Vector competence evaluation of mosquitoes for Tahyna virus PJ01 strain, a new Orthobunyavirus in China

Arbovirus screening of mosquitoes collected in 2022 in Emilia-Romagna, Italy, with the implementation of a real-time PCR for the detection of Tahyna virus

Several Arboviruses (Arthropod-borne virus) are a concrete health risk. While some arboviruses, such as the West Nile virus (WNV) and the Usutu virus (USUV) are actively surveyed, others are neglected, including the Tahyna virus (TAHV). In this work, we tested - searching for all the three viruses - 37,995 mosquitoes collected in 95 attractive traps, baited by carbon dioxide, distributed in the lowlands of Emilia-Romagna, northern Italy, between 19 July and 12 August 2022. Among the 668 pools obtained, WNV was detected in 45 pools of Culex (Cx.) pipiens and USUV was recorded in 24 pools of the same mosquito; ten of these Cx. pipiens pools tested positive for both WNV and USUV. Interestingly, we recorded a significant circulation of both WNV lineage 1 (WNV-L1) and lineage 2 (WNV-L2): WNV-L1 strains were detected in 40 pools, WNV-L2 strains in three pools and both lineages were detected in two pools. TAHV was detected in 8 different species of mosquitoes in a total of 37 pools: Aedes (Ae.) caspius (25), Ae. albopictus (5), Ae. vexans (3), Cx. pipiens (2), Ae. cinereus (1) and Anopheles maculipennis sl (1). The significant number of Ae. caspius-pools tested positive and the estimated viral load suggest that this mosquito is the principal vector in the surveyed area. The potential involvement of other mosquito species in the TAHV cycle could usefully be the subject of further experimental investigation. The results obtained demonstrate that, with adequate sampling effort, entomological surveillance is able to detect arboviruses circulating in a given area. Further efforts must be made to better characterise the TAHV cycle in the surveyed area and to define health risk linked to this virus.

Evaluating the mosquito vector range for two orthobunyaviruses: Oya virus and Ebinur Lake virus

BACKGROUND

Mosquito-borne viruses cause various infectious diseases in humans and animals. Oya virus (OYAV) and Ebinur Lake virus (EBIV), belonging to the genus Orthobunyavirus within the family Peribunyaviridae, are recognized as neglected viruses with the potential to pose threats to animal or public health. The evaluation of vector competence is essential for predicting the arbovirus transmission risk.

METHODS

To investigate the range of mosquito vectors for OYAV (strain SZC50) and EBIV (strain Cu20-XJ), the susceptibility of four mosquito species (Culex pipiens pallens, Cx. quinquefasciatus, Aedes albopictus, and Ae. aegypti) was measured through artificial oral infection. Then, mosquito species with a high infection rate (IR) were chosen to further evaluate the dissemination rate (DR), transmission rate (TR), and transmission efficiency. The viral RNA in each mosquito sample was determined by RT-qPCR.

RESULTS

The results revealed that for OYAV, Cx. pipiens pallens had the highest IR (up to 40.0%) among the four species, but the DR and TR were 4.8% and 0.0%, respectively. For EBIV, Cx. pipiens pallens and Cx. quinquefasciatus had higher IR compared to Ae. albopictus (1.7%). However, the EBIV RNA and infectious virus were detected in Cx. pipiens pallens, with a TR of up to 15.4% and a transmission efficiency of 3.3%.

CONCLUSIONS

The findings indicate that Cx. pipiens pallens was susceptible to OYAV but had an extremely low risk of transmitting the virus. Culex pipiens pallens and Cx. quinquefasciatus were susceptible to EBIV, and Cx. pipiens pallens had a higher transmission risk to EBIV than Cx. quinquefasciatus.

The infection kinetics and transmission potential of two Guaico Culex viruses in Culex quinquefasciatus mosquitoes

Guaico Culex virus (GCXV) is a newly identified segmented Jingmenvirus from Culex spp. mosquitoes in Central and South America. The genome of GCXV is composed of four or five single-stranded positive RNA segments. However, the infection kinetics and transmission capability of GCXV in mosquitoes remain unknown. In this study, we used reverse genetics to rescue two GCXVs (4S and 5S) that contained four and five RNA segments, respectively, in C6/36 ​cells. Further in vitro characterization revealed that the two GCXVs exhibited comparable replication kinetics, protein expression and viral titers. Importantly, GCXV RNAs were detected in the bodies, salivary glands, midguts and ovaries of Culex quinquefasciatus at 4-10 days after oral infection. In addition, two GCXVs can colonize Cx. quinquefasciatus eggs, resulting in positive rates of 15%-35% for the second gonotrophic cycle. In conclusion, our results demonstrated that GCXVs with four or five RNA segments can be detected in Cx. quinquefasciatus eggs during the first and second gonotrophic cycles after oral infection.

Mosquitoes from Europe Are Able to Transmit Snowshoe Hare Virus

Snowshoe hare virus (SSHV) is a zoonotic arthropod-borne virus (arbovirus) circulating in colder areas of the Northern Hemisphere. SSHV is maintained in an enzootic cycle between small mammals and mosquitoes, assumably of the genera Aedes and Culiseta. Symptoms of SSHV human infection can range from asymptomatic to severe neuroinvasive disease. Studies on SSHV transmission are limited, and there is no information available on whether mosquitoes of the genus Culex are able to transmit SSHV. Therefore, we investigated six mosquito species via salivation assay for their vector competence. We demonstrated that SSHV can be transmitted by the abundant European Culex species Cx. pipiens biotype pipiens, Cx. pipiens biotype molestus, and Cx. torrentium with low transmission efficiency between 3.33% and 6.67%. Additionally, the invasive species Ae. albopictus can also transmit SSHV with a low transmission efficiency of 3.33%. Our results suggest that local transmission of SSHV after introduction to Europe seems to be possible from a vector perspective.

Immunoinformatics-based potential multi-peptide vaccine designing against Jamestown Canyon Virus (JCV) capable of eliciting cellular and humoral immune responses

Jamestown Canyon virus (JCV) is a deadly viral infection transmitted by various mosquito species. This mosquito-borne virus belongs to Bunyaviridae family, posing a high public health threat in the in tropical regions of the United States causing encephalitis in humans. Common symptoms of JCV include fever, headache, stiff neck, photophobia, nausea, vomiting, and seizures. Despite the availability of resources, there is currently no vaccine or drug available to combat JCV. The purpose of this study was to develop an epitope-based vaccine using immunoinformatics approaches. The vaccine aimed to be secure, efficient, bio-compatible, and capable of stimulating both innate and adaptive immune responses. In this study, the protein sequence of JCV was obtained from the NCBI database. Various bioinformatics methods, including toxicity evaluation, antigenicity testing, conservancy analysis, and allergenicity assessment were utilized to identify the most promising epitopes. Suitable linkers and adjuvant sequences were used in the design of vaccine construct. 50s ribosomal protein sequence was used as an adjuvant at the N-terminus of the construct. A total of 5 CTL, 5 HTL, and 5 linear B cell epitopes were selected based on non-allergenicity, immunological potential, and antigenicity scores to design a highly immunogenic multi-peptide vaccine construct. Strong interactions between the proposed vaccine and human immune receptors, i.e., TLR-2 and TLR-4, were revealed in a docking study using ClusPro software, suggesting their possible relevance in the immunological response to the vaccine. Immunological and physicochemical properties assessment ensured that the proposed vaccine demonstrated high immunogenicity, solubility and thermostability. Molecular dynamics simulations confirmed the strong binding affinities, as well as dynamic and structural stability of the proposed vaccine. Immune simulation suggest that the vaccine has the potential to effectively stimulate cellular and humoral immune responses to combat JCV infection. Experimental and clinical assays are required to validate the results of this study.

Cell fusing agent virus isolated from Aag2 cells does not vertically transmit in Aedes aegypti via artificial infection

BACKGROUND

Cell fusing agent virus (CFAV) was the first insect-specific virus to be characterized, and has been reported to negatively influence the growth of arboviruses such as dengue, Zika, and La Cross, making it a promising biocontrol agent for mosquito-borne disease prevention. Aedes aegypti Aag2 cells were naturally infected with CFAV. However, the ability of this virus to stably colonize an Ae. aegypti population via artificial infection and how it influences the vector competence of this mosquito have yet to be demonstrated.

METHODS

CFAV used in this study was harvested from Aag2 cells and its complete genome sequence was obtained by polymerase chain reaction and rapid amplification of complementary DNA ends, followed by Sanger sequencing. Phylogenetic analysis of newly identified CFAV sequences and other sequences retrieved from GenBank was performed. CFAV stock was inoculated into Ae. aegypti by intrathoracic injection, the survival of parental mosquitoes was monitored and CFAV copies in the whole bodies, ovaries, and carcasses of the injected F0 generation and in the whole bodies of the F1 generation on different days were examined by reverse transcription-quantitative polymerase chain reaction.

RESULTS

The virus harvested from Aag2 cells comprised a mixture of three CFAV strains. All genome sequences of CFAV derived from Aag2 cells clustered into one clade but were far from those isolated or identified from Ae. aegypti. Aag2-derived CFAV efficiently replicated in the mosquito body and did not attenuate the survival of Ae. aegypti. However, the viral load in the ovarian tissues was much lower than that in other tissues and the virus could not passage to the offspring by vertical transmission.

CONCLUSIONS

The results of this study demonstrate that Aag2-derived CFAV was not vertically transmitted in Ae. aegypti and provide valuable information on the colonization of mosquitoes by this virus.