Equine insect hypersensitivity: skin test and biopsy results correlated with clinical data.

This research focuses on a study conducted on 44 horses in Florida, USA, which exhibited seasonal itching due to suspected insect hypersensitivity. Skin tests and biopsies were conducted on these horses, revealing their hypersensitivity to different insects and allergens. Certain findings were correlated with the time of the year, severity of the condition, and location of skin lesions on the horses.

Research Methodology

• The researchers focused on 44 horses exhibiting pruritus (itching), and 21 horses that showed no symptoms for comparison.
• The horses spanned a wide range of ages and breeds to provide a diverse data set.
• Each horse was tested for hypersensitivity to insects, grass, and mould allergens. This testing involved the injection of allergenic extracts into the horses’ skin.
• Biopsies were also taken from the horses’ skin for histopathological examination to identify any changes related to arthropod (insect) hypersensitivity.

Findings

• The horses’ reactions varied in terms of intensity, ranging from mild to severe responses to the injected extracts. The strongest reactions were observed for extracts made from Culicoides, a type of biting midge.
• The timing of pruritus also varied based on the season. Symptoms were mild towards the end of February until the end of June. The condition worsened from there and remained severe until November before showing improvement.
• Three specific clinical syndromes or patterns of symptoms linked with insect hypersensitivity were identified. These were characterized by lesions that occurred on different parts of the horses’ bodies, categorized as: horses with lesions on the face, ears, mane, withers, rump and tail; horses with lesions on face, ears, intermandibular space, chest, belly and groin; those with a combination of dorsal and ventral lesions.

Interpretation and Conclusion

• The research establishes a clear correlation between allergic reactions in horses and exposure to certain insects, particularly the Culicoides species.
• The severity and timing of these allergic reactions appear to be influenced by the seasonal pattern of these insects’ life cycles, pointing to a direct relationship between insect activity and the observed symptoms in horses.
• The identified clinical syndromes provide further insights into the manifestation of insect hypersensitivity in horses and could aid in improving diagnostic accuracy and determining treatment options.