Intradermal challenge of Icelandic horses in Norway and Iceland with extracts of Culicoides spp.

The research investigates how Icelandic horses react to an antigen from Culicoides spp., predominantly in Norway and Iceland. The findings suggest Culicoides spp. is likely the major cause of recurrent seasonal dermatitis in horses in Norway, but the disease isn’t found in Icelandic horses.

Objective and Methodology

• The researchers were keen to explore the cause of recurrent seasonal dermatitis, a skin condition, in Icelandic horses inhabiting Norway and Iceland. To achieve this, they took extracts from Culicoides spp., a type of small fly that often acts as vectors for several diseases, and used it as an antigen in a skin test survey. Here, “antigen” refers to a toxin that induces immune responses in the body, particularly the production of antibodies.
• The investigators injected the antigen intradermally (within or between the layers of the skin) into 11 horses that had previously suffered from recurrent seasonal dermatitis and 33 clinically normal horses in Norway. Additionally, 110 horses in Iceland were also part of the test group.

Findings and Implications

• Of the 11 horses with a past record of dermatitis, all showed an immediate hypersensitivity response to the intradermal injection of the antigen. Essentially, this suggests that these horses had reacted negatively to the Culicoides spp. extract, indicating an allergic reaction that might have been the cause of their skin condition.
• In contrast, all but one horse from the clinically normal group in Norway showed no skin reaction, suggesting their bodies did not identify the antigen as a threat or toxin.
• The implication here is significant; it denotes that Culicoides spp. might majorly be the cause for the skin disease in horses in Norway. This is because an allergic reaction to an antigen often means that the body considers the substance harmful, in this case, implying that exposure to Culicoides spp. could lead to skin diseases in horses.
• However, in the case of the horses tested in Iceland, only one out of the 110 showed a weak reaction. The remaining horses were not sensitized to the Culicoides allergen, suggesting that they may have developed a tolerance or naturally have a stronger immune response. Since the disease has never been reported in Iceland, it provides evidence against Culicoides spp. being a universal cause for the disease in horses, and regional factors may play a critical role.

Concluding Remarks

• This research contributes significantly to understanding the role of Culicoides spp. in causing recurrent seasonal dermatitis in horses, especially in Norway. Further studies might explore the reasons for the non-reactive or weak reaction in Icelandic horses, potentially paving the way towards preventive and therapeutic measures against the skin condition.