Comparison of cellular and humoral immunoassays for the assessment of summer eczema in horses.

This study involves a comparison and analysis of three diagnostic methods for a type of allergic dermatitis in horses called summer eczema. The researchers found that allergy tests using effector cells (mast cells, basophils) are more accurate in diagnosing this condition than serological analysis by enzyme-linked immunosorbent assay (ELISA).

Research Objective and Methodology

• The study’s primary aim was to compare and investigate three common diagnostic methods for summer eczema (SE) in horses. SE is an allergic skin condition caused by the bites of Culicoides species.
• Eighteen horses were involved in the study, nine with a medical history of SE, and nine control animals.
• The research unfolded by intradermally challenging the horses with whole body extracts (WBE) and the saliva of both native (C. nubeculosus) and exotic (C. sonorensis) Culicoides species.
• Samples of the horses’ blood and serum were then examined for basophil reactivity through a histamine release test (HRT) and for Culicoides-specific serum immunoglobulin E (IgE) and G (IgG) by ELISA.

Findings of the Study

• The intradermal testing (IDT) revealed significant differences 30 minutes (immediate reactivity) and 4 hours (late-phase reactivity) after challenge with most insect preparations between horses with and without SE.
• Overall, the HRT showed the most accurate results with a sensitivity of 1.00 for all Culicoides preparations and specificities of 0.78 (WBE) and 1.00 (saliva).
• The delayed reactions of the IDT (24 hours), and the levels of Culicoides-specific IgE and IgG in the native serum showed little to no distinction between allergic and non-allergic horses.
• However, the use of purified serum IgE and IgG suggested the possibility for increased titers of insect-specific serum immunoglobulins in horses with SE.
• The IDT and HRT did not display obvious differences in onset and intensity of positive reactions for the native verses exotic Culicoides species. However, ELISA showed slightly higher numbers of positive reactions for serum IgG with the indigenous species.
• Saliva, compared to WBE, was found to have improved sensitivity and/or specificity for the HRT and for the late-phase immune reactions measured by IDT.

Conclusion

• The study concludes that allergy tests utilizing effector cells, such as mast cells and basophils, are more accurate in diagnosing SE in horses than serological analysis by ELISA.