Equine sinusitis is the most common disease affecting the paranasal sinuses in horses.

Sinusitis is an inflammatory condition that often involves excessive nasal discharge. Horses with sinus diseases can also experience swelling in the face or reduced appetite.

The causes of sinusitis vary but can include dental disease or bacterial infection of the upper respiratory tract.

Treatment for this condition often presents a challenge to veterinarians because of the large size of the horse’s sinus structures, their complex anatomy, difficulties accessing the area, and the advanced state of the disease before a diagnosis is made. [1][2]

What is Sinusitis in Horses?

There are two general types of equine sinusitis: primary and secondary.

Primary sinusitis involves a viral or bacterial infection and is usually caused by an upper respiratory tract infection of the paranasal sinuses. It can occur in horses of any age.

Secondary sinusitis is more common and is typically seen in horses over four years of age. It is the result of another problem that occurred first which then led to the development of sinusitis. [1]

Secondary sinusitis is usually related to dental disease in the horse.

Cases of sinusitis can be acute (severe but having a fairly short duration) or they can be chronic (recurring or lasting a long period of time).

Unfortunately, horses with chronic sinusitis tend to experience worsening symptoms over time.

Symptoms of Sinusitis in Horses

Chronic or recurring nasal discharge from one nostril that isn’t resolved with normal antibiotic treatment is the most common symptom of equine sinusitis. The discharge is usually thick and may be green or yellow.

Clinical signs of secondary sinusitis are similar to those of primary sinusitis, but nasal discharge may be foul-smelling with secondary sinusitis. [1]

The second most common sign of equine sinusitis is facial distortion, more common with secondary than primary sinusitis. Facial distortion worsens in chronic stages of the disease, especially in young horses. [1][3]

Horses with sinusitis can develop excessive tearing of the eyes, known as epiphora. [4]

Sinus disease may also cause abnormal respiratory noise. If a fungal infection or tumors within the sinuses are present, a condition known as exophthalmos in which one or both eyes bulge may occur. [1][9]

Other symptoms that can appear with chronic sinusitis cases include lethargy, a decreased appetite, and/or weight loss.

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Causes of Sinusitis

Dental disease is the most common cause of all sinusitis cases, usually involving the first molar, fourth premolar, and third premolar teeth. Occasionally, more than one tooth is involved. [1]

The second most common cause of sinusitis is a bacterial or viral infection, often involding Streptococcus equi and Streptococcus zooepidemicus pathogens.

Secondary sinusitis is often the result of infection from mixed bacteria populations, including anaerobes. Anaerobic infections are more difficult to treat than many other types of infections due to the slow growth of anaerobic organisms. [1][2][3]