Rhinitis in dogs is caused when the mucous membrane lining the nasal cavity becomes inflamed due to infections, allergies or injuries. Rhinitis often results when the sinuses get inflamed too. It is the most common among the disease conditions affecting the upper respiratory tract.
The proper functioning of the nasal passages is important to the health of the lower respiratory tract because they perform a filtration function, protecting the airways and the lung from dust, allergens and infectious agents. Deterioration of the nasal lining results in the lung being exposed to higher loads of microbes and their spores contained in the inhaled air.
In dogs, the acute forms of rhinitis as well as sinusitis may be the result of viral infections. For example, distemper, canine influenza, as well as other viral diseases caused by canine adenoviruses, both type 1 and type 2 can cause rhinitis. In dogs, bacterial infections causing rhinitis usually appear following a viral infection. Bacterial infections rarely initiate rhinitis in dogs, but the bacterium Bordetella bronchiseptica, responsible for the infectious form of bronchitis is one of the exceptions to this.
Both rhinitis and sinusitis resulting from allergies are usually seasonal, occurring at the time of high pollen counts. If they occur round the year allergy to molds or household dust could be the cause. Damage to the lining of the nose and the sinuses from inhaling smoke or gases that cause irritation may result in rhinitis as well as sinusitis. Foreign bodies that get stuck in the nasal passages also may cause inflammation and nasal discharge.
Lymphoplasmacytic rhinitis is a chronic inflammatory condition that may result from various reasons such as foreign bodies, parasites, fungal infections, traumatic injuries and tumors. Infections in the roots of upper teeth may result in abscesses that can affect the sinuses and cause inflammation of their lining as well as that of the nasal passages.
The typical symptoms of rhinitis are sneezing, breathing with the mouth open and snoring in addition to copious discharge from the nostrils. If the dog repeatedly paws at its face, the rhinitis could be due to foreign bodies lodged in the nasal passages. Severe rhinitis is usually accompanied by a continuous flow of tears and conjunctivitis, as the membrane lining the eyes become inflamed too. The discharge from the nose is usually light and clear unless there is a secondary bacterial infection which causes the mucus to thicken and become pus-filled.
Sneezing is more common in acute rhinitis as it is an effort to clear out the nasal discharge. Aspiration reflex, which is generally referred to as reverse sneeze is common in dogs with rhinitis as they try to clear the nostrils by taking in short, noisy breaths.
In chronic rhinitis, the dog may have intermittent bouts of sneezing. Chronic fungal diseases, chronic inflammation of the sinuses and the nasal passages or tumors in the upper respiratory tract is the usual cause of this condition. Rhinitis resulting from tumors and certain fungal infections usually begins as a one-sided nasal discharge but eventually it may involve both sides. Another symptom is thick mucus discharge containing pus which later becomes blood-stained.
The veterinarian may try to determine the underlying cause of rhinitis through x-ray, endoscopy, or a CT scan, in addition to physical examination. The recent medical history of the dog may also help in diagnosing the cause. A biopsy of the nasal tissues may be done when other causes are ruled out.
Recently occurring rhinitis which is mild in nature is usually treated with medications to relieve the symptoms. If bacterial diseases are present, antibiotics may be prescribed. They are not effective against viruses, but since the probability of bacterial infections developing immediately following viral infections, the vet may give antibiotics as a preventive measure too. Prolonged anti-fungal treatment is necessary if the sinusitis or rhinitis is due to fungal infections. The specific fungus that is causing the condition should be determined first through laboratory tests. Most of these therapies may not be effective against chronic inflammatory rhinitis, which is difficult to treat as a definite cause for the inflammation is not identified. Surgical intervention or radiation therapy may be necessary to treat tumors that cause rhinitis.