Culex Flavivirus During West Nile Virus Epidemic and Interepidemic Years in Chicago, United States

Negevirus Piura Suppresses Zika Virus Replication in Mosquito Cells

We investigated the interaction between the insect-specific virus, Piura virus (PIUV), and the arbovirus Zika virus (ZIKV) in Aedes albopictus cells. We performed coinfection experiments in C6/36 cells. Piura virus (Cor 33 strain, Colombia) and ZIKV (PRVABC58 strain, Puerto Rico) were co-inoculated into C6/36 cells using two multiplicity of infection (MOI) combinations: 0.1 for both viruses and 1.0 for ZIKV, 0.1 for PIUV. Wells were infected in triplicate with either PIUV and ZIKV coinfection, ZIKV-only, or PIUV-only. Mock infected cells served as control wells. The cell suspension was collected daily 7 days post-infection. Zika virus load was titrated by TCID50 on Vero 76 cells. The ZIKV-only infection and PIUV and ZIKV coinfection experiments were also quantified by RT-qPCR. We also investigated whether ZIKV interfered in the PIUV replication. PIUV suppressed the replication of ZIKV, resulting in a 10,000-fold reduction in ZIKV titers within 3 days post-infection. PIUV viral loads were not reduced in the presence of ZIKV. We conclude that, when concurrently infected, PIUV suppresses ZIKV in C6/36 cells while ZIKV does not interfere in PIUV replication.

West Nile virus in Mexico: Why vectors matter for explaining the current absence of epidemics

Since 2002, West Nile Virus (WNV) has been reported in 18 states in Mexico, either by PCR or serological testing. However, it is believed that the virus is present in more states. Only four states (out of 32) have reported confirmed human cases, and one state has serological evidence. In the country, WNV is present in mainly horses and birds, but its presence extends to crocodiles, felines, canines, swines, donkeys, caprines, antilopes, cattle, bats, and camelids. Positive mosquito species include Aedes and Culex spp. Different hypotheses have been proposed to explain the absence of WNV epidemics in Latin America. Since some regions of Mexico and the United States share ecological and climatic conditions, these hypotheses may not be sufficient to account for the absence of WNV outbreaks or epidemics. This paper discusses the proposed ideas and attempts to contextualize them for Mexico, particularly for the U.S.-Mexico border, where WNV infections have been reported in humans, horses, and mosquitoes. We propose that integration of urban ecology and entomology knowledge is needed to better understand the absence of WN cases in Mexico.

Negeviruses Reduce Replication of Alphaviruses during Coinfection

Negeviruses are a group of insect-specific viruses (ISVs) that have been found in many arthropods. Their presence in important vector species led us to examine their interactions with arboviruses during coinfections. Wild-type negeviruses reduced the replication of several alphaviruses during coinfections in mosquito cells. Negev virus (NEGV) isolates were also used to express green fluorescent protein (GFP) and anti-chikungunya virus (CHIKV) antibody fragments during coinfections with CHIKV. NEGV expressing anti-CHIKV antibody fragments was able to further reduce replication of CHIKV during coinfections, while reductions of CHIKV with NEGV expressing GFP were similar to titers with wild-type NEGV alone. These results are the first to show that negeviruses induce superinfection exclusion of arboviruses and to demonstrate a novel approach to deliver antiviral antibody fragments with paratransgenic ISVs. The ability to inhibit arbovirus replication and express exogenous proteins in mosquito cells makes negeviruses a promising platform for control of arthropod-borne pathogens. IMPORTANCE Negeviruses are a group of insect-specific viruses (ISVs), viruses known to infect only insects. They have been discovered over a wide geographical and species range. Their ability to infect mosquito species that transmit dangerous arboviruses makes negeviruses a candidate for a pathogen control platform. Coinfections of mosquito cells with a negevirus and an alphavirus demonstrated that negeviruses can inhibit the replication of alphaviruses. Additionally, modifying Negev virus (NEGV) to express a fragment of an anti-CHIKV antibody further reduced the replication of CHIKV in coinfected cells. This is the first evidence to demonstrate that negeviruses can inhibit the replication of important arboviruses in mosquito cells. The ability of a modified NEGV to drive the expression of antiviral proteins also highlights a method for negeviruses to target specific pathogens and limit the incidence of vector-borne diseases.

Insect-Specific Viruses: An overview and their relationship to arboviruses of concern to humans and animals

The group of Insect-specific viruses (ISVs) includes viruses apparently restricted to insects based on their inability to replicate in the vertebrates. Increasing numbers of ISVs have been discovered and characterized representing a diverse number of viral families. However, most studies have focused on those ISVs belonging to the family Flaviviridae, which highlights the importance of ISV study from other viral families, which allow a better understanding for the mechanisms of transmission and evolution used for this diverse group of viruses. Some ISVs have shown the potential to modulate arboviruses replication and vector competence of mosquitoes. Based on this, ISVs may be used as an alternative tool for biological control, development of vaccines, and diagnostic platforms for arboviruses. In this review, we provide an update of the general characteristics of ISVs and their interaction with arboviruses that infect vertebrates.

Transcriptional variation of sensory-related genes in natural populations of Aedes albopictus

BACKGROUND

The Asian tiger mosquito, Aedes albopictus, is a highly dangerous invasive vector of numerous medically important arboviruses including dengue, chikungunya and Zika. In four decades it has spread from tropical Southeast Asia to many parts of the world in both tropical and temperate climes. The rapid invasion process of this mosquito is supported by its high ecological and genetic plasticity across different life history traits. Our aim was to investigate whether wild populations, both native and adventive, also display transcriptional genetic variability for functions that may impact their biology, behaviour and ability to transmit arboviruses, such as sensory perception.

RESULTS

Antennal transcriptome data were derived from mosquitoes from a native population from Ban Rai, Thailand and from three adventive Mediterranean populations: Athens, Greece and Arco and Trento from Italy. Clear inter-population differential transcriptional activity was observed in different gene categories related to sound perception, olfaction and viral infection. The greatest differences were detected between the native Thai and the Mediterranean populations. The two Italian populations were the most similar. Nearly one million quality filtered SNP loci were identified.

CONCLUSION

The ability to express this great inter-population transcriptional variability highlights, at the functional level, the remarkable genetic flexibility of this mosquito species. We can hypothesize that the differential expression of genes, including those involved in sensory perception, in different populations may enable Ae. albopictus to exploit different environments and hosts, thus contributing to its status as a global vector of arboviruses of public health importance. The large number of SNP loci present in these transcripts represents a useful addition to the arsenal of high-resolution molecular markers and a resource that can be used to detect selective pressure and adaptive changes that may have occurred during the colonization process.

Exploiting insect-specific viruses as a novel strategy to control vector-borne disease

Novel insect-specific viruses (ISVs) are being discovered in many important vectors due to advances in sequencing technology and a growing awareness of the virome. Several in vitro and in vivo studies indicate that ISVs are capable of modulating pathogenic arboviruses. In addition, there is growing evidence that both vertical and horizonal transmission strategies maintain ISVs in vector populations. As such there is potential to exploit ISVs for stand-alone vector control strategies and deploying them in synergy with other symbiont control approaches such as Wolbachia-mediated control. However, before the applied potential can be realized, a greater understanding of their basic biology is required, including their species range, ability to be maintained and transmitted in native and non-native vector hosts, and the effect of infection on a range of pathogens.

Metagenomic analysis of Aedes aegypti and Culex quinquefasciatus mosquitoes from Grenada, West Indies

The mosquitoes Aedes aegypti (Linnaeus, 1762) (Diptera: Culicidae) and Culex quinquefasciatus Say, 1823 (Diptera: Culicidae) are two major vectors of arthropod-borne pathogens in Grenada, West Indies. As conventional vector control methods present many challenges, alternatives are urgently needed. Manipulation of mosquito microbiota is emerging as a field for the development of vector control strategies. Critical to this vector control approach is knowledge of the microbiota of these mosquitoes and finding candidate microorganisms that are common to the vectors with properties that could be used in microbiota modification studies. Results showed that bacteria genera including Asaia, Escherichia, Pantoea, Pseudomonas, and Serratia are common to both major arboviral vectors in Grenada and have previously been shown to be good candidates for transgenetic studies. Also, for the first time, the presence of Grenada mosquito rhabdovirus 1 is reported in C. quinquefasciatus.

Mosquito-Borne Viruses and Insect-Specific Viruses Revealed in Field-Collected Mosquitoes by a Monitoring Tool Adapted from a Microbial Detection Array

Several mosquito-borne diseases affecting humans are emerging or reemerging in the United States. The early detection of pathogens in mosquito populations is essential to prevent and control the spread of these diseases. In this study, we tested the potential applicability of the Lawrence Livermore Microbial Detection Array (LLMDA) to enhance biosurveillance by detecting microbes present in Aedes aegypti, Aedes albopictus, and Culex mosquitoes, which are major vector species globally, including in Texas. The sensitivity and reproducibility of the LLMDA were tested in mosquito samples spiked with different concentrations of dengue virus (DENV), revealing a detection limit of >100 but <1,000 PFU/ml. Additionally, field-collected mosquitoes from Chicago, IL, and College Station, TX, of known infection status (West Nile virus [WNV] and Culex flavivirus [CxFLAV] positive) were tested on the LLMDA to confirm its efficiency. Mosquito field samples of unknown infection status, collected in San Antonio, TX, and the Lower Rio Grande Valley (LRGV), TX, were run on the LLMDA and further confirmed by PCR or quantitative PCR (qPCR). The analysis of the field samples with the LLMDA revealed the presence of cell-fusing agent virus (CFAV) in A. aegypti populations. Wolbachia was also detected in several of the field samples (A. albopictus and Culex spp.) by the LLMDA. Our findings demonstrated that the LLMDA can be used to detect multiple arboviruses of public health importance, including viruses that belong to the Flavivirus, Alphavirus, and Orthobunyavirus genera. Additionally, insect-specific viruses and bacteria were also detected in field-collected mosquitoes. Another strength of this array is its ability to detect multiple viruses in the same mosquito pool, allowing for the detection of cocirculating pathogens in an area and the identification of potential ecological associations between different viruses. This array can aid in the biosurveillance of mosquito-borne viruses circulating in specific geographical areas.IMPORTANCE Viruses associated with mosquitoes have made a large impact on public and veterinary health. In the United States, several viruses, including WNV, DENV, and chikungunya virus (CHIKV), are responsible for human disease. From 2015 to 2018, imported Zika cases were reported in the United States, and in 2016 to 2017, local Zika transmission occurred in the states of Texas and Florida. With globalization and a changing climate, the frequency of outbreaks linked to arboviruses will increase, revealing a need to better detect viruses in vector populations. With the capacity of the LLMDA to detect viruses, bacteria, and fungi, this study highlights its ability to broadly screen field-collected mosquitoes and contribute to the surveillance and management of arboviral diseases.

First report of Culex flavivirus infection from Culex coronator (Diptera: Culicidae), Colombia

BACKGROUND

Flaviviruses are important pathogens for humans and animals (Dengue viruses, Yellow fever virus, Zika virus and West Nile virus). Culex flavivirus (CxFV) is an insect-specific virus of the genus Flavivirus, detected in a wide variety of mosquito species.

OBJECTIVE

To detect Flavivirus in mosquitoes of a tropical region of the Colombian Caribbean.

METHODS

In 2014, an entomological surveillance of arboviruses was conducted in the department of Cordoba area of the Caribbean, Colombia. A total of 8270 mosquitoes were captured as follow: Mansonia (n = 3271/39.5%), Culex (n = 2668/32.26%), Anopheles (n = 840/10.15%), Aedeomyia (n = 411/4.9%), Psorophora (n = 397/4.8%), Coquilletidia (n = 369/4.46%), Uranotaenia (n = 261/3.15%) and Aedes (n = 53/0.6%). All mosquito species were collected in dry tropical forest of the Caribbean area. Universal primers for NS5 gene (958 pb), RT-PCR for flavivirus and sequencing were used for molecular identification of viruses detected.

RESULTS

Two pools belonging to Culex coronator were positive for flavivirus RNA sequence by RT-PCR. The sequences of the PCR amplicons, matched that of the Culex flaviviruses, CxFv COL PM_149 (GenBank: KR014201) and CxFv COL PM_212 (GenBank: KT307717). Phylogenetic analysis of the NS5 protein sequences of the Culex flaviviruses sequences with those of reference sequences available in GenBank indicated viruses of Genotype II, closely related to the Brazilian strain, BR_SJRP_01_ (GenBank: KT726939), from Culex sp. The alignment of Culex flavivirus sequences CxFv COL_ PM 212 and CxFv COL_ PM 149 with sequences of strains detected in different geographical regions grouped the strains in a Latin American clade reported in Brazil, Argentina and Mexico.

CONCLUSIONS

The present work illustrated that CxFV was circulating among vectors of human pathogenic arboviruses in Colombia, but the impact of CxFV on other flaviviruses which are endemic in the study area still remains to be explored.

Restriction of Zika virus infection and transmission in Aedes aegypti mediated by an insect-specific flavivirus

Previous studies demonstrated an insect-specific flavivirus, Nhumirim virus (NHUV), can suppress growth of West Nile virus (WNV) and decrease transmission rates in NHUV/WNV co-inoculated Culex quinquefasciatus. To assess whether NHUV might interfere with transmission of other medically important flaviviruses, the ability of NHUV to suppress viral growth of Zika virus (ZIKV) and dengue-2 virus (DENV-2) was assessed in Aedes albopictus cells. Significant reductions in ZIKV (100,000-fold) and DENV-2 (10,000-fold) were observed in either cells concurrently inoculated with NHUV or pre-inoculated with NHUV. In contrast, only a transient 10-fold titer reduction was observed with an alphavirus, chikungunya virus. Additionally, restricted in vitro mosquito growth of ZIKV was associated with lowered levels of intracellular ZIKV RNA in NHUV co-inoculated cultures. To assess whether NHUV could modulate vector competence for ZIKV, NHUV-inoculated Aedes aegypti were orally exposed to ZIKV. NHUV-inoculated mosquitoes demonstrated significantly lower ZIKV infection rates (18%) compared to NHUV unexposed mosquitoes (51%) (p < 0.002). Similarly, lower ZIKV transmission rates were observed for NHUV/ZIKV dually intrathoracically inoculated mosquitoes (41%) compared to ZIKV only inoculated mosquitoes (78%) (p < 0.0001), suggesting that NHUV can interfere with both midgut infection and salivary gland infection of ZIKV in Ae. aegypti. These results indicate NHUV could be utilized to model superinfection exclusion mechanism(s) and to study the potential for the mosquito virome to impact transmission of medically important flaviviruses.

Co-circulation of Flanders Virus and West Nile Virus in Culex Mosquitoes (Diptera: Culicidae) from Chicago, Illinois

West Nile virus (WNV) and Flanders virus (FLAV) co-occur in regions of North America. Because both viruses are maintained in a transmission cycle involving Culex mosquitoes and birds, screening mosquitoes for FLAV has been suggested as an enhancement to WNV surveillance and epidemic prediction. Using samples collected in 2010 and 2012 in Chicago, IL, USA, we demonstrate the presence of FLAV in four out of 287 (1.4%) Culex pools. We estimated minimum infection rates for WNV and FLAV to be 5.66 and 1.22 in 2010 and 8.74 and 0.61 in 2012, respectively. FLAV occurred 1 and 3 wk prior to the peak of WNV transmission in 2010 and 2012, respectively. FLAV sequences from Chicago were genetically diverse and phylogenetically representative of lineage A viruses from across the United States.

Comparative Vector Competence of North American Culex pipiens and Culex quinquefasciatus for African and European Lineage 2 West Nile Viruses

West Nile virus (WNV) is a mosquito-borne flavivirus that is phylogenetically separated into distinct lineages. Lineage 1 (L1) and lineage 2 (L2) encompass all WNV isolates associated with human and veterinary disease cases. Although L1 WNV is globally distributed, including North America, L2 WNV only recently emerged out of sub-Saharan Africa into Europe and Russia. The spread of L2 WNV throughout and beyond Europe depends, in part, on availability of competent vectors. The vector competence of mosquitoes within the Culex genus for WNV is well established for L1 WNV but less extensively studied for L2 WNV. Assessing the vector competence of North American Culex mosquitoes for L2 WNV will be critical for predicting the potential for L2 WNV emergence in North America. We address the vector competence of North American Culex pipiens and Culex quinquefasciatus for L2 WNV. Both mosquito species were highly competent for each of the L2 WNV strains assessed, but variation in infection, dissemination, and transmission was observed. An L2 WNV strain (NS10) isolated during the Greek outbreak in 2010 exhibited a reduced capacity to infect Cx. pipiens compared with other L2 WNV strains. In addition, a South African L2 WNV strain (SA89) displayed a significantly shorter extrinsic incubation period in Cx. quinquefasciatus compared with other L2 WNV strains. These results demonstrate that North American Culex mosquito species are competent vectors of African and European L2 WNV and that emergence of L2 WNV is unlikely to be hindered by poor competence of North American vectors.