Inflammatory phenotype and response to intradermal skin testing are not predictive of equine asthma diagnosis.

Overview

• This study investigated whether inflammatory markers, allergy skin testing, and air quality could predict or explain equine asthma.
• Researchers found that allergy skin tests and blood inflammatory markers did not predict asthma diagnosis or phenotypes, but poor air quality was associated with a specific type of asthma involving mast cells.

Background and Purpose

• Equine asthma is a respiratory condition in horses characterized by inflammation and difficulty breathing, but its causes are not fully understood.
• Factors like inflammation, allergies, and environmental air quality are thought to play a role in equine asthma development.
• This research aimed to evaluate:
  • Serum inflammatory cytokines (proteins involved in inflammation)
  • Intradermal skin testing (IDT) for allergies
  • Air quality at horses’ environments
• The hypothesis was that poor air quality and environmental allergies would be associated with horses diagnosed with asthma.

Methodology

• Fifty-two client-owned horses exhibiting signs of asthma were enrolled in a cross-sectional study.
• Diagnosis was confirmed by bronchoalveolar lavage fluid (BALF) cytology, which examines cells in the lower airways.
• Blood samples were taken to analyze 23 different inflammatory cytokines.
• Intradermal skin testing was performed on a subset of 31 horses to check for allergic reactions to environmental allergens.
• Environmental air quality was measured using aerosol mass fraction concentrations, which were converted into Air Quality Index (AQI) values to assess pollution levels.

Key Findings

• Out of 52 horses, 34 were diagnosed with asthma based on BALF cytology results.
• Among horses tested with IDT:
  • 100% of non-asthmatic horses showed a severe allergic response to at least one allergen.
  • Only 60% of asthmatic horses showed a severe allergic response to at least one allergen.
• This indicates that positive allergy skin tests were not consistently associated with asthma status.
• There was a significant overrepresentation of mastocytic asthma (a subtype involving mast cells) in locations with unhealthy air quality:
  • Expected mastocytic asthma rate at polluted sites: 10.3%
  • Observed mastocytic asthma rate: 24.1%
  • Statistical significance p = 0.0213, indicating a real association
• No significant differences were found in serum inflammatory cytokines between asthmatic phenotypes or between asthmatic and non-asthmatic horses, suggesting these biomarkers are not useful for diagnosing or characterizing equine asthma.

Conclusions and Implications

• Common diagnostic tests for environmental allergies (intradermal skin testing) did not reliably predict asthma diagnosis or phenotype in horses.
• Inflammatory cytokines in the blood were not effective biomarkers for allergic airway disease in this study.
• The study supports a link between poor air quality and the incidence of mastocytic equine asthma, which aligns with similar findings in human asthma research.
• This suggests that environmental management, particularly air quality improvement, may be important in preventing or managing certain types of equine asthma.
• Future research may explore other biomarkers or methods for better diagnosis and phenotype differentiation in equine asthma and further investigate environmental influences.