Utility of the Histological Examination of the Bronchial Mucosa in the Diagnosis of Severe Equine Asthma Syndrome in Horses

Influence of climatic changes on respiratory health in a teaching herd of outdoor-housed horses

Horses maintained outdoors may experience a lower-allergenic environment compared to their stabled counterparts. This study hypothesizes that climatic changes in southern Brazil can influence respiratory status. To test this hypothesis, we evaluated the lower airways of 17 horses from a teaching herd in southern Brazil, maintained outdoors, during winter, spring, and summer. Except for one mare with a history of severe asthma, all horses were considered healthy and underwent a physical examination. Airway endoscopic evaluation included scoring for tracheal mucus (0-5) and bronchial septum thickness (1-5). Bronchoalveolar lavage fluid (BALF) was collected at three time points, while bronchial septum biopsies were performed during spring and summer for airway epithelial investigation. Data analysis involved repeated measures ANOVA and Wilcoxon tests (p < 0.05). Tracheal mucus score and septal thickness did not differ across investigation periods. In BALF cytology, the mean percentage of neutrophils was higher in spring than summer (7.9 ± 13.4 % vs. 4.5 ± 11.7 %, P = 0.037), and eosinophil count was higher in winter than spring (0.64 ± 1.29 % vs. 0.03 ± 0.13 %, P = 0.034) and summer (0.64 ± 1.29 % vs. 0.14 ± 0.60 %, P = 0.023). Histopathological observations showed no differences between time points, and no correlations were observed with BALF analyses (P > 0.05). This study demonstrates that, even in an outdoor environment, horses' airways exhibit cytological modifications associated with different seasons, indicating a need for deeper investigation; endobronchial biopsy did not contribute to the clinical diagnosis.

The amount of hyaluronic acid and airway remodelling increase with the severity of inflammation in neutrophilic equine asthma

BACKGROUND

Equine asthma (EA) is a chronic lower airway inflammation that leads to structural and functional changes. Hyaluronic acid (HA) has crucial functions in the extracellular matrix homeostasis and inflammatory mediator activity. HA concentration in the lungs increases in several human airway diseases. However, its associations with naturally occurring EA and airway remodelling have not been previously studied. Our aim was to investigate the association of equine neutrophilic airway inflammation (NAI) severity, airway remodelling, and HA concentration in horses with naturally occurring EA. We hypothesised that HA concentration and airway remodelling would increase with the severity of NAI. HA concentrations of bronchoalveolar lavage fluid supernatant (SUP) and plasma of 27 neutrophilic EA horses, and 28 control horses were measured. Additionally, remodelling and HA staining intensity were assessed from endobronchial biopsies from 10 moderate NAI horses, 5 severe NAI horses, and 15 control horses.

RESULTS

The HA concentration in SUP was higher in EA horses compared to controls (p = 0.007). Plasma HA concentrations were not different between the groups. In the endobronchial biopsies, moderate NAI horses showed epithelial hyperplasia and inflammatory cell infiltrate, while severe NAI horses also showed fibrosis and desquamation of the epithelium. The degree of remodelling was higher in severe NAI compared to moderate NAI (p = 0.048) and controls (p = 0.016). Intense HA staining was observed in bronchial cell membranes, basement membranes, and connective tissue without significant differences between the groups.

CONCLUSION

The release of HA to the airway lumen increases in naturally occurring neutrophilic EA without clear changes in its tissue distribution, and significant airway remodelling only develops in severe NAI.

Decision Making in Severe Equine Asthma-Diagnosis and Monitoring

Decision making consists of gathering quality data in order to correctly assess a situation and determine the best course of action. This process is a fundamental part of medicine and is what enables practitioners to accurately diagnose diseases and select appropriate treatment protocols. Despite severe equine asthma (SEA) being a highly prevalent lower respiratory disease amongst equids, clinicians still struggle with the optimization of routine diagnostic procedures. The use of several ancillary diagnostic tests has been reported for disease identification and monitoring, but many are only suitable for research purposes or lack practicality for everyday use. The aim of this paper is to assist the equine veterinarian in the process of decision making associated with managing SEA-affected patients. This review will focus on disease diagnosis and monitoring, while also presenting a flow-chart which includes the basic data that the clinician must obtain in order to accurately identify severely asthmatic horses in their everyday routine practice. It is important to note that European and American board-certified specialists on equine internal medicine can provide assistance in the diagnosis and treatment plan of SEA-affected horses.

Bronchoalveolar Lavage Cytology in Severe Equine Asthma: Cytocentrifugated versus Sediment Smear Preparations

Equine asthma is a common respiratory disease that may affect horses of any age. The diagnosis of severe equine asthma (SEA) (historically referred as recurrent airway obstruction or RAO) is based mainly on the history of the animal and clinical signs, which are further supported by the cytological examination of the bronchoalveolar lavage (BAL). This can also be helpful in monitoring the inflammation of the lower airways in response to environmental management and medication. The cytocentrifugated preparation is usually considered the method of choice for BAL cytological interpretation. The aim of this study was to compare the results in terms of differential cell counts (DCC) in BAL cytology performed on sedimented smears and cytocentrifugated preparations. To carry this out, 48 BAL samples were collected from six horses with SEA that were subjected to a process of exacerbation of the disease by environmental stimuli, which was later followed by the appropriate treatment. Each collected BAL fluid was equally divided into duplicate portions: one processed by cytocentrifugation and one by sediment smear from simple centrifugation. Cytologic examination of all BAL by both methods showed poor concordance in DCC, although it was still able to allow diagnostic recognition of severe lung neutrophilic disorders. These results suggest that sediment smear preparation, although remaining a useful method in general equine practice associated with clinical assessments in the diagnosis of SEA under conditions where there is no possibility of using a cytocentrifuge, cannot be considered a comparable alternative.