Potential vectors of bluetongue virus in high altitude areas of Yunnan Province, China

Transcriptomic Investigation of the Virus Spectrum Carried by Midges in Border Areas of Yunnan Province

Yunnan province in China shares its borders with three neighboring countries: Myanmar, Vietnam, and Laos. The region is characterized by a diverse climate and is known to be a suitable habitat for various arthropods, including midges which are notorious for transmitting diseases which pose significant health burdens affecting both human and animal health. A total of 431,100 midges were collected from 15 different locations in the border region of Yunnan province from 2015 to 2020. These midges were divided into 37 groups according to the collection year and sampling site. These 37 groups of midges were then homogenized to extract nucleic acid. Metatranscriptomics were used to analyze their viromes. Based on the obtained cytochrome C oxidase I gene (COI) sequences, three genera were identified, including one species of Forcipomyia, one species of Dasyhelea, and twenty-five species of Culicoides. We identified a total of 3199 viruses in five orders and 12 families, including 1305 single-stranded positive-stranded RNA viruses (+ssRNA) in two orders and seven families, 175 single-stranded negative-stranded RNA viruses (-ssRNA) in two orders and one family, and 1719 double-stranded RNA viruses in five families. Six arboviruses of economic importance were identified, namely Banna virus (BAV), Japanese encephalitis virus (JEV), Akabane virus (AKV), Bluetongue virus (BTV), Tibetan circovirus (TIBOV), and Epizootic hemorrhagic disease virus (EHDV), all of which are capable, to varying extents, of causing disease in humans and/or animals. The survey sites in this study basically covered the current distribution area of midges in Yunnan province, which helps to predict the geographic expansion of midge species. The complexity and diversity of the viral spectrum carried by midges identified in the study calls for more in-depth research, which can be utilized to monitor arthropod vectors and to predict the emergence and spread of zoonoses and animal epidemics, which is of great significance for the control of vector-borne diseases.

Potential roles of Culicoides spp. (Culicoides imicola, Culicoides oxystoma) as biological vectors of bluetongue virus in Yuanyang of Yunnan, P. R. China

Introduction

Culicoides plays a crucial role as an insect vector in the field of veterinary medicine. The transmission of significant viruses such as bluetongue virus (BTV) and African horse sickness virus (AHSV) by this insect poses a substantial threat, leading to the development of severe diseases in domestic animals. This study aimed to explore the Culicoides species, identify their blood-meal sources, and assess the presence of BTV and AHSV carried by Culicoides in Yuanyang County, Yunnan Province. The aim was to gain insights into the potential vectors of these two viruses and elucidate their potential roles in the transmission of pathogens.

Methods

The midges were collected from cattle (Bos indicus), pig (Sus scrofa), and goat (Capra hircus) pens in Yuanyang County, Yunnan Province in June 2020. Initial identification of midges was conducted through morphological characteristics, followed by molecular identification using the cytochrome C oxidase subunit I (COI) gene. The determination of Culicoides blood-meal sources was accomplished using specific primers targeting the cytochrome b (Cyt b) gene from potential hosts. BTV and AHSV RNA were identified in Culicoides pools through the application of reverse transcriptase PCR and quantitative real-time PCR. Nucleotide homology and phylogenetic analysis were performed using MegAlign (DNAStar) and Mega 6.0 software.

Results

A total of 6,300 Culicoides, consisting of C. oxystoma, C. arakawai, C. imicola, and C. innoxius, were collected from cattle, pigs, and goat pens. The engorgement rates for these species were 30.2%, 54.6%, 75%, and 66.7%, respectively. In the cattle pen, the prevailing species is C. oxystoma (100%). In the pig pen, C. arakawai dominates (70%), with C. oxystoma following at 30%. In the goat pen, C. imicola holds the majority (45.45%), trailed by C. oxystoma (25%), C. innoxius (20.45%), and C. arakawai (9.09%). These Culicoides species were identified as feeding on cattle, pigs, goats, chickens (Gallus gallus), and humans (Homo sapiens). The positivity rates for BTV were 20.00% and 11.54% in blood-fed specimens of C. imicola and C. oxystoma, respectively. Conversely, the positivity rates for BTV in non-blood-fed specimens were 0.00% and 6.67% for C. imicola and C. oxystoma, respectively. BTV was not detected in C. arakawai and C. innoxius. The specimens (YY86) from C. imicola that tested positive for BTV had the closest genetic relationship to YTS-4 isolated from Mangshi, Yunnan Province in 1996. All test results for the nucleic acid of AHSV were negative.

Conclusion

The study reveals variations in the species distribution, community composition, blood sucking rate, and blood-feeding sources of Culicoides across different habitats. Notably, C. imicola and C. oxystoma emerge as potential vectors for the transmission of BTV in local animals. Accordingly, this investigation provides crucial insights that can serve as a valuable reference for the prevention and control of BTV in local animals, particularly from the perspective of vector management.

Outlook on RNAi-Based Strategies for Controlling Culicoides Biting Midges

Culicoides are small biting midges with the capacity to transmit important livestock pathogens around much of the world, and their impacts on animal welfare are likely to expand. Hemorrhagic diseases resulting from Culicoides-vectored viruses, for example, can lead to millions of dollars in economic damages for producers. Chemical insecticides can reduce Culicoides abundance but may not suppress population numbers enough to prevent pathogen transmission. These insecticides can also cause negative effects on non-target organisms and ecosystems. RNA interference (RNAi) is a cellular regulatory mechanism that degrades mRNA and suppresses gene expression. Studies have examined the utility of this mechanism for insect pest control, and with it, have described the hurdles towards producing, optimizing, and applying these RNAi-based products. These methods hold promise for being highly specific and environmentally benign when compared to chemical insecticides and are more transient than engineering transgenic insects. Given the lack of available control options for Culicoides, RNAi-based products could be an option to treat large areas with minimal environmental impact. In this study, we describe the state of current Culicoides control methods, successes and hurdles towards using RNAi for pest control, and the necessary research required to bring an RNAi-based control method to fruition for Culicoides midges.

Composition and diversity of Culicoides biting midges (Diptera: Ceratopogonidae) in rural and suburban environments of Algeria

Culicoides biting midges are well known biological vectors of several arboviruses causing more than 100 veterinary and medical diseases worldwide. In Algeria, bluetongue virus, which is transmitted by Culicoides midges, is responsible for one of the most critical insect-borne diseases of sheep. For example, this disease caused clinically severe morbidity of about 2,661 confirmed cases out of 21,175 susceptible sheep in Algeria. This study compared the abundance, richness, and diversity of Culicoides species in rural and suburban environments of semi-arid regions in North Africa. It examined the potential influence of the bio-climatic factors on the variation of population sizes and the elevation distribution of biting midges. Specimen collection was carried out from June to September during two successive years (2018 and 2019) using CDC light traps installed at 15 sites in different environments. Culicoides specimens were dissected, slide-mounted, and morphologically identified using the interactive identification key IIKC and various standard morphological criteria. A total of 1,046 Culicoides specimens (1,024 females and 22 males) were trapped and classified into 22 species, belonged to nine distinct subgenera. Two new species records for Algeria and even North Africa are reported: Culicoides albicans (Winnertz, 1852) and Culicoides nubeculosus (Meigen, 1830). Culicoides newsteadi Austen, 1921 (51.6%) was the dominant species, and it was followed by Culicoides punctatus (Meigen, 1804) (16.3%) and Culicoides odiatus Austen, 1921 (11.5%). These three species, comprising 80% of the collected Culicoides, were the most abundant both outside and inside livestock stables in rural and suburban environments. Species diversity was similar in the two settings, with a slight increase in suburban environments. None of the Culicoides species encountered correlated significantly with the climatic factors (mean temperature, precipitation, and relative humidity). Elevation was the most determinant environmental parameter that affected the abundance and distribution of Culicoides midges in the semi-arid and sub-humid areas studied. The maximum distribution of Culicoides species was detected at mid elevations (400‒800 m). Using a modeling approach, we explored for the first time the variation of composition and diversity in Culicoides communities within different climatic regions, environments and livestock settings in Algeria. This survey deepens our understanding of the relationships among environmental factors, abundance, diversity, and geographic distribution of Culicoides. This is a crucial step to assess the epidemiological situation of the diseases transmitted by these biting midges and to allow mitigation of the associated risks.

Diversity and seasonal abundance of Culicoides (Diptera, Ceratopogonidae) in Shizong County, Yunnan Province, China

Culicoides (Diptera, Ceratopogonidae) are small biting midges, some of which are vectors for animal associated arboviruses such as bluetongue virus (BTV) and Akabane virus (AKAV). BTV and AKAV are both pathogenic for livestock, with BTV in particular posing a major threat to domestic ruminants. Ongoing problems with BTV in ruminants in Shizong County of Yunnan Province, China, promoted a year-long investigation of the Culicoides in Shizong to determine relative abundance and seasonality of midges and to attempt to identify species that might be acting as vectors in the area. Culicoides were collected by UV light trap for one night per week for most weeks between May 2020 and May 2021. More than 21,000 specimens consisting of at least 21 species belonging to six subgenera and one unplaced group, including 5 species previously associated with BTV and one associated with AKAV, were collected. Culicoides tainanus dominated most collections throughout the year although C. sumatrae was often the dominant species over summer. Most species were abundant between May and October. These results indicate that C. tainanus, C. jacobsoni and C. oxystoma are the major midge pests of livestock in Shizong and should be considered in any disease investigation.

Full Genome Sequencing of Three Sedoreoviridae Viruses Isolated from Culicoides spp. (Diptera, Ceratopogonidae) in China

Sedoreoviridae is a family of viruses belonging to the order Reovirales and comprises six genera, two of which, Orbivirus and Seadornavirus, contain arboviruses that cause disease in humans and livestock. Areas such as Yunnan Province in southwestern China, have high arboviral activity due in part to warm and wet summers, which support high populations of biting flies such as mosquitoes and Culicoides. Three viral isolates previously obtained from Culicoides collected at cattle farms in Shizong County of Yunnan Province, China, between 2019 and 2020 were completely sequenced and identified as Banna virus (BAV) genotype A of Seadornavirus and serotypes 1 and 7 of epizootic hemorrhagic disease virus (EHDV) of Orbivirus. These results suggest that Culicoidestainanus and C. orientalis are potential vectors of BAV and EHDV, respectively, and represent the first association of a BAV with C. tainanus and of an arbovirus with C. orientalis. Analysis using VP9 generally agreed with the current groupings within this genus based on VP12, although the classification for some strains should be corrected. Furthermore, the placement of Kadipiro virus (KDV) and Liao ning virus (LNV) in Seadornavirus may need confirmation as phylogenetic analysis placed these viruses as sister to other species in the genus.

Genetic and pathogenic characterisation of a virulent Akabane virus isolated from goats in Yunnan, China

Introduction

Akabane virus (AKAV) has been detected in a variety of host species in China, but there are only limited records of its occurrence in goats. However, more attention needs to be paid to understanding the diversity of viruses in this species. The aim of the study was to explore the genotype characteristics and variation trend of AKAV and their relationship with virulence in Yunnan, China.

Material and Methods

Blood samples were collected from goats during routine surveillance of goat diseases in Yunnan province in 2019. The AKAV CX-01 strain was isolated using BHK-21 cells. To understand pathogenicity, the virus was intraperitoneally (IP) and intracerebrally (IC) inoculated into suckling mice and tissue samples were subsequently analysed histopathologically and immunohistochemically.

Results

Akabane virus CX-01 strain induced encephalitis and impairment of the central nervous system with fatal consequences. Phylogenetic analysis based on the ORF sequences of the small segments indicated that the AKAV isolate used was most closely related to the GD18134/2018 Chinese midge and bovine NM BS/1strains, while phylogenetic analysis based on the medium segments showed a close relationship between CX-01 and the Chinese GLXCH01 strain.

Conclusion

The CX-01 isolate was related to AKAV genogroup Ia and probably originated from a recombination of different strains.

Isolation of Tibet Orbivirus from Culicoides jacobsoni (Diptera, Ceratopogonidae) in China

BACKGROUND

Tibet Orbivirus (TIBOV) is a recently discovered Orbivirus known to infect cattle, Asian buffalo and goats in south-western China. It was first isolated from mosquitoes and subsequently from biting midges (Culicoides spp.) in Yunnan, China, indicating that it is an arbovirus. Little is known of its potential to cause disease, but the economic importance of related viruses promoted an investigation of potential Culicoides spp. vectors of TIBOV.

METHODS

Biting midges were collected approximately once per week between May and December 2020, at a cattle farm in Wulong village, Shizong County, Yunnan Province, China. Approximately 3000 specimens of nine species were subsequently used in attempts to isolate virus, and a further 2000 specimens of six species were tested for the presence of bluetongue virus (BTV) and TIBOV using a RT-qPCR test.

RESULTS

Virus isolation attempts resulted in the isolation of three viruses. One isolate from a pool of Culicoides jacobsoni was identified as TIBOV, while the other two viruses from C. orientalis and C. tainanus remain unidentified but are not BTV or TIBOV. RT-qPCR analysis did not detect BTV in any specimens, but a single pool containing five specimens of C. jacobsoni and another containing five specimens of C. tainanus produced PCR quantification cycle (Cq) values of around 28 that may indicate infection with TIBOV.

CONCLUSIONS

The isolation of TIBOV from C. jacobsoni satisfies one criterion required to prove its status as a vector of this virus. This isolation is supported by a low Cq value produced from a different pool of this species in the RT-qPCR test. The low Cq value obtained from a pool of C. tainanus suggests that this species may also be able to satisfy this criterion. Both of these species are widespread throughout Asia, with C. jacobsoni extending into the Pacific region, which raises the possibility that TIBOV may be more widespread than is currently known.

Detection of bluetongue virus in Culicoides spp. in southern Yunnan Province, China

BACKGROUND

Culicoides (Diptera: Ceratopogonidae) are vectors for many arboviruses. At least 20 species are considered as vectors or potential vectors of bluetongue virus (BTV) which cause bluetongue disease in ruminants. A BTV prevalence of 30-50% among cattle and goats in tropical southern Yunnan Province, China, prompted an investigation of the potential BTV vectors in this area.

METHODS

Culicoides were collected by light trapping at three sites in the tropical region of Yunnan Province. Species were identified based on morphology and DNA sequences of cytochrome c oxidase subunit 1 (cox1). PCR and quantitative PCR following reverse transcription were used to test for the presence of BTV RNA in these specimens. Phylogenetic analysis was used to analyze the cox1 sequences of Culicoides specimens infected with BTV.

RESULTS

Approximately 67,000 specimens of Culicoides were collected, of which 748 were tested for the presence of BTV. Five specimens, including two of Culicoides jacobsoni, one of C. tainanus and two of C. imicola, were identified as infected with BTV. No specimens of C. (subgenus Trithecoides) or C. oxystoma tested were positive for BTV infection.

CONCLUSIONS

To our knowledge this is the first report of C. jacobsoni as a potential BTV vector and the fourth report of an association between C. tainanus and BTV, as well as the first direct evidence of an association between BTV and C. imicola in Asia. A fourth potential cryptic species within C. tainanus was identified in this study. Further analysis is required to confirm the importance of C. jacobsoni and C. tainanus in BTV epidemiology in Asia.