Lungworms in Dogs: A Challenging Respiratory Parasite
Lungworms in dogs are tricky parasites that can be difficult to diagnose. They cause symptoms similar to those of several other varied conditions, making it challenging and often prolonged to determine lungworms as the cause of respiratory problems in dogs.
Caused by the parasitic nematode Oslerus (filaroides) osleri, lungworms are Strongylida parasites that infect the lungs of many mammals. There are several types of lungworms, which, in different ways, infect animals and migrate to the lungs and lower respiratory tract of their chosen host. This migration leads to various respiratory issues, such as bronchitis and pneumonia.
While lungworm infections are more commonly seen in livestock, such as cattle, sheep, and goats, they frequently cause significant losses worldwide. Most livestock farms implement periodic broad-spectrum deworming programs to control and treat these infections.
In dogs, lungworms most commonly affect puppies, who become infected through the saliva or feces of an infected dog, usually their mother. The parasite lives in the nodules of the trachea, laying eggs in the mucus membranes of the trachea. These eggs hatch into large numbers of parasites that then travel further into the 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 more frequent causes of these symptoms, a process of elimination is necessary to diagnose the cause and treat the underlying condition.
Before lungworms are considered as a cause for coughing in younger dogs (less than 2 years old), the following conditions should also be considered, as they are far more widespread.
Common Respiratory Issues to Consider in Dogs
Acute infectious tracheobronchitis, or Kennel Cough, is so named because of the highly contagious and quickly spreading nature of the 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 through exposure to contaminated surfaces. It is most 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 occur at any time during the day, but it is most often noticeable when the dog is excited, exercising, or when pressure is placed on the trachea (such as when walked on a collar and leash). Most dogs infected with kennel cough do not show any other signs of illness except for the distinctive cough. Fortunately, kennel cough symptoms are generally 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 for kennel cough is 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 from their mother’s milk. Roundworm eggs hatch in the intestine, and the larvae are carried to the lungs via the bloodstream to mature. The worms then crawl up the trachea, causing coughing, gagging, and retching, until they are swallowed and taken back to the intestine to grow into adults.
Roundworms, which resemble spaghetti, can grow up to seven inches long and mature quickly, causing severe side effects in puppies as young as a few weeks old. Along with coughing, symptoms include a pot-bellied appearance, poor coat condition, and worms in the stool. If left unchecked, roundworms can lead to pneumonia, intestinal obstructions, and even death.
Heartworm infection is a much more dangerous and potentially deadly parasite that lives in the heart of infected animals. Caused by the parasitic roundworm Dirofilaria immitis, heartworm is spread 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 live for many years.
Signs Your Dog May Have Heartworms
Dogs show virtually no signs of heartworm infection until the worms have matured and reproduced. Adult worms can grow up to 30cm in length. The main symptom of heartworm is coughing, which typically starts only during exercise and progresses 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 parts of the world. Treatment of heartworm is difficult, expensive, and often dangerous. However, heartworm disease is completely preventable with monthly prophylactic medications, available through your veterinarian.
Allergies, allergic bronchitis, and pneumonia must also be considered as possible causes of coughing and respiratory issues. Your veterinarian will examine your pet, take a complete medical history, and decide which 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 or to test for heartworm disease. If other potential causes of coughing are ruled out, lungworms may then 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 performed. This procedure involves taking a sample of fluid directly from the dog’s trachea, which can help identify infections and diagnose respiratory issues. Because lungworms typically reside in this area, their presence may be inadvertently detected through the tracheal wash sample.
If lungworms are identified as the cause of your dog’s respiratory problems, several medications are available that can effectively kill the parasite and prevent further infestations. Preventing lungworms in dogs can be achieved by ensuring that breeding dogs are parasite-free before becoming pregnant, and by regularly treating puppies and young dogs with a broad-spectrum dewormer.
