Dr. Emmanuelle van Erck, DVM, PhD, ECEIM explains her work looking at the link between the presence of fungi and lower airway inflammation
Horses are incredible athletes. Their physiology—the way their body functions—is truly fascinating. They can adapt to training at a phenomenal rate, they have massive hearts that fuel their powerful muscles and pushes them to peak speeds. So what could stop them? Oxygen, or rather the lack of it. Horses experience hypoxemia during racing, which means they enter a state of deficiency in oxygen. The reason for this deficiency is a failure of the respiratory system to effectively ventilate and adequately fuel oxygen to the muscles. Horses are obligate nasal breathers and were endowed with particularly long and narrow upper airways in relation to their body size. These factors increase the resistance to breathing. They are also constrained by the fact that they ventilate at very high rates, which does not allow for effective and rapid renewal of oxygen in the lungs. Even the fittest, best thoroughbreds crave oxygen from mid-race onwards. So maintaining horses in optimal respiratory health is absolutely essential for them to achieve an efficient sprint and optimal performance.
Respiratory diseases are highly prevalent in horses. It is inherent to their living and working conditions. The mere fact that a horse is housed in a box increases his risk of developing airway inflammation. The content in fine dust is naturally high in a horse’s box. Closed or poorly ventilated barns further deteriorate air quality in the horse’s immediate environment. Several studies have shown that horses housed indoors are exposed not only to high amounts of organic dust and ammonia but also germs and endotoxin they produce that trigger a detrimental reaction from the immune system. The problem is that even low-grade respiratory diseases will directly affect the horse’s capacity to perform and recover from strenuous exercise.
With my colleagues, Dr Dauviller and Dr ter Woort, specialists in equine internal medicine, we have investigated the link between the presence of fungi and lower airway inflammation. In our ambulatory referral practice, we go out to the stables and have the opportunity not only to examine the horse but also attentively assess his environment. As we collected respiratory samples and analysed them ourselves, we became aware that the presence of microscopic moulds or fungal elements was frequently associated to lung issues. To investigate this further, we decided to systematically record clinical and environmental data and link it to our findings in the respiratory samples of the horses referred for investigation.
We collected more than 700 cases; the horses included in the study were either referred routine examinations, unexplained poor performance or respiratory symptoms such as coughing or breathing heavily during exercise. All horses had a tracheal and a bronchoalveolar lavage done which allowed us to evaluate their level of respiratory inflammation, as well as estimate the presence of fungi within the airways. We also looked at the state of activation of fungi: if they were inert particles or if they showed signs of active proliferation. Our results were without appeal; the presence of inhaled fungi significantly and negatively affected respiratory health in horses, causing inflammation and in some cases, infection.
In this population, inflammatory airway disease (IAD) was diagnosed in 88% of cases, confirming that respiratory inflammation is very common and often under-diagnosed. Of these positive cases, 81% had evidence of fungi in their airways. The presence of fungi more than doubled the odds of having lung inflammation.