Infectious risk factors and clinical indicators for tracheal mucus in British National Hunt racehorses

The Microbiota and Equine Asthma: An Integrative View of the Gut-Lung Axis

Both microbe-microbe and host-microbe interactions can have effects beyond the local environment and influence immunological responses in remote organs such as the lungs. The crosstalk between the gut and the lungs, which is supported by complex connections and intricate pathways, is defined as the gut-lung axis. This review aimed to report on the potential role of the gut-lung gut-lung axis in the development and persistence of equine asthma. We summarized significant determinants in the development of asthma in horses and humans. The article discusses the gut-lung axis and proposes an integrative view of the relationship between gut microbiota and asthma. It also explores therapies for modulating the gut microbiota in horses with asthma. Improving our understanding of the horse gut-lung axis could lead to the development of techniques such as fecal microbiota transplants, probiotics, or prebiotics to manipulate the gut microbiota specifically for improving the management of asthma in horses.

A Longitudinal Analysis of Equine Asthma Presentation and Response to Treatment Using Lung Function Testing and BAL Cytology Analysis in Combination with Owner Perception

(1) Background: Equine asthma (EA) is a pervasive and important cause of poor performance and respiratory morbidity in horses. Diagnosis of EA includes an owner complaint, clinical scoring, lung function testing, and cytological analysis of bronchoalveolar lavage (BAL) cytology. There is a paucity of information about the longitudinal course of the disease using these outcome assessments; thus, this study sought to describe and quantify, in horses with more than one visit to a specialty pulmonary clinic in New England, the type and range of clinical presentations with an eventual diagnosis of EA. It also aimed to develop and compare the outcomes of scoring systems for owner complaints and veterinary assessments, document and assess the diagnostic methods used, and evaluate the response of the horses to treatment and time. (2) Methods: This study was a retrospective, cross-sectional, STROBE-compliant observational analysis of equine patients who visited the Tufts Cummings Hospital for Large Animals (HLA) for evaluation of equine asthma (EA) from 1999-2023. The horses were categorized as having mild-moderate (mEA) or severe EA (sEA) using the ACVIM consensus statement guidelines. After excluding those with inadequate documentation or only one visit (n = 936), a total of 76 horses were included in the study. Of the 197 visits, 138 (70.0%) resulted in a diagnosis of mEA and 45 (22.8%) resulted in a diagnosis of sEA. Demographic information, owner complaints, clinical examination and scoring, lung function testing, BAL cytology, and recommendations for environmental remediation and pharmacologic treatment were recorded for all the visits. The data were analyzed for agreement between owner complaints (complaint score, CS) and clinical examination findings (examination score, ES), changes in CS and ES, lung function testing, and BAL cytology over time, with 197 visits recorded. (3) Results: A comparison between the CS and ES showed that the owners were more likely than veterinarians to detect cough, and a decrease in cough was the most common owner observation after treatment. The response to the histamine challenge, used to detect airway hyperreactivity, was significantly improved with treatment or time in the horses with mEA, whereas baseline lung function did not significantly change in mEA or sEA. (4) Conclusions: Owners can be astute observers of clinical signs, especially cough, in EA. Tests of airway hyperreactivity are more successful in detecting changes in mEA than are baseline lung function testing and assessment of BAL cytology.

A Scoping Review of Non-Structural Airway Disease as a Cause of Poor Performance in Racehorses

The association between poor performance and respiratory disease in Thoroughbred racehorses that do not have a structural abnormality of the respiratory tract, is often based on anecdotal evidence. The objective of this scoping review was to examine the scientific evidence for such associations. Publications were selected based on a search of three databases (PubMed, Scopus, and CAB Direct), in English and without date restriction, followed by a screening process to exclude non-relevant papers, duplicates, and reviews. This process identified 996 publications of which 20 were analysed using the Quality in Prognosis Studies (QUIPS) tool. The results indicated that the evidence supporting the relationship between proposed diagnostic indicators and poor performance is variable. There is a need for better quality evidence. In particular, there are conflicting reports relating to the impact of equine asthma and EIPH on athletic performance. Furthermore, a lack of standardisation in the measurement of racehorse performance makes it difficult to compare findings from different studies. The industry would benefit from high-level guidance concerning the design of controlled performance studies in Thoroughbred racehorses to collect comprehensive data and facilitate targeted interventions.

Mild-moderate equine asthma: A scoping review of evidence supporting the consensus definition

Current consensus defines mild-moderate equine asthma (mEA; previously inflammatory airway disease) by a hierarchy of indicators of lung pathology: cough, poor performance, increased tracheobronchial mucus, inflammatory bronchoalveolar lavage (BAL) cytology and pulmonary dysfunction. Exclusion criteria include fever, systemic disease, or increased resting respiratory effort. The aim of this review was to inform future research by identifying gaps, strengths and weaknesses in the current body of evidence supporting this consensus-proposed definition. Objectives were to critique evidence supporting the inclusion of each diagnostic indicator in the case definition, by summarising and evaluating evidence for its association with higher-level indicators of lung inflammation. Searches of three databases identified 2275 articles relating to mEA or its diagnostic indicators, from which 298 full-text articles were screened and 45 reviewed in full. Studies (n = 44) had been performed worldwide in clinics, hospitals, racetracks, yards or research herds, in 6092 horses. Studies were predominantly opportunistic observational (n = 13/44: 29.5%) or cross-sectional (n = 11/44; 25%). The median number of horses per study was 74. Where breed and use were reported most were Thoroughbreds (58.2%; 2730/4688) and racehorses (72.8%; n = 3960/5439). Domains rated as high risk of bias in almost 50% of articles were 'study power' and 'masking'. Heterogeneity in clinical and laboratory measures precluded meta-analysis. Evidence was more consistent for certain pairwise relationships (e.g., between cough and tracheobronchial mucus) than others (e.g., BAL cytology and lung function). Findings highlight the need for increased standardisation of diagnostic methods and reporting to facilitate future systematic review and meta-analysis.

Training associated alterations in equine respiratory immunity using a multiomics comparative approach

Neutrophilic airway inflammation is highly prevalent in racehorses in training, with the term mild to moderate equine asthma (MMEA) being applied to the majority of such cases. Our proposed study is largely derived from the strong association between MMEA in racehorses and their entry into a race training program. The objectives of this study are to characterise the effect of training on the local pulmonary immune system by defining the gene and protein expression of tracheal wash (TW) derived samples from Thoroughbred racehorses prior to and following commencement of race training. Multiomics analysis detected 2138 differentially expressed genes and 260 proteins during the training period. Gene and protein sets were enriched for biological processes related to acute phase response, oxidative stress, haemopoietic processes, as well as to immune response and inflammation. This study demonstrated TW samples to represent a rich source of airway cells, protein and RNA to study airway immunity in the horse and highlighted the benefits of a multiomics methodological approach to studying the dynamics of equine airway immunity. Findings likely reflect the known associations between race-training and both airway inflammation and bleeding, offering further insight into the potential mechanisms which underpin training associated airway inflammation.

The Role of Thoracic Ultrasonography and Airway Endoscopy in the Diagnosis of Equine Asthma and Exercise-Induced Pulmonary Hemorrhage

Mild-moderate (MEA), severe (SEA) equine asthma and exercise-induced pulmonary hemorrhage (EIPH) are common respiratory disorders in horses. The present retrospective study aims to evaluate the role of ultrasonography and endoscopy in the diagnosis of these conditions. Three hundred and three horses were included and divided into SEA, MEA and MEA + EIPH groups, on the basis of history, clinical examination and bronchoalveolar lavage fluid (BALf) cytology; scores were assigned to lung ultrasonography, pharyngeal lymphoid hyperplasia (PLH), tracheal mucus (TM) and tracheal bifurcation edema (TB). These scores were compared between groups, and their associations with age, BALf cytology, tracheal wash microbiology and between endoscopic and ultrasonographic scores were statistically analyzed. Ultrasonographic scores were higher in the SEA and MEA + EIPH groups and associated with increased BALf neutrophils and hemosiderophages. The PLH score was higher in younger horses affected by MEA and EIPH and associated with increased eosinophils and hemosiderophages. TM and TB scores were greater in older horses affected by SEA, associated with increased neutrophils and inversely correlated with hemosiderophages. Moreover, TM grade was negatively correlated with mast cells. Thoracic ultrasonography and airway endoscopy can provide useful information about the inflammatory status of upper and lower airways in the horse.

Equine respiratory viruses, airway inflammation and performance in thoroughbred racehorses

Equine asthma is a common cause of poor performance in racehorses but it is unclear if respiratory viruses contribute to its etiology. The objective of the study was to determine if respiratory viruses were associated with clinical signs and bronchoalveolar lavage fluid (BALF) cytology in Thoroughbred racehorses. Equine herpesviruses (EHV-1, 2, 4, 5) and equine rhinitis A and B viruses (ERBV, ERAV) genomes were quantified by qPCR in nasopharyngeal, tracheal, and BALF samples collected after racing. The relationships between virus detection and load and clinical signs, performance, BALF cytology, and environmental exposures were examined with generalized linear mixed models. Ninety-two samples were collected from 31 horses. EHV-1 and ERAV were not found; EHV-4 was detected in only one sample. EHV-2, EHV-5 and ERBV were more likely to be detected in upper airway samples than in BALF (P < 0.0001). Neither respiratory virus detection nor load was associated with clinical signs or performance. Nasopharyngeal detection and load of ERBV and tracheal detection and load of EHV-5 were associated with increased proportions of neutrophils in BALF (P < 0.003). However, nasopharyngeal detection and load of EHV-5 was not (P = 0.11). Nasopharyngeal detection and load of EHV-2 were associated with decreased BALF mast cell proportions. Respirable dust exposures were significantly higher in horses with detection of ERBV when compared to horses with no detectable ERBV (P < 0.001). Our results suggest that ERBV, EHV-2 and EHV-5 are commonly present in upper airways of healthy racehorses; however, the role they play in the etiology of equine asthma remains unclear.

The equine mononuclear phagocyte system: The relevance of the horse as a model for understanding human innate immunity

The mononuclear phagocyte system (MPS) is a family of cells of related function that includes bone marrow progenitors, blood monocytes and resident tissue macrophages. Macrophages are effector cells in both innate and acquired immunity. They are a major resident cell population in every organ and their numbers increase in response to proinflammatory stimuli. Their function is highly regulated by a wide range of agonists, including lymphokines, cytokines and products of microorganisms. Macrophage biology has been studied most extensively in mice, yet direct comparisons of rodent and human macrophages have revealed many functional differences. In this review, we provide an overview of the equine MPS, describing the variation in the function and phenotype of macrophages depending on their location and the similarities and differences between the rodent, human and equine immune response. We discuss the use of the horse as a large animal model in which to study macrophage biology and pathological processes shared with humans. Finally, following the recent update to the horse genome, facilitating further comparative analysis of regulated gene expression between the species, we highlight the importance of future transcriptomic macrophage studies in the horse, the findings of which may also be applicable to human as well as veterinary research.

Equine Asthma: Current Understanding and Future Directions

The 2019 Havemeyer Workshop brought together researchers and clinicians to discuss the latest information on Equine Asthma and provide future research directions. Current clinical and molecular asthma phenotypes and endotypes in humans were discussed and compared to asthma phenotypes in horses. The role of infectious and non-infectious causes of equine asthma, genetic factors and proposed disease pathophysiology were reviewed. Diagnostic limitations were evident by the limited number of tests and biomarkers available to field practitioners. The participants emphasized the need for more accessible, standardized diagnostics that would help identify specific phenotypes and endotypes in order to create more targeted treatments or management strategies. One important outcome of the workshop was the creation of the Equine Asthma Group that will facilitate communication between veterinary practice and research communities through published and easily accessible guidelines and foster research collaboration.

Conflict Between Direct Experience and Research-Based Evidence Is a Key Challenge to Evidence-Based Respiratory Medicine on British Racing Yards

Inflammatory airway disease (IAD) is a commonly diagnosed but variably defined syndrome of equine lower airway inflammation. The most recent American College of Veterinary Internal Medicine (ACVIM) consensus statement, informed by research evidence, recommends a case definition based on clinical signs (poor performance or occasional coughing of at least 3 weeks duration), increased endoscopically-visible tracheal mucus, and bronchoalveolar lavage cytology, and proposes that the condition should be termed ‘mild-moderate equine asthma' (mEA). In British Thoroughbred racehorses, research to date has focused on airway inflammation defined by increased tracheal mucus and inflammatory tracheal wash sample cytology. It has been unclear whether or to what extent the ACVIM consensus statement has influenced the practice of British racing veterinarians. The aim of this qualitative study was to characterize and understand rationales for current practices relating to diagnosing and managing airway inflammation in British racehorses. Audio-recorded focus group discussions were conducted with 25 participants from four veterinary practices in England. Practices were purposively selected to represent those responsible for different types of racehorse, in different geographical regions. Thematic analysis of transcripts identified (i) an over-arching theme of serving the racing industry within which two further themes (ii) disregarding of the consensus and (iii) the pragmatic clinician were nested. The requirement to serve the racing industry was a key driver of clinical approaches, strongly influenced in particular by the trainer. Participants widely disregarded the consensus case definition of IAD/mEA for British racehorses because of perceived differences in etiology, perceived lack of practicability, particularly of BAL sampling, and perceived lack of understanding of the British racing context by consensus authors. Participants shared a strong professional identity as pragmatic clinicians providing an individualized clinical approach based on direct experience, which was often prioritized as the most valuable evidence with which to inform clinical decision-making. Lack of alignment with international consensus presents a barrier to practicing and furthering evidence-based medicine. Improved dialogue and partnership in research would be valuable and further research tailored for this population, including continuing development of contextually acceptable diagnostic methods, may be required.

Tracheal microbial populations in horses with moderate asthma

Background

There are limited data on potential dysbiosis of the airway microbiota in horses with asthma.

Hypothesis/Objectives

We hypothesized that the respiratory microbiota of horses with moderate asthma is altered. Our objectives were (a) to quantify tracheal bacterial populations using culture and qPCR, (2) to compare aerobic culture and qPCR, and (c) to correlate bacterial populations with bronchoalveolar lavage fluid (BALF) cytology.

Animals

Eighteen horses with moderate asthma from a hospital population and 10 controls.

Methods

Prospective case‐control study. Aerobic culture was performed on tracheal aspirates, and streptococci, Pasteurella multocida, Chlamydophila spp., Mycoplasma spp., as well as 16S (bacterial) and 18S (fungal) rRNA subunits were quantified by qPCR.

Results

Potential pathogens such as Streptococcus spp., Actinobacillus spp., and Pasteurellaceae were isolated from 8, 5, and 6 horses with asthma and 3, 0, and 2 controls, respectively. There was a positive correlation between Streptococcus spp. DNA and 16S rRNA gene (r ≥ 0.7, P ≤ 0.02 in both groups), but the overall bacterial load (16S) was lower in asthma (1.5 ± 1.3 versus 2.5 ± 0.8 × 10⁴ copy/μL, P < 0.05). There was no association between microbial populations and clinical signs, tracheal mucus or BALF inflammation.

Conclusions and Clinical Importance

This study does not support that bacterial overgrowth is a common feature of chronic moderate asthma in horses. Lower bacterial load could suggest dysbiosis of the lower airways, either as a consequence of chronic inflammation or previous treatments, or as a perpetuating factor of inflammation.

The Effect of Race Training on the Basal Gene Expression of Alveolar Macrophages Derived From Standardbred Racehorses

Mild-to-moderate equine asthma is prevalent in young racehorses, particularly early in their training period. Although the precise etiopathogenesis remains undetermined, it is possible that the susceptibility of this population might partly reflect an exercise-associated immune derangement at the level of the airway. We performed a genome-wide basal gene expression scan on alveolar macrophages (AMs) isolated from Standardbred racehorses before and after commencement of competition race training with a view to identifying any exercise-associated gene expression modulation consistent with functional alterations, which might reflect training-associated immunological derangement. Microarray technology was used to analyze the basal gene expression profiles of bronchoalveolar fluid-derived AMs, harvested from six systemically healthy Standardbred racehorses before (T0) and after (T1) entry into training. In addition, AM lipopolysaccharide (LPS)-induced TNF-α and IL-10 release at T0 and T1 was assessed. Although the data revealed significant interhorse heterogeneity in relation to the magnitude of individual gene expression at each timepoint, within each horse, several inflammatory-related genes [e.g., chemokine ligands, interferons, and nuclear factor kappa-light-chain-enhancer of activated B cells (NFKB)] declined in expression from T0 to T1. Entry into training did not significantly alter AM LPS-induced TNF-α or IL-10 release. The data support a direct effect of training on AM basal gene expression, particularly with respect to immune-related genes. The pattern of training-associated differential gene expression may indicate relative downregulation of inflammatory-related genes, consistent with an immunosuppressive effect of training and an increased susceptibility to opportunistic pathogens.

Bronchoalveolar lavage fluid from both lungs in horses: Diagnostic reliability of cytology from pooled samples

Cytology of bronchoalveolar lavage fluid (BALF) from one lung may not predict findings in the contralateral lung of the same horse. The aim of this study was to determine whether a pooled BALF from both lungs was representative of corresponding individual samples. Fifty-one horses referred for poor performance and/or respiratory signs and for which a BALF was collected from both lungs, were included in the study. Cytology of pooled and individual BALF samples were performed using a masked protocol. Based on clinical signs and individual BALF cytologies, horses were classified as control (CTL), mild equine asthma (mEA), severe equine asthma (sEA) and/or exercise-induced pulmonary haemorrhage (EIPH). No significant difference was observed between pooled and individual BALF samples for all cell types (P>0.05). Correlations between pooled and individual BALF samples were good (r≥0.9) for neutrophil proportions and haemosiderophages/macrophages ratio, and moderate (r≥0.4) for metachromatic cell and eosinophil proportions. Similarly, intraclass correlation coefficient (ICC) were good (ICC≥0.9) for neutrophil proportions and haemosiderophages/macrophages ratio and substantial (ICC≥0.6) for metachromatic cell proportions. Based on threshold values for pooled samples as determined by receiver operating characteristic (ROC) analysis, categorical agreements were good (κ≥0.97) for diagnosis of mEA/sEA, and substantial (κ=0.74) for EIPH. Using a pooled BALF sample, only one horse was incorrectly classified as CTL instead of mEA and three horses were classified as EIPH instead of CTL. In conclusion, BALF cytology from pooled sample is representative of both individual lungs, and constitutes a valid method to diagnose EA.

Lower Airway Disease in the Athletic Horse

The airways are the first part of the pathway in the oxygen transport chain that is critical to excellent athletic performance, and the lower airways are considered the final gatekeeper before oxygen enters the blood and carbon dioxide exits. Horses are blessed with large airways and lungs that allow them to be superb athletes, but the down side of this largesse on the part of evolution is that unless they are truly elite athletes they may withstand noninfectious disease of the lower respiratory tract for months to years before the owner or trainer notices. The two conditions of the lower respiratory tract that affect the athletic horse during exercise are exercise-induced pulmonary hemorrhage and inflammatory airway disease. The former may be considered, at least at the onset, as a problem of physiology rather than a disease, and the latter is a disease primarily of domestication: both are widespread among the athletic horse population and account for an impressive number of horses that fail to perform to their potential. Because of the high demands for oxygen in the athletic horse, even minor insults to the oxygen-carrying capacity of the body can affect performance, so it is of critical importance to keep the lungs as healthy as possible.

Association of neutrophil morphology with bacterial isolates in equine tracheal wash samples

BACKGROUND

Tracheal wash sample neutrophilia is common in lower airway inflammation of various causes; however, relevance of cytomorphological features to culture of bacterial pathogens has not been established.

OBJECTIVES

To investigate whether the presence of nondegenerate or degenerate neutrophils in tracheal washes is associated with culture of bacteria and, if so, whether this is influenced by age or temporal factors.

STUDY DESIGN

Cross-sectional study.

METHODS

Tracheal wash samples submitted to Rossdales LLP from 1/1/2013 to 31/7/2015 were evaluated using set criteria. Neutrophilia and degenerate neutrophilia (graded ≥2/4 on Rossdales cytological scale [0-4]) were analysed in relation to bacterial isolates considered potentially pathogenic in respiratory disease. Statistical analyses included multivariable logistic regression to identify associations between two separate outcomes: 1) the presence of neutrophilia compared with no neutrophilia and 2) the presence of degenerate neutrophilia compared with nondegenerate neutrophilia and four independent variables.

RESULTS

Sufficient data for inclusion in the multivariable model for nondegenerate neutrophilia were available from 1100 horses. Culture of potentially pathogenic bacteria was associated with increased odds of degenerate neutrophilia compared with samples with negative culture (OR 4.5, 95% CI 3.1, 6.4, P-value<0.001). Horses over 9 years old had lower odds of having degenerate neutrophilia than those aged 1-3 years (OR 0.6, 95% CI 0.4, 0.9, P-value<0.02). In the spring/summer, horses had reduced odds of a degenerate neutrophilia compared with winter (OR 0.4, 95% CI 0.3, 0.7, P-value <0.001).

MAIN LIMITATIONS

The study relied on routine laboratory submissions, with no control over sample collection or submitted clinical history.

CONCLUSIONS

Cytological evaluation of tracheal washes should include cytomorphological features of the neutrophil response. The presence of degenerate neutrophils, especially in young horses, indicates added value of culture and sensitivity for antimicrobial therapeutics. The absence of degenerate changes, in combination with clinical factors, can help support diagnosis of a nonseptic cause of airway neutrophilia.

Multiple molecular detection of respiratory viruses and associated signs of airway inflammation in racehorses

Background

The potential involvement of viruses in inflammatory airway disease (IAD) was previously investigated through either serology or PCR from nasopharyngeal swabs (NS). The aims of this study were to determine the prevalence and incidence of viral genome detection by qPCR in the equine airways, and their association with respiratory clinical signs.

Methods

Both NS and tracheal washes (TW) were collected monthly on 52 Standardbred racehorses at training, over 27 consecutive months (581 samples). Equid herpesviruses (EHV)-1, −4, −2 and −5, equine rhinitis virus-A and -B (ERBV), equine adenovirus-1 and −2, equine coronavirus and equine influenza virus were systematically investigated in both NS and TW. Nasal discharge, coughing, tracheal mucus score and TW neutrophil proportions were simultaneously recorded.

Results

Genome for 7/10 viruses were detected at least once throughout the study; up to 4 different viruses being also concomitantly detected. Monthly incidence in TW was respectively 27.9% (EHV-5), 24.8% (EHV-2), 7.1% (ERBV), 3.8% (EHV-4), 1.9% (EAdV1) and 0.2% (EHV-1; ERAV). Neither agreement nor correlation between NS and TW was found for respectively genome detection and viral loads. Detection of viral genome in NS was not associated with any clinical sign. Coughing was significantly associated with TW detection of EHV-2 DNA (OR 3.1; P = 0.01) and ERBV RNA (OR 5.3; P < 0.001). Detection of EHV-2 DNA in TW was also significantly associated with excess tracheal mucus (OR 2.1; P = 0.02).

Conclusions

Detection and quantification of EHV-2 and ERBV by qPCR in TW, but not in NS, should be considered when investigating horses with IAD.

Electronic supplementary material

The online version of this article (doi:10.1186/s12985-016-0657-5) contains supplementary material, which is available to authorized users.

Association of tracheal mucus or blood and airway neutrophilia with racing performance in Thoroughbred horses in an Australian racing yard

OBJECTIVES

To determine the variation of tracheal mucus scores, tracheal blood scores and transendoscopic tracheal wash (TW) cytology in a population of Thoroughbred (TB) racehorses and assess their association with racing performance.

METHODS

A total of 220 endoscopic examinations were performed and TWs obtained from 155 TB racehorses. Samples were collected 60-120 min following gallop work. Tracheal mucus score, tracheal blood score and TW cytology were analysed and their association with racing performance assessed.

RESULTS

Of the total examinations and samples, 194 from 135 horses fitted the criteria for inclusion. The overall prevalence of visible tracheal mucus was 2.5% (5/194) and of increased tracheal mucus was 0%. The prevalence of visible tracheal blood was 8.8% (17/194) and of increased tracheal blood was 4.6% (9/194). A total of 36% (70/194) of TWs contained elevated percentages of neutrophils and of these, 96% (67/70) occurred in the absence of any visible tracheal mucus. There was no significant association between tracheal mucus score or TW cytology and subsequent racing performance. There was a statistically significant association (P = 0.004) between increased tracheal blood scores and poor racing performance.

CONCLUSIONS

Visible tracheal blood seen after strenuous exercise in clinically normal TB racehorses was a risk factor for poor racing performance, but the presence of airway neutrophilia was not. No horses in this study were found to have increased tracheal mucus, so the association of increased tracheal mucus with racing performance could not be assessed.

Inflammatory Airway Disease of Horses--Revised Consensus Statement

The purpose of this manuscript is to revise and update the previous consensus statement on inflammatory airway disease (IAD) in horses. Since 2007, a large number of scientific articles have been published on the topic and these new findings have led to a significant evolution of our understanding of IAD.

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.