Bit & Bridle

Equine Sinusitis

Other Names

  • Equine Sinus Infection
  • Sinusitis in Horses
  • Primary Sinusitis
  • Secondary Sinusitis
  • Empyema of the Paranasal Sinuses

What is Equine Sinusitis?

Equine sinusitis is an inflammation and infection of the paranasal sinuses — a complex system of air-filled cavities within the horse’s skull that connect to the nasal passages. Horses have a more extensive and anatomically complex sinus system than most other species, which makes them relatively susceptible to sinus disease. The paranasal sinuses include the frontal sinus, the dorsal and ventral conchal sinuses, the caudal maxillary sinus, and the rostral maxillary sinus (which communicates directly with the roots of the upper cheek teeth).

Sinusitis in horses is classified as primary (arising within the sinuses themselves, usually from a viral or bacterial infection) or secondary (resulting from another disease that affects the sinuses, most commonly dental disease of the upper cheek teeth). Secondary sinusitis is actually more common than primary sinusitis in adult horses, which is an important consideration when investigating the cause.

The condition typically presents with a characteristic unilateral (one-sided) nasal discharge. Because the sinus cavities in horses do not drain as freely as in some species, infection can become chronic, resulting in accumulated pus within the sinus cavities — a condition called empyema (pus in the sinuses).

Causes

The causes of equine sinusitis are broadly divided into primary and secondary:

  • Primary sinusitis:
    • Viral upper respiratory tract infections — equine influenza, equine herpesvirus — can damage the sinus mucosal lining and predispose to secondary bacterial colonisation.
    • Bacterial infection as a primary event, though this is less common than secondary sinusitis.
    • Bacterial species involved include Streptococcus equi subsp. zooepidemicus, Pasteurella multocida, and others.
  • Secondary sinusitis:
    • Dental disease: The roots of the upper cheek teeth (specifically the 4th premolar through 3rd molar — the caudal four cheek teeth) sit very close to or directly adjacent to the floor of the caudal maxillary sinus. Apical (root) abscessation or dental caries of these teeth causes infection to spread directly into the sinus. This is the most common cause of sinusitis in horses and produces a characteristic particularly malodorous (foul-smelling) nasal discharge.
    • Ethmoid haematoma: A locally destructive, progressive, bleeding mass arising from the ethmoid area; can cause secondary sinus involvement.
    • Sinus cysts: Fluid-filled cysts within the sinus cavity cause obstruction and secondary infection.
    • Neoplasia: Tumours within the sinuses — though less common — can cause secondary sinusitis.
    • Trauma: Fractures of the skull involving the sinus cavities.

Symptoms and Signs

  • Unilateral nasal discharge: The most characteristic sign — discharge from one nostril only. It is typically mucopurulent (thick, cloudy, yellow-green) and may be foul-smelling, particularly in dental sinusitis. Bilateral discharge is more suggestive of a primary respiratory infection rather than sinusitis.
  • Facial swelling: In some cases, particularly with extensive or chronic sinusitis, swelling or distortion of the facial bones over the affected sinus may be visible or palpable.
  • Submandibular lymph node enlargement: The lymph nodes beneath the jaw on the affected side may be enlarged.
  • Nasal airflow obstruction: The horse may breathe audibly or show increased respiratory effort through the nose.
  • Abnormal breath odour: A foul smell from one or both nostrils is suggestive of dental involvement.
  • Epiphora (excessive tearing): If the nasolacrimal duct (which drains tears from the eye into the nasal passage) is obstructed by sinus swelling.
  • Head pressing or tilting: Occasionally, particularly in severe cases.
  • Reduced performance: Horses with significant sinus disease may show reduced exercise tolerance due to impaired airflow.

Diagnosis

  • Clinical examination: Assess the character and laterality of nasal discharge; palpate facial bones for deformity or pain; check for lymph node enlargement.
  • Endoscopy (rhinoscopy): Passage of an endoscope through the nasal passages allows direct visualisation of the nasopharynx and drainage openings of the sinuses. Purulent discharge draining from a specific sinus opening helps localise the affected sinus.
  • Radiography: Skull X-rays can reveal fluid lines within the sinus cavities, loss of normal sinus architecture, and — importantly — abnormal tooth roots suggesting dental pathology. Radiography provides good information but has limitations due to the complex overlying structures.
  • Computed tomography (CT): The gold standard diagnostic tool for equine sinus disease. CT provides detailed cross-sectional images of all sinus compartments and the teeth, allowing precise identification of the affected sinuses and any dental pathology. Available at specialist equine hospitals and increasingly accessible.
  • Sinoscopy: Passage of a small endoscope directly into the sinus cavity via a small trephine hole in the skull. Allows visual assessment of the sinus interior and collection of samples for bacteriology.
  • Bacterial culture and sensitivity: Samples collected from the sinus guide antibiotic selection.

Treatment

Treatment approach depends on the underlying cause and the extent of infection:

  • Antibiotics: Systemic antibiotics (penicillin, potentiated sulphonamides, or based on culture results) are a key part of management, though they alone are rarely sufficient to resolve established sinusitis — drainage of the accumulated pus is equally important.
  • Sinus lavage: Flushing the affected sinus with saline solution via a small trephine hole (made under standing sedation using local anaesthesia) is highly effective at clearing accumulated pus. Repeated lavage may be required over several days to weeks until discharge clears.
  • Dental extraction: If dental pathology is the underlying cause, extraction of the affected cheek tooth (via oral extraction or a surgical “flap” approach) is essential. Simply treating the infection without removing the tooth will result in recurrence.
  • Sinus surgery (frontonasal flap): For complex cases, extensive empyema, or where sinoscopy and lavage are insufficient, a surgical approach involves creating a bone flap to allow open access to the sinus for thorough debridement and lavage. Performed under general anaesthesia at a referral hospital.
  • Treatment of underlying conditions: Ethmoid haematomas, cysts, and tumours require specific intervention — discuss with your vet the most appropriate referral.
  • NSAIDs: To manage pain and reduce inflammation.

Prevention

  • Regular dental care: Annual dental examinations by a veterinary surgeon or equine dental technician. Early identification of cheek tooth pathology — particularly root disease — allows intervention before sinus infection develops. Never ignore abnormal chewing, dropping food, or quidding.
  • Vaccination: Maintain up-to-date equine influenza and herpesvirus vaccination to reduce viral respiratory disease that predisposes to sinusitis.
  • Good respiratory hygiene: Reduce stable dust, ensure good ventilation, and use high-quality forage to minimise respiratory mucosal irritation.
  • Prompt treatment of respiratory infections: Viral URTIs should be managed with appropriate rest and veterinary oversight to reduce the risk of secondary bacterial sinusitis.

Prognosis

The prognosis for equine sinusitis is generally good to very good when the underlying cause is correctly identified and addressed:

  • Primary sinusitis treated with antibiotics and sinus lavage typically resolves well.
  • Dental sinusitis resolves in most cases following tooth extraction and sinus lavage, though the healing process can take several months.
  • Complex cases involving sinus cysts or surgical intervention generally carry a good prognosis in specialist hands.
  • Ethmoid haematomas and neoplasia carry a more guarded prognosis, depending on extent and type.

When to Call the Vet

Contact your vet if your horse has:

  • Persistent nasal discharge, particularly from one nostril
  • Nasal discharge that is coloured (yellow, green, grey) or foul-smelling
  • Facial swelling, particularly over the cheek or forehead area
  • An abnormal noise during breathing
  • Reduced appetite or signs of dental discomfort alongside nasal discharge

Frequently Asked Questions

Why is equine sinusitis often one-sided?

Most cases of equine sinusitis affect only one side because the left and right paranasal sinuses are largely separate from each other, and typically only one tooth or one sinus becomes infected at a time. A single-sided (unilateral) nasal discharge is therefore a key diagnostic clue pointing to sinus disease rather than a bilateral respiratory infection, which would typically cause discharge from both nostrils simultaneously.

Could my horse’s nasal discharge be from something other than sinusitis?

Yes — nasal discharge has many causes beyond sinusitis, including strangles, equine influenza, equine herpesvirus, guttural pouch disease, exercise-induced pulmonary haemorrhage (EIPH — blood in the discharge after exercise), and nasal polyps, among others. The character (clear vs. coloured), laterality (one or both nostrils), smell, and accompanying signs all help narrow the diagnosis. Persistent or abnormal discharge always warrants veterinary investigation.

How long does it take for sinusitis to resolve in a horse?

This depends significantly on the cause and severity. Primary sinusitis with no underlying structural problem may resolve over 2–6 weeks with appropriate antibiotic treatment and sinus lavage. Dental sinusitis typically requires several months to fully resolve after tooth extraction, as the sinus needs time to clear the infection and for the extraction site to heal. More complex cases involving surgery may require 3–6 months of aftercare. Patience is important — premature return to work can delay healing.

Do I need to have my horse’s teeth checked for sinus problems?

If your horse has a unilateral nasal discharge — even if seemingly minor — dental disease should be on the diagnostic list, particularly in horses between 5 and 15 years of age when tooth root infections are most common. Annual dental examinations, ideally including a full oral examination under sedation and with appropriate equipment, remain the best way to detect dental pathology before it progresses to sinus infection. Early detection of cheek tooth disease makes treatment simpler and less invasive.