Blastomycosis in the dog

Blastomycosis (Blasto) in the dog is a commonly misdiagnosed systemic fungal disease of dogs and humans and other mammals. It is a great masquerader and can be mistaken for cancer, viral infections, Lyme Disease and other systemic fungal diseases such as Valley Fever. Many dogs have been euthanized or had treatment delayed because of an erroneous diagnosis of cancer being made. Blastomycosis in the dog causes weight loss, swollen lymph nodes, draining sores, coughing, poor appetite, fever, blindness, bone lesions, etc. The reason there are so many areas affected is due to the widespread dissemination of the organisms throughout the dog's body from the original site which is usually the lungs. In the environment Blasto is present mostly in the Mississippi, Wisconsin, and Ohio River systems.

Blasto grows in two ways. One form, called the fungal form, occurs in the environment and the organism creates microscopically tiny spores that, once airborne, are able to pass far into the depths of the lungs. These spores are released from the fungus when the soil is disturbed by the dog digging for gophers or simply by the dog probing the soils following the odor trails that they love so much. Much less common in cats (even though cats do their share of digging in dusty soil when they eliminate stool and urine) than in dogs, Blasto is easily inhaled into the dog's lungs. Infective spores are more likely to be present in organic soils such as are present along streams, lakes, ponds and even within the dried mud mortar of beaver lodges. Landscaping soil and even potting soil can harbor Blastomycosis organisms and any cat or dog digging up these soils may be exposed to Blastomycosis.

When in the soil the fungal phase of Blastomycosis releases vast numbers of extremely tiny spores that are cast away into the Chest X-ray of a dog with Blastomycosis dust and dirt stirred up when the soil is disturbed. Especially during dry periods in the environment, where the soil and spores may become more easily airborne, the potential for infection with Blastomycosis is greater. The spores are so tiny that the protective mucous lining of the respiratory tract is unable to attract all of them... and the spores settle deep in the alveolar sacs at the end of the respiratory tree. Finding themselves in a warm, moist and dark environment, rich in nutrients, the spores become infective yeast-like organisms and multiply in huge numbers. While inside the dog, the body's normal defense mechanisms can simply eliminate these spores and no disease results. However, if the load (numbers) of spores inhaled is very great or the dog is immune suppressed or stressed by other diseases or poor diet, the organisms may begin to reproduce rapidly and signs of disease occur. Once the spores have taken hold, they grow as single celled yeast forms rather than the fungal form. This is why the Blasto organism is called a biphasic organism... it can grow in the environment as a fungus and within a mammal as a yeast.

After inhalation of organisms the incubation period for Blasto can be from a few days to many weeks before any signs of disease show up. Fever of 104 to 105 degrees, poor appetite, low grade deep cough, loss of exercise tolerance, and listlessness are cardinal signs of Blastomycosis. Similar to the other systemic fungal infections, Blastomycosis can spread throughout the body from the lungs and invade lymph nodes, joints, eye structures and skin. Often the first evidence a veterinarian has of Blastomycosis is a small draining ulcer that looks like a small abscess. Sudden blindness, lameness, and blood in the urine may be the first signs of disease... sometimes showing up before any coughing is noticed.

The affected pets present with lethargy, lameness, poor appetite, ?not doing right? and may have a fever. Treatment may Examining the stained specimen for organisms. High power view of budding Blasto organisms.also be delayed because it is difficult to get a sample of the organism from a lymph node, skin cytology or trans-tracheal wash.? It is crucial that the organisms be identified under the microscope for establishing a positive diagnosis of a fungal disease such as Valley Fever or Blasto. Culturing infected material may take weeks and the patient simply cannot afford to wait even days for a diagnosis! Blood tests are equivocal. False positives and negatives are common.

The best and most direct method of establishing a definitive diagnosis is to gather tissue or fluid samples from infected areas such as a swollen lymph node, draining skin lesion or material coughed up by the patient. A needle biopsy of a lymph node is commonly done and can be performed without anesthesia. During the office call the veterinarian will stain the specimen cells on a microscope slide and look for the infective organisms. If organisms are seen, BINGO! Start treatment right now. If they aren?t seen, special stains at a diagnostic lab are required. The important thing to do is to BE PERSISTENT in striving to get a diagnosis for the elusive disease in disguise.


In the past, Amphotericin-B was the only known medication useful against Blastomycosis and the other systemic fungal organisms. Long term medication for fungal diseases may be necessary.It had to be given intravenously and with care to keep the dose from harming the kidneys. This medication has saved thousands of canine (and human) lives. Recently, though, researchers have provided us with oral medications just as effective in treating fungal infections. The most popular today are Itraconazole (Sporanox) and Fluconazole (Diflucan). These tablets are administered for three to six months (sometimes even longer) and your pharmacy bill will be substantial... but your formerly infected dog out in the yard playing fetch with the children wouldn?t be alive without it. Almost every dog that survives Blastomycosis will make a complete recovery and will run, play, hunt and live a completely normal life. However, the success of treatment depends upon a number of factors such as location of lesions, the age of the dog, nutritional status, and stage of the disease when treatment has begun. If Blastomycosis has spread to any bones, or the brain or spinal cord, treatment may not be rewarding. It seems as well that the organism often affects the optic nerves and a sudden blindness in an otherwise apparently healthy dog should alert the veterinarian to the possibility of Blasto as the cause. Once blinded by Blasto, the sight is never regained.

Whenever your dog is sick be sure to provide your veterinarian with a detailed patient history. And you should be persistent in seeking a definitive diagnosis. Persistent detective work is your best weapon for unmasking a disease such as Blastomycosis.