, and vectors. Meanwhile, the time-scaled phylogenetic analysis demonstrated that the most recent common ancestor (TMRCA) of TIBOV appeared approximately 797 years ago (95% HPD: 16-2347) and subsequently differentiated at least three times, resulting in three distinct genotypes. The evolutionary rate of TIBOVs was about 2.12 × 10-3 nucleotide substitutions per site per year (s/s/y) (95% HPD: 3.07 × 10-5, 9.63 × 10-3), which is similar to that of the bluetongue virus (BTV), also in the Orbivirus genus. Structural analyses of the viral proteins revealed that the three-dimensional structures of the outer capsid proteins of TIBOV and BTV were similar. These results suggest that TIBOV is a newly discovered and rapidly evolving virus transmitted by various blood-sucking insects. Given the potential public health burden of this virus and its high infectious rate in a wide range of animals, it is significant to strengthen research on the genetic variation of TIBOVs in blood-feeding insects and mammals in the natural environment and the infection status in animals.

Isolation and identification of Tete virus group (Peribunyaviridae: Orthobunyavirus) from Culicoides biting midges collected in Lichuan County, China

In July 2018, a virus (JXLC1806-2) was isolated from Culicoides biting midges collected in Lichuan County, Jiangxi Province, China. The virus isolate showed significant cytopathic effects within 48 hours after inoculation with mammalian cells (BHK-21). JXLC1806-2 virus could form plaques in BHK-21 cells, and the virus titer was 1×105.6 pfu/mL. After inoculation with the virus, suckling mice developed disease and died. The nucleotide and amino sequence analysis showed that the JXLC1806-2 virus genome was composed of S, M and L segments. Phylogenetic analysis showed that the S, M and L genes of JXLC1806-2 virus belonged to the Tete serogroup, Orthobunyavirus, but formed an independent evolutionary branch from the other members of the Tete serogroup. The results showed that the JXLC1806-2 virus, which was named as Lichuan virus, is a new member of Tete serogroup, and this is the first time that a Tete serogroup virus has been isolated in China.

Detection of Viral Genes in Metarhizium anisopliae JEF-290-infected longhorned tick, Haemaphysalis longicornis using transcriptome analysis

Ticks are carriers of viruses that can cause disease in humans and animals. The longhorned ticks (Haemaphysalis longicornis; LHT), for example, mediates the severe fever with thrombocytopenia syndrome virus (SFTSV) in humans, and the population of ticks is growing due to increases in temperature caused by climate change. As ticks carry primarily RNA viruses, there is a need to study the possibility of detecting new viruses through tick virome analysis. In this study, viruses in LHTs collected in Korea were investigated and virus titers in ticks exposed to the entomopathogenic fungus Metarhizium anisopliae JEF-290 were analyzed. Total RNA was extracted from the collected ticks, and short reads were obtained from Illumina sequencing. A total of 50,024 contigs with coding capacity were obtained after de novo assembly of the reads in the metaSPAdes genome assembler. A series of BLAST-based analyses using the GenBank database was performed to screen viral contigs, and three putative virus species were identified from the tick meta-transcriptome, such as Alongshan virus (ALSV), Denso virus and Taggert virus. Measurements of virus-expression levels of infected and non-infected LHTs failed to detect substantial differences in expression levels. However, we suggest that LHT can spread not only SFTSV, but also various other disease-causing viruses over large areas of the world. From the phylogenetic analysis of ALSV glycoproteins, genetic differences in the ALSV could be due to host differences as well as regional differences. Viral metagenome analysis can be used as a tool to manage future outbreaks of disease caused by ticks by detecting unknown viruses.

Crimean-Congo hemorrhagic fever virus in Central, Eastern, and South-eastern Asia

Crimean-Congo hemorrhagic fever (CCHF), caused by Crimean-Congo hemorrhagic fever virus (CCHFV), is endemic in Africa, Asia, and Europe, but CCHF epidemiology and epizootiology is only rudimentarily defined for most regions. Here we summarize what is known about CCHF in Central, Eastern, and South-eastern Asia. Searching multiple international and country-specific databases using a One Health approach, we defined disease risk and burden through identification of CCHF cases, anti-CCHFV antibody prevalence, and CCHFV isolation from vector ticks. We identified 2313 CCHF cases that occurred in 1944-2021 in the three examined regions. Central Asian countries reported the majority of cases (2,026). In Eastern Asia, China was the only country that reported CCHF cases (287). In South-eastern Asia, no cases were reported. Next, we leveraged our previously established classification scheme to assign countries to five CCHF evidence levels. Six countries (China, Kazakhstan, Kyrgyzstan, Tajikistan, Turkmenistan, and Uzbekistan) were assigned to level 1 or level 2 based on CCHF case reports and the maturity of the countries' surveillance systems. Two countries (Mongolia and Myanmar) were assigned to level 3 due to evidence of CCHFV circulation in the absence of reported CCHF cases. Thirteen countries in Eastern and South-eastern Asia were categorized in levels 4 and 5 based on prevalence of CCHFV vector ticks. Collectively, this paper describes the past and present status of CCHF reporting to inform international and local public-health agencies to strengthen or establish CCHFV surveillance systems and address shortcomings.

Genetic Characterization of DH13M98, Umatilla Virus, Isolated from Culex tritaeniorhynchus Giles in Yunnan Province, China

Background: In August 2013, a virus strain (DH13M98) was isolated from Culex tritaeniorhynchus Giles collected in Mangshi, the southwestern border area of Yunnan Province, China. The virus replicated and caused cytopathic effects (CPE) in Aedes albopictus (C6/36) cells, but not in baby hamster Syrian kidney (BHK-21) cells. Materials and Methods: Agarose gel electrophoresis (AGE) analysis revealed that the DH13M98 virus was a 10-segment double-stranded RNA (dsRNA) virus, with a "1-1-1-2-1-1-2-1" pattern. The full genome of the DH13M98 virus was sequenced by full-length amplification of complementary DNAs (FLAC). Results: Phylogenetic analysis of the viral RNA-dependent RNA polymerase (Pol), major subcore-shell (T2), and major core-surface (T13) protein showed that DH13M98 clustered with Umatilla virus (UMAV), and the amino acid (aa) sequences of DH13M98 shared more than 89.5% (Pol), 95% (T2), and 91.1% (T13) identity with UMAV. However, the aa identity of outer capsid protein one (OC1) of DH13M98 with other UMAV was 57.1-79.2%, suggesting that DH13M98 was UMAV, but distinct from other strains of UMAV from the United States, Japan, and Germany at OC1, and it may be a high variant strain of UMAV, even a new serotype. Conclusion: This is the first isolation of UMAV in China, which enriches the resources of virus species in China and provides new insights into the genetic diversity and geographical distribution of the virus.

Optimized In Vitro CRISPR/Cas9 Gene Editing Tool in the West Nile Virus Mosquito Vector, Culex quinquefasciatus

Culex quinquefasciatus mosquitoes are a globally widespread vector of multiple human and animal pathogens, including West Nile virus, Saint Louis encephalitis virus, and lymphatic filariasis. Since the introduction of West Nile virus to the United States in 1999, a cumulative 52,532 cases have been reported to the CDC, including 25,849 (49.2%) neuroinvasive cases and 2456 (5%) deaths. Viral infections elicit immune responses in their mosquito vectors, including the RNA interference (RNAi) pathway considered to be the cornerstone antiviral response in insects. To investigate mosquito host genes involved in pathogen interactions, CRISPR/Cas9-mediated gene-editing can be used for functional studies of mosquito-derived cell lines. Yet, the tools available for the study of Cx. quinquefasciatus-derived (Hsu) cell lines remain largely underdeveloped compared to other mosquito species. In this study, we constructed and characterized a Culex-optimized CRISPR/Cas9 plasmid for use in Hsu cell cultures. By comparing it to the original Drosophila melanogaster CRISPR/Cas9 plasmid, we showed that the Culex-optimized plasmid demonstrated highly efficient editing of the genomic loci of the RNAi proteins Dicer-2 and PIWI4 in Hsu cells. These new tools support our ability to investigate gene targets involved in mosquito antiviral response, and thus the future development of gene-based vector control strategies.

Molecular Characterization of HN1304M, a Cat Que Virus Isolated from Midges in China

The Cat Que orthobunyavirus has been found in mosquitoes, birds, pigs, and humans, suggesting its wide range of hosts and potential public health implications. During arbovirus surveillance in 2013, the HN1304M virus was isolated from naturally occurring Culicoides biting midges in Hunan Province, southern China. The virus was cytopathic to BHK-21 cells and showed stable passage, but was not cytopathic to C6/36 cells. Determination and analysis of the viral genome sequence revealed that HN1304M is an RNA virus with three gene segments, namely, L, M, and S. The nucleotide and amino acid sequence homologies of HN1304M to Cat Que viruses in the Manzanilla species complex were 90.3–99.4%, and 95–100%, respectively, while the homologies to other viruses in this species complex were 74–86.6% and 78.1–96.1%, respectively. A phylogenetic analysis of the viral genes revealed that HN1304M formed an evolutionary branch with other Cat Que viruses isolated from mosquitoes, pigs, birds, and humans, which was completely independent of the other viruses in this complex. The fact that the Cat Que virus was isolated from Culicoides suggests that biting midges may participate in the natural circulation of Cat Que viruses.

Molecular epidemiology of Akabane virus in Taiwan

Background

Akabane virus (AKAV) is a teratogenic and neuropathogenic arbovirus that infects livestock and wild animals. AKAVs are endemic arboviruses from dairy farms in Taiwan in 1989, and the first sequence was detected in cattle with nonsuppurative encephalitis in 1992.

Objectives

This study aims to understand the epidemiological relationships of the akabane viruses between Taiwan and nearby places.

Methods

In this study, 17 specimens were identified or isolated from vector insects, and ruminant fetuses collected from 1992 to 2015 were sequenced and analysed.

Results

Sequence analyses revealed all Taiwanese AKAVs belonged to genogroup Ia but diverged into two clusters in the phylogenetic trees, implying that at least two invasive events of AKAV may have occurred in Taiwan.

Conclusions

The two clusters of AKAVs could still be identified in Taiwan in 2015, and a reassortment event was observed, indicating that the two clusters of AKAVs are already endemic in Taiwan.

Total RNA sequencing of Phlebotomus chinensis, a neglected vector in China, simultaneously revealed viral, bacterial, and eukaryotic microbes that are potentially pathogenic to humans

Phlebotomus chinensis sandfly is a neglected insect vector in China that is well-known for carrying Leishmania. Recent studies have expanded its pathogen repertoire with two novel arthropod-borne phleboviruses capable of infecting humans and animals. Despite these discoveries, our knowledge of the general pathogen diversity and overall microbiome composition of this vector species is still very limited. Here we carried out a meta-transcriptomics analysis that revealed the actively replicating/transcribing RNA viruses, DNA viruses, bacteria, and eukaryotic microbes, namely, the “total microbiome”, of several sandfly populations in China. Strikingly, “microbiome” made up 1.8% of total non-ribosomal RNA and comprised more than 87 species, among which 70 were novel, including divergent members of the genera Flavivirus and of the family Trypanosomatidae. Importantly, among these microbes we were able to reveal four distinguished types of human and/or mammalian pathogens, including two phleboviruses (hedi and wuxiang viruses), one novel Spotted fever group rickettsia, as well as a member of Leishmania donovani complex, among which hedi virus and Leishmania each had > 50% pool prevalence rate and relatively high abundance levels. Our study also showed the ubiquitous presence of an endosymbiont, namely Wolbachia, although no anti-viral or anti-pathogen effects were detected based on our data. In summary, our results uncovered the much un-explored diversity of microbes harboured by sandflies in China and demonstrated that high pathogen diversity and abundance are currently present in multiple populations, implying disease potential for exposed local human population or domestic animals.

Vector competence and immune response of Aedes aegypti for Ebinur Lake virus, a newly classified mosquito-borne orthobunyavirus

The global impact of mosquito-borne diseases has increased significantly over recent decades. Ebinur Lake virus (EBIV), a newly classified orthobunyavirus, is reported to be highly pathogenic in adult mice. The evaluation of vector competence is essential for predicting the arbovirus transmission risk. Here, Aedes aegypti was applied to evaluate EBIV infection and dissemination in mosquitos. Our experiments indicated that Ae. aegypti had the possibility to spread EBIV (with a transmission rate of up to 11.8% at 14 days post-infection) through biting, with the highest viral dose in a single mosquito’s saliva reaching 6.3 plaque-forming units. The highest infection, dissemination and ovary infection rates were 70%, 42.9%, and 29.4%, respectively. The high viral infection rates in Ae. aegypti ovaries imply the possibility of EBIV vertical transmission. Ae. aegypti was highly susceptible to intrathoracic infection and the saliva-positive rate reached 90% at 10 days post-infection. Transcriptomic analysis revealed Toll and Imd signaling pathways were implicated in the mosquito’s defensive response to EBIV infection. Defensin C and chitinase 10 were continuously downregulated in mosquitoes infected via intrathoracic inoculation of EBIV. Comprehensive analysis of the vector competence of Ae. aegypti for EBIV in laboratory has indicated the potential risk of EBIV transmission through mosquitoes. Moreover, our findings support a complex interplay between EBIV and the immune system of mosquito, which could affect its vector competence.

Re-isolation of Wuxiang Virus from Wild Sandflies Collected from Yangquan County, China

We previously isolated a new species of the genus Phlebovirus from wild sandflies collected from Wuxiang County in central China, which named the Wuxiang virus (WUXV). In this study, we re-isolated the WUXV from wild sandflies collected from two villages in Yangquan County, China in 2019. Four virus isolates that caused cytopathic effects in BHK-21 cells were successfully isolated from sandfly specimens collected from chicken pens and sheep pens. Phylogenetic analyses of the L, M and S gene segments of the viruses revealed that the four virus strains represented the previously isolated WUXV. The minimum infection rate (MIR) of the virus isolated from the sheep pen was 3.21, and the MIR of the virus isolated from the chicken pen was 3.45. The positive rates of Wuxiang virus neutralizing antibodies in serum samples of local healthy people and domestic chickens were 8.7% (4/46) and 100% (4/4), respectively, suggesting that Wuxiang virus can infect human and animal. In view of the fact that Wuxiang virus is infectious to humans and animals and has a relatively wide geographical distribution in China, it is of great public health significance to strengthen the investigation and study on the infection status of Wuxiang virus in humans and animals.

Isolation and Identification of a Novel Phlebovirus, Hedi Virus, from Sandflies Collected in China

We report the isolation of a newly recognized phlebovirus, Hedi virus (HEDV), from Phlebotomus chinensis sandflies collected in Shanxi Province, China. The virus’ RNA is comprised of three segments. The greatest amino acid sequence similarity of the three gene segments between this virus and previously recognized phleboviruses is 40.85–63.52%, and the RNA-dependent RNA polymerase (RdRp) amino acid sequence has the greatest similarity (63.52%) to the Rift Valley fever virus (RVFV) ZH-548 strain. Phylogenetic analysis of the amino acid sequence of the virus RdRp indicated that HEDV is close to RVFV and distinct from other phleboviruses, forming its own evolutionary branch. We conclude that it is necessary to increase the monitoring of phleboviruses carried by sandflies in China.

Molecular epidemiology of mosquito-borne viruses at the China-Myanmar border: discovery of a potential epidemic focus of Japanese encephalitis

BACKGROUND

Mosquito-based arbovirus surveillance can serve as an early warning in evaluating the status of mosquito-borne virus prevalence and thus prevent local outbreaks. Although Tengchong County in Yunnan Province-which borders Myanmar-is abundant and diverse in mosquitoes, very few mosquito-based arbovirus investigations have been conducted in the recent decade. Herein, this study aims to evaluate the presence and the diffusion of mosquito-borne pathogens, currently prevalent in this region.

METHODS

We collected 9486 mosquitoes, representing eight species, with Culex tritaeniorhynchus and Anopheles sinensis as the dominant species, during high mosquito activity seasons (July-October) in Tengchong, in 2018. Samples collected from 342 pools were tested using reverse-transcription PCR to determine the species, distribution, and infection rates of virus and parasite, and further analyze their genotypes, phylogenetic relationships, infection rate, and potential pathogenicity.

RESULTS

Fifteen Japanese encephalitis virus (JEV) strains from Cx. tritaeniorhynchus pools were detected. Seven strains of insect-specific flaviviruses (ISFVs), including two Aedes flavivirus (AeFV) and Yunnan Culex flavivirus strains each, one Culex theileri flavivirus, Yamadai flavivirus (YDFV) and Anopheles-associated flavivirus (AAFV) strains each were detected in Aedes albopictus, Cx. tritaeniorhynchus, Cx. vagans, Cx. pseudovihnui, and An. sinensis pools, respectively. The whole-genome was successfully amplified in one strain of JEV and AeFV each. Phylogenetic analysis using the E gene placed all the newly detected JEV strains into the GI-b genotype. They showed highly nucleotide identities, and were most closely related to the strain detected in Tengchong in 2010. The comparison of the E protein of JEV strains and vaccine-derived strain, showed six amino residue differences. The bias-corrected maximum likelihood estimation values (and 95% confidence interval) for JEV in Cx. tritaeniorhynchus collected in Tengchong in 2018 were 2.4 (1.4-3.9).

CONCLUSIONS

A potential Japanese encephalitis epidemic focus with the abundance of host mosquitoes and high JEV infection rate was observed in Tengchong. In addition, at least five species of ISFVs co-circulate in this area. This study highlights the importance of widespread and sustained mosquito-based arbovirus surveillance in local areas to prevent the transmission of JEV, and other emerging/re-emerging mosquito-borne pathogens.

Metagenomic sequencing reveals viral abundance and diversity in mosquitoes from the Shaanxi-Gansu-Ningxia region, China

BACKGROUND

Mosquitoes host and transmit numerous arthropod-borne viruses (arboviruses) that cause disease in both humans and animals. Effective surveillance of virome profiles in mosquitoes is vital to the prevention and control of mosquito-borne diseases in northwestern China, where epidemics occur frequently.

METHODS

Mosquitoes were collected in the Shaanxi-Gansu-Ningxia region (Shaanxi Province, Gansu Province, and Ningxia Hui Autonomous Region) of China from June to August 2019. Morphological methods were used for taxonomic identification of mosquito species. High-throughput sequencing and metagenomic analysis were used to characterize mosquito viromes.

RESULTS

A total of 22,959 mosquitoes were collected, including Culex pipiens (45.7%), Culex tritaeniorhynchus (40.6%), Anopheles sinensis (8.4%), Aedes (5.2%), and Armigeres subalbatus (0.1%). In total, 3,014,183 (0.95% of clean reads) viral sequences were identified and assigned to 116 viral species (including pathogens such as Japanese encephalitis virus and Getah virus) in 31 viral families, including Flaviviridae, Togaviridae, Phasmaviridae, Phenuiviridae, and some unclassified viruses. Mosquitoes collected in July (86 species in 26 families) showed greater viral diversity than those from June and August. Culex pipiens (69 species in 25 families) and Culex tritaeniorhynchus (73 species in 24 families) carried more viral species than Anopheles sinensis (50 species in 19 families) or Aedes (38 species in 20 families) mosquitoes.

CONCLUSION

Viral diversity and abundance were affected by mosquito species and collection time. The present study elucidates the virome compositions of various mosquito species in northwestern China, improving the understanding of virus transmission dynamics for comparison with those of disease outbreaks.

Wuxiang Virus Is a Virus Circulated Naturally in Wuxiang County, China

Background: Wuxiang virus was isolated from sandfly specimens collected in Wuxiang County, Shanxi Province, China in 2018, representing the first reported isolation of sandfly-borne virus from sandflies collected in a natural environment in China. The local sandfly density, seasonal fluctuations, and temporal and spatial distributions of the virus in Wuxiang County remain unclear. Materials and Methods: Four fixed sandfly collection sites were set up in Wuxiang County and sandfly specimens were collected continuously from June to August 2019. All sandfly specimens were subjected to viral isolation and molecular biological analysis. Results: The data on sandfly specimens collected in Wuxiang County from June to August 2019 showed a significant difference in the density of sandflies between June 26 and August 16 (p < 0.05). No statistical difference was found in sandfly density among collection sites (p > 0.05). A total of 33 virus isolates causing cytopathic effects in mammalian (BHK-21) cells were obtained from 7466 sandflies (91 pools) collected from June to August 2019. The results of molecular genetic evolution analysis of the nucleotide sequence of these isolates showed that the L and S genes (encoding NS and N proteins) of the 33 viruses isolated in 2019 are in the same evolutionary branch as the previously isolated Wuxiang virus. No significant difference was found in the virus isolation rate (the pool isolation rate of virus) among sandflies collected at different times from June to August (p > 0.05). The virus isolation rate of sandflies collected at different collection sites showed a statistically significant difference (p < 0.05). Conclusions: The results of this study suggest that the Wuxiang virus is a stable viral population in local sandflies. Strengthened research into Wuxiang virus infection of humans and animals and clarification of the public health hazards posed by Wuxiang virus to both humans and animals are urgently needed.

A Metagenomic Analysis of Mosquito Virome Collected From Different Animal Farms at Yunnan-Myanmar Border of China

Metagenomic analysis of mosquito-borne and mosquito-specific viruses is useful to understand the viral diversity and for the surveillance of pathogens of medical and veterinary importance. Yunnan province is located at the southwest of China and has rich abundance of mosquitoes. Arbovirus surveillance is not conducted regularly in this province particularly at animal farms, which have public health as well as veterinary importance. Here, we have analyzed 10 pools of mosquitoes belonging to Culex tritaeniorhyncus, Aedes aegypti, Anopheles sinensis, and Armigeres subalbatus species, collected from different animal farms located at Yunnan province of China by using metagenomic next-generation sequencing technique. The generated viral metagenomic data reveal that the viral community matched by the reads was highly diverse and varied in abundance among animal farms, which contained more than 19 viral taxonomic families, specific to vertebrates, invertebrates, fungi, plants, protozoa, and bacteria. Additionally, a large number of viral reads were related to viruses that are non-classified. The viral reads related to animal viruses included parvoviruses, anelloviruses, circoviruses, flaviviruses, rhabdoviruses, and seadornaviruses, which might be taken by mosquitoes from viremic animal hosts during blood feeding. Notably, the presence of viral reads matched with Japanese encephalitis virus, Getah virus, and porcine parvoviruses in mosquitoes collected from different geographic sites suggested a potential circulation of these viruses in their vertebrate hosts. Overall, this study provides a comprehensive knowledge of diverse viral populations present at animal farms of Yunnan province of China, which might be a potential source of diseases for humans and domestic animals.

Emergence of Zika Virus in Culex tritaeniorhynchus and Anopheles sinensis Mosquitoes in China

Zika virus (ZIKV) has been isolated from mosquitoes such as Aedes, Mansonia uniformis, and Culex perfuscus; However, the isolation of ZIKV from Anopheles sinensis and Culex tritaeniorhynchus has not yet been reported. In June and July 2018, 22,985 mosquitoes and 57,500 midges were collected in Jiangxi Province in southeastern China. Among them, six strains of ZIKV were isolated from mosquitoes: four from An. sinensis and two from Cx. tritaeniorhynchus. Molecular genetic analysis showed that the ZIKV isolated from An. sinensis and Cx. tritaeniorhynchus belonged to genotype 2 in the Asian evolutionary branch of ZIKV. In addition, the ZIKV strains isolated from An. sinensis and Cx. tritaeniorhynchus had amino acid substitutions identical to ZIKV strains prevalent in South America since 2015. This study is the first to isolate ZIKV from mosquito specimens collected in the wild of Jiangxi Province, China; This is also the first time that ZIKV has been isolated from An. sinensis and Cx. tritaeniorhynchus. Given that An. sinensis and Cx. tritaeniorhynchus have a very wide geographical distribution in China and even in eastern and southern Asia, the isolation of several strains of ZIKV from these two mosquitoes poses new challenges for the prevention and control of ZIKV infection in the mainland of China and countries and regions with the same distribution of mosquitoes.

Spatial heterogeneity and temporal dynamics of mosquito population density and community structure in Hainan Island, China

BACKGROUND

Mosquitoes are vectors of many tropical diseases. Understanding the ecology of local mosquito vectors, such as species composition, distributions, population dynamics, and species diversity is important for designing the optimal strategy to control the mosquito-borne diseases.

METHODS

Entomological surveillance of adult mosquitoes was conducted in five sites representing different ecological settings across Hainan Island from January to December of 2018 using BG Sentinel (BGS) traps and Centers for Disease Prevention and Control (CDC) light traps. In each site, we selected three areas representing urban, suburban and rural settings. Eighteen trap-days were sampled in each setting at each site, and CDC light traps and BGS traps were setup simultaneously. Mosquito species composition, distribution, population dynamics, and species diversity were analyzed. Mosquito densities were compared between different study sites and between different settings.

RESULTS

Nine species of mosquitoes belonging to four genera were identified. Culex quinquefasciatus (80.8%), Armigeres subalbatus (13.0%) and Anopheles sinensis (3.1%) were the top three species collected by CDC light traps; Cx. quinquefasciatus (91.9%), Ae. albopictus (5.1%), and Ar. subalbatus (2.8%) were the top three species collected by BGS traps. Predominant species varied among study sites. The population dynamics of Ae. albopictus, An. sinensis and Cx. quinquefasciatus showed clear seasonal variation regardless of study sites with a varied peak season for different species. Mosquito abundance of all species showed significant differences among different study sites and among urban, suburban and rural areas. Danzhou had the highest mosquito biodiversity, with an α, β, and Gini-Simpson biodiversity index of 8, 1.13 and 0.42, respectively. BGS traps captured Aedes mosquito at a higher efficiency than CDC light traps, whereas CDC light traps captured significantly more Anopheles and Armigeres mosquitoes than BGS traps.

CONCLUSIONS

Mosquitoes were abundant on Hainan Island with clear seasonality and spatial heterogeneity. Population density, species composition, distribution, and species diversity were strongly affected by the natural environment. Different tools are required for the surveillance of different mosquito species.

Depicting the RNA Virome of Hematophagous Arthropods from Belgrade, Serbia

Hematophagous arthropods are important vectors for zoonotic pathogens. To date, a huge number of viruses have been identified in these arthropods, with a considerable proportion of them being human pathogens. However, the viromes of hematophagous arthropods are still largely unresearched. In this study, a number of arthropods were collected from Belgrade, Serbia including mosquitoes, ticks and bedbugs. The viromes of these arthropods were identified and characterized using Illumina MiSeq sequencing. In total, 21 viruses belonging to 11 families were characterized, with 11 of them representing novel species. These results may contribute to our knowledge of RNA viruses in arthropods and the discovery of novel human pathogens.

Origin and evolution of emerging Liao ning Virus (genus Seadornavirus, family Reoviridae)

Background

Liao ning virus (LNV) is a member of the genus Seadornavirus, family Reoviridae and has been isolated from kinds of vectors in Asia and Australia. However, there are no systematic studies describe the molecular genetic evolution and migration of LNVs. With the development of bioinformatics, viral genetic data combining the information of virus isolation time and locations could be integrated to infer the virus evolution and spread in nature.

Methods

Here, a phylogenetic and phylogeographic analysis using Bayesian Markov chain Monte Carlo simulations was conducted on the LNVs isolated from a variety of vectors during 1990–2014 to identify the evolution and migration patterns of LNVs.

Results

The results demonstrated that the LNV could be divided into 3 genotypes, of which genotype 1 mainly composed of LNVs isolated from Australia during 1990 to 2014 and the original LNV strain (LNV-NE97–31) isolated from Liaoning province in northern China in 1997, genotype 2 comprised of the isolates all from Xinjiang province in western China and genotype 3 consisted the isolates from Qinghai and Shanxi province of central China. LNVs emerged about 272 years ago and gradually evolved into three lineages in the order genotype 1, genotype 2 and genotype 3. Following phylogeographic analysis, it shows genotype 1 LNVs transmitted from Australia (113°E-153°E,10°S-42°S) to Liaoning province (118°E-125°E,38°N-43°N) in Northeast Asian continent then further spread across the central part of China to western China (75°E-95°E,35°N-50°N).

Conclusion

LNVs were initially isolated from Liaoning province of China in the Northeast Asia, however, the present study revealed that LNVs were first appeared in Australia in the South Pacific region and transmitted to mainland China then rapidly spread across China and evolved three different genotypes. The above results suggested that LNV had the characteristics of long-distance transmission and there were great genetic diversity existed in the LNV population. Notably, current information of 80 strains of LNVs are limited. It is of great importance to strengthen the surveillance of LNVs to explore its real origin in nature and monitoring of the LNVs’ population variation and maintain vigilance to avoid LNV breaking through the species barrier and further clarify its relationship to human and animal infection.

Genomic and biological features of a novel orbivirus isolated from mosquitoes, in China

A novel orbivirus had been identified as a member of the Orbivirus genus, which was isolated from pooled Culex fatigans mosquitoes in Guangdong of China, named as the Fengkai virus (FKOV). The cytopathic effects (CPEs) on both Aedes albopictus cells (C6/36) and mammalian cell lines (Vero and BHK-21) emerged in the cell cultures inoculated above virus in. Experimental confirmation as the Orbivirus genus was conducted by the Real-time PCR and based on Ion Torrent Next-Generation in sequencing. The Identities of VP1, VP2 and VP3 in amino acid sequences between the Tibet orbivirus (TIBOV) and this strain were 98.6%, 42.9%, and 99.9%, respectively, which indicated that this strain shares the same genus (VP1, Pol) and species (VP3, T2) with TIBOV but was greatly different in VP2 and VP5 (10.3%) of TIBOV. The VP2 and VP5 diversities of both TIBOV and FKOV strains suggested both serotypes are distinct with each other. As natural evolution and circulation, this strain might expand its host ranges and infect human beings as a potential and severe pathogen.

Endemic and Emerging Arboviruses in Domestic Ruminants in East Asia

Epizootic congenital abnormalities caused by Akabane, Aino, and Chuzan viruses have damaged the reproduction of domestic ruminants in East Asia for many years. In the past, large outbreaks of febrile illness related to bovine ephemeral fever and Ibaraki viruses severely affected the cattle industry in that region. In recent years, vaccines against these viruses have reduced the occurrence of diseases, although the viruses are still circulating and have occasionally caused sporadic and small-scaled epidemics. Over a long-term monitoring period, many arboviruses other than the above-mentioned viruses have been isolated from cattle and Culicoides biting midges in Japan. Several novel arboviruses that may infect ruminants (e.g., mosquito- and tick-borne arboviruses) were recently reported in mainland China based on extensive surveillance. It is noteworthy that some are suspected of being associated with cattle diseases. Malformed calves exposed to an intrauterine infection with orthobunyaviruses (e.g., Peaton and Shamonda viruses) have been observed. Epizootic hemorrhagic disease virus serotype 6 caused a sudden outbreak of hemorrhagic disease in cattle in Japan. Unfortunately, the pathogenicity of many other viruses in ruminants has been uncertain, although these viruses potentially affect livestock production. As global transportation grows, the risk of an accidental incursion of arboviruses is likely to increase in previously non-endemic areas. Global warming will also certainly affect the distribution and active period of vectors, and thus the range of virus spreads will expand to higher-latitude regions. To prevent anticipated damages to the livestock industry, the monitoring system for arboviral circulation and incursion should be strengthened; moreover, the sharing of information and preventive strategies will be essential in East Asia.

New strains of Japanese encephalitis virus circulating in Shanghai, China after a ten-year hiatus in local mosquito surveillance

BACKGROUND

Continuous vector pathogen surveillance is essential for preventing outbreaks of mosquito-borne diseases. Several mosquito species acting as vectors of Japanese encephalitis virus (JEV), dengue virus, Zika virus, malaria parasites and other pathogens are primary mosquito species in Shanghai, China. However, few surveys of human pathogenic arboviruses in mosquitoes in Shanghai have been reported in the last ten years. Therefore, in this study, we evaluated mosquito activity in Shanghai, China during 2016 and tested for the presence of alphaviruses, flaviviruses, orthobunyaviruses and several parasitic pathogens.

RESULTS

Five pooled samples were JEV-positive [4/255 pools of Culex tritaeniorhynchus and 1/256 pools of Cx. pipiens (s.l.)] based on analysis of the NS5 gene. Alphaviruses, orthobunyaviruses, Plasmodium and filariasis were not found in this study. Phylogenetic and molecular analyses revealed that the JEV strains belonged to genotype I. Moreover, newly detected Shanghai JEV strains were genetically close to previously isolated Shandong strains responsible for transmission during the 2013 Japanese encephalitis (JE) outbreak in Shandong Province, China but were more distantly related to other Shanghai strains detected in the early 2000s. The E proteins of the newly detected Shanghai JEV strains differed from that in the live attenuated vaccine SA14-14-2-derived strain at six amino residues: E130 (Ile→Val), E222 (Ala→Ser), E327 (Ser→Thr), E366 (Arg→Ser/Pro), E393 (Asn→Ser) and E433 (Val→Ile). However, no differences were observed in key amino acid sites related to antigenicity. Minimum JEV infection rates were 1.01 and 0.65 per 1000 Cx. tritaeniorhynchus and Cx. pipiens (s.l.), respectively.

CONCLUSIONS

Five new Shanghai JEV genotype I strains, detected after a ten-year hiatus in local mosquito surveillance, were genetically close to strains involved in the 2013 Shandong JE outbreak. Because JEV is still circulating, vaccination in children should be extensively and continuously promoted. Moreover, JEV mosquito surveillance programmes should document the genotype variation, intensity and distribution of circulating viruses for use in the development and implementation of disease prevention and control strategies.

Correlation between adult pyrethroid resistance and knockdown resistance (kdr) mutations in Aedes albopictus (Diptera: Culicidae) field populations in China

BACKGROUND

Arboviral disease transmitted by Aedes albopictus such as dengue fever is an important threat to human health. Pyrethroid resistance raises a great challenge for mosquito control. A systematic assessment of Ae. albopictus resistance status in China is urgently needed, and the study of correlation between pyrethroid resistance and knockdown resistance (kdr) mutations would provide information to guide the control of the Ae. albopictus vector.

METHODS

Five field populations of Ae. albopictus were collected from Jinan (JN), Hangzhou (HZ), Baoshan (BS), Yangpu (YP) and Haikou (HK), China in 2017. Insecticide-impregnated papers were prepared with four pyrethroid chemicals, deltamethrin, permethrin, beta-cypermethrin and lambda-cyhalothrin. The susceptibility of Ae. albopictus to pyrethroids was tested by the WHO tube assay. Kdr mutations were identified by PCR and sequencing. Moreover, the correlation analysis between kdr alleles and pyrethroid resistance was performed.

RESULTS

All five populations of Ae. albopictus showed resistance to four pyrethroid insecticides. One kdr mutant allele at codon 1532 and three at 1534 were detected with frequency of 5.33% (I1532T), 44.20% (F1534S), 1.83% (F1534 L) and 0.87% (F1534C), respectively. Both 1532 and 1534 mutation mosquitoes were found in the BS and YP populations. Allele I1532T was negatively correlated with deltamethrin resistance phenotype (OR < 1), while F1534S mutation was positively correlated with deltamethrin and permethrin resistance (OR > 1).

CONCLUSIONS

The five field populations of Ae. albopictus adults were all resistant to deltamethrin, permethrin, beta-cypermethrin and lambda-cyhalothrin. Mutant F1534S was clearly associated with pyrethroid resistance phenotype in Ae. albopictus and this could be developed as a molecular marker to monitor the pyrethroid resistance problem in China.