Cats get pneumonia through two main routes: inhaling infectious agents (bacteria, viruses, or fungi) or aspirating foreign material like vomit into their lungs. The most common cause is a viral infection of the lower respiratory tract, but bacteria, fungal spores, and even oily hairball remedies can also trigger it. Understanding the specific pathways helps explain why some cats are far more vulnerable than others.
Viral and Bacterial Infections
Viruses are the single most common cause of feline pneumonia. Upper respiratory infections, which are extremely prevalent in shelters and multi-cat households, can migrate deeper into the lungs and inflame the airways. Once a virus damages the delicate tissue lining the lungs, bacteria that normally live harmlessly in a cat’s respiratory tract can take advantage and cause a secondary infection. Pasteurella multocida, for instance, is a normal resident of the feline respiratory system that only becomes a problem when the lung’s defenses are already weakened.
Bordetella bronchiseptica deserves special attention. This bacterium thrives in high-density environments: roughly 5% of cats showing upper respiratory symptoms in shelters harbor it, along with about 1.5% of cats that look perfectly healthy. In young cats especially, a Bordetella infection can progress from sneezing and nasal discharge to life-threatening pneumonia without appropriate treatment. Older cats are not immune to this progression either.
Infectious pneumonia can also develop without the pathogen being inhaled at all. If a cat has a bacterial infection somewhere else in the body, those bacteria can travel through the bloodstream and settle in the lungs. Blood vessels branch into tiny capillaries throughout lung tissue, creating an easy entry point for infectious agents circulating in the blood.
Aspiration Pneumonia
Aspiration pneumonia happens when a cat inhales foreign material directly into its lungs. The most common scenario is vomiting: a cat throws up and, in the process, breathes in some of its stomach contents. That material is highly acidic, which immediately irritates and damages the sensitive lung tissues. Worse, vomit often carries bacteria from the small intestine, setting up a secondary infection on top of the chemical injury.
The severity depends on what was inhaled, which bacteria came along with it, and how widely the material spread through the lungs. A small amount of aspirated liquid concentrated in one area may cause mild, localized inflammation. A larger event that reaches multiple lung lobes is far more dangerous. Cats that are sedated, neurologically impaired, or have swallowing difficulties face a higher risk because their normal protective reflexes (the gag and cough that keep foreign material out of the airway) are compromised.
Fungal Pneumonia
Cats can develop pneumonia by inhaling fungal spores from contaminated soil. Two fungi are particularly relevant. Cryptococcus is found worldwide in soil and bird manure, with pigeon droppings being an especially rich source. Histoplasma is concentrated in the midwestern and southern United States, particularly in river valleys and plains where bat and bird populations spread it through the soil. Outdoor cats or cats with access to areas with heavy bird activity face greater exposure. Fungal pneumonia tends to be harder to diagnose and treat than bacterial cases, and it can affect multiple organ systems beyond the lungs.
Lipid Pneumonia From Hairball Products
A lesser-known cause is lipid pneumonia, a type of irritant pneumonia triggered by fat or oil accumulating in the lungs. In cats, this has been linked to petroleum-based products used to treat hairballs and constipation. When a cat licks or swallows a mineral oil preparation and some of it reaches the airways instead of the stomach, the oily substance coats lung tissue and triggers a chronic inflammatory response. While documented cases of this specific type are rare, it is a recognized risk of petroleum-based oral remedies.
Why Some Cats Are More Vulnerable
A cat’s immune status is one of the strongest predictors of whether an exposure will progress to pneumonia. One study of fatal feline pneumonia found that up to 70% of affected cats and kittens had a systemic condition suppressing their immune system. Infection with feline leukemia virus (FeLV) or feline immunodeficiency virus (FIV) was the most common underlying factor. In older cats, chronic diseases like diabetes and kidney disease also contributed to immunosuppression, leaving the lungs poorly defended against organisms that a healthy immune system would clear.
Kittens are disproportionately affected because their immune systems are still developing, and they are often housed in close quarters with other young cats in shelters or breeding facilities. Age alone is a significant risk factor at both ends of the spectrum: very young and very old cats are most susceptible.
How Pneumonia Progresses
Regardless of the initial cause, the progression follows a similar pattern. The invading pathogen or irritant damages the tissue lining the airways, triggering inflammation. The lungs respond by flooding the area with immune cells and fluid, which impairs the normal exchange of oxygen. This is why labored breathing, rapid breathing, and lethargy are hallmark signs. You may also notice nasal discharge, coughing, fever, and loss of appetite.
In severe cases, the inflammation does not stay contained in the lungs. Because the lungs process an enormous volume of blood with every heartbeat, widespread lung infection can spill inflammatory signals into the bloodstream and trigger a body-wide inflammatory response. This systemic reaction is what makes pneumonia potentially fatal rather than just a localized problem. Chest X-rays can reveal increased lung density in later stages, confirming that fluid and inflammatory material have accumulated in areas that should be filled with air.
Treatment and Recovery
Treatment depends on what caused the pneumonia. Bacterial cases are treated with antibiotics, with the specific choice guided by the severity of symptoms. A cat that is still eating and alert may be treated with oral antibiotics at home. A cat showing signs of systemic illness, such as fever, dehydration, or extreme lethargy, typically needs injectable antibiotics and supportive care in a veterinary hospital, sometimes including oxygen therapy and intravenous fluids.
Fungal pneumonia requires antifungal medications, which often need to be given for weeks to months. Aspiration pneumonia may need antibiotics to address the secondary bacterial infection, along with supportive care while the chemical injury to the lung tissue heals. In all cases, follow-up X-rays help confirm that the lungs are actually clearing, since a cat can look better outwardly while the lungs still show signs of disease. Full recovery timelines vary widely, from a couple of weeks for mild bacterial cases to months for fungal or severe aspiration events.