DNA barcode identification and molecular detection of bluetongue virus in Culicoides biting midges (Diptera: Ceratopogonidae) from western Thailand

Genetic analyses of Culicoides peregrinus (Diptera: Ceratopogonidae) reveal population differentiation in southern India a hotspot of bluetongue disease outbreaks and lack of gene flow across its range

Among India's 7 potential vectors of bluetongue virus (BTV), Culicoides peregrinus has assumed importance due to the recent isolation of BTV-23, with several severe bluetongue disease (BTD) outbreaks in Southern India and high abundance throughout India. These factors warrant the elucidation of its genetic structure across various physiographic regions. Adult Culicoides were captured from 14 collection locations across different physiographic areas of India. The study used 2 genetic markers, ie mitochondrial cytochrome oxidase-1 (COX-1) and nuclear ribosomal protein-S2B intron region (EPIC). COX-1 sequences of C. peregrinus from the other areas of its distribution were also considered. A high intraspecific genetic distance, ie 2.46% (within India) and 3.5% (across its distribution range) indicates the possibility of cryptic species. This vector has a relatively uniform genetic structure with a slight difference in the southern Indian population. However, the populations from different countries are genetically distinct and exhibit high genetic distances among themselves. There is evidence of demographic expansion with India as the probable ancestral region with 3 distinct lineages: India-Bangladesh, Thailand-China-Malaysia, and Australia. STRUCTURE analysis using EPIC marker (ribosomal protein-S2B intron region) depicted the distribution of 2 alleles in India but no population substructure. Pairwise FST indicated the south Indian population to have low but significant genetic differentiation with other Indian populations. More fine scale studies to ascertain the genetic differentiation of the Indian population along with direct experimental validation of vector competence is imperative to confirm C. peregrinus as the causative vector of BTD outbreaks.

Host blood meal analysis of Culicoides oxystoma (Diptera: Ceratopogonidae) in Tunisia

Culicoides are small hematophagous biting midges belonging to the family Ceratopogonidae. The genus is distributed worldwide yet remains poorly studied. This study investigated the vector and host specificity of Culicoides oxystoma, a species of significant relevance to the surveillance of vector-borne diseases in Tunisia and globally. The research was conducted in two Tunisian governments: Tozeur and Kairouan. A total of 24,366 adult midges were collected using two types of suction traps: the Center for Disease Control trap and the Onderstepoort Veterinary Institute trap. Females of Culicoides oxystoma were isolated, carefully dissected, and slide mounted in a phenol alcohol balsam mixture. A portion of the abdomen was excised for total DNA extraction to identify the origin of the blood meal. A total of 108 engorged females were analyzed using polymerase chain reaction (PCR) to amplify specific fragments of the cytochrome b gene, followed by sequencing and sequence analysis. However, DNA sequences were successfully obtained for only 56 individuals. Sequence analysis revealed that the midges fed on a variety of mammalian hosts, including humans, with a prevalence of Mus musculus and Bos taurus. This represents the first study aiming to identify a wide range of hosts in Tunisia and North Africa, providing valuable insights into the hosts utilized by Culicoides oxystoma for blood feeding.

Epidemiology of bluetongue virus infection among goat populations in central and western Thailand: Prevalence, risk factors, and serotype analysis

The current status of bluetongue (BT) in Thailand remains unclear, and the serotypes of BT virus (BTV) have not been determined. This study aimed to 1) investigate the epidemiology of BTV infection among goat populations in central and western Thailand; 2) evaluate the test performance of conventional RT-PCR for BTV detection; and 3) identify the BTV serotypes presently circulating in the study area. The herd seroprevalence was 94.6 % (53/56, 95 % CI = 85.3-98.1), while the individual seroprevalence was 74.4 % (434/583, 95 % CI = 70.5-77.6). The odds of BTV infection were higher in goats in the western region (aOR = 10.16, 95 % CI = 5.02-20.55), with the presence of nearby ruminant farms (aOR = 2.21, 95 % CI = 1.23-4.00), and aged ≥3 years (aOR = 14.02, 95 % CI = 6.32-31.08) but lower in goats with an intensive rearing system (aOR = 0.18, 95 % CI = 0.09-0.39). For BTV detection, conventional RT-PCR presented 84.5 % sensitivity and 97.4 % specificity with an AUC of 0.910 (95 % CI = 0.852-0.967). Seven BTV serotypes (2, 3, 4, 7, 12, 16, and 21) were identified. Among these, BTV-2, 12, and 21 were the most prevalent, and BTV-4 was first detected in Southeast Asia. These results illustrated that BT is endemic and spreading widely among goat populations in the study area. Conventional RT-PCR developed in this study proved to be a reliable method for BTV detection. This research provides the first report of BTV serotype distribution in Thailand.

Searching for potential Culicoides vectors of four orbiviruses in Yunnan Province, China

BACKGROUND

Some species of Culicoides (Diptera, Ceratopogonidae) are major vectors for arboviruses, and Yunnan Province is a key area for arbovirus prevalence in China. Therefore, this study attempts to search for potential Culicoides vectors for the common orbiviruses bluetongue virus (BTV), epizootic hemorrhagic disease virus (EHDV), Palyam virus (PALV) and Tibet orbivirus (TIBOV) in Yunnan Province, China.

METHODS

Culicoides specimens were collected from 16 counties in Yunnan Province, China, using UV traps and tested for BTV, EHDV, PALV and TIBOV through one-step reverse transcription-quantitative polymerase chain reaction (RT-qPCR). A total of 543 conspecific pools of Culicoides containing 9895 specimens were tested.

RESULTS

A total of 46 species belonging to 8 subgenera and 2 groups were recognized. A total of 19 species and a Culicoides subgenus Trithecoides complex were tested using RT-qPCR. One pool of Culicoides shortti Smith & Swaminath and one pool of Culicoides orientalis Macfie tested positive for BTV, one pool of Culicoides oxystoma Kieffer tested positive for PALV, and four pools of Culicoides jacobsoni Macfie tested positive for TIBOV. All the tested samples were negative for EHDV, and all the tested C. subgenus Trithecoides midges were negative for any virus.

CONCLUSIONS

Culicoides shortti was identified as a potential BTV vector for the first time. Culicoides jacobsoni was confirmed as a potential TIBOV vector and C. orientalis as a potential BTV vector. Culicoides oxystoma was also shown to be a natural carrier of PALV using the RT-qPCR method.

Culicoides and midge-associated arboviruses on cattle farms in Yunnan Province, China

Culicoides spp. (Diptera: Ceratopogonidae) are small biting midges, some of which are the vectors of arboviruses affecting livestock, i.e., African horse sickness virus (AHSV), bluetongue virus (BTV), and epizootic hemorrhagic disease virus (EHDV). Yunnan Province, located in southwestern China, has a history of high prevalence of arboviruses. The diversity and abundance of Culicoides was observed between March 2022 and March 2023 on two cattle farms in Lufeng County of Yunnan Province, China and virus isolation and PCR detection were attempted from cattle blood and Culicoides spp. collected from the farms. Light trap collections contained 19 species of Culicoides belonging to 8 subgenera and one unplaced species group and were dominated by C. oxystoma (63.4%), C. imicola (16.2%), C. arakawae (13.4%), C. sp. near newsteadi (2.3%), and C. orientalis (1.7%). A total of 8,343 Culicoides were used for statistical analysis; from these collections 997 Culicoides specimens belonging to 10 species were screened for the presence of BTV, EHDV, Yunnan Orbivirus (YUOV), and Yongshan totivirus (YSToV) using reverse transcription quantitative PCR (RT-qPCR). One strain of YUOV was isolated from cattle blood and 7 isolates of YSToV were isolated from 5 different species of Culicoides. BTV and YSToV were detected from 2 and 3 pools of parous C. imicola specimens by RT-qPCR, respectively, which is the first report of a totivirus to be associated with Culicoides. Culicoides imicola is likely to be the major vector of Culicoides-borne arboviruses in Lufeng County, which is a relatively dry locality, and adult C. imicola may play a role of BTV overwintering.

First molecular evidence of potential Culicoides vectors implicated in bluetongue virus transmission in Morocco

BACKGROUND

Bluetongue is a non-contagious viral disease that affects both domestic and wild ruminants. It is transmitted primarily by small hematophagous Diptera belonging to the genus Culicoides (Diptera: Ceratopogonidae). The current study represents the first molecular investigation into the potential role of Culicoides imicola, Culicoides paolae, Culicoides newsteadi, Culicoides spp., and Culicoides circumscriptus as bluetongue virus (BTV) vectors in Morocco. Additionally, the study aimed to evaluate the vectorial activity of midges during the survey seasons.

METHODS

Parous females of these species were captured from several regions of Morocco (6 out of 12) from 2018 to 2021 using Onderstepoort Veterinary Institute (OVI) traps. A total of 2003 parous female specimens were grouped into 55 batches. The midge body of each batch was dissected into three regions (head, thorax, and abdomen), and these regions were analyzed separately using reverse transcription quantitative polymerase chain reaction (RT-qPCR).

RESULTS

BTV RNA was detected in 45 out of the 55 batches tested, indicating a positivity rate of 81.8%. The RT-qPCR-positive pools of the studied Culicoides species exhibited high levels of BTV positivity in each body part (head, thorax, and abdomen), confirming the successful replication of the virus within midge bodies. The BTV circulation was substantial across all three survey seasons (spring, summer, and autumn). High infection rates, calculated using the minimum infection rate (MIR) and maximum likelihood estimation (MLE), were observed during the collection seasons, particularly in autumn and spring, and for all investigated Culicoides species, most notably for C. imicola and C. newsteadi. These increased infection rates underscore the significant risk of Culicoides transmitting the BTV in Morocco.

CONCLUSIONS

The detection of BTV positivity in Culicoides spp. (lacking wing spots that allow their differentiation according to morphological identification keys) suggested that other Culicoides species are competent for BTV transmission in Morocco. The study results indicated, for the first time at the molecular level, that C. imicola and C. newsteadi are the primary potential vectors of BTV in Morocco and that C. paolae and C. circumscriptus are strongly implicated in the propagation of bluetongue at the national level.

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.

Molecular identification of Culicoides oxystoma and Culicoides actoni vectors of bluetongue virus

Bluetongue is a non-contagious viral disease causing significant economic losses throughout the world. The bluetongue vectors Culicoides oxystoma and Culicoides actoni, which play a significant role in the transmission of various pathogens, are distributed across different geographical realms. Adults are minute in size with wide phenotypic variation, so morphology-based species identification is severely constrained by preparatory time and shortage of taxonomic expertise. To make the identification process rapid and effective, a specific primer was designed for the identification of C. actoni based on the multiple sequence alignment of ITS1 sequences of 11 Culicoides species. Along with this, a refined version of existing C. oxystoma specific primer was proposed. The primer sets distinguished C. oxystoma and C. actoni from a pooled sample consisting of other Culicoides species as well as closely related genera such as Forcipomyia and Alluaudomyia. Our findings suggest that the primers were species specific, sensitive and have potential to discriminate vector species C. oxystoma and C. actoni from pooled samples. To the best of our knowledge, these are the first ITS1 sequences generated and submitted in GenBank for Culicoides innoxius, Culicoides shortti, Culicoides palpifer and Culicoides anophelis and the first for Culicoides peregrinus, Culicoides fulvus and C. actoni from India.

Diversity, Abundance and Host Blood Meal Analysis of Culicoides Latreille (Diptera: Ceratopogonidae) from Cattle Pens in Different Land Use Types from Thailand

Biting midges of the genus Culicoides Latreille are significant pests and vectors that transmit pathogens to humans and other animals. Cattle are among the important livestock that can potentially be severely affected by Culicoides. In this study, we examined the species diversity, abundance, and host blood meal identification of biting midges in cattle pens located in three different land use types: villages, agricultural areas, and the forest edge. A total of 12,916 biting midges were collected, and most of these were from cattle pens located in villages (34%) and agricultural land (52%). Morphological identification revealed 29 Culicoides species. The most common species were C. oxystoma, C. mahasarakhamense, C. peregrinus, and C. shortti; taken together, these species represented >80% of all specimens collected. Despite midges being less numerous (14% of the total collection), cattle pens located near the forest showed greater diversity (23) than those from villages and agricultural areas. More diverse immature habitats and host blood sources from wildlife in nearby forests possibly explain the greater diversity in the cattle pens near the forest edge. Host blood meal analysis revealed that most (65%) biting midges had fed on buffalo despite the fact that this animal was much less numerous than cows or chickens. Relatively larger size and black-colored skin could be factors that make buffalo more attractive to biting midges than other host species. In this study, we also provided 67 DNA barcoding sequences of 13 species, three of which (C. flaviscutatus, C. geminus, and C. suzukii) were first reported from Thai specimens. DNA barcode analysis indicated cryptic diversity within C. hegneri and C. flavescens in Thailand, and thus, further investigation is required to resolve their species status.