Isolation and sequence analysis of Culex flavivirus from Culex interrogator and Culex quinquefasciatus in the Yucatan Peninsula of Mexico

Novel strains of Culex flavivirus and Hubei chryso-like virus 1 from the Anopheles mosquito in western Kenya

Surveillance of mosquito vectors is critical for early detection, prevention and control of vector borne diseases. In this study we used advanced molecular tools, such as DNA barcoding in combination with novel sequencing technologies to discover new and already known viruses in genetically identified mosquito species. Mosquitoes were captured using BG sentinel traps in Western Kenya during May and July 2019, and homogenized individually before pooled into groups of ten mosquitoes. The pools and individual samples were then used for molecular analysis and to infect cell cultures. Of a total of fifty-four (54) 10-pools, thirteen (13) showed cytopathic effect (CPE) on VeroB4 cells, eighteen (18) showed CPE on C6/36 cells. Eight (8) 10-pools out of the 31 CPE positive pools showed CPE on both VeroB4 and C6/36 cells. When using reverse transcriptase polymerase chain reaction (RT-PCR), Sanger sequencing and Twist Comprehensive Viral Research Panel (CVRP) (Twist Biosciences), all pools were found negative by RT-PCR when using genus specific primers targeting alphaviruses, orthobunyaviruses and virus specific primers towards o'nyong-nyong virus, chikungunya virus and Sindbis virus (previously reported to circulate in the region). Interestingly, five pools were RT-PCR positive for flavivirus. Two of the RT-PCR positive pools showed CPE on both VeroB4 and C6/36 cells, two pools showed CPE on C6/36 cells alone and one pool on VeroB4 cells only. Fifty individual mosquito homogenates from the five RT-PCR positive 10-pools were analyzed further for flavivirus RNA. Of these, 19 out of the 50 individual mosquito homogenates indicated the presence of flavivirus RNA. Barcoding of the flavivirus positive mosquitoes revealed the mosquito species as Aedes aegypti (1), Mansonia uniformis (6), Anopheles spp (3), Culex pipiens (5), Culex spp (1), Coquilletidia metallica (2) and Culex quinquefasciatus (1). Of the 19 flavivirus positive individual mosquitoes, five (5) virus positive homogenates were sequenced. Genome sequences of two viruses were completed. One was identified as the single-stranded RNA Culex flavivirus and the other as the double-stranded RNA Hubei chryso-like virus 1. Both viruses were found in the same Anopheles spp. homogenate extracted from a sample that showed CPE on both VeroB4 and C6/36 cells. The detection of both viruses in a single mosquito homogenate indicated coinfection. Phylogenetic analyses suggested that the Culex flavivirus sequence detected was closely related to a Culex flavivirus isolated from Uganda in 2008. All four Hubei chryso-like virus 1 segments clusters closely to Hubei chryso-like virus 1 strains isolated in Australia, China and USA. Two novel strains of insect-specific viruses in Anopheles mosquitoes were detected and characterized.

Rapid Generation of Recombinant Flaviviruses Using Circular Polymerase Extension Reaction

The genus Flavivirus is a group of arthropod-borne single-stranded RNA viruses, which includes important human and animal pathogens such as Japanese encephalitis virus (JEV), Zika virus (ZIKV), Dengue virus (DENV), yellow fever virus (YFV), West Nile virus (WNV), and Tick-borne encephalitis virus (TBEV). Reverse genetics has been a useful tool for understanding biological properties and the pathogenesis of flaviviruses. However, the conventional construction of full-length infectious clones for flavivirus is time-consuming and difficult due to the toxicity of the flavivirus genome to E. coli. Herein, we applied a simple, rapid, and bacterium-free circular polymerase extension reaction (CPER) method to synthesize recombinant flaviviruses in vertebrate cells as well as insect cells. We started with the de novo synthesis of the JEV vaccine strain SA-14-14-2 in Vero cells using CPER, and then modified the CPER method to recover insect-specific flaviviruses (ISFs) in mosquito C6/36 cells. Chimeric Zika virus (ChinZIKV) based on the Chaoyang virus (CYV) backbone and the Culex flavivirus reporter virus expressing green fluorescent protein (CxFV-GFP) were subsequently rescued in C6/36 cells. CPER is a simple method for the rapid generation of flaviviruses and other potential RNA viruses. A CPER-based recovery system for flaviviruses of different host ranges was established, which would facilitate the development of countermeasures against flavivirus outbreaks in the future.

Employing Oxford Nanopore Technologies (ONT) for understanding the ecology and transmission dynamics of flaviviruses in mosquitoes (Diptera: Culicidae) from eastern Colombia

Studies focused on identifying the viral species of Flavivirus in vectors are scarce in Latin America and particularly in Colombia. Therefore, the frequency of infection of the Flavivirus genus and its feeding preferences were identified in the mosquito species circulating in the municipality of Puerto Carreño-Vichada, located in the Eastern Plains of Colombia. This was done by sequencing the viral NS5 and vertebrate 12S rRNA genes, respectively, using Oxford Nanopore Technologies (ONT). A total of 1,159 mosquitoes were captured, with the most abundant species being Aedes serratus at 73.6% (n=853). All the mosquitoes were processed in 230 pools (2-6 individuals) and 51 individuals, where 37.01% (n=104) were found to be infected with Flavivirus. In these samples, infection by arboviruses of epidemiological importance, such as dengue virus (DENV), Zika virus (ZIKV), and chikungunya virus (CHIKV), was ruled out by PCR. However, through sequencing, infection by different insect-specific viruses (ISFVs) and a medically important virus, West Nile virus (WNV), were identified in a mosquito of the Culex browni species. Additionally, the feeding patterns showed that most species present a generalist behavior. Given the above, conducting entomovirological surveillance studies is crucial, especially in areas of low anthropogenic intervention, due to the high probability that potentially pathogenic viruses could generate spillover events under deforestation scenarios.

Chimeric Vaccines Based on Novel Insect-Specific Flaviviruses

Vector-borne flaviviruses are responsible for nearly half a billion human infections worldwide each year, resulting in millions of cases of debilitating and severe diseases and approximately 115,000 deaths. While approved vaccines are available for some of these viruses, the ongoing efficacy, safety and supply of these vaccines are still a significant problem. New technologies that address these issues and ideally allow for the safe and economical manufacture of vaccines in resource-poor countries where flavivirus vaccines are in most demand are urgently required. Preferably a new vaccine platform would be broadly applicable to all flavivirus diseases and provide new candidate vaccines for those diseases not yet covered, as well as the flexibility to rapidly pivot to respond to newly emerged flavivirus diseases. Here, we review studies conducted on novel chimeric vaccines derived from insect-specific flaviviruses that provide a potentially safe and simple system to produce highly effective vaccines against a broad spectrum of flavivirus diseases.

Monitoring Mosquito-Borne Arbovirus in Various Insect Regions in China in 2018

Background

Increases in global travel and trade are changing arbovirus distributions worldwide. Arboviruses can be introduced by travelers, migratory birds, or vectors transported via international trade. Arbovirus surveillance in field-collected mosquitoes may provide early evidence for mosquito-borne disease transmission.

Methods

During the seasons of high mosquito activity of 2018, 29,285 mosquitoes were sampled from seven sentinel sites in various insect regions. The mosquitoes were analyzed by RT-PCR for alphaviruses, flaviviruses, and orthobunyaviruses.

Results

We detected three strains of Japanese encephalitis virus (JEV), five strains of Getah virus (GETV), and 45 strains of insect-specific flaviviruses including Aedes flavivirus (AeFV, 1), Chaoyang virus (CHAOV, 1), Culex flavivirus (CxFV, 17), Hanko virus (HANKV, 2), QuangBinh virus (QBV, 22), and Yunnan Culex flavivirus (YNCxFV, 2). Whole genomes of one strain each of GETV, CxFV, CHAOV, and AeFV were successfully amplified. Phylogenetic analysis revealed that the new JEV strains detected in the Shanghai and Hubei Provinces belong to the GI-b strain and are phylogenetically close to the NX1889 strain (MT134112) isolated from a patient during a JE outbreak in Ningxia in 2018. GETVs were found in Inner Mongolia, Hubei, and Hainan and belonged to Group III. They were closely related to strains isolated from swine. HANKV was recorded for the first time in China and other ISFVs were newly detected at several sentinel sites. The bias-corrected maximum likelihood estimation value for JEV in Jinshan, Shanghai was 4.52/1,000 (range 0.80-14.64). Hence, there is a potential risk of a JEV epidemic in that region.

Conclusion

GI-b is the dominant circulating JEV genotype in nature and poses a health risk to animals and humans. The potential threat of widespread GETV distribution as a zoonosis is gradually increasing. The present study also disclosed the dispersion and host range of ISFVs. These findings highlight the importance of tracing the movements of the vectors and hosts of mosquito-borne pathogens in order to prevent and control arbovirus outbreaks in China.

A Novel Highly Divergent Strain of Cell Fusing Agent Virus (CFAV) in Mosquitoes from the Brazilian Amazon Region

Classical insect-specific flaviviruses (cISFs) have been widely detected in different countries in the last decades. Here, we characterize the near full-length genomes of two cISFs detected in mosquitoes collected in the city of Macapá, state of Amapá, Amazon region of Brazil. A total of 105 pools of female mosquitos were analyzed by next-generation sequencing (NGS). Comparative genomics and phylogenetic analysis identified three strains of cell fusing agent virus (CFAV) and two of Culex flavivirus (CxFV). All sequences were obtained from pools of Culex sp., except for one sequence of CFAV detected in a pool of Aedes aegypti. Both CxFV strains are phylogenetically related to a strain isolated in 2012 in the Southeast region of Brazil. The CFAV strains are the first of this species to be identified in Brazil and one of them is highly divergent from other strains of CFAV that have been detected worldwide. In conclusion, CFAV and CxFV, circulate in mosquitoes in Brazil. One strain of CFAV is highly divergent from others previously described, suggesting that a novel strain of CFAV is present in this region.

Detection of novel and recognized RNA viruses in mosquitoes from the Yucatan Peninsula of Mexico using metagenomics and characterization of their in vitro host ranges

A metagenomics approach was used to detect novel and recognized RNA viruses in mosquitoes from the Yucatan Peninsula of Mexico. A total of 1359 mosquitoes of 7 species and 5 genera (Aedes, Anopheles, Culex, Mansonia and Psorophora) were sorted into 37 pools, homogenized and inoculated onto monolayers of Aedes albopictus (C6/36) cells. A second blind passage was performed and then total RNA was extracted and analysed by RNA-seq. Two novel viruses, designated Uxmal virus and Mayapan virus, were identified. Uxmal virus was isolated from three pools of Aedes (Ochlerotatus) taeniorhynchus and phylogenetic data indicate that it should be classified within the recently proposed taxon Negevirus. Mayapan virus was recovered from two pools of Psorophora ferox and is most closely related to unclassified Nodaviridae-like viruses. Two recognized viruses were also detected: Culex flavivirus (family Flaviviridae) and Houston virus (family Mesoniviridae), with one and two isolates being recovered, respectively. The in vitro host ranges of all four viruses were determined by assessing their replicative abilities in cell lines of avian, human, monkey, hamster, murine, lepidopteran and mosquito (Aedes, Anopheles and Culex) origin, revealing that all viruses possess vertebrate replication-incompetent phenotypes. In conclusion, we report the isolation of both novel and recognized RNA viruses from mosquitoes collected in Mexico, and add to the growing plethora of viruses discovered recently through the use of metagenomics.

Co-circulation of Aedes flavivirus, Culex flavivirus, and Quang Binh virus in Shanghai, China

Background

With increases in global travel and trade, the spread of arboviruses is undoubtedly alarming. Pathogen detection in field-caught mosquitoes can provide the earliest possible warning of transmission. Insect-specific flavivirus (ISFV) has been first detected in 1991 and documented worldwide in the latest ten years. Although infection with ISFVs is apparently limited to insects, an increase in the infection rate of mosquito-borne flaviviruses may be able to induce cytopathic effects in vertebrate cells during co-infection with other human pathogens. However, little is known whether ISFVs persist in most regions of China.

Methods

During the mosquito activity season in 2016, a surveillance program was carried out to detect ISFVs in mosquitoes in metropolitan Shanghai, China. The presence of ISFVs was randomly tested in different species of mosquitoes using RT-PCR-based and hemi-nested PCR assays, following by the sequencing of PCR products. Sequences from positive pooled samples were compared with those deposited in GenBank. Thereafter, sequences of representative insect flaviviruses were used for further phylogenetic and molecular evolutionary analyses.

Results

Our investigations showed: (1) the presence of Aedes flavivirus (AEFV) in 11/161 pooled samples (nine pools in Songjiang District, one pool in Huangpu District, and one pool in Qingpu District) of Aedes albopictus, (2) the presence of Quang Binh virus (QBV) in 10/195 pooled samples (all in Chongming District) of Culex tritaeniorhynchus; and (3) the presence of Culex flavivirus (CxFV) in 9/228 pooled samples (six pools in Pudong New Area, two pools in Huangpu District, and one pool in Chongming District) of Cx. pipiens. Furthermore, phylogenetic analyses of the gene sequences of envelope proteins indicated that Shanghai CxFV strains belonged to the Asia/USA genotype. The overall maximum likelihood estimation values (and 95% confidence interval) for CxFV, QBV, and AEFV in mosquitoes collected in Shanghai in 2016 were 1.34 (0.66–2.45), 1.65 (0.87–2.85), and 1.51 (0.77–2.70) per 1000, respectively.

Conclusions

This study reveals the presence and the geographical distribution of ISFVs, and determines the genetic variation and the infection rate of ISFVs in Shanghai, China. At least, three insect flaviviruses including ISFVs, AEFV, CxFV, and QBV, co-circulate in this area. To our knowledge, this is the first report of AEFV in China.

Electronic supplementary material

The online version of this article (10.1186/s40249-018-0457-9) contains supplementary material, which is available to authorized users.

Insect-Specific Viruses: A Historical Overview and Recent Developments

Arthropod-borne viruses (arboviruses) have in recent years become a tremendous global health concern resulting in substantial human morbidity and mortality. With the widespread utilization of molecular technologies such as next-generation sequencing and the advancement of bioinformatics tools, a new age of viral discovery has commenced. Many of the novel agents being discovered in recent years have been isolated from mosquitoes and exhibit a highly restricted host range. Strikingly, these insect-specific viruses have been found to be members of viral families traditionally associated with human arboviral pathogens, including but not limited to the families Flaviviridae, Togaviridae, Reoviridae, and Bunyaviridae. These agents therefore present novel opportunities in the fields of viral evolution and viral/vector interaction and have tremendous potential as agents for biocontrol of vectors and or viruses of medical importance.

Genome sequencing and genetic characterization of Culex Flavirirus (CxFV) provides new information about its genotypes

Background

Culex Flavivirus (CxFV) is an insect-specific virus that is widely distributed and primarily infects mosquito species from the genus Culex. Its hosts include Culex tritaeniorhynchus, Culex quinquefasciatus, and Anopheles sinensis mosquitoes. Since its original identification, CxFV has been reported in several countries. Despite the increasing number of reports on CxFV, little is known about its genomic characteristics. It is unclear whether the phylogenetic relationships between the strains are influenced by host species and geographic location.

Results

We characterized the Brazilian CxFV strain and performed a comprehensive genetic and phylogenetic characterization of CxFV based on all ORF sequences described so far. Our results revealed that the Brazilian strain is in a monophyletic clade with the Mexican strain. Overall, selective pressure indicates that the ORF is undergoing purifying selection.

Conclusions

The phylogenetic analysis revealed a strong association between climate and CxFV ancestry. Also, based on phylogeny and the genetic distance between the main branches of the tree, we propose the classification of the available sequences into two different genotypes. We also suggest the existence of two different subtypes within Genotype 1.

Electronic supplementary material

The online version of this article (doi:10.1186/s12985-016-0614-3) contains supplementary material, which is available to authorized users.

Detection of Culex flavivirus and Aedes flavivirus nucleotide sequences in mosquitoes from parks in the city of São Paulo, Brazil

The dengue viruses are widespread in Brazil and are a major public health concern. Other flaviviruses also cause diseases in humans, although on a smaller scale. The city of São Paulo is in a highly urbanized area with few green spaces apart from its parks, which are used for recreation and where potential vertebrate hosts and mosquito vectors of pathogenic Flavivirus species can be found. Although this scenario can contribute to the transmission of Flavivirus to humans, little is known about the circulation of members of this genus in these areas. In light of this, the present study sought to identify Flavivirus infection in mosquitoes (Diptera: Culicidae) collected in parks in the city of São Paulo. Seven parks in different sectors of the city were selected. Monthly mosquito collections were carried out in each park from March 2011 to February 2012 using aspiration and traps (Shannon and CD C-CO2). Nucleic acids were extracted from the mosquitoes collected and used for reverse-transcriptase and real-time polymerase chain reactions with genus-specific primers targeting a 200-nucleotide region in the Flavivirus NS5 gene. Positive samples were sequenced, and phylogenetic analyses were performed. Culex and Aedes were the most frequent genera of Culicidae collected. Culex flavivirus (CxFV)-related and Aedes flavivirus (AEFV)- related nucleotide sequences were detected in 17 pools of Culex and two pools of Aedes mosquitoes, respectively, among the 818 pools of non-engorged females analyzed. To the best of our knowledge, this is the first report of CxFV and AEFV in the city of São Paulo and Latin America, respectively. Both viruses are insect- specific flaviviruses, a group known to replicate only in mosquito cells and induce a cytopathic effect in some situations. Hence, our data suggests that CxFV and AEFV are present in Culex and Aedes mosquitoes, respectively, in parks in the city of São Paulo. Even though Flavivirus species of medical importance were not detected, surveillance is recommended in the study areas because of the presence of vertebrates and mosquitoes that could act as amplifying hosts and vectors of flaviviruses, providing the required conditions for circulation of these viruses.

Insect-specific flaviviruses, a worldwide widespread group of viruses only detected in insects

Several flaviviruses are important pathogens for humans and animals (Dengue viruses, Japanese encephalitis virus, Yellow-fever virus, Tick-borne encephalitis virus, West Nile virus). In recent years, numerous novel and related flaviviruses without known pathogenic capacity have been isolated worldwide in the natural mosquito population. However, phylogenetic studies have shown that genomic sequences of these viruses diverge from other flaviviruses. Moreover, these viruses seem to be exclusive of insects (they do not seem to grow on vertebrate cell lines), and were already defined as mosquito-only flaviviruses or insect-specific flaviviruses. At least eleven of these viruses were isolated worldwide, and sequences ascribable to other eleven putative viruses were detected in several mosquito species. A large part of the cycle of these viruses is not well known, and their persistence in the environment is poorly understood. These viruses are detected in a wide variety of distinct mosquito species and also in sandflies and chironomids worldwide; a single virus, or the genetic material ascribable to a virus, was detected in several mosquito species in different countries, often in different continents. Furthermore, some of these viruses are carried by invasive mosquitoes, and do not seem to have a depressive action on their fitness. The global distribution and the continuous detection of new viruses in this group point out the likely underestimation of their number, and raise interesting issues about their possible interactions with the pathogenic flaviviruses, and their influence on the bionomics of arthropod hosts. Some enigmatic features, as their integration in the mosquito genome, the recognition of their genetic material in DNA forms in field-collected mosquitoes, or the detection of the same virus in both mosquitoes and sandflies, indicate that the cycle of these viruses has unknown characteristics that could be of use to reach a deeper understanding of the cycle of related pathogenic flaviviruses.

Distribution and phylogenetic analysis of Culex flavivirus in mosquitoes in China

Culex flavivirus (CxFV) is an insect-specific virus of the genus Flavivirus. CxFV strains have been isolated from Cx. pipiens, Cx. quinquefasciatus, and other Cx. species in Asia, Africa, North America, Central America and South America. CxFV was isolated for the first time in China in 2006. As this is a novel flavivirus, we explored the distribution and genetic characteristics of Culex flavivirus in China. A total of 46,649 mosquitoes were collected in seven provinces between 2004 and 2012 and were analysed in 871 pools. 29 CxFV RNAs from Cx. pipiens, Cx. tritaeniorhynchus, Anopheles Sinensis, and Culex spp. tested positive for CxFV in real-time RT-PCR. 6 CxFV strains were isolated from Cx. species collected in Shandong, Henan, and Shaanxi provinces, while no virus or viral RNA was detected in samples from Sichuan, Chongqing, Hubei, and Fujian. Phylogenetic analysis of the envelope gene indicated that Chinese strains formed a robust subgroup of genotype 1, together with viruses from the United States and Japan. This study demonstrates that the geographic distribution of CxFV in China is widespread, but geographical boundaries to spread are apparent. Our findings suggest that CxFV can infect various mosquito species in nature.

Isolation of Japanese encephalitis virus and a novel insect-specific flavivirus from mosquitoes collected in a cowshed in Japan

Cattle do not generally appear to develop severe viremia when infected with Japanese encephalitis virus (JEV), and they can be infected without showing clinical signs. However, two cattle in Japan recently died from JEV infection. In this study, we investigated the presence of different species of mosquitoes and flavivirus in a cowshed in the southwest region of Japan. In this cowshed, the two most common species of mosquitoes collected were Culex tritaeniorhynchus (including Culex pseudovishnui) and Anopheles sinensis. We performed virus isolation from the collected mosquitoes and obtained two flaviviruses: JEV and a novel insect-specific flavivirus, tentatively designated Yamadai flavivirus (YDFV). Phylogenetic analysis revealed that all three JEV isolates belonged to JEV genotype I and were closely related to a JEV strain that was isolated from the brains of cattle exhibiting neurological symptoms in Japan. Genetic characterization of YDFV revealed that the full genome RNA (10,863 nucleotides) showed homology with the Culex-associated insect-specific flaviviruses Quang Binh virus (79% identity) and Yunnan Culex flavivirus (78% identity), indicating that YDFV is a novel insect-specific flavivirus.

Insect-specific flaviviruses: a systematic review of their discovery, host range, mode of transmission, superinfection exclusion potential and genomic organization

There has been a dramatic increase in the number of insect-specific flaviviruses (ISFs) discovered in the last decade. Historically, these viruses have generated limited interest due to their inability to infect vertebrate cells. This viewpoint has changed in recent years because some ISFs have been shown to enhance or suppress the replication of medically important flaviviruses in co-infected mosquito cells. Additionally, comparative studies between ISFs and medically important flaviviruses can provide a unique perspective as to why some flaviviruses possess the ability to infect and cause devastating disease in humans while others do not. ISFs have been isolated exclusively from mosquitoes in nature but the detection of ISF-like sequences in sandflies and chironomids indicates that they may also infect other dipterans. ISFs can be divided into two distinct phylogenetic groups. The first group currently consists of approximately 12 viruses and includes cell fusing agent virus, Kamiti River virus and Culex flavivirus. These viruses are phylogenetically distinct from all other known flaviviruses. The second group, which is apparently not monophyletic, currently consists of nine viruses and includes Chaoyang virus, Nounané virus and Lammi virus. These viruses phylogenetically affiliate with mosquito/vertebrate flaviviruses despite their apparent insect-restricted phenotype. This article provides a review of the discovery, host range, mode of transmission, superinfection exclusion ability and genomic organization of ISFs. This article also attempts to clarify the ISF nomenclature because some of these viruses have been assigned more than one name due to their simultaneous discoveries by independent research groups.

Analysis of Mosquito-Borne Flavivirus Superinfection in Culex tritaeniorhynchus (Diptera: Culicidae) Cells Persistently Infected with Culex Flavivirus (Flaviviridae)

Superinfection exclusion is generally defined as a phenomenon in which a pre-existing viral infection prevents a secondary viral infection; this has also been observed in infections with mosquito-borne viruses. In this study, we examined the superinfection exclusion of the vertebrate-infecting flaviviruses, Japanese encephalitis virus (JEV) and dengue virus (DENV), by stable and persistent infection with an insect-specific flavivirus, Culex flavivirus (CxFV), in a Culex tritaeniorhynchus Giles cell line (CTR cells). Our experimental system was designed based on the premise that wild Cx. tritaeniorhynchus mosquitoes naturally infected with CxFV are superinfected with JEV by feeding on JEV-infected animals. As a result, we found no evidence of the superinfection exclusion of both JEV and DENV by pre-existing CxFV infection at the cellular level. However, JEV superinfection induced severe cytopathic effects on persistently CxFV-infected CTR cells. These observations imply the possibility that JEV superinfection in CxFV-infected Cx. tritaeniorhynchus mosquitoes has an adverse effect on their fitness.

New strains of Culex flavivirus isolated in Argentina

Strains of Culex flavivirus (CxFV), an insect virus isolated initially from Japan, were isolated from different species of Culex sp. mosquitoes collected in Corrientes province, Argentina, during 2009. CxFV was detected by reverse transcription polymerase chain reaction and by isolation in C6/36 cell culture. Phylogenetic analysis of nucleotide sequences showed that these strains are related closely to a CxFV strain isolated from Trinidad. Our study represents the first report of CxFV isolation and characterization in Argentina from the same geographic area where West Nile Virus has been detected. Further evaluation and viral competition studies will be necessary to determine the impact of this insect flavivirus on an infection caused by other pathogenic flaviviruses.

Stormwater drains and catch basins as sources for production of Aedes aegypti and Culex quinquefasciatus

We present data showing that structures serving as drains and catch basins for stormwater are important sources for production of the mosquito arbovirus vectors Aedes aegypti and Culex quinquefasciatus in Mérida City, México. We examined 1761 stormwater drains - located in 45 different neighborhoods spread across the city - over dry and wet seasons from March 2012 to March 2013. Of the examined stormwater drains, 262 (14.9%) held water at the time they were examined and 123 yielded mosquito immatures. In total, we collected 64,560 immatures representing nine species. The most commonly encountered species were Cx. quinquefasciatus (n=39,269) and Ae. aegypti (n=23,313). Ae. aegypti and Cx. quinquefasciatus were collected during all 11 months when we found water-filled stormwater drains, and both were found in stormwater drains located throughout Mérida City. We also present data for associations between structural characteristics of stormwater drains or water-related characteristics and the abundance of mosquito immatures. In conclusion, stormwater drains produce massive numbers of Ae. aegypti and Cx. quinquefasciatus across Mérida City, both in the wet and dry seasons, and represent non-residential development sites that should be strongly considered for inclusion in the local mosquito surveillance and control program.

Detection of Quang Binh virus from mosquitoes in China

Flaviviruses present a wide range of genetic diversity and exhibit diverse host relationships. Mosquito-borne flaviviruses have recently been isolated and characterized worldwide. Yunnan Province of China is one of the richest areas of species diversity and is the center of multi-species evolution in mainland Asia, which supports the circulation of numerous arthropod-borne viruses (arboviruses). In a screening program of arboviruses, mosquitoes were collected during the mosquito activity season in the Yunnan Province from 2007 to 2010. Eleven flavivirus strains, named Yunnan Culex flaviviruses (YNCxFVs), were obtained from Culex tritaeniorhynchus and Anopheles sinensis specimens. Sequence analyses based on partial nonstructural protein (NS) 5 gene indicated that the YNCxFVs shared 92.8-99.6% nucleotide identity with each other and were similar to the Culex-related flaviviruses. The complete genome of one representative isolate, LSFlaviV-A20-09, was sequenced. The genome was 10,865 nucleotides long and contained a single, long open reading frame (ORF) of 10,080 nucleotides that encoded a 3360-aa polyprotein. This genome was most closely related to the Quang Binh virus (QBV) VN180 strain, an insect-specific flavivirus isolated from Culex mosquitoes in Vietnam, but only had 83.0% nucleotide and 93.8% amino acid identities for the ORF sequence. The genome has approximately 66.3%-68.5% nucleotide sequence and 69.3-73.3% amino acid sequence identities to other Culex flaviviruses, and only has 47.9-57.9% nucleotide sequence and 38.7-55.1% amino acid sequence identities to Coquillettidia-related, Mansonia-related and Aedes-related flaviviruses. Phylogenetic analyses revealed that the LSFlaviV-A20-09 fell into the Culex-related flavivirus clade. Our discoveries provide more information regarding the heterogeneity of viruses that infect mosquitoes.

First detection of the Africa/Caribbean/Latin American subtype of Culex flavivirus in Asian country, Taiwan

Culex flavivirus (CxFV), a member of the genus flavivirus, is a novel insect-specific flaviviruses that can be divided into two subtypes, the cytopathic Asia/U.S. and the noncytopathic Africa/Caribbean/Latin American subtypes. The CxFV circulates in several Asian countries, and here we conducted the first study investigating CxFV in Taiwan. A total of 14,016 mosquitoes were collected between 2010 and 2012 and 3.4% (6/179) of the pools were CxFV-positive. The phylogenetic analyses indicate that the Taiwan isolates are closely related to the Africa/Caribbean/Latin American subtype, but form an independent cluster. In the cytology experiments, the CxFV Taiwan isolate infected only mosquito cells and caused cell-cell fusion that might be associated with a unique glycine residue at position 117 within the envelope protein, which is shared with the cytopathic effect-causing Asia/US subtype. This study marks the first time the Africa/Caribbean/Latin American subtype of CxFV has been identified in an Asian country and grouped into a novel cluster.

Construction of an infectious cDNA clone of Culex flavivirus, an insect-specific flavivirus from Culex mosquitoes

Culex flavivirus (CxFV) is an insect-specific flavivirus that has recently been detected in various Culex spp. mosquitoes worldwide. Here, we report the successful construction of a full-length infectious cDNA clone of a Tokyo strain, CxFV-NIID21. The full-length CxFV-NIID21 cDNA was cloned into the low-copy-number plasmid pMW119, which was stably amplified in Escherichia coli. Transfection of a mosquito cell line with in vitro-transcribed RNA from the cDNA clone resulted in the production of recombinant progeny virus with growth properties, cytopathogenicity, and virion morphology similar to the parental virus.

Isolation and identification of a distinct strain of Culex Flavivirus from mosquitoes collected in Mainland China

BACKGROUND

Culexflavivirus (CxFV) is an insect specific virus that has been isolated from Culexpipiens, Culexquinquefasciatus, Culextritaeniorhynchus and other Culex mosquitoes. It is a novel flavivirus isolated in Asia, North America, Central America and Africa. Phylogenetic analysis indicates that, based on the envelope gene (E gene) sequence, the worldwide CxFV strains can be divided into two genotypes.

RESULT

A virus (SDDM06-11) was isolated from Culexpipiens collected in Shandong Province, China in 2006. The strain caused cytopathic effect (CPE) in Aedesalbopictus (C6/36) cells by 3 days post-infection and immunofluorescence assay (IFA) showed a reaction with Japanese encephalitis virus (JEV) polyclonal antibodies. Phylogenetic analysis of the E gene sequence showed CxFV formed two genotypes with the SDDM06-11 strain assigned to genotype 1. Analysis of the E gene nucleotide homology showed the virus possessed characteristic amino acids at specific sites. The nucleotide homology of the open reading frame (ORF) was 94.8%-95.1% between SDDM06-11 and isolates from Japan, Iowa and Texas, and 90.2%-90.5% between SDDM06-11 and isolates from Uganda and Mexico.

CONCLUSION

In this paper we report the first isolation and identification of an isolate of CxFV in mainland China. Phylogenetic analysis indicates the isolate belongs to genotype 1. Our findings provide insight into the occurrence of CxFV in Culex mosquito populations and its distribution on a global scale.

Evidence of efficient transovarial transmission of Culex flavivirus by Culex pipiens (Diptera: Culicidae)

This study determined the transovarial transmission (TOT) potential and tissue tropisms of Culex flavivirus (CxFV), an insect-specific flavivirus, in Culex pipiens (L.). Several hundred mosquito egg rafts were collected in the field, transferred to the insectaries, reared to the fourth larval instar, and identified using morphological characteristics. Cx. pipiens were reared to adults, allowed to oviposit in individual containers, and tested for CxFV RNA by reverse transcription-polymerase chain reaction (RT-PCR) and nucleotide sequencing. Eighteen CxFV RNA-positive females were identified from 26 females that oviposited viable egg rafts. Thirty F1 adults from each positive female were individually tested by RT-PCR for CxFV RNA. Viral RNA was detected in 526 of 540 progeny, and thus, the filial infection rate was 97.4%. Because all 18 positive females produced infected offspring, the TOT prevalence was 100%. These data indicated that efficient TOT of CxFV occurs in nature. To define the tissue tropisms of CxFV, different tissues (salivary glands, ovaries, testes, head, fat bodies, and midguts) were removed from the remainder of the F1 and tested by RT-PCR for CxFV RNA. Viral RNA was detected in all tissues. Additionally, uninfected laboratory-colonized Cx. pipiens were infected with CxFV by needle inoculation, and ovaries were collected at 4, 6, 8, and 12 d postinoculation and tested for CxFV RNA by RT-PCR. Viral RNA was detected at all time points, demonstrating that CxFV infects the ovaries as early as 4 d postinoculation. Surprisingly, however, we were unable to demonstrate transovarial transmission despite the presence of viral RNA in the ovaries. Nevertheless, the experiments performed with field-infected Cx. pipiens demonstrate that TOT is an efficient mechanism by which CxFV is maintained in mosquitoes in nature.