IN-DEPTH: PREVENTATIVE MEDICINE: BEING PROACTIVE IN PRACTICE


consequences such as pulmonary hypertension16,17 and can end up surrendered or euthanized by owners who do not have the ability or finances to manage this chronic disease. Given the significant impacts EA has on issues ranging from optimal equine performance to welfare, it is essential that veterinarians and equine health researchers work to develop a better under- standing of the underlying mechanisms of disease, as well as identify improvedmethods for early recognition, diagnosis, treatment, and prevention. It is well established that in horses with EA, alveo-


larmacrophages and airway neutrophils are activated by airborne organic dust in the breathing zone.2,18,19 What is lesswell known is that healthy horses also ex- perience significant airway neutrophilia in response to organic dust exposure.10,20 Organic dust consists of a mixture of many potential antigens, including particulate matter, endotoxins or lipopolysaccharide, peptidoglycans, noxious gases, and b-D-glucans.2,18 Following exposure to organic dust, alveolar macro- phages become activated and release proinflamma- tory mediators including tumor necrosis factor-a, interleukin-6, interleukin-8 (IL-8), chemokine ligand- 1, and chemokine ligand-2, as well as reactive oxygen species.21–25 In response to these signals, large num- bers of neutrophils are recruited to the airways. Airway neutrophils then release proinflammatory mediators including interleukin-1b, tumor necrosis factor-a, IL-8, interleukin-17, reactive oxygen species, and neutrophil extracellular traps.19,26–29 Similar immunopathology has been identified as causing organic-dust-induced asthma in human agricul- tural workers.2,26 Ongoing research seeks to under- stand why this cycle of inflammation, which happens in both healthy and asthmatic horses, becomes dys- regulated, chronic, and debilitating in horses with sEA. Until more answers are available, strategies of preventive medicine including routine annual exams with comprehensive evaluation of the respiratory system using previously validated scoring systems (discussed below), increased owner education, and mitigation strategies for organic-dust exposure could help improve the lower airway health of all horses.


2. Diagnosing Equine Asthma


tory findings for horses with bothmEA and sEA, their physical exam findings will differ. Horses with mEA have no respiratory abnormalities evident on resting exam,whereas horseswith sEA in exacerbation or cri- sis will have readily identifiable abnormalities at rest


Depending on the clinical case presentation and set- ting (field vs. research), veterinarians can use a com- bination of history, physical exam, rebreathing exam, screening survey,30 clinical respiratory scores,31,32 BAL,12 airway endoscopy and mucus score,12,33,34 ultrasound,33, 35 and lung function testing13,36–38 to diagnose EA. These diagnostics have been reviewed recently.13 While cough and poor performance are common his-


ranging from elevated respiratory rate and increa- sed nostril flare to increased abdominal effort, anal pumping, and abnormalities on thoracic ausculta- tion including crackles and/or wheezes and tracheal rattle due to increased tracheal mucus. One excep- tion to these typical physical exam findings for horses with sEA is horses that have achieved sub- clinical status, often referred to as “remission.” With optimal environmental management practices that reduce exposure to organic dust, horses with sEA can achieve near-normal to normal lung function and dramatically reduce or even eliminate neutrophilic lower airway inflammation.36,39,40 A rebreathing ma- neuver is a useful diagnostic tool in horses with a history of cough or decreased performance but no re- spiratory abnormalities on resting exam. A small bag (i.e., 4- to 8-gallon trash bag) placed over the horse’s nose and mouth is used to induce hyperventilation. The increased respiratory rate and effort create increased air movement and turbulence in the lower airway, which leads to increased sound and an increased ability to detect abnormalities such as crackles or wheezes. The maneuver is commonly per- formed for 90seconds to 3minutes. A healthy horse should easily tolerate the exam, should not cough, and should return to baseline breathing rate and effort within 5 to 8 breaths once the bag is removed. Some horses with mEA will have wheezes or coughs during the maneuver or prolonged recovery following removal of the bag.41,42 TheHorse Owner Assessed Respiratory Signs Index


is a client survey that has been validated and used as a diagnostic aid in multiple studies.43–47 It is a stand- ardized questionnaire that has been shown to predict sEA based on the frequency of cough, the presence of nasal discharge after exercise, the presence of abnor- mal respiration, and an evaluation of the performance of the horse by the owner. A score of 1 means that horses arewithout clinical signs of respiratory disease, a score of 2 or 3 indicates mild or moderate signs, and a score of 4 indicates severe signs of respiratory dis- ease, compatible with severe asthma.43 There are several standardized respiratory score


rubrics that have been used for research investigations of equine asthma including a 21-40 or 23-point scoring system,32,48 the Improved Clinically Detectable Equine Asthma Scoring System (IDEASS) score,31,49 the short score,40 and a visual analog scale score.40 From a research perspective, standardized respiratory score rubrics provide a readily available and inexpensive method to define clinical groups and compare one study population to another using a method that generates quantitative data. From a clinical perspective, potential advantages of using a standardized scoring system are that it promotes a systematic and thorough exam and, if sensitive enough, provides a tool to monitor changes in chronic disease status over time. This is particularly useful when trying to obtain objective data to gauge a patient’s response to season, management changes, or therapeutics. To that end, Calzetta et al. conducted a pairwise and networkmeta-analysis in order to identify


AAEP PROCEEDINGS / Vol. 68 / 2022 407


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