Experimental infection studies of UK Culicoides species midges with bluetongue virus serotypes 8 and 9.

This paper describes a rapid, standardised method for testing the susceptibility to bluetongue virus (BTV) of northern Palaearctic Culicoides species midges that can be used to assess the competence of both field-caught and laboratory-infected midges. The method has been used to show that Culicoides scoticus can replicate btv serotype 8 and BTV serotype 9 strains to more than 3 log(10) TCID50/midge, the first evidence of the potential of this species to transmit BTV.

Incursion and range expansion in the bluetongue vector Culicoides imicola in the Mediterranean basin: a phylogeographic analysis.

The bluetongue (BT) vector Culicoides imicola Kieffer (Diptera: Ceratopogonidae) has undergone widespread range expansion across most of the Mediterranean basin, concomitant with the largest BT epizootic outbreaks on record. Knowledge of the substructure of this vector expansion would be useful for identifying specific source-expansion systems. To this end we analysed the haplotype diversity of the mitochondrial cytochrome oxidase I gene in 273 C. imicola from 88 Mediterranean sites and outgroups. All the C. imicola haplotypes (n = 26) formed a single, distinct clade in comparison with haplotypes of four other species of the Imicola group from southern Africa, confirming C. imicola as a single phylospecies. Haplotype distribution showed extreme differentiation across the Mediterranean basin, with four common haplotypes each predominating in different areas. Eastern and western areas characterized by distinct BT incursions accounted for most of the molecular variance in haplotype composition. Shared common haplotypes identified one area of incursion and expansion encompassing the western half of the Mediterranean basin, with evidence of population growth, and another system encompassing Anatolian Turkey, the Aegean Islands and mainland Greece. A third area of range expansion was identified in the central Mediterranean, with a possible source in Algeria and unsampled parts of central North Africa. We conclude that the expansion of C. imicola in the Mediterranean basin consists of at least three incursions followed by expansions and that the western system experiences conditions promoting high population growth.

Molecular taxonomy and population structure of a Culicoides midge vector.

The biting midge Culicoides imicola Kieffer (Diptera: Ceratopogonidae) is the major Old World vector of the arboviruses that cause African horse sickness (AHS) and bluetongue (BT). Recently, the incidence and geographical scales of AHS and BT outbreaks in the Mediterranean Basin have increased, with serotype distribution in the BT outbreaks being geographically structured. The authors review molecular approaches for assessing the contribution of cryptic species and population subdivision in C. imicola to BT serotype structure in this region. No evidence was found for cryptic species. In contrast, evidence was found for marked matrilineal subdivision between the eastern and western parts of the Mediterranean Basin. This pattern is comparable to the geographic structure of BT serotypes, suggesting that subdivision in the insect vector potentially constrains serotype spread. The authors are presently testing this hypothesis.

Phylogenetic status and matrilineal structure of the biting midge, Culicoides imicola, in Portugal, Rhodes and Israel.

The biting midge Culicoides imicola Kieffer (Diptera: Ceratopogonidae) is the most important Old World vector of African horse sickness (AHS) and bluetongue (BT). Recent increases of BT incidence in the Mediterranean basin are attributed to its increased abundance and distribution. The phylogenetic status and genetic structure of C. imicola in this region are unknown, despite the importance of these aspects for BT epidemiology in the North American BT vector. In this study, analyses of partial mitochondrial cytochrome oxidase subunit I gene (COI) sequences were used to infer phylogenetic relationships among 50 C. imicola from Portugal, Rhodes, Israel, and South Africa and four other species of the Imicola Complex from southern Africa, and to estimate levels of matrilineal subdivision in C. imicola between Portugal and Israel. Eleven haplotypes were detected in C. imicola, and these formed one well-supported clade in maximum likelihood and Bayesian trees implying that the C. imicola samples comprise one phylogenetic species. Molecular variance was distributed mainly between Portugal and Israel, with no haplotypes shared between these countries, suggesting that female-mediated gene flow at this scale has been either limited or non-existent. Our results provide phylogenetic evidence that C. imicola in the study areas are potentially competent AHS and BT vectors. The geographical structure of the C. imicola COI haplotypes was concordant with that of BT virus serotypes in recent BT outbreaks in the Mediterranean basin, suggesting that population subdivision in its vector can impose spatial constraints on BT virus transmission.