African horse sickness is an economically highly important non-contagious but infectious Orbivirus disease that is transmitted by various species of Culicoides midges. The equids most severely affected by the virus are horses, ponies, and European donkeys; mules are somewhat less susceptible, and African donkeys and zebra are refractory to the devastating consequences of infection. In recent years, Bluetongue virus, an Orbivirus similar to African horse sickness, which also utilises Culicoides spp. as its vector, has drastically increased its range into previously unaffected regions in northern Europe, utilising indigenous vector species, and causing widespread economic damage to the agricultural sector. Considering these events, the current review outlines the history of African horse sickness, including information concerning virus structure, transmission, viraemia, overwintering ability, and the potential implications that an outbreak would have for Ireland. While the current risk for the introduction of African horse sickness to Ireland is considered at worst ‘very low’, it is important to note that prior to the 2006 outbreak of Bluetongue in northern Europe, both diseases were considered to be of equal risk to the United Kingdom (‘medium-risk’). It is therefore likely that any outbreak of this disease would have serious socio-economic consequences for Ireland due to the high density of vulnerable equids and the prevalence of Culicoides species, potentially capable of vectoring the virus.

Since the 1960s, the objective for the United Kingdom (UK) government policy and legislation on crop protection practices has been to minimise the impact of pesticide use in agriculture and horticulture to the wider environment. Subsequent European Union (EU) policy and legislation have also targeted this objective through a demanding approvals process, competency tests for users, maximum residue limits, regular post-registration monitoring and the promotion of integrated pest and disease management techniques. However, none of this substantive regulation refers to target reduction levels for pesticide use. Since 1992, the number of arable farms in Northern Ireland has decreased by 61% with a consequent reduction of 34% in the area of arable crops grown. Despite this reduction in area of arable crops grown, the area treated by the major pesticide groups increased by 49% due to intensification, but the weight of major pesticides applied to arable crops decreased by 37%. However, the intensity of application measured by the total quantity of all pesticides applied to the basic area of arable crops treated remained relatively constant at approximately 3.2 kg/ha. Pesticide usage trends and reduction policies in other geographic regions are also discussed for comparative purposes.

The impact of topical applications of deltamethrin and ivermectin to cattle on Culicoides spp. landing and blood-feeding was studied in this work using sticky traps mounted on Friesian heifers’ backs. There was no effect of the insecticides on total numbers of Culicoides trapped or the proportion engorged. Deltamethrin and ivermectin treatment did not prevent blood-feeding on these animals. Deltamethrin did result in significant Culicoides mortality as evidenced by the numbers of dead midges combed from heifers’ upper flanks. The proximity of engorged midges on traps to dead midges in the hair suggests that blood-feeding took place despite midges receiving an ultimately lethal dose of deltamethrin. Ivermectin application resulted in a smaller proportion of nulliparous than parous females caught. There was no significant effect of ivermectin on the numbers of Culicoides that emerged from dung samples (but p was small at 0.095 for the Obsoletus group Culicoides). In cases of suspect animal imports, pour-on or spray applications of deltamethrin could reduce the risk of onward transmission of bluetongue virus.