Abstract
BackgroundBiting midges of the genus Culicoides Latreille, 1809 (Diptera: Ceratopogonidae) cause a significant biting nuisance to equines and are responsible for the biological transmission of African horse sickness virus (AHSV). While currently restricted in distribution to sub-Saharan Africa, AHSV has a history of emergence into southern Europe and causes one of the most lethal diseases of horses and other species of Equidae. In the event of an outbreak of AHSV, the use of insecticide treated nets (ITNs) to screen equine accomodation is recommended by competent authorities including the Office International des Épizooties (OIE) in order to reduce vector-host contact.MethodsSeven commercially avaliable pyrethroid insecticides and three repellent compounds, all of which are licensed for amateur use, were assessed in modified World Health Organization (WHO) cone bioassay trials in the laboratory using a colony line of Culicoides nubeculosus (Meigen), 1830. Two field trials were subsequently conducted to test the efficiency of treated net screens in preventing entry of Culicoides.ResultsA formulation of cypermethrin (0.15 % w/w) and pyrethrins (0.2 % w/w) (Tri-Tec 14®, LS Sales (Farnham) Ltd, Bloxham, UK) applied to black polyvinyl-coated polyester insect screen (1.6 mm aperture; 1.6 mm thickness) inflicted 100 % mortality on batches of C. nubeculosus following a three minute exposure in the WHO cone bioassays at 1, 7 and 14 days post-treatment. Tri-Tec 14® outperformed all other treatments tested and was subsequently selected for use in field trials. The first trial demonstrated that treated screens placed around an ultraviolet light-suction trap entirely prevented Culicoides being collected, despite their collection in identical traps with untreated screening or no screening. The second field trial examined entry of Culicoides into stables containing horses and found that while the insecticide treated screens reduced entry substantially, there was still a small risk of exposure to biting.ConclusionsScreened stables can be utilised as part of an integrated control program in the event of an AHSV outbreak in order to reduce vector-host contact and may also be applicable to protection of horses from Culicoides during transport.
Highlights
Biting midges of the genus Culicoides Latreille, 1809 (Diptera: Ceratopogonidae) cause a significant biting nuisance to equines and are responsible for the biological transmission of African horse sickness virus (AHSV)
World Health Organization (WHO) cone bioassays Mortality observed in exposed C. nubeculosus was found to be best described by a model including the predictors treatment and days post-treatment as fixed effects and treatment batch and within-mesh replicate as random factors (Table 3)
This study has shown that insecticide treated nets (ITNs) have the potential to offer protection to horses from Culicoides in the event of an AHSV epidemic, during international movement through endemic regions for competition and racing, and in reducing biting nuisance
Summary
Biting midges of the genus Culicoides Latreille, 1809 (Diptera: Ceratopogonidae) cause a significant biting nuisance to equines and are responsible for the biological transmission of African horse sickness virus (AHSV). Hypersensitivity reaction to the bites of Culicoides are the primary cause of equine summer seasonal recurrent allergic dermatitis [2], commonly known as ‘sweet-itch’. This condition affects between 2 and 12 % of horses in the UK [2,3,4,5], studies from other countries in northern Europe indicates that this prevalence may be underestimated [6]. A large-scale epidemic of AHSV in the UK could potentially cost the equine industry up to £3.5 billion and the traumatic nature of the disease would be expected to have a severe social impact [14]
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