What's in a name? Inflammatory airway disease in racehorses in training

Evaluation of variants in the ENTPD1 and ENTPD2 genes in athletic horses with exercise-induced pulmonary haemorrhage

BACKGROUND

Exercise-induced pulmonary haemorrhage (EIPH) in athletic horses is characterized by the presence of blood from the lungs in the tracheobronchial tree after intense exercise. Despite the high prevalence of EIPH in horses, the primary aetiology remains unknown. Variants in the genes encoding CD39 and CD39L1 (ENTPD1 and ENTPD2, respectively) were previously reported as potential genetic causes involved in EIPH pathogenesis. However, the role of these variants in haemostatic functions is unknown.

RESULTS

To investigate the association between EIPH and missense variants in the ENTPD1 (rs1152296272, rs68621348, and rs68621347) and ENTPD2 genes (rs782872967), 76 Thoroughbred horses diagnosed with EIPH and 56 without clinical signs of EIPH (control group) by trachea-bronchial endoscopy were genotyped. The rs1152296272 and rs68621347 variants were linked, which explained why the same results were found in all horses. Approximately 96% and 95% of the EIPH and control horses, respectively, carried at least one nonreference allele for these variants. In contrast, 100% of the control horses and 96% of the EIPH horses were homozygous for the reference allele for the rs68621348 variant. In the EIPH group, 1.5% of the horses were homozygotes and 24% were heterozygous for the nonreference allele of the rs782872967 variant. In the control group, the nonreference allele of this variant was observed only in heterozygotes (16%). There were no significant differences between groups for any of the variants.

CONCLUSIONS

The variants previously described in the genes encoding the CD39 and CD39L1 enzymes were highly present in the studied population. However, no association was found between the occurrence of EIPH and the presence of these variants in Thoroughbred horses in this study.

Towards personalized medicine for the treatment of equine asthma

Although horses with asthma share similar clinical signs, the heterogeneity of the disease in terms of severity, triggering factors, inflammatory profile, and pathological features has hindered our ability to define biologically distinct subgroups. The recognition of phenotypes and endotypes could enable the development of precision medicine, including personalized, targeted therapy, to benefit affected horses. While in its infancy in horses, this review outlines the phenotypes of equine asthma and discusses how knowledge gained from targeted therapy in human medicine can be applied to evaluate the potential opportunities for personalized medicine in equine asthma and to suggest avenues for research to advance this emerging field.

Training related risk factors for exercise induced pulmonary haemorrhage in British National Hunt racehorses

BACKGROUND

Exercise induced pulmonary haemorrhage (EIPH) is an important condition of horses performing high intensity exercise, with reported prevalence among racehorses of up to 95%, based on the detection of blood on tracheobronchoscopy. Previously identified risk factors include age, sex, season, race type, years spent in racing and lower airway inflammation.

OBJECTIVES

To estimate the prevalence of EIPH in British National Hunt racehorses as indicated by two outcome measures: presence of tracheal blood on tracheobronchoscopy, and presence of moderate-large (significant) proportions of haemosiderophages in tracheal wash (TW) fluid; and to identify training-related risk factors for these indicators of EIPH.

STUDY DESIGN

Prospective longitudinal study.

METHODS

Data from tracheobronchoscopy and TW cytology were analysed using univariable and multivariable mixed-effects logistic regression.

RESULTS

1184 observations, from 177 horses, were analysed. The prevalence of tracheal blood was 7.2% (95%CI: 5.8, 8.8) and significant haemosiderophages in TW fluid was 36% (95%CI: 33.3, 38.8). Increased time in training was significantly associated with increased odds of EIPH. For each additional year spent in training the odds of tracheal blood and presence of significant proportions haemosiderophages increased approximately 1.5-fold (OR = 1.5; 95%CI: 1.1-2.0; P = .005; and OR = 1.5; 95%CI: 1.3, 1.8; P < .001, respectively). Current inflammation was associated with previous haemorrhage, but not current haemorrhage.

MAIN LIMITATIONS

There are no standardised measures for quantification of TW cytological parameters for EIPH diagnosis. Few horses were examined following jumping. Recent racing dates were not included in analysis.

CONCLUSIONS

Increasing time in training was a risk factor for both indicators of EIPH. Current inflammation was associated with previous haemorrhage, but not current or future haemorrhage, suggesting that haemorrhage leads to inflammation but not that inflammation leads to haemorrhage. Overall, our findings are consistent with the capillary stress failure theory of EIPH. The development of standardised measures for TW cytological diagnosis of EIPH is warranted.

Update on noninfectious inflammatory diseases of the lower airway

Inflammatory airway disease and recurrent airway obstruction are 2 nonseptic diseases of the equine respiratory system with a shared cause of exposure to particulate matter. They appear to occupy 2 ends of a spectrum of disease, but are differentiated by history, clinical signs, and response to treatment. Diagnosis can be made by sampling of respiratory fluids and lung function testing. Treatment consists of environmental modification and pharmacologic treatment with systemic or inhaled corticosteroids and bronchodilators.

Usefulness of the assessment of discharge accumulation in the lower airways and tracheal septum thickening in the differential diagnosis of recurrent airway obstruction (RAO) and inflammatory airway disease (IAD) in the horse

The aim of the present study was to use endoscopic evaluation to compare the grade of accumulation of discharge in the lower airways of horses with recurrent airway obstruction (RAO) and inflammatory airway disease (IAD), and to estimate the usefulness of endoscopic evaluation in differential diagnosis of these diseases. Endoscopic evaluation consists of: the amount of discharge in the lower part of the trachea and tracheal bifurcation, and the assessment of tracheal septum thickness. This study was performed on 248 horses, 10 were healthy, 97 were diagnosed as RAO, and 141 were diagnosed as IAD. In all animals both a clinical and endoscopic examination were performed. During endoscopy, a score of mucus accumulation was estimated in 3/4 lower of the trachea and in the tracheal bifurcation. In addition to this, thickening of the tracheal septum was also assessed. According to the results of this study, it was estimated that the accumulation of mucus in the lower airways was much more advanced in RAO horses compared to horses with IAD. In horses with RAO there was a marked thickening of the tracheal septum compared to IAD horses. The results indicate the efficacy of scoring the amount of mucus in the tracheal lumen and tracheal bifurcation, as well as the efficacy of the assessment of tracheal septum thickness in the diagnosis of these diseases.

Environmental exposures and airway inflammation in young thoroughbred horses

Background

Inflammatory airway disease (IAD) in horses is a widespread, performance‐limiting syndrome believed to develop in response to inhaled irritants in the barn environment.

Objectives

To evaluate changes in bronchoalveolar lavage fluid (BALF) cytology and exposure to particulates, endotoxin, and ammonia during horses' first month in training.

Animals

Forty‐nine client‐owned 12‐ to 36‐month‐old Thoroughbred horses entering race training.

Methods

In this prospective cohort study, a convenience sample of horses was assigned to be fed hay from a net (n = 16), whereas the remaining horses were fed hay from the ground (n = 33). BALF was collected at enrollment and after 14 and 28 days in training. Respirable particulate, inhalable particulate, respirable endotoxin, and ammonia concentrations were measured at the breathing zone of each horse weekly.

Results

Median respirable particulates were significantly higher when horses were fed from hay nets than when fed hay from the ground (hay net 0.28 mg/m³, no hay net 0.055 mg/m³, P < .001). Likewise, inhalable particulate (hay net 8.3 mg/m³, no hay net 3.3 mg/m³, P = .0064) and respirable endotoxin (hay net 173.4 EU/m³, no hay net 59.2 EU/m³, P = .018) exposures were significantly higher when horses were fed from hay nets. Feeding hay from a net resulted in significantly higher BALF eosinophil proportions over time (P < .001). BALF eosinophils were significantly related to respirable particulate exposure (14 days in training r_s = 0.37, P = .012, 28 days in training, r_s = 0.38, P = .017).

Conclusions and Clinical Importance

Pulmonary eosinophilic inflammation develops in response to respirable particulate exposure in young Thoroughbreds, indicating a potential hypersensitivity to inhaled particulate allergens.

Descriptive results from a longitudinal study of airway inflammation in British National Hunt racehorses

REASONS FOR PERFORMING STUDY

Rates of airway inflammation in young racehorses decrease with time but it is not clear whether this is associated with increasing age or time exposed to the training environment. The structure of the British National Hunt (NH) population allowed closer examination of this relationship.

OBJECTIVES

To compare rates of inflammatory airway disease diagnosed by tracheal sampling (trIAD), and its components, in NH racehorses by age and training history and with published rates in young racehorses.

METHODS

A prospective, longitudinal study was conducted on 5 NH yards over 2 years. Period sample prevalences of nasal discharge, tracheal mucus, airway neutrophilia and trIAD (defined by a combination of tracheal mucus and airway neutrophilia) were estimated and compared between horses with different ages and time in training.

RESULTS

Horses new to training had twice the odds of visible tracheal mucus as ex-flat trained horses (OR 2.0; 95% CI: 1.4-2.8; P<0.001) but no significantly increased odds of airway neutrophilia (OR 1.3; 95% CI: 0.8-1.9; P = 0.3) and inconclusive evidence of increased odds of trIAD (OR 1.8; CI: 0.9-3.5; P = 0.08). However, a lower median time in training was significantly associated with the presence of visible mucus (P<0.001), increased mucus (P = 0.005) and trIAD (P = 0.03). No disease measure varied significantly with age.

CONCLUSIONS

Tracheal mucus and trIAD, but not neutrophilia detected in tracheal wash samples, were less prevalent in horses that had been exposed to the training environment for longer, explaining previously reported associations with age.

POTENTIAL RELEVANCE

Neutrophil proportion in tracheal wash samples is not as useful a clinical tool as measures of visible tracheal mucus for identifying horses requiring treatment or changes in management. The inclusion of tracheal wash neutrophils in the assessment of equine airways, or at least their relative weighting in definitions of trIAD, should be re-evaluated.