Blastomycosis in Dogs

Overview of Canine Blastomycosis

Blastomycosis, commonly referred to as “Blasto”, is a systemic disease that can occur in dogs caused by a fungus present in the soil of certain regions, such as Mississippi, Missouri and Ohio River Valley. The organism is present in the soil and infection occurs by inhalation of the fungus. Once infection is established in the lung, the fungus changes its characteristics by converting from the mycelial form into the yeast form and spreads to other organs causing a disseminated infection.

This fungus exists in two different forms:

Hunting dogs that spend a lot of time outdoors and live in endemic areas are at risk for inhaling this organism and developing the disease.

Some animals may be infected but not show clinical signs for a long time. These animals are not a risk for contagion of other animals and people because the stage of the organism present in the animal’s tissues is not that of an infectious stage.

If left untreated, these dogs can become seriously ill. Dogs may develop infection in the kidneys, eyes, brain and bones. According to the organ that is affected, the clinical signs may vary. They may have ocular problems or neurological signs like seizures and head tilt. In some dogs lameness may be the primary complaint due to infection in the bones.

What to Watch For

Symptoms of blastomycosis in dogs may include:

Diagnosis of Blastomycosis in Dogs

Suspicion of blastomycosis comes from the history of living in an area at risk for this infection, especially in animals that hunt or spend a lot of time outside. Clinical signs may not be very specific.

Treatment of Blastomycosis in Dogs

Home Care and Prevention

It is important that you administer the medications as instructed by your veterinarian and that you monitor the appetite and bowel movements of your pet. Some drugs may induce nausea and vomiting. If your pet stops eating, your veterinarian needs to be notified immediately.

There is no vaccine or effective way of disinfecting the contaminated soil.

In-depth Information on Blastomycosis in Dogs

Other medical problems can cause symptoms similar to those encountered in pets with blastomycosis. Your vet will exclude these conditions as necessary before establishing a diagnosis of blastomycosis:

Blastomycosis is a systemic disease caused by a fungus (Blastomyces dermatidis) present in the soil of certain geographic regions like Mississippi, Missouri and Ohio River Valley). Dogs and people are most commonly infected.

Infection occurs by inhalation of spores from the “mycelial” form of the organism found in the environment, especially moist soil. After the organism becomes established in the lung, dissemination throughout the body occurs. Blastomycosis is endemic in the Mississippi, Missouri and Ohio River valleys.

Young male dogs, especially hunting dogs, are at increased risk presumably because of increased contact with contaminated soil. The yeast form of the organism found in infected body tissues is not contagious, and thus the disease is not readily transmissible between animals or from animals to people.

The prognosis depends on the extent and severity of lung involvement. In dogs, blastomycosis affects the lungs (80 percent of cases), eyes (40 percent of cases), skin (20 to 40 percent of cases), and bones (30 percent of cases).

Most affected animals have systemic symptoms such as fever, lethargy, loss of appetite, and weight loss. Lung involvement leads to respiratory symptoms such as exercise intolerance, cough, and difficulty breathing. The animal’s peripheral lymph nodes often are enlarged. These are found under the neck, in the shoulder region and behind the knee. Bone involvement may occur and result in lameness.

Infection of the urogenital tract, for example the prostate gland in male dogs, occasionally may occur and cause clinical symptoms like blood in the urine or difficult urinations. Nervous system involvement may cause seizures, uncoordination, head tilt, and other symptoms.

Eye involvement can lead to squinting due to pain and light sensitivity. Involvement of the retina may lead to blindness. Involvement of the iris of the eye may be complicated by glaucoma, which is high pressure within the eye. Draining nodules may be found in the skin, and microscopic examination of this material often discloses the organism and yields a diagnosis.

In-depth Information on Diagnosis

Certain diagnostic tests must be performed to confirm the diagnosis of blastomycosis and exclude other diseases that may cause similar symptoms. Tests may include:

In-depth Information on Treatment

Treatment of blastomycosis must be individualized based on the severity of the condition and other factors that must be evaluated by your veterinarian. Therapy is aimed at relief of specific symptoms (e.g. difficulty breathing, coughing, eye problems) and elimination of the fungus from the body. Treatment may include one or more of the following:

Follow-up Care for Dogs with Blastomycosis

Optimal treatment for your dog requires a combination of home and professional veterinary care. Follow-up with your veterinarian is essential. Administer all medications as directed and call your veterinarian if you have questions or problems administering medications to your pet.

Follow-up with your veterinarian for physical examinations and blood tests.

The prognosis is guarded for dogs with severe lung involvement and for those with eye or nervous system involvement. Approximately half of dogs with severe lung involvement experience a worsening of the respiratory function during the first week of treatment. This complication is thought to be caused by rapid killing of the fungal organisms and can lead to death. It is very difficult to treat animals with nervous system involvement. Those with advanced eye involvement have a poor prognosis for return of vision.

The agar gel immunodiffusion test tends to remain positive after treatment and cannot be used to gauge response to treatment. Therapy should be continued for at least a month past resolution of all clinical signs. Most dogs with mild to moderate disease will require 60 days of therapy. If severe disease is present 90 days may be required. Recurrence within one year occurs in 20 percent of cases.

No vaccine is available. Even if areas are identified as infected, sterilization of the soil is not possible.