Respiratory Ills, Heart Disease

By James C. Keith, Jr.

Respiratory diseases are very important in dogs and cats. They account for a large percentage of illnesses and include diseases which affect the nose and throat, those which affect the trachea, and those which affect the lungs. Viral, bacterial, and parasitic infections all occur in both species. Congenital defects also occur which can interfere with normal respiratory function.

Clinical signs are similar in dog or cat respiratory diseases. One of the most reliable signs is a cough. When severity of the disease process increases, labored breathing develops. As a general rule it is more difficult to detect these signs in cats, due in part to their stoic personalities.

Cleft palate is the most common congenital defect of the nasal cavity. It is caused by failure of the hard palate (the roof of the mouth) to form completely. This condition is diagnosed in kittens and puppies when milk is seen running out of the nose while they are nursing. In addition to difficulty with eating, the animals often inhale the milk and this causes pneumonia to develop.

In breeds such as the bulldog, pekingese and pomeranian, narrowing of the nostrils and excessive length of the soft palate are often combined to cause difficulty in breathing. Another disease which occurs in these and other miniature breeds is the collapsing trachea syndrome. This disease may be manifested early in life, or may not become a problem until much later. The condition is caused by a congenital weakness in the tracheal rings, which are composed of cartilage.

Infectious diseases of the nose, throat and trachea also occur, but they will be mentioned only briefly. Several are covered in greater detail elsewhere in this section of the Yearbook.

Upper respiratory disease complex is a viral disease which causes devastating problems in young kittens. The pares (openings of the nose) become blocked by inflammatory secretions, and the kitten will not eat if it can't smell. Viral infections of the nose and throat also occur in the dog, but they are mild in comparison to the feline syndrome.

Often during a viral upper respiratory infection, bacterial infections develop and cause an even more severe disease. Dogs can contract kennel cough which is usually caused by combined viral and bacterial infections. It often develops after the animal has been boarded at a commercial kennel facility, hence the name of the disease.

Trauma (injury) to the nose, throat or trachea can cause profound problems in dogs and cats. Trauma to the nose usually results in nosebleeds. Airway obstruction can occur if the injury results in fracture of the nasal bones.

Excessive pulling on a leash can produce a fracture of the larynx in the throat, and this can cause life threatening airway obstruction.

Dogs can get several chest diseases, and probably the most well known is canine distemper. It causes a mild viral pneumonia, but secondary bacterial pneumonias often develop.

Primary bacterial pneumonias also occur in dogs and are diagnosed by bacteriologic techniques and x rays. Fungal infections of the lungs and chest occur and can be difficult to treat. Cancerous tumors rarely develop in the chest cavity or the lungs as the primary site. However, it is common for cancer to spread to the lungs from other organs.

Cats also can acquire many lung and chest diseases. Following an upper respiratory infection, cats can develop a bacterial infection of the chest called pyothorax. Large amounts of inflammatory fluid accumulate in the chest and cause severe breathing problems. Often this disease can be caused by wounds suffered in cat fights, so the disease is more common in non-neutered male cats.

Cancer within the chest cavity is much more common in cats. The most common type is a form of feline leukemia.

Lungworms can infect cats, and cause severe respiratory problems. The immature forms can be found in a stool sample from the affected animals.

Feline asthma can cause breathing problems in cats. The most current information indicates that this condition is probably an allergic disease, as with people.

Heart Disease

This occurs in dogs and cats with moderate regularity. Two general types have been documented. They are congenital defects which are present at birth, and acquired heart diseases which occur with variable incidence and appear to depend on the particular breed of animal.

Fortunately for both species, the classic "heart attack" almost never occurs. They hardly ever develop the high levels of blood cholesterol responsible for causing the blood vessel blockages which result in heart attacks in humans.

Dogs and cats will exhibit similar signs when affected with heart diseases, although the signs may be more difficult to detect in cats due to their more sedentary lifestyle.

The most common signs include coughing at night during sleep, coughing during exercise, inability to exercise, fainting spells during exercise, development of blue gums during exercise, open mouth breathing at rest (not panting, which is the dog's normal way of perspiring), reluctance or inability to breathe when lying down, and development of a large pendulous abdomen due to the accumulation of fluid in the abdomen.

Rarely, sudden death may occur with no previous signs of problems. Swelling of the extremities seldom is seen.

Congenital heart defects are more common in purebred dogs and cats, although the overall incidence in cats is much lower than in dogs. If the defects are severe or multiple, the puppies or kittens may die at birth or shortly after. However, if the defects are less severe they may survive for extended periods of time.

Depending on the severity and the type of defect, medical or surgical treatment may be feasible. If the defect lends itself to medical management or surgical correction, the owners should be advised against breeding the animal and possibly spreading the undesirable trait.

Patent ductus arteriosus (PDA) is the most common defect. It results from failure of a small duct to close. When open the duct allows blood to bypass the lungs in the developing fetus since the lungs are nonfunctional in the uterus. In the normal animal the duct closes immediately after birth when the lungs begin to function.

This defect causes a severe strain on the left side of the heart, and heart failure will result if the defect is not corrected. Fortunately, correction is easily done by simply closing the duct during open chest surgery.

Other congenital defects such as narrowing of the aorta, narrowing of the vessels leading to the lungs, or defects of the interior of the heart are more difficult to correct.

Acquired heart disease has several causes. Once again the incidence can vary depending on the breed of dog or cat.

Degenerative diseases of the heart valves occur very commonly in dogs. Generally, these abnormalities begin slowly and increase in severity as the animal ages. The defects rarely cause heart failure before the animal is 10 to 15 years old.

As the valves degenerate their deteriorating function places increasing stress on the heart, until it begins to fail.

This results in clinical signs of heart failure.

Bacterial infections of the heart valves, or the heart muscle itself, can also cause heart failure in the dog and cat. Although these are difficult to diagnose, they sometimes can be treated with long-term antibiotic therapy.

Cancerous tumors occasionally can spread to the heart and replace the normal muscle, causing heart failure. In these cases, little can be done.

A degenerative disease of the heart muscle called cardiomyopathy can affect both dogs and cats. This disease occurs with a higher frequency in cats, but a significant number of dog cases also are reported.

One form of the disease causes the heart to develop massive amounts of muscle wall at the expense of the heart's interior chambers. This results in poor cardiac function. The other form of cardiomyopathy causes loss of cardiac muscle, and the heart becomes a dilated, inefficient pump. The dilated form can be treated for only a short period of time before terminal heart failure occurs.

One parasite problem that affects the dog's heart is heart-worm disease. Until a few years ago, it was limited to those areas along the coast where mosquitoes were present, since the infective stage is spread by mosquitoes. Today the disease is found throughout the country. Presence of adult heartworms causes vessels leading to the lungs to thicken, and this thickening eventually causes the heart to fail.

Several techniques are used to diagnose heart conditions in dogs and cats. Just as in human medicine, x rays of the chest, electrocardiograms and dye studies of the heart are used to determine the type and severity of heart disease present.

James C. Keith, Jr. is Assistant Professor, Virginia-Maryland Regional College of Veterinary Medicine, Virginia Tech, Blacksburg.