8.2.2: Equine asthma Flashcards
How do we categorise equine asthma?
- Mild-moderate equine asthma (IAD)
- Severe equine asthma (RAO)
Equine asthma was formerly known as broken wind, heaves, chronic obstructive pulmonary disease (COPD), recurrent airway obstruction (RAO), inflammatiry airway disease)
True/false: in mild-moderate equine asthma, there are subtle clinical signs at rest.
False
Only in severe equine asthma are there signs at rest.
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On cytology for severe asthma, neutrophils make up what % of the TNCC?
25%
On cytology for mild-moderate asthma, neutrophils make up what percentage of the TNCC?
10-25%
We also see increased mast cells in mild-moderate asthma
True/false: all horses which have mild asthma will eventually develop into those with severe asthma.
False
Not all horses will mild form show progression to severe form
Aetiology of equine asthma
- Strong association with environment and feeding
- Mechanisms are poorly understood
- It is a non-allergic inflammatory response e.g. to endotoxins, moulds, noxious gases; but there can also be an allergic reaction component that involves Type I and Type III hypersensitivity
- There seems to be a familial risk for moderate and severe equine asthma so some suggest genetic testing should be performed
How can environment and feeding impact equine asthma?
- Airborne respiratory dust (ARD) causes and exacerbates the disease
- Some particles in the breathing zone and stable zone, if small enough (<5µm) will make it into the lower airways but not back out - these particles e.g. moulds and fungi trigger disease
- There is a lower concentration of these in steamed hay
- Hay dust exacerbates asthma - even a horse in remission can be affected
- Higher concentrations from nets (4x higher respirable dust)
- The breathing zone is 30cm around the horse’s nose
Which organisms may play a role in the hypersensitivity allergic reactions that may come with asthma?
- Faenia rectivirgula
- Aspergillus fumigatus
- Thermoactivenomyces vulgaris
Pathophysiology of equine asthma
- Airway hyper-responsiveness
- Bronchospasm
- Inflammation
- Mucus accumulation
- Tissue remodelling
Discuss how bronchospasm occurs in equine asthma
- Occurs secondary to inflammation
- Bronchodilators are effective
Discuss the signs of inflammation we can see on cytology of the horse with equine asthma
- Airway neutrophilia
- Activation of macrophages occurs
Describe how mucus accumulation plays a role in equine asthma
- Consistent finding in equine asthma
- Perhaps associated with the neutrophilia but not sure
- Long persistence (even during remission)
- Exacerbations increase viscoelasticity (and just generally will increase the production of mucus by goblet cells)
Describe how tissue remodelling plays a role in equine asthma
- Increased smooth muscle mass -> increased contraction force
- Peribronchial fibrosis
- Epithelial hyperplasia
- Bronchiectasis: inflow of air into some segments of lower airways, and outflow impaired by these issues. This means there is too much air in the alveoli -> they burst and form larger balloon-like structures
Which small particles (<5µm) can cause disease?
- Moulds and fungi
- Pollen
- Endotoxins
- Chemicals: ammonia, smoke, exhaust fumes
Diagnosis of equine asthma
- History
- Physical exam
- Auscultation - use a rebreathing bag
- Endoscopy
How can a rebreathing bag be used to help diagnose equine asthma?
- Place bag around the horse’s muzzle. This will increase CO2, and thereby increase depth ad effort of respiration
- This makes it easier to hear respiratory sounds on auscultation
- Check for tolerance, cough, recovery
- This is especially important for horses with mEA -> they will not tolerate the bag for very long
- May hear wheezes, crackles, tracheal rattles
⚠️Do not use a rebreathing bag if the horse is in respiratory distress⚠️
How can endoscopy be helpful in investigation of equine asthma?
- Rule out upper airway disease
- Can see tracheal mucus
- Perform 1hr post exercise
- Make sure to visualise the carina
Who has equine asthma?
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SPAOPA
Summer pasture-associated obstructive pulmonary disease
What broad classes of drugs can be used to treat horses with asthma?
Horses with mEA only may benefit from:
* Immune modulation (interferon-alpha)
* Omega-3 supplementation
Horses with mEA and sEA may benefit from:
* Glucocorticoids
* Bronchodilators
Why are glucocorticoids used to treat equine asthma?
- High efficacy and extensive use
- Impact on lung function, airway inflammation, bronchial remodelling
- Side effects include: adrenal suppression, adrenal gland atrophy, immune suppression, laminitis
- Inhaled therapy may be preferable to systemic for long-term treatment
How could you use glucocorticoids to treat the horse with acute sEA?
- IV dexamethasone (0.04-0.1mg/kg SID)
- Followed by PO dexamethasone 0.05 mg/kg OR prednisolone 1mg/kg SID - give until respiratory effort and nasal discharge resolve
- Then follow with inhaled glucocorticoids: ideally fluticasone 2000µg BID, otherwise Beclomethasone diproprionate 3750µg BID
Characteristics of ciclesonide for treatment of sEA
Ciclesonide
* Glucocorticoid
* Pro-drug
* Does not affect cortisol
* Dose: 8 activations BID for 5 days, then 12 activations SID
Glucocorticoid treatment protocol for mEA
- Start PO dexamethasone 0.05mg/kg OR prednisolone 1mg/kg SID - for 4 weeks
- Follow this with inhaled glucocorticoids:
- Initially fluticasone 2000µg BID, tapered over 4 weeks to 1000µg every 48hrs
- Can then use Beclomethasone diproprionate 500-1500µg BID
What bronchodilators are available for treatment of equine asthma and how should you use them?
Use bronchodilators alongside glucocorticoids
* There are beta-adrenergic and parasympatholytic options
Beta-adrenergic
* e.g. Clenbuterol, albuterol, salbutamol
* Give inhaled for mEA, systemic for sEA
* Systemic: Clenbuterol PO starting at 0.8µg/kg BID then increasing to 3.2µg/kg BID; clenbuterol IV not recommended due to side effects
* Inhaled: salmeterol (0.5-1µg/kg q6hrs) or albuterol (0.8-2µg/kg q1-6hrs)
Parasympatholytic
* = ipratropium bromide (0.4-0.8µg/kg q4hrs)
How could you use interferon-alpha in the treatment of equine asthma?
- 50-150 U / horse/ day
- May see positive response to treatment and decreased relapse rate
- However practical experience is mixed
How could cromoglicate be used in treatment of equine asthma?
- Used in mast-cell mediated mEA
How could omega-3 fatty acids be used in treatment of equine asthma?
- 1.5-3g DHA for both mEA and sEA
Side effects of glucocorticoids
- Adrenal suppression
- Adrenal gland atrophy
- Immune suppression
- Laminitis
Systemic beta-adrenergic bronchodilators
- Cardiovascular remodelling
- Tachyphylaxis
What must you take into account and warn the owner about if their horse is on long term treatment for equine asthma? Where is a good place to look for the required information?
- Each drug and delivery method has a detection time
- The treatment should be discontinued before that time
- Times may vary according to pathology and other factors
- These times change so should be rechecked regularly (see BHA website or individual competition information)
