Why Is My Cat Coughing? A Vet’s Guide to Feline Asthma, Heartworm, and Airway Disease
A coughing cat is rarely a simple case. The same dry, hacking cough can point to feline asthma, heartworm disease, a lungworm infection, a bacterial airway infection, or even heart disease. Several of these look almost identical at first glance. The goal is not to guess. It is to work through a short, ordered list of differentials until the pattern fits.
This guide walks veterinary teams through that process: how to confirm the cough is real, characterize it, localize it, and then separate the conditions that matter most. Two of those conditions, feline asthma and heartworm-associated respiratory disease (HARD), overlap so closely that they are constantly mistaken for each other. Telling them apart changes everything about treatment and prognosis.
Key takeaways
- Most coughing cats fall into a few overlapping groups: feline asthma and chronic bronchitis, HARD, infectious airway disease, lungworm, and cardiac disease.
- Confirm it is truly a cough first. Retching, reverse sneezing, and open-mouthed breathing all get mistaken for coughing and send the workup the wrong way.
- Asthma and HARD share signs (cough, wheeze, vomiting, eosinophils) but differ in cause, treatment, and prevention.
- Work it up in stages: two-view radiographs, then CBC and chemistry, then paired heartworm antigen and antibody testing, then a Baermann fecal, then BAL, with echo or CT as needed.
- Normal radiographs do not rule out HARD or early lungworm.
First, Look Before You Touch
Before any test is ordered, the initial assessment has three jobs: confirm the cough is real, describe its pattern, and pin down where it is coming from.
Step 1 — Start with signalment and history
Age and breed shift the odds before you lay a hand on the cat. Young Siamese and related Oriental breeds are overrepresented for feline asthma and allergic bronchitis. Middle-aged and older cats push the list toward heart disease, lung tumors, and chronic bronchitis. A kitten or young adult with gaps in its vaccine history raises infection right away.
History should pin down the cough itself: acute or chronic, episodic or constant, dry or productive. Ask what triggers it. Exercise, a new allergen, a particular room, a change of season. Then ask about lifestyle: outdoor access, recent travel, and whether the cat lives in or came from a heartworm-endemic region. Those answers reshape the differential more than almost anything else.
Step 2 — Make sure it is actually a cough
A true cough is an active, forceful expiratory effort. The cat builds pressure against a closed glottis, then releases it as the glottis snaps open, so air rushes out at high velocity. The posture is hard to miss: neck extended, body crouched low, sometimes bringing up froth and sometimes nothing at all.
Three things get mistaken for it:
- Retching — the dry-heave that comes before vomiting.
- Reverse sneezing — a rapid, repetitive inspiratory snort that usually settles on its own.
- Open-mouth breathing — not a cough at all, but a red flag for serious respiratory distress.
Confuse these and the workup goes wrong from the very first step.
Step 3 — Examine from a distance, then hands-on
Start across the room. Watch the respiratory rate and effort, the posture, any nostril flare, and whether the abdomen is pumping to help the cat breathe. Do all of this before you touch the patient. A cat in open-mouthed distress gets oxygen and stabilization first. Handling a dyspneic cat can tip it over the edge, so keep handling minimal until the cat is stable.
Then auscultate, and do it properly: across both lung fields in all three planes (dorsal, ventral, lateral).
- Wheezes point to lower airway narrowing, the classic asthma finding.
- Crackles suggest fluid, fibrosis, or consolidation.
- Muffled or absent ventral sounds point to pleural effusion.
Listen to the heart in the same sitting. A murmur or arrhythmia nudges you toward cardiogenic edema. Finish with the upper airway, the peripheral lymph nodes, and a quick abdominal palpation for context.
The Main Suspects: Lower Airway Disease
Lower airway disease drives most chronic coughs in cats. Three conditions deserve the closest look: feline asthma, heartworm-associated respiratory disease (HARD), and infectious bronchitis. All three cough. They diverge sharply on cause, workup, and treatment.
Feline asthma and chronic bronchitis
Think of asthma and chronic bronchitis as two ends of one spectrum, feline lower airway disease. Asthma involves reversible airway narrowing driven by a hypersensitivity reaction. Chronic bronchitis is persistent inflammation that slowly remodels the airway. In practice, plenty of cats sit somewhere in between, and you often cannot cleanly separate the two at presentation. For early management that rarely matters. For long-term expectations it does.
It is a common problem. Lower airway disease affects roughly 1% of all cats. The classic patient is young to middle-aged, with paroxysmal bouts of coughing and expiratory effort. Some episodes escalate into a true asthma attack, with open-mouth breathing, cyanosis, and collapse. Between attacks the cat can look completely normal.
On radiographs, look for a bronchial pattern. Peribronchial thickening shows up as “doughnuts” on end-on view and “tramlines” in longitudinal section. Air trapping during or just after an attack can hyperinflate the lungs and flatten the diaphragm.
BAL cytology is the clincher in the right context. Classic asthma is eosinophilic. Here is the catch worth remembering, though: many cats with lower airway disease show neutrophilic or mixed inflammation instead, and eosinophils alone are not proof. Heartworm and lungworm produce overlapping cytology.
Heartworm-associated respiratory disease (HARD)
HARD is the great pretender. It coughs, it wheezes, and it often comes with intermittent vomiting, which is exactly why it gets labeled as asthma. Early in the course, the chest films can look near-normal.
Testing is the difference-maker, and a single test will not cut it. Cats carry low worm burdens, sometimes a single worm and sometimes worms of only one sex, so antigen tests can miss infections that are genuinely present. The current American Heartworm Society approach pairs antigen and antibody testing, and recommends running the antigen test on heat-treated serum to break up immune complexes that would otherwise hide a positive result. Interpret both alongside the cat’s clinical picture and regional risk. Radiographs may show bronchial or vascular changes, but normal imaging never rules HARD out. Echocardiography helps in selected cases.
Infectious lower airway disease
Bacteria play a role too, mostly in multi-cat households, shelters, and young animals. Bordetella bronchiseptica is the less common one and tends to cause acute tracheobronchitis. Mycoplasma felis turns up more often in chronic airway inflammation, but it can represent either active infection or simple colonization, which makes culture results harder to read. Viruses such as feline herpesvirus-1 and calicivirus mainly hit the upper airway. Lower down, their role is usually indirect: they ramp up airway reactivity and open the door to secondary bacterial infection rather than causing the primary disease.
Asthma vs HARD vs infectious bronchitis at a glance
| Feature | Feline asthma | Heartworm-associated respiratory disease (HARD) | Infectious bronchitis |
|---|---|---|---|
| Typical signs | Episodic, often expiratory wheeze; paroxysmal attacks possible | Cough plus intermittent vomiting; acute collapse possible | Cough with concurrent upper-respiratory signs |
| Signalment / risk | Siamese overrepresented; seasonal or allergen-linked | Exposure in an endemic region | Multi-cat household, shelter, young cats |
| Airway cytology (BAL) | Eosinophilic (but often neutrophilic or mixed in practice) | Eosinophilic or mixed inflammatory patterns | Neutrophilic |
| Imaging | Classic bronchial pattern | Vascular changes; may look normal early | Alveolar pattern if pneumonia develops |
| Worth remembering | The default label, and often an overused one | Frequently misdiagnosed as asthma | May respond to targeted antimicrobial therapy |
A Step-by-Step Diagnostic Workup
Do not reach for one big panel. Work in stages, and let each result point you to the next test.
1. Thoracic radiographs — two views, always
A single lateral view can hide a real lesion. Take two orthogonal views and read for:
- Bronchial pattern — asthma, chronic bronchitis, early HARD, parasitic airway disease.
- Alveolar pattern — pneumonia or pulmonary edema.
- Vascular changes — cardiac disease or HARD.
- Pleural space and mediastinal abnormalities.
2. CBC and serum biochemistry
- Eosinophilia fits asthma, parasitic disease, or HARD.
- Neutrophilia with a left shift suggests bacterial infection.
- Biochemistry flags systemic illness and helps you judge anesthetic risk before procedures like bronchoscopy.
3. Paired heartworm serology (antigen + antibody)
Test any cat that lives in, or has traveled from, an endemic area, especially when the signs mimic asthma. Antigen testing alone misses infections, so run antigen and antibody together, with the antigen test on heat-treated serum. The American Heartworm Society now recommends routine screening in cats, not just testing on suspicion.
4. Baermann fecal exam
A simple, non-invasive test for lungworm. Run it on outdoor cats even when the radiographs look clean, because early infection may not show yet. Larval shedding is intermittent, so a negative result does not fully clear it. Repeat the sample if suspicion stays high.
5. Bronchoalveolar lavage (BAL) with cytology and culture
This is the single most informative test for lower airway disease.
- Eosinophilic inflammation points to asthma or parasites.
- Neutrophilic inflammation points to infection.
- Mixed patterns need to be read against the rest of the picture.
Culture and sensitivity guide antibiotic choice when bacteria are involved.
6. Echocardiography and thoracic CT
Save the echo for cats with a real cardiac signal: a murmur, a gallop, or a suggestive radiograph. Reach for CT when plain films do not explain the signs, or when you need a closer look at the airways, mediastinum, or pleura.
What each radiographic pattern suggests
| Radiographic pattern | Commonly seen with |
|---|---|
| Bronchial | Feline asthma; chronic bronchitis; early HARD; parasitic airway disease |
| Alveolar | Bacterial pneumonia; pulmonary edema; pulmonary hemorrhage; neoplasia |
| Vascular changes | HARD; cardiogenic pulmonary edema; pulmonary hypertension; thromboembolic disease |
One caveat for cats: radiographic heart failure does not read the way it does in dogs. Cats in congestive failure often show variable patterns and frequently pleural effusion, rather than the textbook venous distension. Keep that in mind before you lean on imaging alone.
Pulling It Together
Once you have run the main differentials, resist the urge to judge each one in isolation. Most coughing cats fit one of a handful of overlapping patterns, and the diagnosis usually falls out when you line up history, exam, imaging, and targeted testing side by side.
Three things steer the call more than any single result: the radiographic pattern, the type of airway inflammation, and the exposure history. When the picture is still murky, a treatment trial plus a follow-up recheck often settles it.
Frequently Asked Questions
Can a cat cough from heartworm and still test negative on an antigen test? Yes. Cats often carry very low worm burdens, so antigen tests can read negative despite a real infection. Pair antigen with antibody testing, and run the antigen test on heat-treated serum where possible.
How do you tell feline asthma from heartworm disease? You usually cannot on signs alone, because both cause cough, wheeze, and vomiting. The split comes from paired heartworm serology, the radiographic pattern, exposure history, and BAL cytology, all read together.
Is a normal chest radiograph enough to rule out lower airway disease? No. Early HARD and low-burden lungworm can both produce normal films. Negative imaging lowers suspicion, but it does not close the case.
What is the most useful single test for a chronic feline cough? BAL with cytology and culture gives the most information about the airway itself. Even so, it is interpreted alongside imaging and serology, not in place of them.
Conclusion
A cough in a cat almost never points to one tidy diagnosis. It reflects a small, overlapping group of airway, infectious, parasitic, and cardiac problems that look alike on the surface and behave very differently underneath.
Start with the history and the physical exam. Add imaging and a few well-chosen tests. More often than not, the answer emerges from the pattern, from radiographs, airway cytology, and response to treatment, rather than from one lab value standing alone. Work the cough methodically and you will miss far fewer of the cases that hide in plain sight.
Keep Learning
Want to go deeper on feline respiratory disease? VetandTech’s on-demand, RACE-approved webinars cover respiratory medicine, diagnostic imaging, and feline internal medicine. You can also browse upcoming veterinary CE conferences, where these topics come up regularly. For a related feline workup, see our guide to hyperthyroidism in cats.
