Tracheal Worms (Oslerus osleri) in Dogs
Definition of Tracheal Worms (Oslerus osleri)
Oslerus osleri, also known as Filaroides osleri and more commonly called tracheal or lung worms, are fairly small parasites that infect and irritate the windpipe. They have been reported in many countries and are found in mink, polecats, monkeys, cats, dogs and a number of Australian marsupials. Tracheal worms spend most of their lives inside their hosts. Puppies can become infected by parasite larvae in the saliva of their infected mother. Dogs also can become infected with tracheal worms by ingesting larvae in infected regurgitated food or feces. Ultimately, the parasite larvae molt and migrate through the dog’s bloodstream, maturing into adults in the dog’s upper respiratory tract. They end up forming lumpy nodules in the trachea (windpipe). Despite their small size, tracheal worms can cause fairly severe respiratory illness in some dogs, although in others they cause only mild symptoms. At times, they go undetected.
Causes of Tracheal Worms (Oslerus osleri)
Tracheal worms do not require an intermediate host to complete their life cycle. In other words, they live most if not all of their lives inside of their canine hosts. This is called a “direct lifestyle.” Dogs become infected with Oslerus osleri through several routes. Puppies can become infected with tracheal worm larvae from the saliva of their mother, while she is licking or cleaning them. Dogs also can become infected by eating regurgitated food and by ingesting larvae from infected feces. Trachael worm larvae can be transferred through airway secretions, as well.
Oslerus osleri larvae enter the dog’s small intestine. They molt and migrate through the bloodstream into the trachea and bronchi, where they mature into adults. The worms trigger an inflammatory reaction inside the dog’s upper respiratory tract, which causes fibrotic nodules (lumps) to form inside the trachea. Eggs laid by adult tracheal worms hatch into larvae inside these thin-walled nodules and can be quite irritating. They are coughed up and swallowed by the infected dog, where they again land in the small intestine. The larvae are then either excreted in feces or migrate back to the trachea and large bronchi.
Symptoms of Tracheal Worms (Oslerus osleri)
Despite their small size, tracheal worms can cause fairly severe illness in some companion dogs, while in others the signs are mild and nonprogressive. Dogs with tracheal worms may develop one or more of the following symptoms:
- Cough (usually persistent/chronic, dry/unproductive and hacking; can be severe)
- Difficulty breathing (dyspnea; respiratory distress)
- Wheezing sounds when breathing in (on inspiration); mild to severe
- Panting (usually not pronounced except in advanced cases)
- Exercise intolerance
- Retching (may be productive; may bring up white or blood-tinged mucus)
- Abdominal discomfort
- Skin inflammation (dermatitis; rash; uncommon)
Dogs At Increased Risk
Individual dogs can be infected with tracheal worms, but more commonly Oslerus osleri infection is a kennel-wide problem. This reportedly is especially true in large groups of greyhounds, although the reason for this particular association is not clear. Tracheal worms are seen mainly in young dogs less than 2 years of age. When they infect older dogs, these parasites often cause no significant symptoms.
Diagnosing Tracheal Worms (Oslerus osleri)
In most cases, tracheal worms in dogs go undetected. When signs do show up, the diagnosis often can be made by finding the parasite eggs or larvae in fresh fecal samples. Unfortunately, Oslerus osleri larvae are often sluggish and only periodically shed in an infected dog’s stool. This makes bronchoscopy a better diagnostic technique.
Bronchoscopy involves inserting an endoscope, which is a wand-like medical instrument with a camera on its tip, down into the dog’s trachea. The camera enables the veterinarian to see the small, thin-walled, cream-colored growths that contain the parasites and protrude from the lining of the trachea. Sometimes, larvae can be seen peeking out from those nodules. The veterinarian can brush the nodules and examine the brushings under a microscope, either in a saline solution or in a special stain, to identify tracheal worm larvae. If this is not diagnostic, she can also use the endoscope to snip out and retrieve (biopsy) a small sample of affected tracheal tissue for submission to a diagnostic laboratory.
Chest X-rays (thoracic radiographs) can sometimes be helpful, especially if the infection is advanced and the nodules caused by the parasites inside the trachea are large and obvious. Finally, the lining of the trachea can be washed with a special solution, which is then drawn back into a syringe or tube and analyzed microscopically for the presence of tracheal worm larvae. This procedure is known as a trans-tracheal wash.
Treating Tracheal Worms (Oslerus osleri)
Treatment protocols for tracheal worms in companion dogs are still somewhat experimental. Some of the medications that have been used include albendazole, fenbendazole, levamisole, thiabendazole, thiacetarsamide sodium, diethylcarbamazine, prednisone and ivermectin. Some of these have been used successfully in combination with surgical removal of the parasitic nodules. However, removing the nodules is no longer widely recommended, because there typically are so many of them. Treatment with drugs alone (chemotherapy) often makes the dog feel better and shrinks the size of the parasitic nodules, but it usually does not eliminate all of the worms. There still is no one accepted treatment program for dogs with tracheal worms.
The attending veterinarian is in the best position to recommend an appropriate treatment protocol and advise a dog’s owner about the correct drug, dosage and duration of treatment for tracheal worm infection. If the dog has become dehydrated, it may need to be supplemented with intravenous or subcutaneous fluids until proper hydration is reestablished.
The prognosis for dogs with tracheal worms is usually quite good, provided that appropriate treatment is administered for the proper length of time. Most veterinarians recommend repeating fresh fecal examinations monthly for up to 6 months, to look for the presence of eggs or larvae. Unfortunately, the outlook for young animals that develop pneumonia and/or prolonged and severe bloody diarrhea is guarded.