Bronchointerstitial pneumonia is one of the most common causes of respiratory distress in foals. It is a sporadic, rapidly progressive disease characterized by acute respiratory distress and high mortality in foals between one week and eight months of age. Other causes of respiratory distress are viral or bacterial pneumonia, chest trauma, heart defects, and allergic reactions to vaccines.
Bronchointerstitial tells us that the disease affects the airways (bronchi) and the interconnecting tissue (interstitial) of the lungs. The fact that both areas are damaged is the reason that foals go into distress.
Bronchointerstitial pneumonia causes respiratory distress by filling air sacs that normally exchange oxygen and carbon dioxide with fluid and damaged cells. The air sacs are rendered useless. The lung goes from spongy and air-filled to a rubbery and fluid filled. The damaged lungs try desperately to inhale and exhale, but the heavy lungs are too stiff, and the airsacs no longer allow oxygen to diffuse into the blood stream. Consequently, the entire body becomes deprived of oxygen.
Foals present with a history of sudden onset of respiratory distress, high fever, coughing, and nasal discharge.
No one cause of bronchointerstitial pneumonia has been identified. It is most likely that bronchointerstitial pneumonia is actually a rogue inflammatory response of the lung to varying insults. Researchers suspect that diseases such as Rhodococcus equi, a serious cause of bacterial pneumonia in foals of this age group, or Pneumocystis carinii, a more rare fungal cause of pneumonia in people and horses whose immune systems are depressed, may be the underlying triggers of bronchointerstitial pneumonia.
A common factor in many cases of bronchointerstitial pneumonia is the use of erythromycin, an antibiotic that is invaluable in the treatment of Rhodococcus equi. Erythromycin might suppress the lung's ability to mount an immune response, thus allowing 'oddball' infections, such as Pneumocystis carinii, to become established in the lung. Also, erythromycin has been shown to cause primary hyperthermia (overheating) in a small subset of foals.
Researchers speculate that bronchointerstitial pneumonia may be complicated by hyperthermia in some cases – in essence, the signs of distress in bronchointerstitial pneumonia may be due to thermal injury to the lung, or hyperthermic effects on the body.
This type of pneumonia is generally seen on farms where there are multiple mares and foals, so there may be a stress or infectious cause that is more likely to appear on breeding farms. Yet another potential cause of bronchointerstitial pneumonia is plant toxins, although none have been conclusively identified as yet.
Death rates from bronchointerstitial pneumonia are high. It progresses rapidly, and is often refractory to treatment.
Watch to Watch For
Many cases of bronchointerstitial pneumonia appear during hot weather, especially if the foal has been transported in hot weather.
Foals will suddenly appear ill, or there may have been a mild cough or nasal discharge, prior to the onset of respiratory distress.
Foals are depressed and stop nursing the mare.
Foals will have a dramatic elevation of respiratory rate (some over 100 breaths per minute).
The nostrils will be flaring and the foal will often extend his head and neck in an effort to get more air.
The foal will often appear to be 'pumping' with his abdomen, and he may show paradoxical breathing. Paradoxical breathing refers to a pattern in which the abdomen springs out during inhalation, but the chest goes in — the chest normally goes out with inhalation, so this is 'paradoxical.'
The foal may even have a visible 'heave line' due to his effort to breath out. The 'heave line', or visible extra effort and delineation of the muscles of the flank, is usually only seen in older horses with clinical signs of heaves, or recurrent airway obstruction.
The foal may or may not have a cough and nasal discharge. Often, the effort to breath is so great that the foal doesn't have the time or the energy to cough.
The foal will often be dehydrated.
You will notice that the even the slightest effort exhausts the foal.
If you can examine the foal's mucous membranes, you will usually see that they are dusky, or cyanotic, indicating that the foal is not able to get enough oxygen into the body.
In some foals the clinical course of disease is so rapid, that the foal is found dead. Typical signs of bronchointerstitial pneumonia are found on autopsy.
Oftentimes, the foal is so severely affected that the veterinarian does not have time for an in-depth examination and history until the foal has been stabilized with oxygen administration. At that time, most foals are referred to a facility that can provide continual critical care treatment.
Once the foal has been stabilized, your veterinarian will take a thorough medical history, looking for clues to underlying respiratory disease – did the foal have a cough at all prior to this episode? Did the foal become overheated during the prior day or two? Has the foal or mare been treated with erythromycin for any reason? Has the foal had a snotty nose or other pre-existing respiratory signs?
The foal must be stabilized immediately – cool him down by placing him in a cool, well ventilated stall. If it's hot, consider a make-shift air-conditioned stall. Oxygen may also be necessary.
Once the foal has been stabilized, your veterinarian will perform an in-depth physical examination and will focus on auscultation of the lungs and thorax, noting whether the foal has a high heart rate, rapid respiratory rate, and abnormal lung sounds. The lungs usually have loud breath sounds over the larger airways and diminished sounds in the lung periphery. Lung percussion demonstrates the lack of air in the lung.
Once the foal has been stabilized, your veterinarian will usually perform laboratory tests. The CBC usually shows a high white cell count and a high fibrinogen, which is a non-specific finding that indicates that your foal has some cause of inflammation and/ or infection. The chemistry profile usually shows signs of dehydration and may show signs of damage to the liver and kidneys due to the lack of oxygen in the body. A blood gas analysis shows that the foal has severe lack of oxygen and a high level of carbon dioxide in the body. This confirms that the foal is unable to ventilate properly.
Your veterinarian will usually perform X-rays that usually show some evidence of lung disease, although the findings are not consistent. There may merely be evidence of underlying bacterial or viral pneumonia, or there may be a diffuse pattern indicating that the rubberizing process has begun.
A transtracheal aspirate (TTA) or bronchoalveolar lavage (BAL) can both be very useful. These procedures allow visualization of cells and possibly bacteria or other infectious agents from the interior of the lung. However, your veterinarian will often choose not to perform these tests in foals with bronchointerstitial pneumonia, because the risk of hurting the foal with our diagnostic procedures is high.
The first thing that the foal needs is COOLING DOWN. If the foal is hyperthermic, it will be necessary to keep him in a cool environment. An air-conditioned stall is ideal, but often unavailable. Other effective methods for cooling down a foal include cool water baths and fans. Your veterinarian may also choose to give cool fluids intravenously and by a nasogastric tube, and may administer a cool water enema. Avoid pure alcohol baths, as the foal can absorb excessive amounts through his skin.
Oxygen is essential. Your veterinarian will often start by placing a small tube inside the foal's nose, which is then attached to an oxygen line. This intranasal oxygen can be life-saving.
The foal also needs treatment with corticosteroids. This may seem contradictory at first, because corticosteroids are used to suppress the immune system and inflammation. However, the immune system and the inflammatory response have essentially gone haywire with bronchointerstitial pneumonia, and are responsible for turning the lung into that rubbery mass that results in the foal's inability to absorb oxygen. Thus, strong drugs that can stop this response in its tracks are necessary. Non-steroidal anti-inflammatory drugs, such as Banamine, may also be used.
Antibiotics can be useful in treating underlying bacterial infections.
Drugs such as albuterol, which work to dilate the airways, can be useful.
Aminophylline, a bronchodilator with other supportive properties, is commonly used.
Intravenous fluid therapy is necessary to counteract dehydration.
Home Care and Prevention
Be vigilant in making sure that foals do not become overheated. If you must transport a foal during hot weather, do so at night, or in the cool of the early morning. If you must travel during the day, make sure that you have excellent ventilation, and make frequent stops to have the foal drink water and/or nurse. Make liberal use of water to wash the foal down every 1/2 hour or so.
Be especially vigilant if you have a foal that is being treated with erythromycin. Keep an eagle eye on all young foals to make sure that you don't miss subclinical lung disease. Remember, a cough and a snotty nose may be common in this age group, but it is not normal and should not be tolerated for any length of time.