Eucoleus aerophilus is a nematode parasite, or roundworm, that resides in the respiratory systems of various animals. Commonly known as the fox lungworm, it primarily infects wild carnivores like foxes but is also found in domestic dogs and cats. The adult worms, which are thin and can be up to 32mm long, embed themselves in the lining of the windpipe (trachea), bronchi, and smaller bronchioles. While distributed worldwide, infections are associated with environments where wildlife hosts are common.
Lifecycle and Transmission
The transmission of Eucoleus aerophilus begins with an infected host, where adult female worms lay eggs within the airways. These eggs are coughed up from the lungs, swallowed by the animal, and then passed into the environment through feces. The eggs are not immediately infectious; they must undergo a development period in the soil that can take five to six weeks before they contain an infective larva. These mature eggs are resilient and can survive in the environment for months.
A new host becomes infected by ingesting soil, food, or water contaminated with these infective eggs. Once ingested, the larvae hatch in the small intestine, penetrate the intestinal wall, and migrate through the bloodstream to the lungs. This migration process takes about 7 to 10 days, and the larvae mature into adults in the airways approximately 40 days after the initial infection.
The lifecycle can also involve a paratenic host, most commonly an earthworm. An earthworm may ingest the parasite eggs from the soil, and the eggs can hatch into larvae within the earthworm’s body. A dog or cat can then become infected by eating the infected earthworm. This indirect transmission makes pets that dig or are prone to eating things they find outdoors more susceptible.
Clinical Signs and Diagnosis
Many animals infected with Eucoleus aerophilus show no outward signs of illness, particularly with light parasite burdens. When symptoms do appear, the most common is a persistent, dry, or wheezing cough. Other signs can include labored breathing, exercise intolerance, sneezing, and nasal discharge. In more severe infections, especially in younger or immunocompromised animals, bronchopneumonia can develop.
A veterinarian diagnoses the infection primarily by identifying the parasite’s eggs in a fecal sample. Using a fecal flotation test, a vet can microscopically find the characteristic barrel-shaped eggs, which have plugs at both ends and a pitted or net-like outer surface. These eggs measure approximately 65 by 30 micrometers. These must be differentiated from the eggs of other parasites, like the whipworm Trichuris.
If fecal tests are negative but an infection is still suspected, other procedures can be used. A transtracheal wash or a bronchoalveolar lavage involves collecting fluid directly from the lower airways to check for eggs. These methods can be more direct but are also more invasive than a standard fecal examination.
Treatment and Prevention
Treatment for Eucoleus aerophilus infection involves specific deworming medications prescribed by a veterinarian. Drugs such as fenbendazole, often administered daily for a period of 10 to 14 days, are effective. Certain macrocyclic lactones, including ivermectin, milbemycin oxime, and moxidectin, are also effective. The veterinarian will determine the appropriate drug and dosage based on the animal’s health and species.
Preventing infection centers on environmental management and routine parasite control. Many monthly heartworm preventatives that also protect against a broad spectrum of other parasites are effective against this lungworm. Promptly cleaning up feces from the yard prevents eggs from contaminating the soil. Discouraging pets from eating soil or earthworms also helps prevent infection.
The prognosis for pets diagnosed and treated for this condition is generally excellent. While human infection with Eucoleus aerophilus has been reported, it is exceptionally rare and not considered a significant public health concern.