If your canine pal is a 2- to 4-year-old, intact male, large-breed dog and you live in either the Mississippi, Missouri, and Ohio river valleys; the Middle Atlantic states; southern Saskatchewan; Manitoba; Quebec; or southern Ontario — beware of the disease blastomycosis — it's potentially lethal. Introduced by the dimorphic, infectious fungus Blastomyces dermatitidis that invades via inhalation, this shapeshifting, ubiquitous spore then morphs into a deadly yeast that infects the lungs and spreads throughout a dog's body, from the central nervous system to the brain. And more bad news — it infects people, too — but you can't catch it from your dog. Contaminating sandy, acidic soil near fresh bodies of water, such as lakes and particularly rivers, this dangerous organism thrives on the high organic matter in the soil, a rich stew of decaying wood, animal excreta and moisture, that promotes its growth.
Early detection and treatment via antifungal therapy can head off the severe symptoms of this systemic fungal disease and offers a good prognosis for recovery unless the dog is immunocompromised. On the other hand, if blastomycosis goes undetected or signs of illness in a dog are neglected, the two most important negative prognostic factors are central nervous system involvement and severe lung disease. Further, dogs with pulmonary blastomycosis may rapidly deteriorate during the first three days of treatment. And sadly, the ratio for a fatal outcome is 50 percent within the first seven days of therapy. Similarly, If the brain is infected, the dog usually will die.
What is a systemic fungal disease and what will blastomycosis do to my dog.
You may wonder why 2-to-4-year-old, intact, large-breed dogs are more at risk for blastomycosis. Well, if that describes your dog, you probably already know — these big guys have a tendency to roam, sniff, and dig in the soil. Consequently, sporting dogs and hounds, for example, bloodhounds, are at greater risk for exposure during hunting. But dogs, in general, are more susceptible to blastomycosis than many other species — an estimated 10 times more likely than humans, and 100 times more likely than cats to become infected.
A primary fungal infection like blastomycosis is known as a systemic mycosis and dogs become infected by inhaling fungal spores. Settling into the airways, the spores start reproducing and travel through the body infecting other internal organs. Once the spores enter the lungs, the dog's body temperature converts them into large, invasive yeasts which form characteristic broad-based buds.
What symptoms and clinical signs of illness will I see in my dog if he has blastomycosis?
Recognizing the clinical signs of blastomycosis sooner, rather than later, makes all the difference in the world for your dog.
While many dogs show only vague signs of illness, seek veterinary care at once if he shows any of these common, non-specific signs of blastomycosis which occur in 40-to-60 percent of infected dogs:
- Loss of appetite and weight loss.
- Lethargy or lack of energy.
- Fever with higher than 103-degrees-Fahrenheit temperature.
Lung pathology occurs in 65-to-85 percent of dogs with blastomycosis. Watch for these clinical signs of compromised lungs in your dog:
- Exercise intolerance.
- Difficulty breathing or respiratory distress.
- Abnormally rapid breathing (tachypnea).
- Purple or bluish discoloration of mucous membranes and skin, which is caused by the tissues near the skin's surface having low oxygen saturation (cyanosis).
- Lung lesions are clinically silent, so although you can't see them, they may exist. A thoracic radiograph examination is typically recommended for suspected cases of blastomycosis, so ask your vet about it.
30-to-50 percent of dogs will present with one or more enlarged peripheral lymph nodes and lymphoid reactive hyperplasia, the normal response of the lymph nodes to infection or inflammation.
Ocular lesions occur in 20-to-50 percent of blastomycosis cases with inflammation of the interior of the eye(endophthalmitis) the most common abnormality. To preserve vision, a quick diagnosis and aggressive treatment are required. If your dog is showing any signs of blindness, it goes without saying, seek veterinary care immediately. Similarly, a long list of other ocular manifestations of blastomycosis such as granulomatous retinal detachment, vitreal hemorrhage, and corneal edema bode serious outcomes if not caught in time and treated.
Telltale signs of blastomycosis occur when the skin is affected. Manifesting in 30-to-50 percent of infected dogs, dermatologic issues such as masslike lesions and ulcerated skin lesions draining purulent fluid are common. This mode of infection affects the nasal planum, face, and nail beds.
When a solitary bone is infected with the Blastomyces dermatitidis organism, it causes lameness, another easy-to-spot clinical sign of blastomycosis. This occurs in up to 30 percent of infected dogs. Typically affecting the bones of the distal limbs, cytology or biopsy is the only way to distinguish between fungal and neoplastic disease. Symptoms, in this case, will be soft tissue swelling.
How is blastomycosis diagnosed in dogs?
Your veterinarian evaluates cues from your dog such as systemic inflammatory response and the site or sites of infection to help diagnose blastomycosis. Once the infection is suspected, several diagnostic tools come into play to arrive at a definitive diagnosis. Complete blood count and serum chemistry tests are conducted and any abnormalities are usually non-specific but reflect chronic inflammation. Thoracic radiograph imaging is a standard for blastomycosis diagnosis and may reveal lung lesions. Visibly identifying the organism through cytologic or histologic examination of infected tissues is also a typical diagnostic procedure which includes ocular and skin lesions, often expediting the diagnosis. In addition, serologic, urinary antigen, and polymerase chain reaction (PCR) tests seek to find evidence of the infection.
A relatively new antigen urine and serum test called enzyme immunoassay or EIA may aid veterinarians in diagnosing blastomycosis, so if blastomycosis is suspected in your dog, ask your veterinarian about its availability.
Treatment protocol and prognosis for blastomycosis in dogs, recovery, and relapse.
A review of the symptoms and manifestations of blastomycosis in dogs makes it clear that the prognosis for this infection is guarded, and variable. Tragically, not all infected dogs will survive. But, in spite of the odds, many dogs do survive and have antifungals — fluconazole and itraconazole — to thank for their recovery. With relatively few side effects, these drugs are administered over the long-term, often at least four-to-six-months, with success in many cases. Other drugs, including amphotericin B, ketoconazole, or a combination of anti-fungal drug therapies are also used with encouraging results in many dogs.
Nevertheless, blastomycosis is an insidious, potentially devastating disease that often claims its victims in relapse — more common when the fungus affects the nervous system, the testicles, or the eyes. Drugs often are not effective in penetrating the natural defensive barriers of the dog's body, thus making eradication of the organisms from these systems more difficult. Castration may be required to eliminate a testicular source of infection, and likewise, removal of one or both eyes is indicated in ocular infection, particularly if the dog has already been blinded by the disease.
Follow-up urinalyses with the MiraVista urine antigen test, evaluate treatment efficacy and is generally considered the benchmark to discontinue the medication.
Is blastomycosis contagious, and am I at risk of getting infected by my dog?
Good news! You won't become infected with blastomycosis directly from your dog — if you're healthy. However, frequenting the same area where your dog was infected; for example, at a river bank or any area surrounding a fresh body of water, puts you at risk of infection. Further, strict hygiene, such as wearing rubber gloves, is only common sense when handling and caring for any draining lesions associated with the illness. And even though the disease is not known to be contagious to humans, if your dog is diagnosed with blastomycosis, it's wise to consult with a physician if any of the human members of the household are:
- Infants or toddlers.
- Organ transplant patients.
- Undergoing chemotherapy.
- Diagnosed with HIV/AIDS.
Always check with your veterinarian before changing your pet’s diet, medication, or physical activity routines. This information is not a substitute for a vet’s opinion.