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), Troglostrongylus brevior and T. subcrenatus, and Oslerus rostratus. Cats can become infected by swallowing infective stages of parasitic lungworm. The exact means of becoming infected varies according to the life cycle of the particular parasite.
Adult female Aelurostonglosus, Oslerus, and Troglostrongylus worms lay their eggs in an infected cat's sacs of the lungs (alveoli). 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 cats. Cats can become infected by eating slugs or snails or by eating another animal, such as a snake, lizard, mouse, or bird that has eaten a slug or snail.
"Cats can become infected by eating slugs or snails or by eating another animal, such as a snake, lizard, mouse, or bird that has eaten a slug or snail."
Eucoleus is often transmitted through the environment as infected cats shed infective eggs, although they may also be transmitted by earthworm ingestion. Once swallowed, infective stages of the parasite complete their life cycle by migrating through the body from the intestinal tract to their final destination, either 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, 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 ocular or nasal discharge.
"Signs may be more pronounced in kittens due to their immature immune system."
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 that 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. Radiographic changes can be very similar to chronic airway diseases like asthma. If your cat shows signs of breathing difficulty, the radiographs 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. Although diagnosing a lungworm infection can be done by identifying the parasite in an infected animal’s feces using a Baermann test, it 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 instill 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?
Since wheezing, coughing, and lethargy symptoms are non-specific, 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 her symptoms. In young outdoor cats, parasitic lungworm infection is a more likely diagnosis, while in older cats, one of the other diseases 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 the rare case where a cat has severe respiratory distress, hospitalization for oxygen therapy and other supportive treatments may be necessary.
What is the success rate of treatment?
Although the success rate of treatment depends on the severity of symptoms and the number of parasites present, the prognosis for recovery is generally good.
Can my cat pass the infection to other pets?
It depends on the species of lungworm that is causing the infection. Suppose it is 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 aerophilus has the potential to spread to humans (zoonotic), causing bronchitis symptoms. Any symptoms should be reported to your physician.
"Eucoleus aerophilus has the potential to spread to humans causing bronchitis symptoms."
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, she can be infected again.
