Upper respiratory tract (URT) infection in dogs involves all or part of the upper airways, which include the bronchi, trachea, throat and nasal cavities. Infections of these airways can become very serious, and can even be fatal.
Causes of Upper Respiratory Tract Infection in Dogs
Infections of the upper respiratory tract are common in domestic dogs and usually are caused by a combination of primary and secondary pathogens, including viruses, bacteria and/or mycoplasma. Bordetella bronchiseptica is the most common primary bacterial pathogen; it causes infectious canine tracheobronchitis, commonly called "kennel cough". Among viral causes of URT infection, the canine influenza virus and the canine distemper virus are seen most frequently. Less often, canine URT infections are associated with nasal mites (Pneumonyssoides caninum) or lung flukes (Paragonimus kellicotti). Most of these infectious pathogens are highly contagious and spread rapidly between dogs, especially in multi-pet households and high-density areas such as pet stores, animal shelters, grooming facilities, boarding kennels, dog parks and dog shows, especially when those areas are not kept clean.
Prevention of Upper Respiratory Tract Infection
Most canine URT infections are preventable with proper use of vaccines and appropriate sanitation and quarantine measures. Companion dogs with strong immune systems that are supported by good nutrition, a healthy lifestyle and proper environmental hygiene can usually overcome the adverse effects of URT ailments without prolonged treatment. Because these infections are perpetuated by the shedding of pathogens in respiratory secretions, it is important to practice cleanliness and good hygiene in areas where dogs congregate in close quarters. Dogs with URT infections should be isolated from other dogs until their infection has resolved.
Uncomplicated upper respiratory tract infections usually can be successfully treated with outpatient supportive care, exercise restriction, non-steroidal anti-inflammatory drugs (NSAIDs), cough suppressants, bronchodilators and possibly antibiotics. However, some primary and secondary respiratory infections are very serious, particularly in young puppies, elderly dogs and dogs with compromised immune systems. Dogs with severe disease may need to be hospitalized. The canine distemper virus can cause severe systemic disease and frequently is fatal, especially to very young, unvaccinated dogs.
The classic signs of canine upper respiratory tract (URT) infection are very similar to the symptoms of the common cold in people. The symptoms of clinical disease in domestic dogs will depend upon the underlying cause of the condition.
Symptoms of Upper Respiratory Tract Infection in Dogs
Dogs with URT infections typically develop one or more of the following symptoms:
Coughing (deep, dry and hacking, or moist and productive)
Production of pale, frothy foam from the mouth
Nasal irritation (evidenced by scratching, pawing, head/face/nose rubbing and head-shaking)
Ocular (eye) discharge
Difficulty breathing (dyspnea)
Loss of appetite (inappetence; anorexia)
Dogs with an URT infection caused by Bordetella bronchiseptica (so-called "kennel cough") generally have a deep, dry, hacking and nonproductive cough, without other signs of illness or discomfort. Clinical signs of kennel cough can worsen with exercise or excitement. Symptoms normally develop 4 or 5 days after exposure to an infected dog, which usually happens in areas where dogs congregate in what can be less-than-ideal hygienic conditions.
The signs associated with URT infection caused by Bordetella bronchiseptica are indistinguishable from the early signs of infection caused by secondary bacterial pathogens, such as Pseudomonas, Escherichia coli, Klebsiella, Pasteurella, Streptococcus, Mycoplasma and several other microorganisms. Secondary bacterial infections often progress to bronchopneumonia, which can become very severe. Dogs with pneumonia generally have extreme difficulty breathing (dyspnea) and may have trouble rising or moving. They frequently refuse to participate in normal activities, develop a low-grade fever and lose their appetite. Dogs with pneumonia should be taken to a veterinarian promptly.
The symptoms of URT infection caused by the canine influenza virus are similar to those caused by other organisms. In addition to coughing, dogs infected with canine influenza virus typically develop a clear, watery nasal discharge that progressively thickens and becomes yellowish-green due to secondary bacterial infection. The canine distemper virus causes respiratory, gastrointestinal and central nervous system symptoms, together with a high fever. Distemper can lead to generalized central nervous system signs, including vision disturbances, vomiting, diarrhea, paralysis, hardening of the footpads, muscle tremors, spasms, seizures and death. Distemper is much more common in puppies than in adults. Canine parainfluenzavirus infection (CPI) and canine adenovirus Type 2 infection (CAV-2) both damage the lining of the upper respiratory tract and cause a dry, raspy cough and a clear, thin nasal discharge, mimicking "kennel cough." These viruses can damage the respiratory lining so severely that affected dogs are especially prone to developing serious secondary upper airway disease, including bronchopneumonia.
The canine nasal mite, Pneumonyssoides caninum, causes sneezing, chronic nasal discharge (runny nose), coughing, inflammation, swelling of the nasal mucosa and epistaxis (nose bleeds). These mites also commonly cause head-shaking, pawing at the nose and reverse sneezing. They predispose infected dogs to secondary bacterial infections of the upper respiratory tract. Dogs with lung flukes (Paragonimus kellicotti) often have no symptoms at all. When they do, the most common sign is a deep, chronic cough that is unresponsive to antibiotic therapy.
Dogs at Increased Risk
Puppies, unvaccinated animals, elderly dogs and dogs with impaired immune systems have an increased risk of developing upper respiratory tract infections.
Upper respiratory tract (URT) infections are provisionally diagnosed based upon the symptoms shown by the affected animal and by ruling out non-infectious causes of those signs. It is not particularly difficult to diagnose an upper respiratory tract infection. It is, however, important to accurately identify the causative organism, so that an appropriate treatment protocol can be developed.
How Canine Upper Respiratory Tract Infections Are Diagnosed
When a dog comes into a clinic with signs of an upper respiratory tract infection, the veterinarian will perform a thorough physical examination and take a complete history from the owner. Dogs that are young, immunocompromised, unvaccinated, elderly or closely in contact with a number of other dogs (adopted from shelters or pet shops, at a dog show or dog park, etc.) have an increased risk of developing upper respiratory tract infections. The physical examination of a dog with an URT infection usually is unremarkable, except that the veterinarian may easily be able to elicit a cough by palpating or pressing on the dog's windpipe (trachea). There may also be a mild discharge coming from the nose or eyes of infected animals.
Most veterinarians will also perform an initial database of blood work (complete blood count and serum chemistry panel) and a urinalysis. The results of these tests are often unremarkable in cases of simple, or uncomplicated, URT infection, although they may disclose evidence of infection or inflammation. More advanced diagnostic tools include chest radiographs (X-rays) and sampling of upper airway fluids and cells for culture by performing a transtracheal wash or a tracheobronchial lavage. A heartworm test should be done to rule out heartworm infection as a cause of chronic cough in areas where heartworm is prevalent. Fecal tests are used to identify lung fluke infestation, and canine nasal mites can be diagnosed based upon the dog's symptoms and the actual appearance of mites around the nostrils (nares; nasal openings).
Often, advanced testing is delayed pending assessment of how the dog responds to antibiotic therapy.
The goals of treating uncomplicated cases of canine upper respiratory tract (URT) infection are to suppress the dog's cough, relieve other symptoms of illness and prevent secondary bacterial infections from developing. Supportive care and antibiotics are the main treatment options in most cases. Respiratory infections that are caused by nasal or lung parasites are treated with anti-parasitic medications.
Most simple cases of canine URT infection are treated on an outpatient basis. Supportive therapies include: providing excellent nutritional support through a high-quality diet and free access to fresh water; exercise restriction and enforced rest for at least 2 to 3 weeks in uncomplicated cases (2 to 4 months in more serious cases); and housing the dog in a clean, quiet, warm, comfortable and non-stressful environment away from other pets. Because most of the pathogens that cause URT infections in dogs are highly contagious, veterinarians typically prefer that owners treat their dogs at home whenever possible.
In complicated cases, medical treatment may be necessary in addition to good supportive care. If a dog develops bronchopneumonia, the therapeutic goals expand to include identifying and eradicating the causative bacterial or viral agents, reducing and ultimately eliminating the cough, sneezing and other symptoms; improving air flow and ease of breathing; and resting the dog so that the lining of its upper respiratory tract can repair. Dogs with severe symptoms may require hospitalization, so that they can receive intravenous fluids and other appropriate medical and nutritional support.
Drug therapy may include anti-inflammatories, antitussives (cough suppressants), bronchodilators and/or antibiotics. Mild cases can be treated initially with anti-inflammatory medications such as corticosteroids or non-steroidal anti-inflammatory drugs (NSAIDs). Using steroids and NSAIDs at the same time is discouraged, because the combination heightens the risk of gastric ulceration. Uncomplicated cases of dry, nonproductive coughing may benefit from cough suppressants (antitussive medications), such as butorphanol, hydrocodone bitartrate or dextromethorphan. Cough suppressants normally are not recommended for dogs with pneumonia, as it usually is better for a dog with pneumonia to cough productively, if possible. If a dog has difficulty breathing, bronchodilators may provide temporary relief.
In cases that involve pneumonia or other advanced respiratory disease, the attending veterinarian may recommend empirical antibiotic treatment while waiting for the results of culture and sensitivity on samples of upper respiratory tract secretions. The results of those tests will identify which pathogens are causing the dog's illness, and will enable the veterinarian to select the best antibiotic or antiviral therapy. Empirical antibiotic therapy is a "let's-take-our-best-guess" approach that often is successful and has few, if any, adverse side effects (except for possible gastrointestinal upset and contribution to antibiotic resistant strains of infectious bacteria). Dogs with bacterial pneumonia usually are treated with antibiotics for 1 to 4 weeks after the radiographic signs of pneumonia are resolved. A veterinarian is the best person to recommend an appropriate treatment protocol for a dog showing signs of upper respiratory tract disease.
If a respiratory infection is caused by lung flukes or canine nasal mites, which is uncommon in North America, a course of anti-parasitic medication may be prescribed. While there currently are no drugs approved for use in dogs for the treatment of nasal mites, many veterinarians recommend ivermectin or milbemycin oxime as an off-label treatment. Both of these drugs typically provide prompt resolution of clinical signs.
Owners of dogs with upper respiratory tract infections should be conscious of the fact that their dogs probably are infectious to other dogs for several months after their own symptoms are resolved.
Dogs with URT infections usually have a good to excellent prognosis, as long as the infection is diagnosed and treated promptly. The outlook becomes more guarded if the infection progresses to bronchopneumonia.