Blastomycosis is a fungal infection caused by the fungus Blastomyces dermatitidis. This fungus is commonly found in the river valleys of Tennessee, St. Lawrence, Ohio, Mississippi, and Missouri, as well as, the southern Mid-Atlantic States.
Exposure to this organism usually occurs within areas close to water ways and in areas where the ground has recently been disturbed. This fungus lives in the soil and soil disruption causes aerosolization of the fungal spores that are then inhaled. Inhalation is the primary route of infection. This disease cannot be transmitted directly from your pet to you; however, you live in the same environment as your pet, so you can also be exposed to the organism. . You should seek out the advice of a physician if any symptoms develop.
Once inhaled, the spores of the fungus can spread to other parts of the body. Where the spores end up will determine the clinical signs. Some signs you may notice in your pet include the following:
Eyes: Redness, discharge, swelling, squinting, elevation of the third eyelid, and blindness. Blasto can cause inﬂammation inside of the eye as well, leading to retinal detachment and glaucoma (see glaucoma handout). Oftentimes, ocular disease is the only sign of infection with Blastomyces. Fifty percent of infected dogs with ocular lesions will have evidence of disease in both eyes.
Skin: Draining or crusting skin lesions that are slow to heal.
Respiratory System: Coughing or increased breathing effort or rapid breathing.
Other: Decreased appetite, weight loss, fever, lameness, enlargement of lymph nodes and changes in mentation (neurologic abnormalities), which are more often observed in cats.
Notice many of these are fairly nonspecific signs and may result from many different disease processes, so an evaluation by your veterinarian is important.
Dogs are at high risk of infection: about 10 times more susceptible than humans and 100 times more susceptible than cats. The typical Blastomycosis patient is a large breed, male dog that spends a lot of time outdoors.
On average, it can take 5-12 weeks from the time of infection to the development of clinical signs (incubation time).
Depending on the clinical signs your pet is showing, your doctor may recommend certain tests. Blood, urine and skin lesion samples are commonly obtained. Sometimes a sample may be directly taken from the eye.
Your doctor may recommend chest radiographs (x-rays) because lung lesions can be present without any other clinical signs. If lung lesions are present, their resolution can be used to determine how long treatment will be necessary.
The treatment of choice is the oral antifungal Itraconazole. Depending on the severity of clinical signs, your doctor may recommend treatment for up to 9 months. While Itraconazole is a very safe drug, side effects may include liver disease and gastrointestinal upset. For these reasons, we recommend regular blood work to monitor for any side effects that may require changes to medication. Appropriate treatment for the eyes often includes anti-inﬂammatory eye drops, as well as, anti-glaucoma medications. Other oral medications and injections may also be recommended. Depending on the severity of clinical signs and inﬂammation within the eye, medical therapy may not be successful in keeping your pet visual and/or comfortable. At that point, surgical therapy may be required; if this is the case, your doctor will explain the options available for your pet. General supportive care may be necessary. Your doctor will work together with your referring veterinarian to make sure your pet is getting complete appropriate treatment.
Although some dogs lose their vision due to this infection, most recover from Blastomycosis and live healthy and happy lives following treatment. Most dogs do not have a recurrence of the disease, but re-infection is possible, which is why it is very important to monitor for return of any of the above clinical signs. If you see any, see your veterinarian as soon as possible. Although very rare, some dogs do not survive infection with Blastomyces.
While it is impossible to prevent Blastomycosis, being aware of your environment and knowing what clinical signs to look for are important. Be mindful of when and where you hike with your dog, especially near waterways and areas of significant ground disturbance, as is common with construction sites. Even superficial digging of the ground by your dog can release infectious spores into the air. Become familiar with the clinical signs mentioned above and talk to your doctor. If you are ever in doubt, do not hesitate to ask.