Potential Vectors Of Bluetongue Virus Research Articles

Spatial distribution and habitat selection of culicoides imicola: The potential vector of bluetongue virus in Tunisia.

The increasing threat of vector-borne diseases (VBDs) represents a great challenge to those who manage public and animal health. Determining the spatial distribution of arthropod vector species is an essential step in studying the risk of transmission of a vector-borne pathogen (VBP) and in estimating risk levels of VBD. Risk maps allow better targeting surveillance and help in designing control measures. We aimed to study the geographical distribution of Culicoides imicola, the main competent vector of Bluetongue virus (BTV) in sheep in Tunisia. Fifty-three records covering the whole distribution range of C.imicola in Tunisia were obtained during a 2-year field entomological survey (August 2017 – January 2018 and August 2018 – January 2019). The ecological niche of C. imicola is described using ecological-niche factor analysis (ENFA) and Mahalanobis distances factor analysis (MADIFA). An environmental suitability map (ESM) was developed by MaxEnt software to map the optimal habitat under the current climate background. The MaxEnt model was highly accurate with a statistically significant area under curve (AUC) value of 0.941. The location of the potential distribution of C. imicola is predicted in specified regions of Tunisia. Our findings can be applied in various ways such as surveillance and control program of BTV in Tunisia.

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

BackgroundCulicoides (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.MethodsCulicoides 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.ResultsApproximately 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.ConclusionsTo 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.Graphical

Molecular identification of Culicoides (Diptera: Ceratopogonidae) species in Algeria

Bluetongue is a serious vector-borne viral disease that infects wild and domestic ruminants. The causative virus is transmitted by midges of the genus Culicoides, which consists of at least 1350 species worldwide. Since 1998, bluetongue disease has spread to Europe and northern Africa, including Algeria. To better understand the distribution of Culicoides species in Algeria, adult midges were collected from 17 different regions in Algeria from 2009 to 2015. At first, 492 specimens were grouped into 52 batches by wing patterns and geographic area of Algeria. Analysis of 60 nucleotide sequences of the mitochondrial cytochrome oxidase subunit I (COI) gene showed that the presence of 14 species including five unknown species, which were belonged to seven distinct subgenera. At least five species (C. imicola, C. obsoletus, C. puncticollis, C. kingi, and C. newsteadi) were discussed as potential vectors of bluetongue virus (BTV). The present study provides important insights into the genetic diversity of Culicoides and the potential spread of BTV in Algeria.

Ecological niche modelling to estimate the distribution of Culicoides, potential vectors of bluetongue virus in Senegal

BackgroundVector-borne diseases are among the leading causes of morbidity and mortality in humans and animals. In the Afrotropical region, some are transmitted by Culicoides, such as Akabane, bluetongue, epizootic haemorrhagic fever and African horse sickness viruses. Bluetongue virus infection has an enormous impact on ruminant production, due to its high morbidity and mortality rates.MethodsA nationwide Culicoides trapping campaign was organized at the end of the 2012 rainy season in Senegal. A Maximum Entropy approach (MaxEnt), Boosted Regression Tree (BRT) method and Ecological Niche Factor Analysis (ENFA) were used to develop a predictive spatial model for the distribution of Culicoides, using bio-climatic variables, livestock densities and altitude.ResultsThe altitude, maximum temperature of the warmest month, precipitation of the warmest quarter, mean temperature of the wettest quarter, temperature seasonality, precipitation of the wettest quarter and livestock density were among the most important factors to predict suitable habitats of Culicoides. Culicoides occurrences were, in most of the cases, positively correlated to precipitation variables and livestock densities; and negatively correlated to the altitude and temperature indices. The Niayes area and the Groundnut basin were the most suitable habitats predicted.ConclusionWe present ecological niche models for different Culicoides species, namely C. imicola, C. oxystoma, C. enderleini and C. miombo, potential vectors of bluetongue virus, on a nationwide scale in Senegal. Through our modelling approach, we were able to determine the effect of bioclimatic variables on Culicoides habitats and were able to generate maps for the occurrence of Culicoides species. This information will be helpful in developing risk maps for disease outbreaks.

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

BackgroundBluetongue disease of ruminants is a typical insect-borne disease caused by bluetongue virus (BTV) of the genus Orbivirus (family Reoviridae) and transmitted by some species of Culicoides (Diptera: Ceratopogonidae). Recently, the detection of BTV in yaks in high altitude meadows of the Shangri-La district of Yunnan Province, China, prompted an investigation of the Culicoides fauna as potential vectors of BTV.MethodsA total of 806 Culicoides midges were collected by light trapping at three sites at altitudes ranging from 1800 to 3300 m. The species were identified based on morphology and the 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 Culicoides spp. A phylogenetic analysis was used to analyze the cox1 sequences of some specimens.ResultsFour species dominated these collections and cox1 barcoding revealed that at least two of these appear to belong to species new to science. Culicoides tainanus and a cryptic species morphologically similar to C. tainanus dominated low altitude valley collections while C. nielamensis was the most abundant species in the high-altitude meadow. A species related to C. obsoletus occurred at all altitudes but did not dominate any of the collections. BTV RT-qPCR analysis detected BTV RNA in two specimens of C. tainanus, in one specimen closely related to C. tainanus and in one specimen closely related to C. obsoletus by barcode sequencing.ConclusionsThis study suggests that BTV in high altitude areas of Yunnan is being transmitted by three species of Culicoides, two of which appear to be new to science. This research may be useful in improving understanding of the effects of global warming on arboviral disease epidemiology and further study is important in research into disease control and prevention.

A Mini-review of Culicoides (Diptera: Ceratopogonidae) Fauna and its Vectorial Role in Tunisia

Following the bluetongue outbreaks in Tunisia from 1999 to 2006, bluetongue virus serotype 2 was isolated and several entomological investigations were performed. The present study reviewed the current status of Culicoides fauna in Tunisia and their role as proven and potential vectors of bluetongue virus based on the available and scattered reports. In total, about 35 species of Culicoides are known to occur in the country. Culicoides imicola is considered as the main and the proven vector of bluetongue virus. Other species of the genus Culicoides were suggested as potential vectors bluetongue virus. We cited mainly Culicoides obsoletus, Culicoides scoticus, Culicoides dewulfi and Culicoides pulicaris. Priority recommendations to prepare the country for future veterinary health challenges were suggested.

Laboratory rearing of immature Culicoides peregrinus Kieffer, a potential vector of bluetongue virus.

Culicoides peregrinus (Kieffer) (Diptera: Ceratopogonidae) was reared from egg to adult using four different combinations of food and substrate (T1: absorbent cotton, mud broth with 2% yeast; T2: 1% agar, mud broth with 2% yeast; T3: absorbent cotton, nutrient broth; T4: absorbent cotton, 2% yeast). Field-collected engorged females exhibited mean fecundity of 82.45 ± 4.00. The highest rate of emergence and largest adults were obtained in T1, and the lowest rate of emergence was observed in T4. Two-way analyses of variance with post hoc Tukey tests showed significant differences in age at pupation, pupal weight and wing length among the various treatments, although the sex ratio was 1 : 1 in all food/substrate combinations. The successful rearing of immature C. peregrinus is an encouraging step towards the establishment of a laboratory colony of this prevalent species associated with livestock.

Are Bogs Reservoirs for Emerging Disease Vectors? Evaluation of Culicoides Populations in the Hautes Fagnes Nature Reserve (Belgium)

Several species of Culicoides (Diptera: Ceratopogonidae) biting midges serve as biological vectors for the bluetongue virus (BTV) and the recently described Schmallenberg virus (SBV) in northern Europe. Since their recent emergence in this part of the continent, these diseases have caused considerable economic losses to the sheep and cattle industries. Much data is now available that describe the distribution, population dynamics, and feeding habits of these insects. However, little is known regarding the presence of Culicoides in unusual habitats such as peaty marshes, nor their potential vector capacity. This study evaluated Culicoides biting midges present in the bogs of a Belgian nature reserve compared to those residing at a nearby cattle farm. Culicoides were trapped in 2011 at four different sites (broadleaved and coniferous forested areas, open environments, and at a scientific station) located in the Hautes Fagnes Nature Reserve (Belgium). An additional light trap was operated on a nearby cattle farm. Very high numbers of biting midges were captured in the marshy area and most of them (70 to 95%) were Culicoides impunctatus, a potential vector of BTV and other pathogens. In addition, fewer numbers of C. obsoletus/C. scoticus species, C. chiopterus, and C. dewulfi were observed in the bogs compared to the farm. The wet environment and oligotrophic nature of the soil were probably responsible for these changes in the respective populations. A total of 297,808 Culicoides midges belonging to 27 species were identified during this study and 3 of these species (C. sphagnumensis, C. clintoni and C. comosioculatus) were described in Belgium for the first time.

Seasonal dynamics of biting midges (Diptera: Ceratopogonidae: Culicoides), the potential vectors of bluetongue virus, in Sweden

The outbreak of bluetongue (BT) in northern Europe 2006 initiated the monitoring of vectors, biting midges of the genus Culicoides in Sweden. In order to determine the diversity, distribution and seasonal dynamics of Culicoides, weekly collections were made during 2008 and during March–December 2009 using the Ondestepoort Veterinary Institute black light trap. Twenty sampling sites were selected in 12 provinces. In total of 30,704 Culicoides were collected in 2008 and 32,252 in 2009. The most abundant species were the potential vectors of BTV Culicoides obsoletus/C. scoticus that comprised of 77% of the total catches. Other biting midges collected were Culicoides impunctatus (9%), Culicoides grisescens (3%), Culicoides punctatus (2%), Culicoides chiopterus (2%) and Culicoides pulicaris (2%). Culicoides obsoletus/C. scoticus were most abundant during May–June and August–September. The majority of the species were active from March to November in 2008 and April to October in 2009. Species considered as potential vectors of bluetongue virus (BTV) occurred as far north as latitude 65°N (Kalix).

Synthèse des études sur la compétence vectorielle en Europe : que savons-nous ? que reste-t-il à apprendre ?

The correct identification of all potential vectors of bluetongue virus (BTV) is crucial for the implementation of integrated control measures, disease risk analysis and management of this disease. The collection of Culicoides midges and virus isolation from the captured midges will give an indication of what Culicoides species may be involved in the transmission of the virus. The number of midges collected with light traps will give an indica­tion of the risk of the virus spreading in the area. Reliable detection of BTV from field-collected vectors is dif­ficult due to several constraints related to the vector itself and to laboratory procedures. A clear recommendation will be to maximise insect collections after viraemias are detected in mam­mals. Where possible, captured individuals should be identified to species level and populations’ age graded. Virus detection in the collected midges is conducted by using molecular tech­niques [e.g. polymerase chain reaction (PCR)], and virus isola­tion is performed using either embryonated chicken eggs or cell cultures. Positive results from either pools or individuals have different meanings in terms of vector competence and need to be evaluated with care. Individually analysed parous midges from which virus could be isolated indicate that the insect has fed on a viraemic host. It does, however, not show that the virus has replicated in the vector and that transmission could be related to that species. Current laboratory techniques for measuring vector competence have several drawbacks, e.g. low blood feeding rates (especially so for European Culicoides species), the small size of Culicoides species involved, and the limited availability of laboratory colo­nies of European Culicoides species. Some techniques, as for example multiplex PCR, have increased the number of sam­ples which can be processed in one day (up to 800 insects). A recent trial, with field-collected Culicoides fed and incubated in the laboratory, showed transmissible infection levels in C. scoticus for BTV-9 and 8 similar to that reported from the field. Future needs in this field are the evaluation of cell types, e.g. Culicoides cell lines for virus isolation, detection of the virus in the saliva of Culicoides, the development of a reference colony (i.e. C. sonorensis), the sequencing of its genome, as well as the standardisation of experimental procedures run across wide geographic areas.

An assessment of Culicoides surveillance techniques in northern Europe: have we underestimated a potential bluetongue virus vector?

Summary 1. Bluetongue virus (BTV), a pathogen of ruminants transmitted by Culicoides midges, has emerged dramatically across Europe since 1998. Surveillance of Culicoides is currently carried out in every European country affected by BTV, most commonly using standardized light-suction traps that sample the population of adult Culicoides present. To date, however, it is not clear whether these trap catches accurately reflect the biting population of Culicoides . 2. In our study, we carried out 192 drop-trap catches at dusk on Poll Dorset sheep, drawing comparisons with surveillance samples taken using standard trapping protocol at the same site. A multiplex polymerase chain reaction technique was optimized for high-throughput processing of cryptic species to allow Culicoides collected to be identified to species level, the first time this has been achieved in this region for an ecological study. A mathematical model was then constructed to describe rates of midge biting under the meteorological conditions recorded during trials. 3. Light-trapping surveillance was found to substantially underestimate the numbers of Culicoides chiopterus present on sheep. This finding is extremely significant given that, due to the low numbers of this species caught at light traps across northern Europe, C. chiopterus had not been seriously considered as a potential vector of BTV. 4. The models constructed of successful blood feeding predict that while biting rates on sheep are significantly reduced under conditions adverse to midge flight (wind speeds that exceeded 3 mps, wind turbulence of greater than 40 degrees change in direction during the trial and solar intensity exceeding 200 Wm ‐2 ), low levels of biting can also occur under sub-optimal meteorological conditions, that have the potential to span entire days in the later part of the adult season. 5. Synthesis and applications. It is clear from these results that light-trapping surveillance does not provide an accurate reflection of the biting population of Culicoides present. Given that the surveillance systems are already in wide employment across Europe, but provide misleading results as we have demonstrated, and considering the huge economic and animal welfare impact of BTV incursions, it is vital that alternative/additional methods of surveillance are explored. Additionally, the vector competence of C. chiopterus as a potential vector of arboviruses requires urgent assessment, along with a clearer understanding of diel periodicity of Culicoides attacks throughout the adult season.

Diversity of biting midges of the genus Culicoides Latreille (Diptera: Ceratopogonidae) in the area of the Yacyretá Dam Lake between Argentina and Paraguay.

The Culicoides communities have been analyzed between 1993/1998 in the area influenced by the Yacyret Dam Lake (Paran River, Argentina-Paraguay). Adults of Culicoides were collected monthly by using CDC light traps exposed for 24 h in 9 sampling sites located at both margins of the river; 21 species were recorded. Highest values of species richness were recorded during 1993/1994, being Quiteria and Corpus the sites with the higest number of species (10 and 11, respectively). The species diversity was elevated in Quiteria, Zaim n, Candelaria, Santa Tecla, Capit n Meza and Corpus (Shannon's diversity index 1.0-1.9) while Corate , Ituzaing and Aguapey showed less richness and diversity. The more abundant species were C. insignis, C. venezuelensis, C. leopoldoi, C. limai, C. flinti, C. debilipalpis, C. paraensis and C. guttatus. C. insignis, potential vector of bluetongue virus (BTV) to domestic and wild rumiants in the Neotropical region, is the predominant species in the area and was the only species widely distributed. C. paraensis, a proven vector of Oropouche virus to humans, is a common and abundant species. C. pusillus and C. lahillei, potential vectors of BTV and a filarial parasite, respectively, were occasionally collected. The taxonomic structure of communities was constant during the study period. The occasional species were not characteristic to one particular site and their presence could be related to non-intrinsic conditions.

Seasonal variations in population size, fecundity, and parity rates of Culicoides insignis (Diptera: Ceratopogonidae) in Florida, USA.

Culicoides insignis constituted more than 99.9% of the Culicoides midges caught by light traps operated for 2 years at a cattle feedlot in southern Florida, USA. Males and nulliparous females were present in all collections except during the exceptionally cold winter months of 1982. Fecundity was examined and the mean number of eggs/clutch ranged from 79.0 in July 1980 to 107.1 in February 1980. The number of eggs was influenced by female size and by the ambient temperature during development of immatures. Because of the common occurrence of antibodies to bluetongue in south Florida, the absence of an established C. variipennis population, and the close association between cattle and C. insignis, this species must be considered a primary potential vector of bluetongue virus in southern Florida.

Observations on breeding sites and light-trap collections of Culicoides during an outbreak of bluetongue in Cyprus

AbstractDuring an epizootic of bluetongue virus disease of sheep in Cyprus in the autumn of 1977, 16 species of Culicoides were collected in light-traps and 4 species were collected from breeding sites. Two of the species found breeding in close association with sheep and goats are potential vectors of bluetongue virus. The possibility of a third species being a vector in Cyprus is discussed.