E710
Respiratory Problems - Infectious Causes & Small Airway Inflammatory Disease

Introduction: There are many organisms that affect the respiratory system in horses. While foals are probably the most at risk, any horse may be affected, particularly if they are not in good health. Some common respiratory agents are discussed in this section.

Causative Agent: Streptococcus zooepidemicus is a bacterium that affects the upper respiratory tract of foals. In some cases, the organism can spread into the bronchi and cause bronchitis.

Clinical signs: Foals (particularly weanling foals) may have a cough and can also have nasal discharge.

Disease Transmission: Streptococcus zooepidemicus can be spread through nasal discharge and cough secretions. It also tends to progress when the animal’s immune system is compromised.

Diagnosis: A veterinarian may decide to take X-rays of the foal to see if there is a certain pattern visible inside the lungs. Another method for diagnosing this disease is to take a sample of the infection from the lungs and examine it using a microscope or culture it to see what organisms will grow.

Treatment: An extended treatment of antibiotics, such as penicillin and trimethoprimsulfa, will clear up most infections. The key to treatment is to keep the foal on the medicine for the entire treatment time (or at least three weeks). This is critical because this organism can be difficult to cure and will often cause a relapse.

 

Causative Agent: Rhodococcus equi is a bacterial infection that is most commonly seen in foals between one to six months of age. As protection from maternal antibodies fades, the likelihood of this infection increases.

Clinical Signs: Foals may have nasal discharge, a cough, and appear depressed (lethargic). If the disease spreads to the abdomen, the animal may experience peritonitis (inflammation of the lining of the abdomen), diarrhea, or colic. Some may experience arthritis, while others may develop abscesses on the lungs.

Disease Transmission: Rhodococcus equi can be spread through the nasal discharge and feces from mares and infected animals. It also can survive in the soil in dusty or dry paddocks.

Diagnosis: One of the best ways for positive identification of Rhodococcus equi is to culture a sample from the animal’s throat. It can also be possible to identify an abscess in the chest by tapping on the rib cage while listening with a stethoscope. The abscess can also be confirmed using chest X-rays.

Treatment: Treatment with antibiotics is difficult because Rhodococcus equi survives inside cells, where many antibiotics cannot reach. However, a combined treatment of erythromycin estolate or phosphate and rifampin for two or more months may be successful. The two must be used together to avoid resistance to rifampin. During treatment several side effects may be observed, including an orange color to urine and mild diarrhea. It is also important to keep treated animals cool on hot days to help avoid death by overheating (hyperthermia).

Prevention: To help reduce possible infection of Rhodococcus equi, remove animals from dry, dusty paddocks and turn them out into more grassy areas. Treating young foals with hyperimmune plasma at 2-3 weeks has also shown to be an effective way to provide them with additional protection during that critical time when the mother’s antibody levels decrease.

 

Causative Agent: Acute respiratory distress syndrome (ARDS) is a challenging disease because the direct cause is not known. Cultures from infected animals identify many different bacteria as possible causes.

Clinical Signs: Mostly affecting foals, ARDS has a very quick onset. Some animals will actually succumb to the disease and be found dead before any other symptoms are seen. Other animals can display difficulty breathing or rapid breathing as the first signs. These animals are very susceptible to overheating (hyperthermia).

Diagnosis: Chest radiographs may show a specific bronchial pattern that indicates possible ARDS. Also a culture of the throat or nasal passageways can help identify bacteria that may be causing the problem.

Treatment: Antibiotics alone often do not solve the problem. Many times it is necessary to use antibiotics coupled with oxygen therapy and corticosteroids to yield the best recovery rates. It is also important to keep the animals cool during the disease to avoid hyperthermia.

 

Causative Agent: Infection occurs when the animal’s immune system is compromised. Many bacteria and organisms can contribute to the infection, including Actinobacillus equuli, E. coli, Streptococcus zooepidemicus, and Clostridial spp.

Clinical Signs: Symptoms may include shallow breathing, depression, and signs that seem to indicate colic such as slow, stiff movements and pain manifested during examination of the chest. A dull sound may also be heard when listening to the animal’s chest and tapping on its side.

Diagnosis: A dull sound heard on the underside (ventral side) of the animal’s chest while tapping is a key symptom. Chest radiographs or ultrasound can show abscesses, fluid, or other patterns consistent with infection. A cytology or culture may also be done.

Treatment: Depending on the severity of infection, the animal’s chest may need to be drained. Long-term treatment using antibiotics and anti-inflammatory drugs is necessary in most cases.

Introduction: Small airway inflammatory disease or SAID is a general term used to describe inflammation of the small bronchi and bronchioles in the lungs. It is also sometimes referred to as small airway disease or SAD. Chronic obstructive pulmonary disease (heaves – see page E305) is a more severe form of SAID where the horse has repeated severe airway inflammation that results in permanent thickening of the airways. Most scientists agree that SAID is caused mainly by non-infectious agents like dusts and allergens. It is also thought that some SAID cases can be the result of repeated viral infections. In most situations, a case of SAID can be distinguished from contagious/ infectious causes of cough because a SAID horse will not have a fever, will have fairly normal blood work, and will act normal when not exercising.

Causative Agents: The majority of small airway inflammatory disease cases are caused by materials or allergens that irritate the lining of the lungs. These allergens include dust, pollution (smoke, air pollution), chemicals, and possibly even molds, bacteria and viruses.

Clinical Signs: Some of the early signs of SAID are a lack of energy during exercise (exercise intolerance) and a mild to moderate cough. The cough is usually intermittent, sometimes producing mucous. Many horse owners will notice that their horse is lethargic and will not respond like it did before. This is especially true of horses that are worked at speeds and perform in high endurance competitions.

Most of the signs of SAID are more apparent in the summer time when allergens and heat are at their peak. When the lungs are listened to with a stethoscope, they often sound very normal in mild cases. If a veterinarian performs an endoscopic exam, mucous is commonly found in the respiratory tract.

Diagnosis: Because it causes such vague symptoms and is often very mild in the early stages, SAID is often difficult to diagnose in every case. This often means that many different tests may have to be used before a diagnosis can be reached. Some of the more common procedures used to diagnose SAID include physical exam, chest X-ray or radiograph, endoscopy, bronchoalveolar lavage (BAL), histamine challenge, and lung function tests. In many cases, the physical exam, chest X-ray or radiograph, and endoscopy tests are normal and BAL and lung function tests are necessary to diagnose the problem. A brief description of the findings of these procedures and a description of the BAL procedure will be given in the following information:

Physical Exam: This is often normal in early/mild cases of SAID.

Chest X-ray or radiograph: Often the X-rays appear normal, with some cases showing a bronchointerstitial pattern.

Endoscopy: When examining a horse with SAID, there will often be differing amounts of mucus secretion found in the trachea. This mucus is more obvious after exercise. It is important to note that not all horses with mucus in the trachea will have SAID.

Bronchoalveolar lavage (BAL): During this procedure, saline is placed into the horse’s lungs and then is drawn out of the lungs using suction. After the fluid is collected, the different types of cells found in the solution are evaluated. Horses with SAID typically have increased numbers of neutrophils, mast cells and occasionally eosinophils.

Treatment: The common treatments for SAID revolve around three major areas: bronchodilators, anti-inflammatory agents and environmental control efforts.

Bronchodilators: First off, bronchodilators are given to open up the airways and give the horse some immediate relief. New masks such as the Equine Aeromask have been designed to help administer these types of products. See a picture of this product below and a link to a video segment of how it works. Different types of bronchodilators include albuterol, clenbuterol (Ventipulmin – Page G906), and Combivent.

Anti-inflammatory agents: These typically include corticosteroids that are aerosolized or inhaled. These tend to be safer for the horse and seem to be the most effective. Products such as nedocromil sodium (Tilade), disodium cromoglycate (Intal), fluticasone inhaler (FloVent 220) and, in severe cases, oral prednisone are commonly used.

Environmental control efforts: Avoiding allergens such as dust, pollution (smoke, air pollution), chemicals, and possibly even molds, bacteria and viruses is essential in the long-term control of SAID. The bronchodilators and steroids will only treat the problems as they occur; they will not stop the allergens that started the problem in the first place. It is also important to vaccinate the horse regularly for the common respiratory diseases.