Dogs - Lung Conditions

COMMON RESPIRATORY PROBLEMS

Respiration is the process by which gas exchange between the atmosphere and the lung tissue occurs, it is driven by the mechanical process of breathing created by movement of the rib cage and diaphragm. Within the lungs the oxygen is picked up by the blood and carbon dioxide discharged into the air. The blood is circulated to the lungs by the right side of the heart, it is returned to the left side of the heart and thence pumped around the body.

The airways start with the trachea (windpipe) which runs from the larynx to the chest, in the chest it divides into two bronchi which branch off into each lung. In the dog the left lung has 2 lobes and the right lung is split into 4 lobes.

The lungs and chest cavity are lined by membranes known as the pleura. The space between these membranes is referred to as the pleural cavity.

Disorders of the respiratory system can be due to infectious causes, inflammatory or immune related disorders, cancer, or structural abnormalities. Respiratory problems can also be manifestations of disease in other body systems, for example heart problems.

Canine Distemper Virus

This is a condition which affects the nervous system, the gastrointestinal system and the respiratory system. The highest incidence is in the 3-6 month age group.

Similar virus to that which causes human measles (morbillivirus). Spread by air in droplets from the respiratory tract, the virus does not survive for long in the environment, so spreads most rapidly when dogs are in close contact. Now largely controlled by vaccination.

Infection occurs by inhaling the virus. It replicates in the lymphoid system, then spreads to the nervous tissue and the epithelial cells lining the intestinal and respiratory passages. In most dogs the immune response will eliminate the infection. In those who do not the disease takes up to 2 weeks to develop, nervous signs do not appear until 4-5 weeks after initial infection.

Onset is gradual, often with a wide variety of clinical signs, initially dull, inappetant, high temperature, conjunctivitis, vomiting and diarrhoea then develop followed by a cough and increased respiratory rate. Thick nasal discharge, sneezing and conjunctivitis are next, this can last for 2-3 weeks.

By the third week of illness hyperkeratosis (thickening of skin) on the foot pads occurs. By the fourth week nervous signs such as muscle spasms, twitching, restlessness, apprehension, even classical epileptic fits can develop. Severely affected animals can get a hind limb paralysis, milder cases develop balance problems and difficulty with coordination. Animals that survive can have permanent neurological defects

Treatment options are limited, once nervous signs appear the prognosis becomes extremely poor. Aside from antibiotics to prevent secondary infection and phenobarbitone to control fits treatment is symptomatic. Typical support therapy will include fluids, electrolytes, B vitamins, and nutritional support

Vaccination is an extremely effective means of control. Around 95% of pups at 13 weeks old will mount an effective immune response.

Kennel cough (infectious tracheobronchitis)

Kennel cough can be caused by a number of bacterial and viral agents. The most commonly isolated causes are a bacterium called Bordetella bronchiseptica and canine parainfluenza virus. It usually develops after a period of close contact with other dogs in situations such as kenneling and dog shows. It can however develop in animals with no obvious group contact. Middle to late summer is the most common period. Animals are infected by inhaling the organisms which then multiply along the respiratory tract. It is most severe in those individuals that already suffer from other respiratory or heart conditions which predispose to coughing.

Dry, harsh, hacking, often paroxysmal coughing is the main clinical sign. This will often worsen on exercise so activity should be restricted during the course of the illness. Gagging, retching and nasal discharge can occur. If the dog appears lethargic, inappetant, and feverish then it may indicate a pneumonia developing on top of the kennel cough.

If not treated this can take several weeks to clear. Antibiotics can be given for up to 10 days if necessary, suitable drugs include trimethoprim-sulphonamides, oxytetracycline and cephalexin.

Avoiding lead exercise to prevent pressure from collars worsening the problem or use of chest harnesses is advisable.

Vaccination can be carried out and is recommended prior to introducing your animal to a high risk environment. This will reduce the probability of your dog succumbing to kennel cough, but because of the wide variety of causative organisms it is not guaranteed to provide complete protection. To be most effective a vaccine should be administered at least 5 days prior to immunity being required, revaccination should take place every 6-10 months to maintain immunity.

Lungworm Filaroides osleri

This is a parasitic disease often seen in younger dogs as a kennel related problem, it does not present until after 4-6 months of age even if infection has been present since birth. It is thought to be more prevalent in Greyhounds. The larvae are coughed up and swallowed and then passed out in faeces. Pups are infected by ingestion of the larvae which migrate from the intestine through the body tissues to the lungs where the adults develop in nodules in the lung passages. It takes 3-4 months from the initial infection to the establishment of the adult worms.

Persistent coughing over a period of several months is common, severe cases may have difficulty breathing, especially after exercise, mild cases may show no clinical signs. Spasms of coughing are common and often end with a retching action. Periods of remission lasting days or weeks may occur. Affected animals usually appear bright and lively when not coughing.

Diagnosis can be made by examining the faeces for larvae and passing an endoscope down the windpipe to directly visualise the nodules.

Treatment is with fenbendazole for 7 consecutive days.

Actinomycotic infections

Infections of the pleural cavity with Actinomyces spp cause a pleural effusion and respiratory difficulty. Localised infection often found in the skin, any infection tends to be in combination with other bacteria. Infection can occur through inhalation, direct penetration via puncture wounds, or spread from another site in the body.

In cases of pleural effusion it presents as acute respiratory difficulty, this can be preceded in some cases by inappetance, weight loss and fever. Exercise can cause collapse. Xrays will show fluid in the chest which when drained appears cloudy and granular, this is sufficient for diagnosis.

Treatment involves draining the chest fluid and elimination of infection by antibiotic treatment. Tetracyclines or sulphonamides are suitable. As the problem develops it becomes more difficult to drain the fluid from the thorax. The prognosis is reasonable when treated early but worsens with disease progression.

Allergic Pulmonary Disease

This is a form of illness induced by malfunction of the immune system. There are only 2 main conditions in this group which are commonly seen in dogs.

P.I.E. Syndrome

This is the result of exposure, and subsequent sensitisation, to natural environmental allergens. Antibody or cell mediated reactions occur against these allergens and it is this that is responsible for the disease process, which is essentially an inflammatory response in the lung tissue. Often the antigen causing the disease is not identified.

The chronic presentation starts with a persistent, non-productive cough with harsh breath sounds. The sudden onset syndrome presents with respiratory distress, inappetance and often fever. Cell samples taken from the lung passages can be used for diagnosis as they contain substantial numbers of eosinophil cells.

This syndrome responds well to corticosteroid therapy, if these require to be used long term then this should be done on the lowest effective dose.

Eosinophilic Bronchitis

This condition is similar to asthma, it is common in cats but relatively rare in dogs. The reaction to the antigen causes constriction of the lung passages resulting in sudden onset coughing or gagging, occasionally a gradual onset syndrome can present over a period of a few days. Chest x-rays may show bronchial change. This condition also responds well to corticosteroid treatment.

Bronchial Foreign Bodies

These are inhaled into the trachea or bronchi and result in sudden onset paroxysmal coughing. Large obstructions can cause a degree of upper airway obstruction interfering with breathing and requiring emergency removal, fortunately this is rare. Smaller objects such as grass awns or fragments of sticks lodge further down the respiratory tract in the bronchi and cause coughing and occasionally bleeding from the nose (haemoptysis). If the object is not dislodged then persistent coughing and bad breath (halitosis) develop.

X-rays of the trachea and chest may aid diagnosis, bronchoscopy can usually visualise the object directly and occasionally remove it, otherwise thoracic surgery may be required for removal. Surgical removal and appropriate antibiotic treatment is curative. Occasionally migration of the foreign body into the lung tissue induces the formation of a localised lung abscess. In isolated cases removal of an entire lung lobe can be required.

Bronchiectasis

This is the result of chronic airway disease leading to a dilatation of the bronchi and a collection of mucus and cell debris within the air passages. It is commonly found in those animals that have been suffering from chronic bronchitis or bronchopneumonia.

The presentation is similar to chronic bronchitis with soft productive coughing and harsh respiratory sounds. Because the bronchi are dilated they are prominent on x-rays and are usually combined with signs of other respiratory disease. The diagnosis is confirmed by observing the dilated bronchi by bronchoscopy.

Treatment depends on antibiotics (sulphonamides, amoxycillin-clavulanate) to control infection, expectorants and percussion to encourage removal of trapped mucus.

Chronic Bronchitis

This term covers a group of conditions that all present with persistent coughing in the absence of other pulmonary disease. Small breeds in late middle or old age, often carrying excessive weight are predisposed to this condition. To qualify for this diagnosis an animal must have been coughing for a period of 2 months within the previous year. The precise cause is unknown, as in man it is thought that chronic exposure to inhaled allergens (environmental pollutants and smoke) may play a part. Bacterial pathogens such as Bordetella spp are often isolated but their significance is poorly understood. The prolonged course eventually results in irreversible changes to the airway wall with an increased mucus production and fibrosis of the mucosal lining.

The clinical signs vary from mild intractable coughing to severe respiratory difficulty, exercise intolerance and substantial production of mucus when coughing. Also apparent may be changes such as increased rate of respiration, wheezing or crackling when breathing and weight loss in some severely affected individuals. Most animals are however bright and alert with a healthy appetite and no fever. Sequels to this condition may include some right sided heart enlargement or slight liver enlargement due to a raised pulmonary blood pressure. Periods of acute flare ups can occur if secondary infection with organisms such as Bordetella, Pseudomonas, and Pasteurella develops.

Thorough investigation of this condition is required as it is often complicated by concurrent conditions such as tracheitis, tracheal collapse, heart failure, and bronchopneumonia. It is important to identify the primary problem in order to prescribe appropriate treatment. The changes that can be seen on x-ray include thickening of the bronchial passages and indications of cellular infiltration and fibrosis in the peribronchial region. If evidence of heart disease is present then an ECG or ultrasound heart scan is useful to assess its significance. Blood tests can help identify allergic lung disease or pneumonia, most purely bronchitic animals have no changes on their haematology profiles. Bronchoscopy can show a narrowing of the bronchi and inflammation of the lining mucosa.

This condition is not curable, by the time the disease develops and is diagnosed irreversible change has occurred in the lung passages, however it is usually possible to control the problem with palliative treatment and management changes. No single drug is always effective in all animals, treatment needs to be tailored for each individual. It is important to eliminate such factors as smoke, environmental pollutants, dust and excessive exercise. Antibiotics play a role in controlling secondary infection, courses of sulphonamides, tetracycline's, or amoxycillin-clavulanate should be continued for 14 days. Bronchodilators such as theophylline or etamiphylline can be used to relieve constriction of the lung passages, the response to these agents can only be determined by trial treatment. The physical condition of the animal is of importance since obesity compromises respiratory function and weight loss will ease respiratory effort. Mucus build up in the lungs also hinders air flow, the viscosity of the mucus (and therefore the ease with which it is cleared) depends on its water content. It is easy to increase the water content by simple methods such as air humidification (in a steamy bathroom). Chest physiotherapy (percussion of the chest with the palm of the hand) also helps to shift mucus. If the animal is producing mucus when coughing then cough suppressants should not be used.

Lung Tumours

Most lung tumours in the dog arise as a result of tumour spread from other tissues, such as mammary glands, bone, abdominal organs or skin. Tumour spread occurs through the blood and tissue fluid. Of those tumours which do originate in the lungs the most common is the pulmonary adenocarcimoma, most of these are malignant, and the majority occur in animals older than 11 years.

The clinical signs often start with coughing and increased respiratory rate. In most cases these do not respond to initial therapy, and are of increasing severity until severe respiratory difficulty develops. General lethargy, fever, weight loss, chest pain (manifest as reluctance to move), and lameness (due to the development of h ) can also be part of the presenting picture. Harsh respiratory sounds develop, and pleural effusion can collect between the chest wall and the lungs.

To diagnose this condition it is essential to X-ray the chest, the tumours may appear as single or multiple distinct masses, or as a diffuse pattern spread throughout the lung fields. Before any single mass can be detected on x-ray it has to have a diameter of at least 5mm. If it is necessary to determine the specific type of tumour involved then cytology of the bronchial exudate, or even a needle biopsy taken across the chest wall can be used.

Treatment is limited. In those cases where the mass is solitary surgery to remove the affected lung lobe may be attempted, however the high likelihood of tumour spread warrants a grave prognosis. Chemotherapy has not had encouraging results. Radiotherapy of pulmonary tumours has not been properly evaluated in dogs. In most cases when quality of life begins to deteriorate then euthanasia becomes the most likely outcome.

Pneumonia

Although normally taken to refer to lung infection, the term pneumonia actually refers to any form of lung inflammation, whether infectious or non-infectious.

The causes can include aspirated food, fluids, or foreign bodies, allergens, lungworms, bacteria (Bordetella, Pasteurella, Streptococci), and viruses (distemper, parainfluenza, adenovirus). Viral infections are usually complicated by secondary bacterial infections. The onset of clinical signs is rapid and involves coughing, increased respiratory rate, breathing difficulty, nasal discharge, fever, inappetance and lethargy. Young animals housed outside are especially prone to developing this problem.

Investigating the case may require chest x-rays, blood tests and bronchoscopy, however the clinical history is very useful and combined with the clinical findings is often sufficient for a presumptive diagnosis to be made. The changes that would be seen on x-ray often lag behind the development of the clinical signs in the progression of the disease. The radiographic pattern can be diffuse or localised with consolidation of some parts of the lung. Blood changes involve a change in the types of white blood cells (leukocytosis and neutrophilia). Bronchoscopy can show an inflammatory exudate collecting in the airways.

The consequences of pneumonia can involve lung consolidation with irregular areas of fibrosis, pleurisy can be found overlying the affected lung tissue. Longer term complications include lung abscesses, suppurative pleurisy, cor pulmonale and pneumothorax.

Treatment centers around antibiotic therapy, cephalosporins, gentamycin and ampicillin are suitable but ideally the drug choice should be based on sensitivity testing of the bacteria involved. Drugs such as doxycycline and potentiated sulphonamides also achieve good penetration into the lung tissue. Nursing care with appropriate nutrition and fluid therapy and chest percussion, steam inhalation and mucolytic agents can ease respiratory discomfort. Whatever treatment is used it must be vigourous and prompt.

Tracheal collapse

The trachea is the windpipe leading to the lungs. It consists of numerous C-shaped cartilage rings with the gap bridged by tracheal muscle. The structure is semi rigid which allows alteration of its diameter but the cartilage prevents complete collapse. In dogs suffering from collapsing trachea a flattening of the structure occurs during inspiration. It is almost invariably seen in small breeds of dogs such as Yorkshire Terriers, Pomerians and Minature poodles. The severity of the condition depends on the degree of collapse and on the presence of concurrent disease. If the condition is severe it will present in the young animal and an attempt at surgical correction may be required, in mild cases it may cause no problems until middle or old age. All cases present with an initial dry hacking, or 'honking' cough, respiratory difficulty will be present to some degree, worsened by exercise. The worst cases will collapse and faint, the condition is worsened if the animal is overweight. Coughing can be easily elicited by palpating the trachea and in some animals a flaccid trachea can be palpated.

Diagnosis can be confirmed occasionally by X-rays, or when available flouroscopy. These will demonstrate a narrowing of the trachea at some point during the respiratory cycle. The difficulty with X-rays is exposing the film at the same time as the trachea is narrowed. Flouroscopy is a form of continuously exposing an x-ray and viewing the tissue movement on a monitor.

The condition is progressive with an insidious onset then gradual deterioration. Treatment varies with the severity of the clinical signs. Surgery is only necessary in severe conditions in the young animal, various techniques have been described but outcome is variable and success cannot be guaranteed. Treatment in mild cases centers around dieting to reduce or avoid obesity, use of a halter rather than a collar and avoiding excessive exercise. Medical therapy is often only palliative and involves bronchodilators, antitussives, corticosteroids, and antibiotics (only if secondary infections).

There is currently no treatment which allows resolution of the problem, in severe cases the long term prognosis is guarded.