Bluetongue virus infection in naïve cattle: Identification of circulating serotypes and associated Culicoides biting midge species in Trinidad.

To better understand risks associated with trading cattle, it is important to know which serotypes of Bluetongue virus (BTV) are circulating within the exporting and importing country. Hence, this study was conducted to identify the circulating serotypes of BTV in Trinidad. Blood samples were collected monthly from sixty BTV- naïve imported cattle over a six month period after their arrival in the country. Virological (PCR and virus isolation) and serological (ELISA) analyses were carried out on the samples and CDC light traps were placed near the cattle enclosure to trap and identify the species of Culicoides biting midges that were present. All of the cattle seroconverted for BTV antibodies within three months of their arrival in the country and real-time reverse transcription PCR (rRT-PCR) detected BTV-RNA in the samples throughout the remainder of the study. The patterns of infection observed in the cattle indicated serial infections with multiple serotypes. A combination of BTV serotype-specific rRT-PCR on the original blood samples and virus isolation followed by serotype-specific rRT-PCR on selected samples, confirmed the presence of BTV serotypes 1, 2, 3, 5, 12 and 17. This is the first report of BTV-2 and BTV-5 in Trinidad. Light-suction traps placed in close proximity to the cattle predominantly trapped Culicoides insignis Lutz 1913 species (96%), with a further six Culicoides species making up the remaining 4% of trapped samples. The circulation of multiple BTV serotypes in Trinidad underlines the need for regular surveillance, which will contribute to the development of risk assessments for trade in livestock.

Culicoides Latreille (Diptera: Ceratopogonidae) taxonomy: current challenges and future directions.

Culicoides Latreille biting midges (Diptera: Ceratopogonidae) cause a significant biting nuisance to humans, livestock and equines, and are the biological vectors of a range of internationally important pathogens of both veterinary and medical importance. Despite their economic significance, the delimitation and identification of species and evolutionary relationships between species within this genus remains at best problematic. To date no phylogenetic study has attempted to validate the subgeneric classification of the genus and the monophyly of many of the subgenera remains doubtful. Many informal species groupings are also known to exist but few are adequately described, further complicating accurate identification. Recent contributions to Culicoides taxonomy at the species level have revealed a high correlation between morphological and molecular analyses although molecular analyses are revealing the existence of cryptic species. This review considers the methods for studying the systematics of Culicoides using both morphological and genetic techniques, with a view to understanding the factors limiting our current understanding of Culicoides biology and hence arbovirus epidemiology. In addition, we examine the global status of Culicoides identification, highlighting areas that are poorly addressed, including the potential implementation of emerging technologies.

Does covering of farm-associated Culicoides larval habitat reduce adult populations in the United Kingdom?

Culicoides biting midges (Diptera: Ceratopogonidae) are the biological vectors of a range of internationally important arboviruses of livestock, including bluetongue virus (BTV) and the recently emerging Schmallenberg virus (SBV). Culicoides species in the subgenus Avaritia (in the UK: Culicoides obsoletus Meigen, Culicoides scoticus Downes & Kettle, Culicoides dewulfi Goetghebuer and Culicoides chiopterus Meigen) have been implicated in BTV transmission in northern Europe and to a varying degree utilise cattle dung as a larval development substrate. The collection of cattle dung into heaps on farms provides a localised source of Culicoides emergence in close proximity to livestock. This study assesses the impact of covering dung heaps prior to the onset of adult Culicoides activity with the aim of reducing recruitment to the local adult populations at four livestock farms in England. Light suction trap catches of adult Culicoides from these farms were compared with those from four untreated control farms from a wide geographic range across the UK. It was demonstrated that implementing control of emergence from dung heaps did not have a significant impact upon the local adult subgenus Avaritia abundance at the treated farm holdings and that the onset of Culicoides activity was similarly unaffected. Use of this method in isolation is unlikely to have an effect in reducing the risk of BTV and SBV transmission. The implications of these results for control of farm-associated Culicoides in Europe are discussed.

Larval development and emergence sites of farm-associated Culicoides in the United Kingdom.

Culicoides biting midges (Diptera: Ceratopogonidae) are the biological vectors of internationally important arboviruses of livestock including bluetongue virus (BTV). Information on the habitats used by Culicoides for larval development is valuable for establishing targeted vector control strategies and for improving local scale models of vector abundance. This study combines emergence trap collections of adult Culicoides identified using molecular markers and physiochemical measurements of habitats to investigate larval development sites of Palaearctic Culicoides in South East England. The known range of larval habitats for several Culicoides species is extended and the potential BTV vector species C. obsoletus and C. scoticus are confirmed to co-occur in many larval habitats. The presence of emerging C. obsoletus was favoured by increasing substrate moisture level [odds ratio (OR) 6.94 (2.30; 20.90)] and substrate pH [OR 4.80 (1.66; 13.90)] [bias-corrected Dxy : 0.68; area under the curve (AUC): 0.86] rather than any particular larval habitat type, as expected for a species with relatively wide larval habitat preference. Of the newly emerged sub-genus Avaritia individuals collected, 23% were observed to have a degree of abdominal pigmentation commonly inferred to indicate parity. If consistent across species and locations, this observation represents a potential source of error for age structure analyses of Culicoides populations.

Collection of Culicoides (Diptera: Ceratopogonidae) using CO2 and enantiomers of 1-octen-3-ol in the United Kingdom.

The host kairomones carbon dioxide (CO2) and 1-octen-3-ol elicit a host seeking response in a wide range of haematophagous Diptera. This study investigates the response of Culicoides biting midges (Diptera: Ceratopogonidae) to these cues using field-based experiments at two sites in the United Kingdom with very different species complements. Traps used for surveillance (miniature CDC model 512) and control (Mosquito Magnet Pro) were modified to release ratios of (R)- and (S)-1-octen-3-ol enantiomers in combination with CO2 and, in the case of the latter trap type, a thermal cue. Abundance and species diversity were then compared between these treatments and against collections made using a trap with a CO2 lure only, in a Latin square design. In both habitats, results demonstrated that semiochemical lures containing a high proportion of the (R)-enantiomer consistently attracted a greater abundance of host-seeking Culicoides females than any other treatment. Culicoides collected using an optimal stimulus of 500 ml/min CO2 combined with 4.1 mg/h (R)-1-octen-3-ol were then compared with those collected on sheep through the use of a drop trap. While preliminary in nature, this trial indicated Culicoides species complements are similar between collections made using the drop trap in comparison to the semiochemical-baited CDC trap, and that there are advantages in using (R)-1-octen-3-ol.