English
Shipping fever is a lower respiratory tract infection seen in horses transported over long distances or experiencing unusual or stressful events. [1]
Known causes of shipping fever include prolonged periods of head elevation, strenuous exercise, anesthesia or complications from a viral illness. [2]
These events increase the amount of debris aspirated by the horse and inhibit the horse’s ability to clear debris from the lungs. Stress also compromises the immune system, making horses susceptible to a viral respiratory infection.
Without prompt medical intervention, shipping fever can develop into pleuropneumonia, which is a dangerous form of equine pneumonia. It is caused by fluid build-up in the lungs and pleural cavity, which is the space between the lungs and chest wall.
Early recognition and treatment of shipping fever are key to a good prognosis. If you are planning on shipping or travelling with your horse, preventative steps can support the immune system and reduce the chance of infection.
Shipping Fever in Horses
Shipping fever is a transport-associated syndrome seen in horses and other livestock animals, causing pyrexia (fever) and other respiratory symptoms. [3]
The stress of travel, combined with exposure to unfamiliar pathogens, can cause various symptoms ranging from mild to severe.
Shipping fever is characterized by the presence of bacteria and other irritants (i.e. hay particles, dust, chemicals) in the lower airway. Longer distances and travel times carry a higher risk of lower airway infection. [3]
Most shipping fever cases present with a general systemic inflammatory response. [4] Signs of infection usually appear within 1-3 days following shipment or arrival at destination and can worsen quickly.
Between 9 – 12% of horses transported for distances between 1,000 – 1,300 km experience shipping fever. [3]
The terms shipping fever and pleuropneumonia are often used interchangeably. However, pleuropneumonia is technically a consequence of severe shipping fever.
Cause & Pathology
Long-distance travel can cause significant stress for the horse, with eleveated levels of the stress hormone cortisol.
High cortisol levels affect the body’s ability to fight off infection, in part by reducing neutrophil counts in the blood. Neutrophils are a type of white blood cell or immune cell that help the body fight infections.
As a result, pulmonary defence mechanisms can become overwhelmed, allowing infection to develop in the lungs. [5] Pneumonia or lung abscesses can develop and extend into the pleural cavity (the fluid-filled space surrounding the lungs). [6]
Shipping fever infection is often polymicrobial (caused by many different bacteria), which may be resistant to certain antibiotics. Infection can worsen quickly, making some cases difficult to treat.
The most common aerobic organisms that cause infection in horses are Streptococcus equi zooepidemicus, Escherichia coli, Actinobacillus and Pasteurella. [4][7]
Common anaerobic organisms include Bacteroides, Clostridium, Peptostreptococcus and Fusobacterium.
Clinical Signs
Before travelling with your horse, ensure that you are able to identify the signs and symptoms of shipping fever. Early detection is important to prevent serious infection.
The following signs indicate shipping fever in the horse: [4][7][8]
- Nasal discharge
- Thoracic (chest) pain
- Elevated body temperature (pyrexia)
- Cough
- Rapid, shallow breathing
- Lethargy
- Depression
- Abducted (turned out) elbows
- Loss of appetite
- Reluctance to drink
- Reluctance to move
Many cases of shipping fever do not present with respiratory signs. Severe pain can inhibit the horse’s ability to cough.
Secondary conditions may develop in advanced cases of shipping fever. These include pulmonary abscessation, colitis and laminitis. [9]
Risk Factors
While any horse can develop shipping fever, competition horses and racehorses have a higher risk due to frequent travel and time spent at high-risk areas (i.e. racetracks and competition grounds). [4][10]
Competition horses are also more likely to come into close contact with horses from different origins, increasing their potential exposure to pathogens.