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 (Eucoleus aerophilus) – Feline and canine bronchial capillarid.
Aelurostrongylus abstrusus is the most common lungworm to affect cats.
It was once thought to be a 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, however, it is most common among cats allowed outside who hunt.
The geographical distribution of both worms is worldwide.
- Capillaria aerophila – This parasite has a direct life cycle which means it does not need an intermediate host to complete its life cycle. Infected rodents can transmit infection and earthworms may act as an intermediate host by when they ingest eggs in the environment. Cats become infected by ingestion of food (including prey) or water infected with larvae.
- Aelurostrongylus abstrusus – Ingestion of intermediate host 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. The adult 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.
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
- Shortness of breath (dyspnea), especially upon exertion
- Open-mouthed breathing
- Lethargy and exercise intolerance
- Loss of appetite (anorexia)
Complications may include interstitial emphysema (a collection of air outside of the normal air space of the pulmonary alveoli) , 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 immunocompromised cats.
Your veterinarian will perform a physical examination of your cat and obtain a history from you. It will be necessary to perform diagnostic tests which can include:
- Tracheal wash: A tiny plastic tube (catheter) is passed into the airways. Through this tube, a small amount of fluid can be washed into and out of the lung may reveal the presence of larvae in fluids.
- Fecal examination (Baermann technique): A fecal sample is suspended in water in the bowl of the glass for several hours, which gives lungworm larvae the opportunity to migrate out of the feces and into the water. This may require several tests as 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.
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 will be necessary.
In addition to anti-parasite treatment, some cats will need additional care which may include the following:
- Antibiotics to treat secondary infections which sometimes occur.
- Corticosteroids to treat inflammation.
Humans can catch lungworms but it is not possible for you to catch lungworm from an infected cat. Wash fruit and vegetables thoroughly before consumption.
- The best way to prevent lungworm in cats indoors so they can not hunt.
- Make sure cats who do have access to ourdoors are up to date on their worming medication.
- Speak to 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