Tracheobronchitis is an acute or chronic inflammation of the trachea and bronchial airways; it may be primary or secondary depending on the etiologic agent. Bronchitis may extend from the bronchioles to the lung parenchyma.

Etiology

Canine infectious tracheobronchitis (kennel cough, see Respiratory Diseases of Small Animals: 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. 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. 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.

Clinical Findings

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. The 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.

Lesions

During the acute and subacute inflammatory stages, the air passages are filled with frothy, serous, or mucopurulent exudate. In chronic bronchitis, they contain excessive viscid mucus. The epithelial linings are roughened and opaque, a result of diffuse fibrosis, edema, and mononuclear cell infiltration. There is hypertrophy and hyperplasia of the tracheobronchial mucous glands and goblet cells. The act of coughing is an attempt to remove the accumulations of mucus and exudate from the respiratory passages.

Diagnosis

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).

Treatment

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. Persistent, nonproductive coughing is best controlled by antitussives that contain codeine. If conservative medical management is unsuccessful, radiographs should be taken of the thorax and cervical trachea, and laboratory tests 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 anti-microbial 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.

Infectious Tracheobronchitis of Dogs

(Kennel cough)

Infectious tracheobronchitis results from inflammation of the upper airways. It is a mild, self-limiting disease but may progress to fatal bronchopneumonia in puppies or to chronic bronchitis in debilitated adult or aged dogs. The illness spreads rapidly among susceptible dogs housed in close confinement (eg, veterinary hospitals or kennels).

Etiology

Canine parainfluenza virus, canine adenovirus 2 (CAV-2), or canine distemper virus can be the primary or sole pathogen involved. Canine reoviruses (types 1, 2, and 3), canine herpesvirus, and canine adenovirus 1 (CAV-1) are of questionable significance in this syndrome. Bordetella bronchiseptica may act as a primary pathogen, especially in dogs <6 mo old; however, it and other bacteria (usually gram-negative organisms such as Pseudomonas sp, Escherichia coli, and Klebsiella pneumoniae) may cause secondary infections after viral injury to the respiratory tract. Concurrent infections with several of these agents are common. The role of Mycoplasma sp has not been clearly established. Stress and extremes of ventilation, temperature, and humidity apparently increase susceptibility to, and severity of, the disease.

Clinical Findings

The prominent clinical sign is paroxysms of harsh, dry coughing, which may be followed by retching and gagging. The cough is easily induced by gentle palpation of the larynx or trachea. Affected dogs demonstrate few if any additional clinical signs except for partial anorexia. Body temperature and WBC counts usually remain normal. Development of more severe signs, including fever, purulent nasal discharge, depression, anorexia, and a productive cough, especially in puppies, indicates a complicating systemic infection such as distemper or bronchopneumonia. Stress, particularly due to adverse environmental conditions and improper nutrition, may contribute to a relapse during convalescence.

Diagnosis

Tracheobronchitis should be suspected whenever the characteristic cough suddenly develops 5–10 days after exposure to other susceptible or affected dogs. Severity usually diminishes during the first 5 days, but the disease persists for 10–20 days. Tracheal trauma secondary to intubation may produce a similar but generally less severe syndrome.

Treatment

Preferably, affected dogs should not be hospitalized because the disease is usually highly contagious (and also self-limiting). Appropriate management practices, including good nutrition, hygiene, and nursing care, as well as correction of predisposing environmental factors, hasten recovery. Cough suppressants containing codeine derivatives, such as hydrocodone (0.25 mg/kg, PO, bid-qid) or butorphanol (0.05–0.1 mg/kg, PO or SC, bid-qid), should be used only as needed to control persistent nonproductive coughing. Antibiotics are usually not needed except in severe chronic cases; cephalosporins, quinolones, chloramphenicol, and tetracycline are preferable because they reach effective concentrations in the tracheobronchial mucosa. When needed, the antibiotic should be selected by culture and sensitivity tests of specimens collected by transtracheal aspiration or bronchoscopy. Antibiotics given PO or IM may not significantly reduce the numbers of B bronchiseptica in the distal trachea or major bronchi. Thus, in severely affected dogs that are not responsive to parenteral antibiotics, kanamycin sulfate (250 mg) or gentamicin sulfate (50 mg) diluted in 3 mL of saline may be administered by aerosolization bid for 3 days. Aerosolization treatment should be preceded by administration of bronchodilators. Endotracheal injection of antibiotics (eg, gentamicin) is a possible alternative to aerosolization. Corticosteroids may help alleviate clinical signs but should be used concurrently with an antibacterial agent; they are contraindicated in severely ill, coughing dogs.

Prevention

Dogs should be immunized with modified live virus vaccines against distemper, parainfluenza, and CAV-2, which also provides protection against CAV-1. Commercial products frequently combine these agents and may include modified live parvovirus and leptospiral antigens. An initial vaccination should be given at 6–8 wk and repeated twice at 3- to 4-wk intervals until the dog is 14–16 wk old. Revaccination should be performed annually. When the risk of B bronchiseptica infection is significant, use of a live, avirulent, intranasal vaccine is preferable to parenteral products containing inactivated bacteria or bacterial extracts. A combination of an avirulent B bronchiseptica and a modified live parainfluenza vaccine is available for intranasal use. One inoculation is administered to puppies >3 wk old.

Last full review/revision March 2012 by Ned F. Kuehn, DVM, MS, DACVIM; Steven L. Marks, BVSc, MS, MRCVS, DACVIM