Lungworms are parasitic infections that target the respiratory system of domestic cats. The most common species, Aelurostrongylus abstrusus, causes feline lungworm disease (aelurostrongylosis). These small, slender parasites reside in the lung tissue, causing inflammation and damage to the airways. While some infections are mild or asymptomatic, a significant parasitic burden can lead to severe respiratory distress and death if not treated promptly.
How Cats Become Infected
The life cycle of the feline lungworm requires an intermediate host to become infectious. This host is typically a gastropod, such as a snail or a slug, which ingests the first-stage larvae (L1) passed in the cat’s feces. Inside the mollusk, the larvae develop into the infective third-stage larvae (L3).
Cats rarely consume snails or slugs directly. They become infected by eating paratenic hosts, which are animals that have consumed the infected mollusks. Common paratenic hosts include small rodents, birds, frogs, lizards, and snakes. Once consumed, the L3 larvae are released in the stomach and intestines, where they penetrate the intestinal wall. The larvae then migrate through the lymphatic system and blood vessels until they reach the lungs, where they mature into adult worms.
Observable Symptoms in Cats
Clinical signs of lungworm infection range from a lack of symptoms to life-threatening respiratory failure, depending on the worm burden and the cat’s immune response. The most noted sign is a chronic, persistent cough, which an owner might mistake for a hairball or feline asthma. This cough is often non-productive and can worsen during periods of exercise or excitement.
As the parasites cause inflammation and damage to the small airways, cats may develop difficulty breathing (dyspnea) or exhibit wheezing. Owners might observe open-mouth breathing or an increased breathing rate (tachypnea). Systemic signs include loss of appetite, lethargy, and weight loss, especially in severe or chronic cases. Young kittens and cats with compromised immune systems are vulnerable to severe disease.
Veterinary Diagnosis and Treatment
A veterinarian may suspect lungworm infection based on respiratory symptoms and a history of outdoor access or hunting behavior. Confirming the diagnosis requires specific laboratory testing, as clinical signs mimic other common feline respiratory diseases. The gold standard for diagnosis is the Baermann sedimentation technique, which isolates the first-stage larvae (L1) from a fresh fecal sample.
Since the larvae are shed sporadically, a veterinarian may recommend collecting samples over three consecutive days to increase the chance of detection. Chest X-rays are also a helpful diagnostic tool, revealing characteristic patterns of inflammation, such as bronchointerstitial lung disease, caused by the parasites and their eggs. In some cases, advanced diagnostics like a bronchoalveolar lavage, where fluid is collected directly from the lungs, may be used to find the larvae.
Treatment involves specific anti-parasitic medications, as common dewormers are often ineffective. Veterinarians commonly prescribe drugs such as fenbendazole for an extended course, or topical spot-on treatments containing moxidectin, imidacloprid, or selamectin. The duration of treatment is often several weeks to ensure all parasite stages are eliminated. For cats experiencing severe respiratory distress, supportive care is necessary, including anti-inflammatory medications like corticosteroids to reduce lung swelling, and sometimes oxygen therapy, to stabilize the animal while the anti-parasitic drug takes effect.
Strategies for Prevention
The most effective strategy for preventing lungworm infection is minimizing the cat’s exposure to intermediate and paratenic hosts. Keeping cats indoors significantly reduces their opportunity to hunt and ingest infected rodents, birds, or amphibians. This is important in regions where the parasite is prevalent.
For cats that spend time outdoors, managing the yard environment helps by removing debris, such as piles of leaves or wood, where slugs and snails hide. Owners can also discuss broad-spectrum parasite preventatives with their veterinarian. Certain monthly topical medications are effective against lungworms and can be incorporated into a routine parasite control plan, offering protection against accidental ingestion of an infected host.