Transportation and "Shipping Fever"
Transportation, particularly over long distances, is likely the single most important predisposing factor for pleuropneumonia (aka "shipping fever") in horses. Pleuropneumonia is a very serious condition in horses that occurs when an infection in the lungs (pneumonia, typically bacterial pneumonia) spreads to the outer surface of the lungs (the pleura) and contaminates the space between the lungs and the chest wall (the pleural cavity). The inflammation of the pleura (which is also very painful) usually results in accumulation of infected fluid around the lungs (photo right: drainage of pleural fluid in a horse using a chest tube). The disease can be difficult to treat, and affected horses can end up with a lot of scarred lung and adhesions between their lungs and chest wall, as well as lung abscesses and other problems.
The main reason this condition is so often associated with transportation (which is why the illness is often called shipping fever) is primarily due to the fact that most horses are transported with their heads tied. This prevents the animals from lowering their heads, a motion that regularly allows drainage of the normal respiratory secretions which naturally accumulate in the lower trachea (windpipe) and further down the respiratory tract. The accumulation of this fluid, including the many bacteria from the throat and upper trachea that it normally contains, results in contamination of the lower airways and lungs, which are normally almost sterile. In many cases, the animal’s natural defensive mechanisms are still able to prevent disease from developing, but in others this large amount of contamination results in bacterial pneumonia or pleuropneumonia after transport. Illness is more likely to occur in horses with one or more other predisposing factors, such as viral respiratory infection (which can be acquired through exposure to other horses during shipping), corticosteroid therapy, other illness, or animals that are exercised immediately following transport. The same phenomenon occurs if horses are restrained with their heads in an elevated position for a long period of time, even without the stress of transportation. Horses should be transported in such a way that they can freely lower their heads, whenever this can be done safely.
Because pleuropneumonia is most often caused by the bacteria that are naturally found in a horse's own respiratory tract, it is not considered transmissible between horses. However, viral respiratory infections can predispose horses to developing more severe disease such as pleuropneumonia, and these infections certainly are transmissible. A few basic infectious disease control measures to help prevent these infections include:
- Ensure that horses are appropriately vaccinated for viruses such as equine influenza and equine herpesvirus (types 1 and 4) prior to transportation.
- Don't ship sick horses or those that have been exposed to infectious diseases. This increases the risk to the individual horse and all others it encounters.
- Keep new horses and horses returning from shows and competitions isolated from other horses in the facility so they do not spread any viruses to which they were exposed to the other horses.
- Immediately isolate any horse that develops early signs of respiratory disease, and have it examined by your veterinarian. Follow your veterinarian's instructions regarding treatment and the need for ongoing isolation. Do NOT treat the horse with antibiotics (even if it has a fever) unless advised to do so by a veterinarian.
