Researchers seek early predictors to combat equine asthma

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The above video includes images from an endoscope procedure used before a bronchoalveolar lavage (lung wash). Through the use of an endoscope, vets can assess the mucosa in the trachea and bronchi for secretions, blood, purulent material and look for other indicators impacting respiratory health. Narrowing of the airway indicates a reduced ability to pass air in and out of the lung. Excess mucous secretions are a secondary sign that reflects inflammation.

A group of specialists in equine asthma say that until the advent of early diagnostics, the focus on dealing with the disease needs to be on prevention, followed by management and environmental improvement.

The advice stems from the 2019 Havemeyer Workshop where about 50 participants including microbiologists, clinicians, pathologists and other researchers shared information, culminating in a collaborative research paper that has been published in the journal Frontiers in Veterinary Science.

Ontario Veterinary College researcher Dr Dorothee Bienzle said the workshop was a “wonderful opportunity to get together with people from all over the world who study equine asthma and respiratory disease”.

The workshop provided a chance to share ideas on topics such as what early-onset versus late-stage asthma looks like, and how it manifests in horses affected by pasture environments versus stable-associated asthma. There was discussion of fungal spore inhalation off the pasture grasses in asthma found in hot, humid climates in comparison to asthma found in Northern climates where researchers are confident contributors to asthma are a combination of fungal spores, bacterial components and most likely dust.

Through use of an endoscope, the mucosa in the trachea and bronchi can be assessed for secretions, blood, and purulent material and to find other indicators impacting respiratory health.
Through the use of an endoscope, the mucosa in the trachea and bronchi can be assessed for secretions, blood, and purulent material and to find other indicators impacting respiratory health. © Equine Guelph

Bienzle and her team concentrate on the host response to challenges such as dusty barn air by looking at the epithelium in the lung. By the time a horse presents with severe equine asthma (= heaves) – they are looking at the disease close to the end-stage. By taking biopsies of the epithelium in horses with heaves, they look at the genes and proteins that are present and expressed. Changes often include airway remodeling, inflammation and fibrosis, to name a few.

“The goal would be to identify the disease early during onset, which might allow the disease to be reversed,” says Bienzle.

Through next-generation sequencing, Bienzle and her team have distinguished differences in gene expression between asthmatic and non-asthmatic horses. They have looked at signature variants that may indicate a susceptibility to asthma. They have identified a lack of certain anti-inflammatory proteins such as CCSP. A lack of repair functions has been observed in horses with end-stage equine asthma such as a reduced ability to produce cytokines in adequate numbers and the inability to recruit undifferentiated epithelial cells to repair epithelial damage.

Unfortunately, at this time there are no early predictors of equine asthma. It may be possible that bouts of inflammatory airway disease at a younger age could predispose horses to asthma in later years but as yet such evidence is not available. Bienzle explains the need to follow a large group of horses over their lifespan to come up with better predictors.

Take-aways for horse owners dealing with heaves include early diagnostics, aggressive treatment and, most importantly, environmental management. Intervention is recommended at the first sign of a cough, especially if the cough is repetitive or persistent. Bronchoalveolar lavage (BAL) is the gold standard diagnostic test for asthma. Corticosteroids administered with a bronchodilator may be prescribed to help the horse recover from bouts of equine asthma but environmental improvement is the key. The best advice is to get them out of dusty barns and into fresh air.

The current understanding and future directions of Equine Asthma research. Laurent Couetil, Jacqueline M. Cardwell, Renaud Leguillette, Melissa Mazan, Eric Richard, Dorothee Bienzle, Michela Bullone, Vinzenz Gerber, Kathleen Ivester, Jean-Pierre Lavoie, James Martin, Gabriel Moran, Artur Niedźwiedź, Nicola Pusterla, and Cyprianna Swiderski. Front Vet Sci. 2020; 7: 450. doi: 10.3389/fvets.2020.00450

 

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