Integrative taxonomy uncovers a new Culicoides (Diptera: Ceratopogonidae) biting midge species from Thailand

DNA barcoding and host blood meal identification of Culicoides Latreille (Diptera, Ceratopogonidae) from Malaysia

Mitochondrial cytochrome oxidase I (COI) sequences were used to determine the genetic diversity and species identification efficacy of Culicoides from Malaysia. In total, 100 COI sequences were obtained from 13 morphologically identified species. Intraspecific genetic divergence varied from 0.48 % in C. parahumeralis to 14.88 % in C. palpifer. However, most (8 of 13) had low (<3 %) intraspecific genetic divergence. Identification of these species based on best match (BM) and best close match (BCM) methods revealed a high efficiency of the COI sequences with 100 % and 99 % success for BM and BCM, respectively. Identification in the BOLD database revealed that 10 species were successfully determined and agreed with morphological identifications. There remained three taxa which were ambiguous (C. jacobsoni) or had no species level identity match (C. palpifer and C. flavescens). Phylogenetic analyses found that all Malaysian specimens were clustered with conspecifics except C. palpifer. Specimens of this taxon separated into two divergent clades, one with members of a BIN (BOLD:ADT9601) of C. palpifer whereas the other formed a novel genetic lineage. Molecular species delimitation identified the morphologically identified species of the Malaysian Culicoides in the respective species. The exceptions were two divergent lineages found in C. palpifer because they were treated as two different taxa. Molecular identification of the host blood meal source revealed that all were from water buffalo (Bubalus bubalis).

A preliminary account of Culicoides (Diptera: Ceratopogonidae) from the Andaman and Nicobar Islands with 13 new records and updated species inventory from India

BACKGROUND

The detection of multiple bluetongue virus serotypes, increasing trend in livestock density, rich biological diversity with high endemism, and the status of the Andaman and Nicobar Islands as a popular tourist destination underscore the need for a faunistic survey of medically and veterinary significant vector species, specifically Culicoides, in this region. Moreover, scattered information on Indian Culicoides species complicates the planning and implementation of preventive measures for pathogens transmitted by these vectors. This study aims to provide the first comprehensive account of the Culicoides fauna in the Andaman and Nicobar Islands, India, along with an updated checklist of Indian Culicoides species and their state-wise distribution.

METHODS

Surveys were conducted across various habitats in the Andaman and Nicobar Islands in September 2022 and 2023. Midges were collected using CDC light traps, light sheets, Malaise traps, and manual collection from exposed body parts of the author and volunteers (biting collection). Identification was carried out using relevant taxonomic keys and original descriptions. Additionally, an updated checklist of Indian Culicoides, based on published and grey literature from 1910 to the present, is provided, with an emphasis on their potential role in pathogen transmission.

RESULTS

A total of 3529 adult Culicoides were trapped during the survey, representing 5 subgenera and 3 unplaced species groups. The study recorded 23 Culicoides species, including 13 new species records for India: C. barnetti, C. gouldi, C. flaviscutellaris, C. flavipunctatus, C. hui, C. histrio, C. guttifer, C. perornatus, C. okinawensis, C. quatei, C. obscurus, C. coronalis, and C. kusaiensis.

CONCLUSIONS

The Indian Culicoides fauna now includes 93 valid species, with many of them recognized as confirmed or potential vectors of important pathogens of animal health. The enriched species composition highlights the importance of systematic surveys in this island ecosystem and the need to determine the role of midges, if any, in pathogen transmission.

Seasonal dynamics, Leishmania diversity, and nanopore-based metabarcoding of blood meal origins in Culicoides spp. in the newly emerging focus of leishmaniasis in Northern Thailand

BACKGROUND

Clinical cases of leishmaniasis caused by Leishmania (Mundinia) parasites have been increasingly reported in Southeast Asia, particularly Thailand. Recent evidence has shown that Leishmania (Mundinia) parasites successfully developed into infective metacyclic promastigotes in Culicoides biting midges, strongly supporting their putative role in disease transmission. However, Culicoides diversity, host preference, and Leishmania prevalence in endemic areas remain largely unknown.

METHODS

We investigated the seasonal dynamics, infection prevalence, and blood meal identification of Culicoides collected from the emerging focus of visceral leishmaniasis in Lampang Province, Northern Thailand, during 2021-2023. Midge samples were molecularly screened for Leishmania using SSU rRNA-qPCR and ITS1-PCR, followed by Sanger plasmid sequencing, and parasite haplotype diversity was analyzed. Host blood meal origins were comparatively identified using host-specific Cytb-PCRs and a nanopore-based metabarcoding approach.

RESULTS

A total of 501 parous and gravid females and 46 blood-engorged ones belonging to at least 17 species of five subgenera (Remmia, Trithecoides, Avaritia, Hoffmania, and Meijerehelea) and two species groups (Shortti and Calvipalpis) were collected with temporal differences in abundance. Leishmania was detected by SSU rRNA-qPCR in 31 samples of at least 11 midge species, consisting of Culicoides oxystoma, C. guttifer, C. orientalis, C. mahasarakhamense, C (Trithecoides) spp., C. innoxius, C. shortti, C. arakawae, C. sumatrae, C. actoni, and C. fulvus, with the overall infection prevalence of 5.7%. The latter six species represent the new records as putative leishmaniasis vectors in Northern Thailand. The ITS1-PCR and plasmid sequencing revealed that Leishmania martiniquensis was predominantly identified in all qPCR-positive species, whereas L. orientalis was identified only in three C. oxystoma samples. The most dominant haplotype of L. martiniquensis in Thailand was genetically intermixed with those from other geographical regions, confirming its globalization. Neutrality test statistics were also significantly negative on regional and country-wide scales, suggesting rapid population expansion or selective sweeps. Nanopore-based blood meal analysis revealed that most Culicoides species are mammalophilic, with peridomestic and wild mammals (cow, pig, deer, and goat-like species) and humans as hosts, while C. guttifer and C. mahasarakhamense fed preferentially on chickens.

CONCLUSIONS

This study revealed seasonal dynamics and sympatric circulation of L. martiniquensis and L. orientalis in different species of Culicoides. Evidence of human blood feeding was also demonstrated, implicating Culicoides as putative vectors of human leishmaniasis in endemic areas. Further research is therefore urgently needed to develop vector control strategies and assess the infection status of their reservoir hosts to effectively minimize disease transmission.

Seasonal Abundance and Diversity of Culicoides Biting Midges in Livestock Sheds in Kanchanaburi Province, Thailand

Culicoides biting midges were collected using UV light traps from nine livestock farms in Kanchanaburi Province, Thailand. Collections were made one night per month from June 2020 to May 2021 to determine the seasonal changes and spatial distribution of the Culicoides assemblage. The influence of four environmental factors (temperature, rainfall, humidity, and wind speed), types of animals in each shed (cattle, pigs, and avians), and neighboring animals (those in the other sheds and their proximity) were assessed. A subsample of 130,670 out of a total of 224,153 specimens collected was identified and counted. The collections were predominantly female (76.9%), though males were also commonly collected (23.1%). The dominant species included C. peregrinus (97,098 individuals; 43.0%), C. oxystoma (55,579; 24.6%), C. arakawae (45,996; 20.4%), and C. imicola (15,703; 7.0%), while other species accounted for the remaining 9777 individuals (4.4%). Trap captures were strongly influenced by seasons and animal sheds. Cattle exhibited the greatest effect on the community, likely due to their large biomass. Humidity and temperature had a positive effect on trap captures, whereas wind speed exhibited a negative effect. Cattle positively influenced all major species, except for C. arakawae, which showed a positive association with avians. A "neighboring effect" was also observed. Additionally, the lowest dispersal ability of C. arakawae was suggested.

Nanopore-Based Surveillance of Leishmania Parasites in Culicoides Latrielle (Diptera: Ceratopogonidae) Caught from the Affected Community and Tham Phra Cave in Chiang Rai Province, the Endemic Area of Leishmaniasis in Northern Thailand

In this research, we elucidated the species composition of Culicoides biting midges, infection prevalence, and genetic diversity of Leishmania parasites circulating in the affected community in Chiang Rai Province, being the most endemic area in Northern Thailand. A total of 146 parous and gravid females, belonging to at least twelve Culicoides species in five subgenera and one species group, were trapped from three collection sites with an overall Leishmania prevalence of 26.7% (39/146). Leishmania was detected, using ITS1-PCR, in C. mahasarakamense (15), C. guttifer (11), C. (Trithecoides) spp. (8), C. jacobsoni (2), C. oxystoma (2), and C. orientalis (1). The evidence of Leishmania infection in these last five species represents new records in Northern Thailand. Given a high infection rate in cavernicolous specimens, this indicates an increased risk of parasite exposure when visiting the cave. Using the nanopore amplicon sequencing, L. martiniquensis was ubiquitously identified in all positives, and more than half of these were also co-infected with L. orientalis. The genetic diversity analysis revealed 13 and 17 unique haplotypes for L. martiniquensis and L. orientalis, respectively. Higher haplotype diversity and relatively low nucleotide diversity were observed in both parasite populations, suggesting recent population divergence. Neutrality tests (Tajima's D and Fu and Li's D) showed to be significantly negative, indicating rapid population growth or a selective sweep. Moreover, dominant haplotypes of both Leishmania species were 100% identical to those in all leishmaniasis patients previously reported from Northern Thailand, strongly supporting the imperative role of Culicoides spp. in disease transmission. Essentially, this research provides the first entomological surveillance data representing the sympatric existence, transmission dynamics, and genetic complexity of two autochthonous Leishmania (Mundinia) parasites in several Culicoides species in the endemic area of Northern Thailand. This would contribute to a more complete understanding of the epidemiology of vector infection and facilitate the development of vector control programs to effectively reduce the transmission of this neglected tropical disease in endemic areas of Northern Thailand.

Natural infection with Leishmania (Mundinia) martiniquensis supports Culicoides peregrinus (Diptera: Ceratopogonidae) as a potential vector of leishmaniasis and characterization of a Crithidia sp. isolated from the midges

The prevalence of autochthonous leishmaniasis in Thailand is increasing but the natural vectors that are responsible for transmission remain unknown. Experimental in vivo infections in Culicoides spp. with Leishmania (Mundinia) martiniquensis and Leishmania (Mundinia) orientalis, the major causative pathogens in Thailand, have demonstrated that biting midges can act as competent vectors. Therefore, the isolation and detection of Leishmania and other trypanosomatids were performed in biting midges collected at a field site in an endemic area of leishmaniasis in Tha Ruea and a mixed farm of chickens, goats, and cattle in Khuan Phang, Nakhon Si Thammarat province, southern Thailand. Results showed that Culicoides peregrinus was the abundant species (>84%) found in both locations and only cow blood DNA was detected in engorged females. Microscopic examination revealed various forms of Leishmania promastigotes in the foregut of several C. peregrinus in the absence of bloodmeal remnants, indicating established infections. Molecular identification using ITS1 and 3'UTR HSP70 type I markers showed that the Leishmania parasites found in the midges were L. martiniquensis. The infection rate of L. martiniquensis in the collected flies was 2% in Tha Ruea and 6% in Khuan Phang, but no L. orientalis DNA or parasites were found. Additionally, organisms from two different clades of Crithidia, both possibly new species, were identified using SSU rRNA and gGAPDH genes. Choanomastigotes and promastigotes of both Crithidia spp. were observed in the hindgut of the dissected C. peregrinus. Interestingly, midges infected with both L. martiniquensis and Crithidia were found. Moreover, four strains of Crithidia from one of the clades were successfully isolated into culture. These parasites could grow at 37°C in the culture and infect BALB/c mice macrophages but no multiplication was observed, suggesting they are thermotolerant monoxenous trypanosomatids similar to Cr. thermophila. These findings provide the first evidence of natural infection of L. martiniquensis in C. peregrinus supporting it as a potential vector of L. martiniquensis.

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.

DNA Barcoding of Culicoides Latreille (Diptera: Ceratopogonidae) From Thailand Reveals Taxonomic Inconsistencies and Novel Diversity Among Reported Sequences

Recent focus on Culicoides species diversity in Thailand was prompted by a need to identify vectors responsible for the transmission of African Horse Sickness in that country. To assist rapid genetic identification of species, we sampled mitochondrial cytochrome c oxidase subunit I (COI) DNA barcodes (N = 78) from 40 species of Culicoides biting midge from Thailand, including 17 species for which DNA barcodes were previously unavailable. The DNA barcodes were assigned to 39 Barcode Identification Numbers (BINs) representing terminal genetic clusters at the Barcode of Life Data systems (BOLD). BINs assisted with comparisons to published conspecific DNA barcodes and allowed partial barcodes obtained from seven specimens to be associated with BINs by their similarity. Some taxonomic issues were revealed and attributed to the possible misidentification of earlier reported specimens as well as a potential synonymy of C. elbeli Wirth & Hubert and C. menglaensis Chu & Liu. Comparison with published BINs also revealed genetic evidence of divergent population processes and or potentially cryptic species in 16 described taxa, flagged by their high levels of COI sequence difference among conspecifics. We recommend the BOLD BIN system to researchers preparing DNA barcodes of vouchered species for public release. This will alert them to taxonomic incongruencies between their records and publicly released DNA barcodes, and also flag genetically deep and potentially novel diversity in described species.

First Evidence of Co-Circulation of Emerging Leishmania martiniquensis, Leishmania orientalis, and Crithidia sp. in Culicoides Biting Midges (Diptera: Ceratopogonidae), the Putative Vectors for Autochthonous Transmission in Southern Thailand

Since 1996, autochthonous cases of emerging leishmaniasis caused by Leishmania (Mundinia) martiniquensis and Leishmania (Mundinia) orientalis have been more frequently reported, especially in the northern and southern parts of Thailand. However, the accurate identification of their natural vectors and reservoirs remains unconfirmed. Previous studies have suggested that these emerging parasites might be transmitted by other non-phlebotomine vectors. Herein, we speculated that Culicoides biting midges might act as the competent vectors responsible for autochthonous leishmaniasis in southern Thailand. In this research, 187 non-engorged, parous and gravid Culicoides females and 47 blood-engorged ones were trapped from the residences of two recently diagnosed visceral leishmaniasis patients in Sadao District and the unaffected site in Rattaphum District, Songkhla Province, southern Thailand. Species diversity and abundance of biting midges varied among the trapping sites. Using ITS1-PCR and BLASTn analysis, L. martiniquensis was predominantly detected in several Culicoides species, including C. peregrinus, C. oxystoma, C. mahasarakhamense, and C. huffi from the vicinity of patients’ houses; and in C. fordae and C. fulvus from the unaffected site. L. orientalis was also co-circulated in C. peregrinus and C. oxystoma caught near the second patient’s house. Additionally, Crithidia sp. were also detected using SSU rRNA-PCR across Culicoides spp. Host blood meal analysis of eight different Culicoides species from the unaffected site also revealed that all trapped Culicoides had fed on cows and goats, indicating the possible role of these mammalian species as reservoir hosts. Essentially, this study is the first entomological investigation, revealing the co-circulation of emerging trypanosomatids among several species of Culicoides biting midges and strongly supporting the potential role of this insect group as the main vectors responsible for the epidemiology of autochthonous leishmaniasis in southern Thailand.

Population Genetic Structure and Population History of the Biting Midge Culicoides mahasarakhamense (Diptera: Ceratopogonidae)

Biting midges of the genus Culicoides Latreille are significant pests and vectors of disease agents transmitted to humans and other animals. Understanding the genetic structure and diversity of these insects is crucial for effective control programs. This study examined the genetic diversity, genetic structure, and demographic history of Culicoides mahasarakhamense, a possible vector of avian haemosporidian parasites and Leishmania martiniquensis, in Thailand. The star-like shape of the median joining haplotype network, a unimodal mismatch distribution, and significant negative values for Tajima's D and Fu's F_S tests indicated that populations had undergone recent expansion. Population expansion time was estimated to be 2000-22,000 years ago. Population expansion may have been triggered by climatic amelioration from cold/dry to warm/humid conditions at the end of the last glaciations, resulting in the increased availability of host blood sources. Population pairwise F_ST revealed that most (87%) comparisons were not genetically different, most likely due to a shared recent history. The exception to the generally low level of genetic structuring is a population from the northern region that is genetically highly different from others. Population isolation in the past and the limitation of ongoing gene flows due to large geographic distance separation are possible explanations for genetic differentiation.

DNA Barcoding of genus Culicoides biting midges (Diptera: Ceratopogonidae) in the Brazilian Amazon

Culicoides biting midges are capable to transmit Oropouche virus, Bluetongue virus and Mansonella spp. This study aimed to assess the utility of DNA barcode as an alternative method in the Culicoides species identification. The study was conducted in Jamari National Forest. Biting midges were collected using HP light traps during four months, February, April, August and October, 2018. Insects were morphologically identified to the species level, and rest of the body were subjected to DNA extraction and PCR targeting a fragment of the cytochrome c oxidase subunit I (COI) gene, which were analyzed and deposited in GenBank. A phylogenetic gene tree was reconstructed using RAxML software, and the sequences were assigned at Molecular Operational Taxonomic Unit (MOTU) level by species delimitation algorithms. According to morphological approach, 18 species of 2 subgenera and 7 species groups were identified. A total of 191 new COI barcodes from 18 species were generated. Of these, fifteen species have been deposited for the first time in all datasets in the world. These sequences allowed the correct identification of 188 and 187 specimens according to the BM and BCM criteria, respectively. The intraspecific genetic distances ranged from 0 to 16.5%, while the interspecific ones ranged from 2.1 to 27.1%. The nominal species Culicoides glabellus and C. tetrathyris splitted into three and two MOTUs, respectively, except for mPTP, indicating a cryptic diversity in these species. Also, sequences of C. pseudodiabolicus formed two MOTUs using all algorithms, except for PTP and ABGD, suggesting the existence of two potential species. In contrast, some barcodes of C. quasiparaensis and C. paraensis merged into a single MOTU, which can be explained by the complex characteristics of the paraensis group, since these species have similar morphological characters. Here, we provided the first COI barcodes for biting midges in Rondônia and Brazil, and demonstrates that these are sufficient to discriminate between some species.

Culicoides Latreille (Diptera: Ceratopogonidae) as potential vectors for Leishmania martiniquensis and Trypanosoma sp. in northern Thailand

Biting midges of genus Culicoides (Diptera: Ceratopogonidae) are the vectors of several pathogenic arboviruses and parasites of humans and animals. Several reports have suggested that biting midges might be a potential vector of Leishmania parasites. In this study, we screened for Leishmania and Trypanosoma DNA in biting midges collected from near the home of a leishmaniasis patient in Lamphun province, northern Thailand by using UV-CDC light traps. The identification of biting midge species was based on morphological characters and confirmed using the Cytochrome C oxidase subunit I (COI) gene. The detection of Leishmania and Trypanosoma DNA was performed by amplifying the internal transcribed spacer 1 (ITS1) and small subunit ribosomal RNA (SSU rRNA) genes, respectively. All the amplified PCR amplicons were cloned and sequenced. The collected 223 biting midges belonged to seven species (Culicoides mahasarakhamense, C. guttifer, C. innoxius, C. sumatrae, C. huffi, C. oxystoma, and C. palpifer). The dominant species found in this study was C. mahasarakhamense (47.53%). Leishmania martiniquensis DNA was detected in three samples of 106 specimens of C. mahasarakhamense tested indicating a field infection rate of 2.83%, which is comparable to reported rates in local phlebotomines. Moreover, we also detected Trypanosoma sp. DNA in one sample of C. huffi. To our knowledge, this is the first molecular detection of L. martiniquensis in C. mahasarakhamense as well as the first detection of avian Trypanosoma in C. huffi. Blood meal analysis of engorged specimens of C. mahasarakhamense, C. guttifer, and C. huffi revealed that all specimens had fed on avian, however, further studies of the host ranges of Culicoides are needed to gain a better insight of potential vectors of emerging leishmaniasis. Clarification of the vectors of these parasites is also important to provide tools to establish effective disease prevention and control programs in Thailand.

Culicoides are known to be vectors of several pathogens, including arboviruses and parasites. However, other investigations have demonstrated that Culicoides could be involved in the transmission of Leishmania and Trypanosoma parasites. Our studies demonstrated the first detection of L. martiniquensis in Culicoides mahasarakhamense and Trypanosoma sp., which is closely related to avian Trypanosome in C. huffi from an endemic area of leishmaniasis in northern Thailand. The finding of this work suggested that Culicoides biting midges are suspected to be the potential vector of L. martiniquensis and Trypanosoma parasites in Thailand.

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

Biting midges of the genus Culicoides Latreille are biological vectors of bluetongue virus (BTV), a member of family Reoviridae, genus Orbivirus. About 30 species of Culicoides have been identified as competent BTV vectors worldwide. Even though high seroprevalence of BTV has been reported among livestock ruminants from western Thailand, the Culicoides species which contribute to BTV transmission remain unclear. In the present study, Culicoides were collected from eight sampling sites, located in two BTV prevalent provinces in western Thailand. Adult Culicoides were identified using wing morphology and cytochrome c oxidase subunit I (COI) mtDNA molecular marker. A total of 9,677 Culicoides specimens belonging to 7 subgenera, 3 species groups, and 23 species were identified. After comparing sequencing results with available data from GenBank, COI sequences of five species were reported for the first time from Thailand. The most abundant potential BTV vector species collected were C. peregrinus, followed by C. orientalis, C. imicola, C. oxystoma, and C. fulvus. Out of 72 Culicoides pools, 9 pools (4 from C. orientalis, 2 from C. imicola, 2 from C. oxystoma, and 1 from C. fulvus) were positive by BTV RT-PCR analyses. These results are new to Culicoides BTV vector knowledge in Thailand and will contribute to further BTV studies in this particular region.

Molecular detection of avian haemosporidian parasites in biting midges (Diptera: Ceratopogonidae) from Thailand

Culicoides biting midges are vectors of many haemosporidian parasite species. These parasites are found in several wild and domestic avian species in Thailand but knowledge of the insect vectors is very limited. In this study, a molecular approach was used to detect haemosporidian parasites in six biting midge species in Thailand. A total of fifteen cytochrome b haplotypes of three haemosporidian parasites were detected from 1,165 specimens of six different Culicoides species. Comparisons of these sequences with those recorded in a public database revealed that they were comprised sequences of three species, Leucocytozoon sp., Plasmodium juxtanucleare and P. gallinaceum. All of these haemosporidian parasite species were detected in Culicoides mahasarakhamense Pramual, Jomkumsing, Piraonapicha, & Jumpato while P. juxtanucleare was also detected in C. huffi Causey and C. guttifer Meijere and Leucocytozoon sp. were also detected in C. guttifer. All of these parasites are commonly found in chickens in agreement with information that these biting midge species will bite chickens. Detection DNA of Leucocytozoon sp. in biting midges reported here provides the second record of this parasitic genus infecting Culicoides. This study also provides the first records of P. juxtanucleare and P. gallinaceum in biting midge species. Further investigation is required to determine whether Culicoides biting midge species are competent vectors of these parasites.