Pneumonia is an inflammation of the lungs and airways that causes breathing difficulties and deficiency of oxygen in the blood. There are many possible causes. The most common cause of pneumonia is a viral infection of the lower respiratory tract. Feline calicivirus, for example, causes damage to the airways and makes the animal susceptible to development of pneumonia. Infections with bacteria (such as Mycoplasma and Chlamydia) and protozoa (such as Toxoplasma gondii) can also cause pneumonia.
Parasites (such as lungworms and flukes) can invade the bronchi and result in pneumonia. Fungal pneumonia also occurs in cats. Injury to the mucous membranes of the bronchial tubes and inhalation of irritants may cause pneumonia directly, as well as predispose the animal to bacterial infection. Aspiration pneumonia (see below) may result from persistent vomiting, force feeding, or improperly administered medications. It may also occur after suckling in a newborn with a cleft palate.
Signs of pneumonia include lethargy, loss of appetite, and a deep cough. Labored breathing, “blowing” of the lips, and bluish mucous membranes may be evident. Body temperature is moderately increased. Diagnosis usually involves a combination of history, physical examination, and appropriate tests. In the later stages of pneumonia, the increased lung density can be seen on chest x-rays. Analysis of fluid used to “wash” the airways is valuable for the diagnosis of bacterial infections.
Animals with pneumonia benefit from a warm, dry environment. If the mucous membranes are very bluish (indicating poor oxygen in the blood) the veterinarian may administer oxygen. Antibiotics are usually given, although the treatment may be modified based on the results of laboratory cultures, so that the drugs given best match the type of infection found. Medications called bronchodilators may also be necessary to improve breathing. The cat may need to be reexamined frequently, including periodic chest x-rays, to watch for improvement or recurrence, to follow an underlying disease (if one is present), or to detect any possible complications.
Aspiration pneumonia is a lung infection caused by inhalation of foreign material. The severity of the inflammation depends on the material inhaled, the type of bacteria inhaled, and the distribution of foreign material in the lungs. A common cause of aspiration pneumonia is the improper administration of liquid medicines. Animals that breathe in vomit or attempt to eat or drink while partially choked are at risk for aspiration pneumonia as well. Animals with disorders of the throat or esophagus and those weakened by other diseases have an increased risk for aspiration pneumonia. Disturbances in the normal swallowing mechanism, such as in anesthetized or comatose animals, or in animals with deformities such as cleft palate, may also lead to aspiration pneumonia. Cats are particularly susceptible to aspiration pneumonia caused by aspiration of tasteless products, such as mineral oil.
A history suggesting that a foreign substance might have been inhaled is the most important clue to diagnosing this disease. Signs include labored or rapid breathing, coughing, rapid heart rate, and fever. Other signs include bluish mucous membranes and airway spasms. A sweetish, off-smelling breath may be detected, which becomes more intense as the disease progresses. This is often associated with a nasal discharge that sometimes is tinged reddish brown or green. Occasionally, evidence of the breathed-in material (for example, oil droplets) can be seen in the nasal discharge or coughed-up material.
As with nearly all disease conditions, prevention is better than treatment. This is especially the case for aspiration pneumonia, because the outlook is poor even with treatment. The rate of death is high, and recovered animals often develop lung abscesses. Veterinarians normally use drugs and other precautions to minimize the risk of an animal inhaling fluid (such as saliva) during surgery. When giving liquid medications, it is important to not deliver them faster than your cat can swallow. If a cat is known to have inhaled a foreign substance, broad-spectrum antibiotics are usually prescribed without waiting for signs of pneumonia to appear. Care and supportive treatment are the same as for other types of pneumonia.
Fungal pneumonia (also called mycotic pneumonia) is a fungal infection of the lung that leads to the development of pneumonia. A number of fungi have been shown to cause fungal pneumonia in domestic animals (see list below. Often these fungi are found in animals with compromised immune systems, but they can cause disease in healthy animals as well. The source of most fungal infections is believed to be inhalation of spores from the soil.
In cats, the fungus Cryptococcus tends to colonize in the nasal cavity where it causes inflammation of the nasal and sinus lining. Sneezing, a thick discharge of mucus from the nose, and swelling on the top of the nose may be seen.
Animals with fungal pneumonia often have a short, productive cough. As the disease progresses, labored breathing, weight loss, and generalized weakness develop. Inflammation of lymph nodes can cause airway compression, making it more difficult for the cat to breathe. Periodic fever can occur, possibly caused by bacterial infections. Depending on the fungus, signs may also be seen in other parts of the body (such as the skin, nervous system, bones, digestive tract, or eyes).
A tentative diagnosis of fungal pneumonia can be made if an animal with longterm respiratory disease shows the typical signs and does not respond to antibiotic therapy. (Antibiotics are effective against bacteria but not against fungi or other organisms.) However, a definite diagnosis requires identification of the fungus using appropriate laboratory tests. X-rays, blood tests, and evaluation of tissue samples may be useful.
Antifungal drugs are used to treat fungal pneumonia. Extended drug therapy, which may be needed for several months after symptoms have disappeared, is usually necessary to effectively treat the infection.
Also see professional content regarding pneumonia in small animals.