Pleuropneumonia (Shipping Fever) in Horses

Pleuropneumonia is a painful, potentially debilitating condition that requires early treatment to ensure good outcomes. Immediate veterinary attention is required.

Pleuropneumonia is uncommon in horses overall. This condition is more common in horses that have recently traveled long distances, especially when their head has been tied high.

Pleuropneumonia occurs in horses that have inhaled particulates into the lungs and have not been able to clear them. This can happen, for example:

• During races or other exercise, especially when several horses are together in close contact on a dusty surface
• As a result of dusty stables
• Storing hay and other dusty materials near stalls

Other risk factors relate to the lung health and overall condition of the horse, including:

• Recent viral infection, such as influenza
• Recent episode of exercise-induced pulmonary hemorrhage
• Recent anesthesia, intubation or surgery
• Stress due to changes in the routine, especially an increase in training intensity or competition
• Other diseases or conditions that result in tissue death within the lung

The severity of pleuropneumonia depends on how much fluid accumulates in and around the lungs, how effective the treatment is at controlling the inflammation, and what associated conditions are also present.

Mild pleuropneumonia results in the accumulation of fluid in the chest cavity, but does not prevent the horse from breathing properly. Horses with severe pleuropneumonia have a significant amount of fluid in the lungs which causes difficulty breathing. In the most severe cases, the inflammation causes scar tissue to develop between the lung and the chest wall, which permanently limits the ability of the lung to expand. This condition is irreversible and typically ends the career of competition horses.

In some cases, mild pleuropneumonia clears quickly with treatment. In other cases, the infection does not resolve, or resolves temporarily only to return later, despite careful treatment. In some cases, more than one infectious organism is present in the pleural space, which complicates treatment.

Pleuropneumonia is commonly associated with laminitis, a severely painful condition of the hooves. Symptoms of laminitis include:

• Unwillingness to move
• Sawhorse stance where the horse leans backwards with the front feet extended forwards
• Increased temperature of the hooves
• Severe lameness

Pleuropneumonia is caused by infective organisms infiltrating the lungs and the space around the lungs (the pleural space). The infective organisms are typically bacteria, but other organisms such as fungi or parasites are also sometimes involved. The infection causes inflammation as the immune system attempts to clear the infection, causing the accumulation of fluid in the lungs and pleural space.

In order for these infections to take hold, the defense mechanisms of the lung must be impaired. In most cases, this is the result of the inhalation of particles into the lungs or due to underlying lung problems. Usually a horse clears inhaled particles by coughing or lowering the head and allowing the mucus that traps the particles to drain through its nose. In some cases, where the horse’s head has been tied up or where the horse is too busy with exercise, the normal process of clearing the particles does not take place. The presence of these particles causes an initial inflammatory response which creates an environment for bacteria to reproduce, resulting in pleuropneumonia.

Pleuropneumonia can also cause chest pain, which is demonstrated by grunting when touched or breathing, flinching, taking shorter than usual strides, standing with elbows pointing out, anxious facial expressions, a reluctance to move or lie down, and generally avoiding anything that jostles the chest cavity.

Diagnostic tools to confirm pleuropneumonia include:

• Physical examination
• Ultrasound of the chest
• Bloodwork
• Thoracocentesis (draining the fluid from the thoracic space)
• Measuring oxygen levels in the blood

Treatments include:

• Antibiotics
• Anti-Inflammatories
• Pain relief
• Drainage of the fluids and other materials from the pleural space and lungs
• Lavage of the pleural cavity
• Surgical thoracotomy (an incision between the ribs to allow access to the lungs and pleural space)

In many cases, close monitoring over the course of treatment is required to ensure that the infection is resolving.

After recovery, a prolonged period of rest is required. In mild cases, a minimum of 30 days is recommended. In more severe cases, a minimum of 3 months is necessary.

For mild cases of pleuropneumonia that benefit from early treatment, the prognosis is good, depending on how quickly the horse responds to treatment. In severe cases and cases where treatment is delayed, the prognosis is guarded.

The length of time required for the treatment of pleuropneumonia varies case by case. Some horses recover within a month while others require half a year or longer to recover.

In cases where scar tissue has limited the lungs ability to expand, it is unlikely that the horse can return to athletic competition.

Strategies for the prevention of pleuropneumonia include:

• Keeping as dust free an environment as possible
• Allowing the horse free movement of its head particularly after heavy exercise
• Avoiding racing, competition, or traveling after incidents of viral infection, influenza, exercise-induced pulmonary hemorrhage, or other lung-related health problems
• Avoiding stress when possible

For horses that are traveling long distances, strategies include:

• Allowing the horse a free head as much as possible during the trip
• Breaking for rest regularly
• Feeding and watering the horse regularly along the way
• Ensuring excellent ventilation and air-exchange in the horse compartment
• Avoiding travel in cases where there is an existing respiratory infection

Pleuropneumonia is an uncommon condition in horses.

• Antibiotics
• Anti inflammatories
• Drainage
• Lavage