Beyond steroids and bronchodilators – investigating additional therapies for horses with severe equine asthma.

The research article “Beyond steroids and bronchodilators – investigating additional therapies for horses with severe equine asthma” explores ideas beyond the typical treatments for horses with severe equine asthma, suggesting a need for a deeper understanding of the various causes and possible new therapies.

Terminology and Classification

• The study discusses the various terminologies used to describe chronic inflammatory airway disease in horses, such as heaves, COPD, IAD, and RAO, including a variant specifically linked to summer pasture life – SPRAO.
• The American College of Veterinary Internal Medicine (ACVIM) suggested in 2016 that all these terms could be grouped under the more general term of ‘equine asthma syndrome’, with IAD and RAO being split into mild or severe equine asthma.
• The authors explain this change in terminology was a result of understanding that chronic airway inflammation in horses can present in various forms (phenotypes), which may have differing root causes – similar to the syndrome of asthma seen in humans.

Differences Between Equine Asthma Phenotypes

• The article posits the need to investigate the potential differences between these various asthma phenotypes in horses.
• They suggest a consideration of the main types of inflammatory cells drawn into the airways, the potential role of infectious agents, the airway microbiome, and any genetic factors.

Treatments Currently in Use

• The authors highlight corticosteroids and bronchodilators as the most common treatments for horses with asthma.
• They explain that corticosteroids, administered by injection or aerosol, can quickly improve lung function, but note some horses may require long-term treatment.
• In contrast, aerosolised bronchodilators provide immediate relief from bronchospasm, helping with mucus clearance, but lack anti-inflammatory properties, making them unsuitable as standalone treatments.

Antimicrobial Therapies

• The study also explores the use of certain antimicrobial macrolides (specifically azithromycin and clarithromycin) which have immunomodulatory properties.
• These are sometimes used to treat persistent asthma in humans that cannot be controlled through steroids and bronchodilators alone, particularly those with a neutrophilic asthma phenotype.
• Similar therapies might be useful for horses, particularly those cases that do not respond frequently to conventional treatment.