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Feline Lower Airway Disease (FLAD)


We frequently divide disease conditions in animals according to their causes. Allergic, infectious, tumors, and parasitic are examples of partitions we use in this type of disease classification system. When it comes to lower airway disease of cats, frequently a combination of these causes contribute to a cat’s illness. In some cases, it can be difficult to determine what is causing the illness. To complicate things, multiple factors may be acting within each cause category. For example, an infectious condition may be due to a primary virus, with complicating secondary invasion by bacteria.

Hang in there—we can explain!

Most of the lower airway conditions in cats are due to non-infectious causes, with inflammatory airway disease associated with allergies or unknown triggers being the most common. Reactive airways result from ongoing irritation. These reactive airways tend to narrow the airways (bronchoconstriction) and produce excess mucus, leading to difficulty breathing, fast breathing, and sometimes, cough and nasal discharge.

Signs of illness do not correlate with the specific cause of the illness. It is not uncommon for affected cats to be clear of signs! Generalized signs such as fever, reduced activity and poor appetite may or may not occur. Over time, if the airways continue to experience inflammation, dilation and thickening of the airways occurs (bronchiectasis), and sometimes, parts of the lung collapse (atelectasis) or become over-inflated with air (hyperinflation).

Feline Lower Airway Disease (FLAD) is an umbrella term to describe the conditions that lead to lung airway pathology. Chronic bronchitis, chronic bronchiolitis, pneumonia, alveolitis, and toxic/irritant/cancer/lipid disorders are some of the components of the FLAD syndrome.

Pneumonia is an infection or inflammation of the lung tissues (not frequently diagnosed in cats).

Bronchitis/bronchiolitis is an inflammation of the bronchi and bronchioli, the large and small airways of the lung.

Alveolitis is inflammation of the little air sacs at the end of the airways of the lung where exchange of gases occurs.

Crowding, stress, mixing cats from different sources, poor nutrition, poor air quality, or poor medical care and other chronic health problems lead to increased risk of infection or other airway disorders.

Household cats carrying respiratory disease agents may not clear them, and some develop long-term waxing and waning symptoms. If these cats are stressed, chronically ill (e.g., cancer) or receiving immune system suppressing drugs (steroids, other cancer drugs) this may increase the likelihood of disease signs recurring after the initial illness.

Cats that go outdoors and cats in multi-cat households are at higher risk for contracting infections than solo indoor cats. Note that Siamese cats have been over-represented for FLAD. All cats are susceptible though.

Historically, veterinarians tended to focus on upper airway disease in cats. Common signs such as sneezing, nose or eye discharge, eye inflammation such as conjunctivitis, and ulcers of the eye, tongue and gums are easy to see. As well, the majority of infectious agents cause upper respiratory signs. Cats do not tend to cough, unlike people and dogs.

This means that unless one is able to hear obvious changes in lung sounds using a stethoscope, or see obvious changes on chest X-rays, one might not appreciate how much is going on in the lungs!

Lower airway disease does not always show up on X-ray or produce classical abnormal lung sounds in cats, so we can be fooled into thinking the lungs are OK when they are not.

More advanced second line diagnostics such as:

  • Trans-tracheal washes and bronchoalveolar lavage, with cell sample analysis
  • Bacterial culturing, including antibiotic sensitivity assays
  • Thoracentesis (fine needle aspirate of lung tissue through the body wall)
  • Endoscopic or keyhole biopsy
  • Advanced imaging (endoscopic camera, ultrasound, MRI, “CAT” scans).

This means we can look much more closely than in the past. We are finding that cats experience lots of lower airway disease. In fact, it has become evident that they frequently do not show signs that an owner can pick up at home, or that a vet will pick up on first pass!

Pneumonia may be associated with germs and parasites, or be sterile (associated with inflammation or immune processes without infection). In one study, 36% of cats with infectious pneumonia had no clinical signs of respiratory tract disease and 41% had no general signs of malaise or changes in their blood counts—only 8% of cats with pneumonia coughed!

Infectious agents may be inhaled from the environment in droplets, inhaled during aspiration of vomit, or come to the lungs via the bloodstream from other infected body tissues.

Infectious causes include :

Bacteria—account for about a half of pneumonias in one study (frequently more than one type of bacterium is present at a time).

Examples of lung infectious agents include:

  • Streptococcus spp,
  • Pasteurella multocida
  • Salmonella
  • E. Coli
  • Enterobacter
  • Enterococcus
  • Staph spp
  • Bacteroides
  • Corynebacterium
  • Pseudomonas spp
  • Bordetella bronchiseptica
  • Fusobacterium spp
  • Peptostreptococcus spp
  • Dysgenic/eugonic fermenter type 4
  • Nocardia

Bordetella is an agent that cats are frequently exposed to and that does not always cause disease. Proximity of dogs and cats with Bordetella can lead to cross-species infections. Cats with calicivirus may be more prone to developing serious disease with Bordetella (acting as a secondary invader).

Viruses —these account for almost 1/3 of cases in one study.

Examples of viruses that infect the respiratory tract include:

Often latent in the nervous system, the herpes virus is famous for re-activating later when a cat is stressed.

Fungi—account for about 15% of cases reported in one study.

Some examples of fungal infectious agents include:

  • Cryptococcus neoformans
  • Candida albicans.


  • Protozoa parasites—best known is Toxoplasma gondii
  • Lungworms—the Aleurostrongylus abstrusus worm is sometimes responsible for serious lung disease.

Primitive bacteria-type organisms —Mycoplasma is normally found in the back of the throat as a part of the surface colony of the membranes in about 1/3 of normal healthy cats, but is also found in cats with upper respiratory disease. If isolated from the lungs, this disease agent is associated with lung disease.

Non-infectious causes include:

  • Toxins, irritants (smoke, air pollution)
  • Aspiration pneumonia due to inhaled vomit or food, lipids etc.
  • Lipid disorders (internal)
  • Fibrosis (scarring)
  • Inflammatory pneumonitis (lymphocytic)
  • Cancer

If you hear your cat coughing and it is not due to hairballs, it is usually highly significant! Following up with your veterinarian is essential for a diagnosis to be made.

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