Lungworm Infections in Cats

What causes lungworm infection?

Lungworm infection is caused by one of several parasitic roundworms. In North America, many parasitic lungworms infect cats; the most common species is Aelurostrongylus abstrusus.

Less common infections occur with Eucoleus aerophilus (formally known as Capillaria aerophilus), Oslerus rostratus, Troglostrongylus breviora and T. subcrenatus.

How do these parasites cause infection?

Cats can get a lungworm infection by swallowing infective stages of parasitic lungworm. The exact way that a cat is infected varies according to the life cycle of the parasite.

Adult female worms lay their eggs in an infected cat's alveolar sacs in the lungs. The eggs hatch, and the larvae move to the upper airways (bronchi) and are then coughed up and swallowed. The larvae are excreted with feces and then ingested by slugs or snails. After the larvae enter the slug or snail, they develop into their infective stage, capable of infecting other cats. Cats can become infected by eating slugs or snails, or by eating another animal that has eaten a slug or snail, such as a snake, lizard, mouse, or bird.

Eucoleus aerophilus is often transmitted through the environment as infected cats shed infective eggs, although they may also be transmitted when a cat eats an earthworm. Once swallowed, infective stages of the parasite complete their life cycle by migrating through the body from the intestinal tract to their destination: the nose, bronchi, or alveoli.

Are there areas where these infections are more common?

• Aelurostrongylus abstrusus and Eucoleus aerophilus have been found worldwide.
• Troglostrongylus is believed to affect wild cats mostly; however, domestic cat infections have increased in Europe’s Mediterranean and Balkan areas.
• Oslerus rostratus has been found in cats in Southern Europe, Hungary, Israel, Sri Lanka, the Pacific Islands, and the United States.

What are the clinical signs of lungworm infection?

The clinical signs of a lungworm infection depend on the number of parasites present in the lungs, the immune status of the infected cat, and the site of infection. Signs may be more pronounced in kittens due to their immature immune system. Signs can include coughing, heavy breathing, wheezing, sneezing, poor appetite or anorexia, weight loss, fever, enlarged lymph nodes, and eye or nasal discharge. Signs are generally caused by the body’s reaction to the parasites. Many cats show no visible symptoms of the disease, and the infection may be discovered incidentally when your veterinarian performs tests for another reason.

How is lungworm infection diagnosed?

Your veterinarian may suspect your cat has a lungworm infection based on clinical signs and potential exposure to the parasite. Radiographs (X-rays) of an infected cat's chest or upper airways may show thickening of the airways or abnormal spots or nodules in the affected airways or lung lobes. These changes can be very similar to chronic airway diseases like asthma.

If your cat shows signs of breathing difficulty, the X-rays may also show signs of pneumonia. Depending on the case, your veterinarian may recommend an examination of the airways with an endoscope (bronchoscopy) to obtain samples of cells from these nodules.

There are no blood tests to diagnose one of these parasitic infections. However, an infected cat may have a high number of eosinophils – a type of white blood cell that increases in number in response to parasites or allergic reactions. A lungworm infection can be diagnosed by identifying the parasite in an infected animal’s feces using a Baermann test, but this test can produce false negatives and miss the infection.

The organisms may be identified after a lung wash (bronchoalveolar lavage or BAL). A BAL is performed using an endoscope to flush sterile saline into the lower airways and then retrieve the fluid for analysis. Polymerase chain reaction (PCR) testing can detect small amounts of DNA from fecal samples and throat swabs.

Could the symptoms be caused by something else?

Wheezing, coughing, and lethargy are non-specific symptoms, so other diseases can cause them, including asthma, bacterial or viral infections, heart disease, cancer, and chest trauma. Your cat’s age will help your veterinarian decide the most likely cause of the symptoms. In young outdoor cats, parasitic lungworm infection is a more likely diagnosis, while in older cats, another disease may be more likely.

How is lungworm treated?

The treatment goals are to eliminate the parasite and control symptoms caused by inflammation. The parasites can be killed with specific antiparasitic drugs, depending on the type of lungworm. Effective medications include ivermectin, fenbendazole (Panacur®), moxidectin + imidacloprid (Advantage Multi®), selamectin (Revolution®), and emodepside + praziquantel (Profender®). Depending on the severity of your cat’s infection, the medication will be prescribed for several weeks to several months.

If your cat’s symptoms are moderate, your veterinarian may prescribe medication to alleviate inflammation. In rare cases where the cat has severe respiratory distress, hospitalization for oxygen therapy and other supportive treatments may be necessary.

What is the success rate of treatment?

Generally, the prognosis for recovery is good, although the success rate for treatment depends on the severity of the symptoms and the number of parasites present.

Can my cat pass the infection to other pets?

It depends on the species of lungworm that is causing the infection.

• If the infection is caused by Aelurostrongylus abstrusus, Troglostrongylus subcrenatus, or Oslerus rostratus, the infection cannot be passed directly from one cat to another because the parasite needs another host (snail or slug) to complete its life cycle.
• If the infection is caused by Eucoleus aerophilus, cats can become infected from your cat’s feces. There is one report of a cat spreading Troglostronylus brevior to her kittens.

Eucoleus aerophilous has the potential to spread to humans (zoonotic), causing bronchitis symptoms. Any symptoms should be reported to your physician.

Can my cat be re-infected?

Yes, if your cat is re-exposed to a contaminated environment or continues to prey on the intermediate host species, the cat can be infected again.