Lungworms in Dogs

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Lungworms in dogs are a tricky parasite that can be difficult to diagnose. Causing symptoms similar to those of several other varied conditions, determining lungworms to be the cause of respiratory problems in dogs  can be difficult and prolonged.

Caused in dogs by the parasitic nematode Oslerus (filaroides) osleri, lungworms are Strongylida parasites that infect the lungs of many mammals. There are many types of lungworms identified, which in varying ways infect animals and migrate to the lungs and lower respiratory tract of their chosen host, causing a variety of respiratory problems such as bronchitis and pneumonia.

More commonly seen in livestock such as cattle, sheep and goats, lungworm infections are frequently the cause of livestock losses throughout the world.  Most livestock farms employ periodic broad-spectrum deworming programs that can control and treat lungworm infections.

In dogs, lungworms most commonly affect puppies, becoming infected from the saliva or feces of an infected dog, usually their mother. The parasite lives in the nodules of the trachea, laying eggs into the mucus membranes of the trachea, hatching out large numbers of the parasite, which then begin to travel further into bronchi and respiratory tract.

The most common symptoms of lungworm infection include airway irritation and persistent coughing. However, because lungworms are not terribly common in dogs, and there are many other, much more frequent causes for these same symptoms, a process of elimination must take place to diagnose the cause and treat the underlying condition.

Before lungworms should be considered as a cause for coughing in younger (less than 2 year old) dog, the following conditions should also be considered, as they are far more widespread.

Acute infectious tracheobronchitis, or Kennel Cough, is so named because of the highly contagious and quick spreading nature of this infection.  Most often caused by the bacteria Bordetella bronchiseptica or the virus canine adenovirus, kennel cough is spread through the air by infected dogs sneezing and coughing, as well as with exposure to contaminated surfaces. It is most extremely common in areas where dogs are housed together or come into contact with each other, such as kennels, pet stores, shelters, dog shows and groomers.

The hallmark symptom of kennel cough is a harsh, hacking, non-productive cough, and a gagging “reverse sneeze”. The coughing may be seen at anytime during the day, but is most often evident when the dog is exited, exercising, or when any pressure is put on the trachea (such as when be walked on a collar and leash). Most dogs infected with kennel cough do not show any other signs of illness except for the terrible sounding cough. Fortunately, generally the symptoms of kennel cough are self-limiting, and most cases will resolve without medical intervention within 14 days. However, in rare cases the disease can progress to life-threatening pneumonia. Your veterinarian can prescribe medication to help shorten the length and severity of symptoms. The best prevention of kennel cough is through vaccination, and limiting exposure to areas where kennel cough is commonly seen.

In young puppies, other parasites such as roundworms should be considered when coughing and respiratory problems are present. As many as 85% of puppies are born with roundworms, transmitted to them from their mothers milk. . Roundworm eggs hatch in the intestine, and the larva are then carried to the lungs via the bloodstream to mature. The worms begin to crawl up the trachea, causing coughing, gagging and retching, until they are swallowed and taken back to the intestine to grow into adults.

Appearing quite spaghetti-like, roundworms can grow up to seven inches long, and mature quickly, causing severe side effects in puppies only a few weeks old. Along with coughing, a pot-bellied appearance, poor hair-coat and worms in the stool are signs of a worm infestation. If allowed to continue unchecked, the worms can cause pneumonia, intestinal obstructions and death.

Heartworm infection is a far more dangerous and potentially deadly parasite that lives in the heart of infected animals. A parasitic roundworm caused by the Dirofilaria immitis, heartworm is spread from animal to animal through the intermediate host, the mosquito. An infected mosquito bite spreads heartworm larvae through the bloodstream, and adult worms come to rest in the pulmonary artery of the dog, where they can reside for many years.

Signs of Heartworms

Dogs show virtually no signs of heartworm infection until the time the worms have grown and reproduced, with adult worms up to 30cm in length. The main symptom of heartworm is coughing, first only during exercise, and progressing to coughing up blood, congestive heart failure and eventually, death. Heartworms are prevalent in virtually every part of the United States and Canada, as well as many other places in the world. Treatment of heartworm is difficult, expensive, and often dangerous. Heartworm is completely preventable with the use of monthly prophylactic medications, available from your veterinarian.

Allergies, allergic bronchitis and pneumonia must also be considered as possible cause for coughing and respiratory problems. Your veterinarian will examine your pet, take a complete medical history and decide what tests may be necessary to assist in diagnosis. Chest X-rays to check for pneumonia or abnormal lung appearance may be recommended as well as blood tests to determine if an infection is present in the dog, and to test for heartworm disease.  If other potential causes of coughing have been ruled out, lungworms may be considered as the culprit. A fecal examination is the most common way to diagnose lungworms in dogs.

In severe cases of pneumonia or respiratory problems, a trans-tracheal wash may be employed. This procedure takes a sample of fluid directly from the trachea of the dog, and can be useful in identifying infections and diagnosing respiratory issues. Because lungworms typically reside in this area, their presence may be inadvertently diagnosed through the trachea wash by the presence of lungworms in the sample.

If lungworms are identified as the cause of your dogs respiratory problems, several medications are available that will readily kill the parasite, and can be used to prevent further infestations. Preventing lungworms in dogs can be accomplished by ensuring that breeding dogs are parasite free before they become pregnant, and puppies and young dogs are treated with a broad-spectrum dewormer regularly.

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