Effects of nebulized dexamethasone on the respiratory microbiota and mycobiota and relative equine herpesvirus‐1, 2, 4, 5 in an equine model of asthma

Abstract

Background: Prolonged exposure to environmental antigens or allergens elicits an immune response in both healthy horses and those with mild asthma. Corticosteroids often are used to treat lower airway inflammation.Objective: To investigate the changes in equine herpesvirus (EHV)-1,2,4,5 glycoprotein B gene expression and changes in respiratory bacterial and fungal communities after nebulized dexamethasone treatment of horses with asthma.Animals: Horses with naturally occurring mild asthma (n = 16) and healthy control horses (n = 4).Methods: Prospective, randomized, controlled, blinded clinical trial. Polymerase chain reaction amplification of EHV-1,2,4,5 in bronchoalveolar lavage fluid, and 16S (microbiome) and ITS2 (mycobiome) genes with subsequent sequencing was performed on DNA extracted from nasal swabs and transendoscopic tracheal aspirates before and after 13 days treatment with nebulized dexamethasone (15 mg q24h) and saline (control).Results: Nebulized dexamethasone treatment decreased microbial diversity; relative abundance of 8 genera in the upper respiratory tract were altered. For both the microbiota and the mycobiota, environment had a dominant effect over treatment.Alternaria, an opportunistic pathogen and allergen in humans recognized as a risk factor for asthma, asthma severity, and exacerbations, was increased with treatment.Treatment affected relative quantification of the equine gamma herpesviruses (EHV-2 and -5); EHV-2 DNA levels increased and those of EHV-5 decreased.Conclusions: Nebulized dexamethasone treatment affected the upper respiratory tract microbiota, but not the mycobiota, which was overwhelmed by the effect of a sustained dusty environment. K E Y W O R D S equine herpesvirus, mild equine asthma, qPCR, respirable dust, REST analysis Abbreviations: EHV, equine herpesvirus; BALF, bronchoalveolar lavage fluid; OTU, operational taxonomic unit; PCoA, principal coordinates analysis.

Glucocorticoid treatment in horses with asthma: A narrative review

“…62 The nebulization of dexamethasone (15 mg q24h, 13 days) does not modify BALF cytology in mild asthma. 74 Combined, these results suggest that the environment, rather than GC, is mainly responsible for the improvement of airway neutrophilic inflammation in many studies.…”

“…Inhalation of budesonide (1500 g q12h, 10 days) decreased airway neutrophilia in horses with SEA, but the treatment was accompanied by a low‐dust environment and there was no control group 62 . The nebulization of dexamethasone (15 mg q24h, 13 days) does not modify BALF cytology in mild asthma 74 …”

“… 62 The nebulization of dexamethasone (15 mg q24h, 13 days) does not modify BALF cytology in mild asthma. 74 …”

“…The interactions between the inflammatory pulmonary microenvironment and microorganisms in asthma are poorly understood, but a role for virus, bacteria, altered microbiome, and fungus in the pathogenesis of the disease is suspected 67 , 74 , 132 , 133 , 134 , 135 and was recently reviewed. 136 The study of airway microbiome in equine asthma is at its onset and follows the growing interest in understanding the crosstalk between the lung and gut microbiota and immune functions in humans.…”

“… 67 The nebulization of dexamethasone (15 mg q24h, 13 days) decreases the microbiota diversity in mild asthma in upper, but not in lower airways, and it does not modify the upper airway mycobiota nor the nasal equine herpesvirus‐2 DNA expression from nasal swabs. 74 Oral and pharyngeal fungal infections are a possible complication of inhaled GC in humans. This has not been observed to our knowledge in the equine species and no fungal growth occurred from pharyngeal swabs of horses with SEA treated with beclomethasone.…”