What Is Uveitis?
Feline uveitis, or intraocular inflammation in cats, has previously been discussed in our newsletter. Uveitis is a form of ocular inflammation which affects the uvea or pigmented layers of the inside of the eye and is also a very common diagnosis in dogs. Just as dogs and cats can have differing personalities, they also are affected by unique conditions to their species. A potential cause of uveitis which is seen more commonly in dogs is a fungal infection known as blastomycosis. This type of infection affects a dog’s systemic health, and can also lead to uveitis, discomfort, loss of vision or even loss of an eye. Depending on a dog’s eye exam, age, breed and travel history, blastomycosis testing may be recommended as this is a potentially treatable disease.
What Is Blastomycosis?
Blastomycosis is a fungal infection caused by inhaling the Blastomyces fungal organism. In dogs, the most common organism is Blastomyces dermatidis. This fungus lives in the soil as infective spores which are present in the environment. These spores can be inhaled by dogs and then change their form in infected
tissues inside of the body. Most often, infection starts in the lungs and can lead to decreased appetite and activity, fever, weight loss, serious respiratory disease and even skin lesions. Close to half of dogs infected with Blastomyces dermatidis develop ocular signs, and half of those dogs can have involvement of both eyes.
What Ocular Signs Are Seen From Blastomycosis?
On the eye examination, your ophthalmologist may notice inflammation inside of the front part of the eye, inflammation of the structures at the back of the eye (retina, choroid, optic nerve), retinal bleeding or retinal detachment. A predisposition for large breed, intact, young dogs exists with blastomycosis testing, however, any dog living in or traveling to an endemic area can be exposed to the organism. In the United States, Blastomyces is endemic to the Ohio and Mississippi River valleys and the Great Lakes.
What Tests Are Performed?
If a dog presents with intraocular inflammation and there is any suspicion of a fungal infection, tests to assess for infection and systemic health will be recommended. Tests which are commonly recommended for dogs with uveitis include systemic bloodwork and urine testing to screen for signs of infection, endocrine disease, kidney disease and other systemic illness. Abdominal ultrasound may be recommended to look for evidence of cancer. Chest x-rays are useful in looking for cancer that has spread to the lungs, but they can also aid in a diagnosis of fungal infection since changes in the appearance of the lungs on x-rays is a common finding in dogs with a systemic fungal infection. A urine Blastomyces test is a non-invasive and effective way of diagnosing blastomycosis in dogs. Biopsy or tissue sampling can be challenging based on the location of infection. However, lymph node aspirates may also be recommended.
How Is Blastomycosis Treated?
If a diagnosis of blastomycosis is confirmed, oral anti-fungal therapy may be recommended. Traditional oral antifungal therapy is continued past the time that a negative blastomycosis test is achieved. Aggressive oral and topical anti-inflammatory therapy is utilized to control intraocular inflammation and provide comfort. Even with aggressive medical therapy, many dogs can go on to develop painful glaucoma and blindness, at which time surgical removal of the eye (enucleation) and biopsy may be recommended to improve comfort.
The goal with treatment of any canine uveitis case is to determine the underlying cause, preserve vision, control inflammation and improve ocular comfort. If Blastomyces fungal infection is suspected, a non-invasive urine test and chest x-rays can help make a diagnosis in addition to systemic blood work. If a diagnosis of blastomycosis is made, oral antifungal therapy and a monitoring plan can be started promptly.