Lungworms are slim, hair-like worms which are approximately 1 cm in length. There are several species of lungworm, however, the most common to affect cats are:
- Aelurostrongylus abstrusus - Feline lungworm.
- Capillaria aerophila (also known as Eucoleus aerophilus) - Feline and canine bronchial capillarid.
Aelurostrongylus abstrusus is the most common lungworm to affect cats.
It was once believed to be a somewhat rare infection in cats, but an Australian study found 16% of cats at a shelter were infected with lungworm. Cats of any age, sex or breed can become infected with lungworm, however, it is most common among cats allowed outside who hunt.
The geographical distribution of both worms is worldwide.
How do cats become infected with lungworms?
- Capillaria aerophila has a direct life cycle and may be transmitted via earthworms and rodents. Cats become infected by ingestion of food or water infected with larvae.
- Aelurostrongylus abstrusus by ingesting intermediate hosts such as a snail or slug, or more commonly by consuming animals who have been feeding on snails and slugs such as birds, rodents, and lizards.
After ingestion of both species, the larvae pass into the intestine. They then penetrate their way through the intestinal wall and migrate to the lungs via the blood. They remain in the terminal respiratory bronchioles and alveolar ducts of the lungs where they mature. Once they have become adult worms, the female worm lays her which hatch into microscopic larvae, they then travel up the trachea and are swallowed into the stomach before being passed into the environment via the cat's feces. Larvae appear in the feces around 40 days post infection.
What are the symptoms of lungworms in cats?
Cats are commonly asymptomatic to lungworm, but clinical signs may develop in kittens, cats who have a heavy infestation and/or a weakened immune system. Symptoms may include:
- Chronic dry cough
- Dyspnea (shortness of breath), especially upon exertion
- Open-mouthed breathing
- Lethargy and exercise intolerance
Symptoms are typically noticed in younger cats. The most common symptom is coughing, which can easily be confused with more common disorders such as hairballs.
Complications may include interstitial emphysema , pulmonary edema (fluid in the air sacs of the lungs), pneumothorax (air in the pleural cavity) and secondary bacterial pneumonia. Lungworm can be particularly serious in kittens and cats whose immune systems are compromised.
How are lungworms diagnosed?
Your veterinarian will perform a physical examination of your cat and obtain a history from you. Lungworm is diagnosed by finding first stage larvae in the feces. Other tests your veterinarian may wish to perform include:
- Tracheal wash may reveal the presence of larvae in fluids.
- Fecal examination for the presence of eggs or larvae. A technique known as Baermann is used. This may require several tests as eggs and larvae are not always present in the feces.
- X-rays to determine if the coughing is caused for other reasons as well as to assess the condition of the lungs.
How are lungworms treated?
Your veterinarian will recommend a worming medication to eradicate the parasites. Treatment can be difficult and it may be necessary to continue anti-worming medication for up to 8 weeks, in some cases more than one anti-parasitic medication may be used.
Commonly used medication to treat lungworm include:
Secondary infections can sometimes occur in which case your cat may also be prescribed antibiotics.
Corticosteroids may also be prescribed to treat inflammation.
Can humans catch lungworms from infected cats?
Humans can catch lungworms but it is not possible for you to catch lungworm from an infected cat. Wash fruit and vegetables before consuming, this is especially important for food which is eaten raw.
How do I prevent lungworm in my cats?
The best way to prevent lungworm in cats is to keep him indoors so that he can't hunt. If he does go outside, make sure he is up to date on his worming medication. See your veterinarian for advice on the best lungworm preventative treatment for your cat.
If you notice your cat has developed a cough, see your veterinarian.
 Merck Veterinary Manual