Equine insect hypersensitivity (EIH) is a seasonal disease which is caused by the bites of female Culicoides spp.. Two of the most common Culicoides species found around horses in the Netherlands are C. obsoletus (94,1% in 2006 and 95,34% in 2007) and C. pulicaris (5,81% in 2006 and 4,54% in 2007). The diagnosis of EIH is usually based on history, clinical signs and exclusion of other potential causes. Because horses with EIH normally don’t show any signs in the winter, it is very hard to determine whether horses are affected or not in this season. Maybe in the future, the intradermal skin test will be a helpful method to diagnose EIH. In the present study, three different extracts (C. obsoletus non-blood-fed, C. obsoletus blood-fed and C. pulicaris) were used in two different concentrations (1:1000 w/v and 1:5000 w/v) to determine whether there’s a difference in reaction towards these extracts using the intradermal test between horses suffering from EIH and horses who are not affected by this disease. For this experiment 20 horses were used. The horses used were paired, forming a couple of one horse suffering from EIH and the other unaffected. All the horses had to be on the current location for at least one year. The horses were not sedated. The injection sites were evaluated on wheal diameter (in mm) and firmness 30 minutes, 1 hour, 4 hours and 24 hours after the extracts where injected. The most effective points of evaluation were the controls at 1 and 4 hour. There was a significant difference in reaction to all of the extracts at these times between the horses with and without EIH. It was not possible to distinguish between the sensitivity of horses with EIH towards the different extracts (C. obsoletus, C. obsoletus blood-fed and C. pulicaris) used in this study
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