Evaluation of an in vitro sulphidoleukotriene release test for diagnosis of insect bite hypersensitivity in horses.

The study evaluates the efficacy of a diagnostic test called the Cellular Antigen Stimulation Test (CAST) in identifying Insect Bite Hypersensitivity (IBH) in horses. According to the results, the CAST demonstrates significant precision in the diagnosis of IBH, potentially offering a strong tool for the identification of affected, yet symptomless horses, and a deeper understanding of the allergens involved in the condition.

Study Objective and Methodology

• The research aims to enhance the diagnosis capabilities of IBH in horses, an allergic skin inflammation caused by the bites of two specific insect species, Culicoides and Simulium.
• The means of achieving this was through an assessment of the CAST using extracts from these two insect types in a study group comprising both IBH-affected and healthy horses.
• Throughout a year, varying results of the test were analyzed, including the potential cross-reactivity with different insect extract types.
• 314 mature horses were subjected to the CAST for this study. Other factors like the severity of clinical signs, gender, and age were also viewed and a group of 32 horses underwent repeated tests over the span of a year.
• To gauge the agreement of test results with different insect extracts, the kappa reliability test was utilized.

Findings of the Research

• Horses suffering from IBH released significantly higher amounts of sLT (sulphidoleukotriene, a signaling molecule involved in inflammation) in reaction to both the Culicoides nubeculosus and Simulium vittatum extracts when compared to control subjects.
• When adult Culicoides nubeculosus extracts were deployed with the CAST, the highest diagnostic sensitivity and specificity, 78% and 97% respectively, were achieved. This finding indicates that the majority of horses affected by IBH have a sensitization to Culicoides allergens.
• Apart from Culicoides allergens, a portion of IBH-affected horses were additionally sensitized to the allergens of Simulium spp.
• The CAST showed minimum 80% positive and negative predictive accuracy for an inherent prevalence range of 12-52% in IBH, as observed when utilized in conjunction with C. nubeculosus.
• In the one-year follow-up study, the ratio of IBH-affected horses with a positive test result oscillated between 90% in November to 68% in March. The test results were not significantly swayed by the severity of clinical manifestations or age. However, male horses affected by IBH yielded conspicuously more positive test results than affected females.

Conclusions Derived from the Study

• The CAST, when used with adult C. nubeculosus, attested high specificity and commendable sensitivity in the diagnosis of IBH. It underscores that horses affected by IBH are primarily sensitized to Culicoides allergens, with some also demonstrating sensitization to allergens from Simulium spp.
• The study concludes that the CAST could be a potent diagnostic tool for IBH, even allowing detection in horses that are affected but do not exhibit noticeable symptoms. In addition, the employment of this test could contribute to our understanding of the allergens responsible for this condition.