Although asthma can be treated so that most people can do the activities they love, why asthma happens is unknown, and there is no cure. That’s where a veterinarian and a 20-year-old horse become part of the picture.
Heaves in horses - Asthma in humans
Immune systems in horses and people react to certain triggers that cause airway inflammation and tightening of the associated muscles.
Immune systems in horses and people react to certain triggers that cause airway inflammation and tightening of the associated muscles. Some of the triggers are even the same — dust, debris from mites, weather.
But why the immune system reacts the way it does in some people and some horses is unknown. Apparently some genetic factors, combined with exposure to certain environmental factors, result in human asthma and equine inflammatory airway disease and heaves, also called recurrent airway obstruction.
Dr. Virginia Buechner-Maxwell is investigating what causes the diseases and how to prevent long-term damage from the diseases and the treatments. The goal is better treatments or cures for both horses and humans.
“Horses are superb models for studying airway diseases because they develop these illnesses spontaneously, like humans,” explains Buechner-Maxwell, a professor of large animal internal medicine in the Virginia-Maryland Regional College of Veterinary Medicine at Virginia Tech. “They also are the only animals besides people that experience chronic changes of the disease as they age.”
Buechner-Maxwell first learned about the human and the equine forms of breathing disorders when she was very young. Her mother had severe asthma and her first horse was heavy. But her interest in the science was sparked when she was studying for a master’s degree at the University of Pennsylvania and she attended seminars given by their immunology group, which was investigating regulation of the immune response.
“As my understanding of the immune system grew,” she recalls, “I became specifically interested in understanding the events that direct and regulate the immune response because it seems to me that a responsive, well-regulated immune system is critical to good health.”
Asthma and heaves often are the immune system’s response to an allergy, especially to airborne particles. “Allergies in general are a good example of what happens when the immune response is disproportionately intense relative.
Heaves in horses is much like asthma in adult humans, especially older people, because they may have worsening disease and long-term lung damage from the disease. Inflammatory airway disease in horses is more like pediatric asthma.
In either case, horses and people can be treated the same ways — by keeping them away from the triggers as much as possible and taking some of the same drugs. Horses have even been fitted with surgical mask-type devices so that they can inhale the medication just like people.
Inhaled corticosteroids to minimize inflammation and bronchodilators to open constricted airways are the standard medication now for long-term control of asthma to relieve inflammation. One bronchodilator that is used is albuterol, a beta2–agonist that provides fast-acting relief of airway constriction and often is taken through an inhaler before participating in sports.
New research in human medicine suggests that this medication also may influence the nature of the body’s inflammatory response associated with asthma, says Buechner-Maxwell.
Horses age faster than humans, so immune response, drug effects, and long-term disease progression can be studied faster than in human patients. Both horses and humans develop the disease spontaneously making the species is a more comparable model with humans than a mouse, a rat, or some other organism engineered to simulate suffering from asthma-like disease.
Horse use as a model for asthma is also important because cell samples can be taken for testing of the immune response without harming the horse. In addition, horses age faster than humans so results of immune responses, drug effects, and long-term disease progression can be studied faster than in human patients.
This is an especially important factor when one of the research goals is to better understand chronic lung and bronchial tube changes that occur in people and animals with life-long airway disease.
Research on cytokine expression is ongoing by Buechner-Maxwell and her research team. Currently, they know that some of the signaling that stimulates cytokine response is different in heavy horses’ lymphocytes, a type of im-mune cell, when compared to the lymphocytes from a horse not plagued by the disease.
“My hope is that by better understanding the events that lead to the ‘inappropriate’ response of the immune system in diseases like heaves and asthma, more can be learned about what promotes and maintains the normal immune response,” Buechner-Maxwell says.