Lungworms are parasitic worms that affect the respiratory system of cats. These infections can lead to notable health concerns, as the worms primarily reside in the lungs and airways, causing inflammation and damage. Early recognition and intervention can significantly improve outcomes for infected cats.
Understanding Lungworm Types and How Cats Get Infected
Two primary lungworm species affect cats: Aelurostrongylus abstrusus and Capillaria aerophila (also known as Eucoleus aerophila). Aelurostrongylus abstrusus is the most common feline lungworm globally. It has an indirect life cycle, requiring an intermediate host to complete its development. Adult A. abstrusus worms live in the alveolar ducts and terminal respiratory bronchioles of the cat’s lungs.
Female worms lay eggs that hatch into first-stage larvae (L1) within the lungs. These L1 larvae migrate up the bronchial tree, are swallowed, and then passed in the cat’s feces. Slugs and snails act as intermediate hosts, ingesting the L1 larvae which then develop into infective third-stage larvae (L3) inside them. Cats become infected by eating these infected slugs or snails, or more commonly, by consuming paratenic hosts like rodents, birds, amphibians, or reptiles that have eaten infected mollusks. Once ingested by the cat, the L3 larvae are released in the intestines and migrate to the lungs, maturing into adult worms.
Capillaria aerophila, sometimes called the fox lungworm, also infects cats and has a different life cycle. This parasite has a direct life cycle, where adult worms inhabit the trachea and bronchi. Eggs laid by female worms in the respiratory tract are coughed up, swallowed, and shed into the environment via feces. Cats become infected by ingesting these infective eggs directly from a contaminated environment. Earthworms can act as facultative paratenic hosts, allowing infection if cats eat them. After ingestion, the larvae migrate through the bloodstream and lymphatic system to reach the respiratory tract, where they mature into adult worms.
Recognizing the Signs of Lungworm Infection
Clinical signs of lungworm infection in cats can vary considerably, ranging from no apparent symptoms to severe respiratory distress. The severity often depends on the number of worms present and the cat’s overall health. Many infected cats, especially those with mild infections, may show no visible signs.
As the infection progresses, cat owners might observe respiratory symptoms such as coughing, which can be mild but persistent, or become severe and productive. Other common signs include wheezing, difficulty breathing (dyspnea), and rapid breathing (tachypnea). Sneezing and nasal discharge can also be present.
Beyond respiratory issues, cats with lungworm infections may exhibit more general signs of illness. These can include lethargy, decreased appetite (anorexia), and noticeable weight loss. Exercise intolerance, where a cat tires easily during play, might also be observed. Kittens and cats with compromised immune systems are particularly susceptible to more severe symptoms due to their smaller airways and less developed immune responses.
Diagnosis and Treatment Approaches
Diagnosing lungworm infections in cats involves a combination of methods, as symptoms can mimic other respiratory conditions like asthma or bronchitis. Veterinarians begin with a physical examination, including listening to the cat’s lungs and heart. A strong indicator for lungworm is a history of outdoor access or hunting.
The primary diagnostic method for Aelurostrongylus abstrusus involves a fecal examination using the Baermann technique, which helps to isolate the larvae from the stool. For Capillaria aerophila, direct fecal flotation or identification of eggs in tracheal washes are common diagnostic approaches. Chest X-rays are performed to identify changes in the lungs, such as thickening of airways, abnormal spots, or nodules, which can indicate inflammation or the presence of worms. In more complex or persistent cases, a veterinarian may recommend a bronchoscopy to visually inspect the airways and collect fluid samples for analysis.
Once diagnosed, lungworm infections are primarily treated with antiparasitic medications. Common choices include fenbendazole, given orally, and topical spot-on formulations containing selamectin, emodepside, or moxidectin. Treatment duration often spans several weeks, up to two months, to ensure complete elimination of the parasites. In severe cases, additional supportive care like corticosteroids to reduce airway swelling or antibiotics for secondary bacterial infections may be prescribed.
Prevention and Prognosis
Preventing lungworm infections in cats largely centers on reducing exposure to intermediate and paratenic hosts. Limiting a cat’s outdoor access significantly decreases the likelihood of them encountering infected slugs, snails, rodents, birds, or other small animals that carry the infective larvae. For cats that do go outdoors, regular deworming protocols, as recommended by a veterinarian, can help manage and prevent infections. Over-the-counter dewormers may not target lungworm species, so veterinary guidance for specific medications is needed.
Maintaining a clean environment, including promptly cleaning litter boxes, can help reduce the spread of Capillaria aerophila eggs. Washing a cat’s bedding at high temperatures can also help eliminate any eggs that may be present. The prognosis for cats diagnosed with lungworms is favorable with timely and appropriate treatment. Most cats make a full recovery, especially those with mild infections. However, severe or chronic cases, particularly in young or immunocompromised cats, can lead to lasting lung damage or, rarely, be fatal. While Capillaria aerophila has a very low potential for zoonotic transmission to humans, the primary health concern remains for the infected cat.