Abstract
BACKGROUND:
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). 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.
METHODS:
Seven
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.
RESULTS:
A
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.
CONCLUSIONS:
Screened
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.
