Tracheobronchitis in Small Animals

Canine infectious tracheobronchitis (kennel cough, see Infectious Tracheobronchitis of Dogs) is often secondary to viral infection of the respiratory system. Other causes of tracheobronchitis in dogs include parasites, eg, Aelurostrongylus abstrusus (also in cats), Capillaria aerophila, Crenosoma vulpis, and Oslerus osleri.

Tracheitis may be secondary either to diseases of the oropharynx or to chronic coughing related to heart disease or noncardiac pulmonary disease. Other causes include smoke aspiration and exposure to noxious chemical fumes. Exacerbation of a chronic bronchitis affecting middle-aged and older dogs may follow sudden changes in the weather or other environmental stresses. Feline bronchial asthma (allergic bronchitis) is a syndrome in cats with similarities to asthma in people. Young cats and Siamese and Himalayan breeds are most affected. Feline asthma is associated with airway hyperresponsiveness, airflow obstruction, airway remodeling, and eosinophilic airway inflammation. Asthma in cats is induced by an aberrant immune response with upregulation of cytokines, leading to IgE production. Foreign bodies in the airway and developmental abnormalities such as laryngeal deformities may predispose to bronchitis. Chronic bronchitis most often affects small breeds of dogs, although it is also seen in large breeds. It is characterized by persistent cough for at least 2 mo in the absence of specific pulmonary disease. Bronchiectasis may occur as the end stage of chronic bronchitis in dogs. Recognition of tracheobronchitis as an often secondary disease syndrome underlies the importance of diagnosis and control of an associated primary disease.

Spasms of coughing are the outstanding sign. These are most severe after rest or a change of environment or at the beginning of exercise. On auscultation, respiratory sounds may be essentially normal. In advanced cases, inspiratory crackles and expiratory wheezes are heard. Body temperature may be slightly increased. The acute stage of bronchitis passes in 2–3 days; the cough, however, may persist for 2–3 wk. Severe bronchitis and pneumonia are difficult to differentiate; the former often extends into the lung parenchyma and results in pneumonia. Feline bronchial asthma may result in cyanosis and dyspnea and may be accompanied by eosinophilia.

The diagnosis is made from the history and clinical signs and by elimination of other causes of coughing. In chronic bronchitis, chest radiographs may show an increase in linear and peribronchial markings. Bronchoscopy reveals inflamed epithelium and often mucopurulent mucus in the bronchi. In addition, the procedure allows collection of biopsy and swab samples for in vitro assay. Bronchial washing is an additional diagnostic aid that may demonstrate causative agents or significant cellular responses (eg, eosinophils).

In mild or acute cases, supportive therapy may be effective, but treatment of concurrent disease is also indicated. Rest, warmth, and proper hygiene are important. Broad-spectrum antimicrobial chemotherapy is indicated for treatment of cough when infection is documented. Corticosteroids are the mainstay of therapy to reduce airway inflammation in dogs with chronic bronchitis. Persistent, nonproductive coughing is best controlled by antitussives that contain codeine. If conservative medical management is unsuccessful, laboratory tests and radiographs of the thorax and cervical trachea should be evaluated to eliminate other differential diagnoses. Bronchoalveolar lavage or transtracheal wash for cytology and culture sensitivity may be indicated to identify an etiologic agent and to determine appropriate antimicrobial chemotherapy. Pulmonary physiotherapy consisting of sodium chloride nebulization and gentle coupage may loosen secretions and stimulate expectoration. A bathroom environment with steam from a hot shower may be substituted for nebulization.

Oral (prednisolone, dexamethasone) or inhaled (fluticasone, budesonide) corticosteroids are indicated for treatment of feline asthma. Bronchodilators (albuterol, terbutaline) may be considered for adjunctive therapy in combination with glucocorticoids but not as sole therapy for feline asthma. Feline aerosol chambers and inhaler therapy are available for aerosol drug delivery in cats with feline asthma. Cyprohepatidine, an antiserotonergic drug, has been suggested; however, studies have failed to show significant reduction in eosinophilic airway inflammation. Experimental studies suggest that cyclosporine A therapy may hold promise to inhibit development of eosinophilic airway inflammation and airway remodeling through inhibition of T-cell activation and cytokine synthesis. Avoidance of environmental aeroallergens (eg, cigarette smoke, perfumes, pollens, molds, dust) must be considered in management of these cats.