Abstract
BackgroundCulicoides spp. biting midges transmit bluetongue virus (BTV), the aetiological agent of bluetongue (BT), an economically important disease of ruminants. In southern India, hyperendemic outbreaks of BT exert high cost to subsistence farmers in the region, impacting on sheep production. Effective Culicoides spp. monitoring methods coupled with accurate species identification can accelerate responses for minimising BT outbreaks. Here, we assessed the utility of sampling methods and DNA barcoding for detection and identification of Culicoides spp. in southern India, in order to provide an informed basis for future monitoring of their populations in the region.MethodsCulicoides spp. collected from Tamil Nadu and Karnataka were used to construct a framework for future morphological identification in surveillance, based on sequence comparison of the DNA barcode region of the mitochondrial cytochrome c oxidase I (COI) gene and achieving quality standards defined by the Barcode of Life initiative. Pairwise catches of Culicoides spp. were compared in diversity and abundance between green (570 nm) and ultraviolet (UV) (390 nm) light emitting diode (LED) suction traps at a single site in Chennai, Tamil Nadu over 20 nights of sampling in November 2013.ResultsDNA barcode sequences of Culicoides spp. were mostly congruent both with existing DNA barcode data from other countries and with morphological identification of major vector species. However, sequence differences symptomatic of cryptic species diversity were present in some groups which require further investigation. While the diversity of species collected by the UV LED Center for Disease Control (CDC) trap did not significantly vary from that collected by the green LED CDC trap, the UV CDC significantly outperformed the green LED CDC trap with regard to the number of Culicoides individuals collected.ConclusionsMorphological identification of the majority of potential vector species of Culicoides spp. samples within southern India appears relatively robust; however, potential cryptic species diversity was present in some groups requiring further investigation. The UV LED CDC trap is recommended for surveillance of Culicoides in southern India.Electronic supplementary materialThe online version of this article (doi:10.1186/s13071-016-1722-z) contains supplementary material, which is available to authorized users.
Highlights
Culicoides spp. biting midges transmit bluetongue virus (BTV), the aetiological agent of bluetongue (BT), an economically important disease of ruminants
Phylogenetic analysis Full length primer truncated DNA barcode sequences of 658 bp were recovered from 71 of the 73 specimens sampled from India, representing 12 morphologically identified species: C. actoni; C. anophelis Edwards, 1922; C. brevitarsis; C. huffi Causey, 1938; C. imicola; C. innoxius Sen & Das Gupta, 1959; C. kepongensis Lee, 1988; C. mesghalii Navai, 1973; C. oxystoma; C. peliliouensis Tokunaga, 1936; C. peregrinus; and C. similis Carter, Ingram & Macfie, 1920 (Additional file 1: Table S2), and one currently unidentified species
Species clades represented in the Bayesian Inference (BI) phylogeny were concordant with morphological identifications with the exception of one specimen, TPI:ENT:IBVNET-CULI-TN-65, which could not be assigned to a species based on the morphological descriptions currently available in the literature, and is recorded as ‘Unknown Species (I)’ (Fig. 4, Additional file 1: Table S2 and Additional file 2: Table S3)
Summary
Culicoides spp. biting midges transmit bluetongue virus (BTV), the aetiological agent of bluetongue (BT), an economically important disease of ruminants. In southern India, hyperendemic outbreaks of BT exert high cost to subsistence farmers in the region, impacting on sheep production. The aetiological agent of BT, bluetongue virus (BTV), is biologically transmitted between ruminant hosts by competent vectors of the genus Culicoides (Diptera: Ceratopogonidae) [3]. The combination of multiple potential vector species and a huge diversity of BTV strains [16, 17] makes India one of the most challenging areas in which to dissect transmission cycles and highlights the importance of this region due to it sharing features of the Afrotropical, Saharo-Arabian, Oriental and Australasian ecozones [6]. While broad relationships between Culicoides spp. abundance and transmission have been suggested [1], these remain very poorly defined and unpredictable
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