Intradermal challenge of Icelandic horses with extracts of four species of the genus Culicoides.

The research performed an intradermal test on Icelandic horses to understand their reactions to extracts of four different species of biting midges. Emphasizing the relationship between the horses’ sensitivity to these midges and summer eczema, the results indicate that affected horses generally have a higher skin reaction to these antigens than the unaffected ones.

Research Objective

• The main aim of this study was to examine the skin reaction of Icelandic horses to different extracts from four species of the genus Culicoides, often referred to as biting midges. The researchers sought to better understand the potential correlation between the horses’ skin reactions, specifically in connection to the occurrence of summer eczema.

Methodology

• Twenty-three Icelandic horses were used for this study. Fourteen out of these displayed signs of summer eczema.
• Each horse was challenged intradermally (inside the skin) by injecting 0.1 mL of whole-body extracts from four different species of biting midges. These included C. pulicaris, C. chiopterus, C. obsoletus and C. impunctatus.
• The extraction concentrations used were either 0.01 or 0.005 percent weight/volume, with the aim of discerning the impact of varying antigen levels.
• The team observed and recorded skin reactions at several intervals: 30 minutes, 60 minutes, three hours, four hours, 24 hours, and 48 hours after injection.

Findings

• The horses’ skin reactions varied depending on the concentration of the antigen – the higher the concentration, the stronger the reaction generally was.
• The majority of unaffected horses (8 out of 9) didn’t respond strongly to any of the four tested antigens. The exception – one horse – presented a noticeable reaction to two of the four tested antigens.
• In the affected group, 10 out of 14 horses reacted to at least three of the four antigens. Surprisingly, two horses from this group didn’t show any significant reaction.
• Horses suffering from summer eczema displayed significantly stronger reactions to C. chiopterus, C. obsoletus and C. impunctatus after 30 minutes, 60 minutes, and four hours of the test.
• The 24-hour readings also indicated a significant difference in the reaction of affected horses to C. chiopterus and C. impunctatus, with these horses demonstrating a heightened skin response.

Conclusion

• This study draws connections between Icelandic horses’ sensitivity to bite extracts from the Culicoides species and the occurrence of summer eczema. Higher skin reactions were generally observed in horses that were affected by this condition, suggesting a possible underlying immunological cause for summer eczema in these animals.