Capillaria in Dogs

By Malcolm Weir, DVM, MSc, MPH; Catherine Barnette, DVM

What is Capillaria?

Capillaria is a small internal parasite, often less than half of a centimeter in length. They are closely related to intestinal worms, though they can live in a variety of locations within the body. Capillaria can affect both dogs and cats, although dogs are more frequently affected.

There are several species of Capillaria that affect dogs:

Pearsonema plica (also known as Capillaria plica): This parasite typically invades the wall of the bladder, although it can also lodge in portions of the kidney. This species affects both dogs and cats.
Eucoleus aerophilus (also known as Capillaria aerophilus): This parasite affects the respiratory tract, with adult worms attaching both within the lungs and along the trachea. This species affects both dogs and cats.
Eucoleus boehmi (also known as Capillaria boehmi) can live in the membranous tissue of the nasal passages and the sinuses. Dogs are affected more often than cats.

How is a dog infected with Capillaria?

Dogs acquire Capillaria infections from the environment.

Capillaria species that live in the bladder (P. plica) shed their eggs into the urine. These eggs are then released into the environment when the dog urinates. Capillaria species that live in the respiratory tract (E. aerophilus, E. boehmi) lay their eggs within the dog’s airways. The infected dog then coughs these eggs up, swallows them, and passes the intact eggs in its stool.

"Some Capillaria species lay eggs that can immediately be ingested by a new host."

Once the eggs are released into the environment, the mechanism by which they infect a new host depends on the Capillaria species. Some Capillaria species lay eggs that can immediately be ingested by a new host. For example, a dog may walk through soil contaminated with Capillaria eggs, lick his paw, and then become infected with Capillaria. Other species have a more complicated life cycle; they lay eggs that must be ingested by an earthworm and the new host becomes infected by eating the infected earthworm.

What are the signs of Capillaria?

In many cases, dogs infected with Capillaria show no signs of illness. When signs do occur, they relate to the specific Capillaria species and its site of infection. P. plica affects the walls of the bladder and the kidneys; therefore, an infection may lead to blood in the urine, urinary accidents, and straining to urinate. E. aerophilus lives in the lungs and airways, causing coughing, wheezing, and shortness of breath. E. boehmi lives in the sinuses and nasal passages and may cause sneezing and nasal discharge.

How is Capillaria diagnosed?

The diagnosis of Capillaria varies depending on the species involved. Diagnosis can be difficult because the eggs of Capillaria are shed only on an intermittent basis. Therefore, even if your veterinarian suspects Capillaria and obtains the correct laboratory samples, the diagnosis can be difficult to confirm.

"Diagnosis can be difficult because the eggs of Capillaria are shed only on an intermittent basis."

P. plica which affects the urinary tract, may be diagnosed based on urinalysis. When the urine is examined under a microscope, your veterinarian may see signs of inflammation, including blood and/or inflammatory cells. Further examination may reveal the microscopic eggs of the parasite, which are shed into the urine.

E. aerophilus, which affects the respiratory tract, may be diagnosed on fecal examination. Although radiographs (X-rays) of the chest may show inflammation corresponding to lungworm infection, the worms themselves are not large enough to be seen on radiographs and they do not show findings specific to Capillaria infection. For this reason, a microscopic examination of the feces must be performed to look for the parasite’s eggs, which are coughed up and swallowed by the pet.

E. boehmi can be diagnosed on a fecal examination, as the eggs are often passed in the feces. E. boehmi may also be seen in the nasal passages on rhinoscopy. In this procedure, your veterinarian will anesthetize your dog and pass a small camera into the nasal passages to determine the cause of your dog’s nasal signs. Less commonly, whole or partial E. boehmi worms may be found in a microscopic examination of nasal mucous.

How is Capillaria treated?

Once diagnosed, Capillaria is relatively easy to treat. A variety of dewormers are effective against Capillaria species, including fenbendazole (Panacur®), ivermectin (Ivomec®, Heartgard®), and milbemycin (Interceptor®). Some of these are given as a one-time treatment, while others are repeated daily for three to five days. Treatment with the application of a topical spot-on containing moxidectin (Advantage Multi®, Imoxi™) is effective for E. boehmi and E. aerophile. While the parasite is easily eliminated with a dewormer, some pets may require additional medications to decrease the inflammation associated with the infection.

Your pet may also require additional nursing or supportive care during the recovery period. Follow-up fecal examinations to make sure that Capillaria eggs are no longer present may also be recommended. Overall, the prognosis for Capillaria is good with appropriate treatment.

Can anything be done to prevent Capillaria?

The likelihood of infection can be decreased by limiting your dog’s ability to eat earthworms. In many cases, earthworms serve as the source of Capillaria infection.

Can I get Capillaria from my dog?

E. aerophilus (the lungworm form) can infect humans. Make sure to use appropriate hygiene measures (such as handwashing and gloves) when cleaning areas that may be contaminated with infected feces. Frequent removal of feces is also advised.

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