The most common upper respiratory tract malfunction is rhinitis (inflammation of the mucous membranes of the nose) or other damage to the nasal mucous membranes. It is often associated with sinusitis, or inflammation of the lining of the sinuses. If the nasal passages deteriorate and fail to function properly, a major filtration function is removed. This exposes the lungs to much heavier loads of dust and microorganisms.

Viral infection is the most common cause of acute rhinitis or sinusitis in dogs. Canine distemper, canine adenovirus types 1 and 2, and canine parainfluenza are most frequently involved. Infection with bacteria frequently occurs after the initial viral infection; bacterial rhinitis without an initial viral infection is extremely rare in dogs. (One exception is infection with Bordetella bronchiseptica, an organism that causes infectious tracheobronchitis.) Allergic rhinitis or sinusitis occurs seasonally in association with pollen production, and year-round, probably in association with house dusts and molds. Inhalation of smoke or irritant gases, or foreign objects lodged in the nasal passages, also may cause rhinitis.

Underlying causes of chronic rhinitis include chronic inflammatory disease (such as lymphoplasmacytic rhinitis), trauma, parasites, foreign bodies, tumors, or fungal infection. Rhinitis or sinusitis may result when a root abscess on an upper tooth extends further upward.

Signs of rhinitis include nasal discharge, sneezing, snoring, open-mouth breathing, and/or labored breathing. Pawing at the face is occasionally seen and often suggests the presence of a foreign object. Tears and inflammation of the membrane surrounding the eyes (conjunctivitis) often accompany inflammation of the upper respiratory passages. The nasal discharge is clear but may become mucus-like or contain pus as a result of secondary infection. Sneezing, in an attempt to clear the upper airways of discharge, is seen most frequently in acute rhinitis and tends to come and go in cases of chronic rhinitis. Affected dogs may also experience an aspiration reflex (“reverse sneeze”), a short rapid inhalation in an attempt to clear the nose. Tumors, fungal disease, or chronic inflammatory rhinitis can cause a chronic nasal discharge that starts out as 1-sided but becomes 2-sided; another sign is discharge that starts out as mucus or pus but later contains blood.

Diagnosis is based on the dog's history, physical examination, x-ray findings (especially computed tomography), endoscopic examination, nasal biopsy, and elimination of other causes of nasal discharge and sneezing.

In mild cases or those that are recent in onset, treatment to relieve signs may be effective. The veterinarian may prescribe antibiotics if bacterial infection is present or suspected (antibiotics are not effective against viruses). Fungal rhinositis and sinusitis can be treated with antifungal therapy once the particular fungus has been identified. Chronic inflammatory rhinitis is a frustrating disease that often does not respond to various therapies. Animals that evade definitive diagnosis may require surgery. Radiation therapy is usually the most successful treatment for tumors in the nose (see Lung and Airway Disorders of Dogs: Cancers and Tumors of the Lung and Airway in Dogs).

Last full review/revision July 2011 by Ned F. Kuehn, DVM, MS, DACVIM; Neil W. Dyer, DVM, MS, DACVP; Joe Hauptman, DVM, MS, DACVS; Steven L. Marks, BVSc, MS, MRCVS, DACVIM; Stuart M. Taylor, PhD, BVMS, MRCVS, DECVP