Leo was the picture of health until one day, one of his eyes seemed to bulge and cloud over. Suspecting glaucoma, his owner, Rachel Rehberg, raced the 4-year-old Saluki to the University of Florida College of Veterinary Medicine, where the ophthalmologist confirmed the eye was already blind. As is usually the case at teaching hospitals, a veterinary student performed a head-to-toe exam on Leo. The student pointed out a small sore between his foot pads.
“We were wondering why the ophthalmologist seemed so interested in his foot, when it was his eye that was the problem,” recounts Rehberg. “She quizzed me about his history, and I mentioned he’d moved in with me about 6 months earlier, moving down from Illinois when his former owner died. That seemed to really get the vet’s attention, and she started giving orders to culture his sore. And again, I’m thinking, it’s his eye, not his foot!”
Then, the vet revealed her suspicion: blastomycosis, a systemic fungal infection. When most people hear “fungal infection,” they think of athlete’s foot, ringworm, or something that seems pretty minor. But that couldn’t be further from the truth. Systemic fungal diseases are fungal infections that affect the entire body or multiple organs or systems within it, and are potentially deadly to both people and pets.
What Is Blastomycosis?
Blastomycosis is a common systemic fungal infection in dogs, says Dr. Andrew Hanzlicek, DVM, MS, DACVIM (SAIM), Director of Veterinary Medicine at MiraVista Diagnostics. “Blastomycosis is one of the most common invasive fungal infections in dogs and is a very important clinical consideration, especially in endemic areas (eastern US and Canada),” he explains. “It’s estimated that dogs are at least 10 times as likely as humans to get blastomycosis.” However, he notes that no reliable data exists on exactly how many dogs are infected each year.
“Across several published studies, long term survival (6-months after diagnosis) in dogs with blastomycosis is approximately 65%,” says Dr. Hanzlicek. “Thus, we still have much room for improvement in the areas of early diagnosis, treatment, and monitoring treatment.”
How Do Dogs Get Blastomycosis?
Dogs are more susceptible to many fungal diseases than humans, including blastomycosis. This could be because they’re always sniffing things on the ground. Dogs most often acquire the infection by inhaling the spores of the fungus Blastomyces dermatitis (B. dermatitidis), which lives in soil and decomposing wood and leaves. These spores are most common in the upper Midwest, but have also been found in almost the entire eastern part of the United States. The states with the highest incidence are Wisconsin, Minnesota, Missouri, Illinois, Michigan, Kentucky, West Virginia, Arkansas, Tennessee, North Carolina, South Carolina, Louisiana, and Mississippi. Other states include Indiana, Iowa, Ohio, Virginia, Georgia, Alabama and Vermont.
The spores travel to the lungs, where body heat transforms them to yeast. The infection may go unnoticed for weeks or months before causing any problems. In some cases, the dog’s immune system will kill the infection, and the dog is fine. But in other dogs, it can spread throughout the body. This can cause disease in various organs, which is what happened to Leo. The eyes are a common site for blastomycosis spread.
Dr. Klein, Chief Veterinarian at the American Kennel Club, notes that sporting and hound group breeds seem to be predisposed to blastomycosis. This is most likely because of increased exposure to high-risk areas during hunting. “Residence near a river or lake and access to recently excavated sites have been demonstrated to increase the risk of infection,” says Dr. Klein. “Most cases of canine blastomycosis are diagnosed in late summer or early fall.”
What Are Symptoms of Blastomycosis?
The symptoms of blastomycosis depend on which organs are affected. Since blastomycosis is inhaled, it settles in the lungs of about 65 to 85% of infected dogs. Patients most commonly have a cough, difficulty breathing, fever, and lethargy. Symptoms can vary greatly, since the disease can settle in many different organs and tissues.
When Blastomycosis affects the eyes, it’s known as ocular involvement. This happens in 20 to 50% of dogs infected with blastomycosis. Dog’s symptoms can include inflammation of the eyes, or sudden onset of blindness. These can happen before respiratory signs occur.
Another symptom is skin lesions of open, draining wounds without any known trauma. Wounds such as those Leo had on his foot affect about 30 to 50% of infected dogs. These lesions usually appear on the face, nose, or nail beds.
Bone involvement causing lameness affects about 30% of dogs. Less often, the testes, mammary glands, prostate, heart, and brain can be affected.
Your vet will consider blastomycosis when a dog has lethargy, fever, weight loss, and or lymph node enlargement. This, along with any or multiple of these signs, could point to blastomycosis.
How Is Blastomycosis Diagnosed?
Cell Sample Tests
When possible, vets will look at cells to see if samples like typical of blastomycosis. These cells are usually samples from skin lesions, lymph nodes, or tracheal washes. Veterinarians can usually identify blastomycosis in its yeast form, “Blastomyces.” But negative results don’t mean the dog isn’t infected with blastomycosis.
“Finding Blastomyces organisms (yeasts) in pathology samples confirms the diagnosis,” says Dr. Hanzlicek. But this diagnosis option isn’t always possible. Dr. Hanzlicek says that sometimes yeast can be too low to test positive.
Veterinarians can also use samples to grow a colony of Blastomyces. While this is a definitive test, it can take weeks to get results. Most patients can’t afford to wait that long.
Urine and Blood Samples
When a pathology sample doesn’t find any yeast, the dog could still be infected. As a precaution, a veterinarian should also send out a urine sample for an antigen test. Because antigen test results monitor infection levels during treatment, they’re also indicated when pathology does find Blastomyces. Dr. Hanzlicek says that with successful treatment, these antigen concentrations should decrease. When the disease relapses, they’d see an increase in antigen levels. Checking a urine sample when the disease is first suspected provides a baseline antigen level to see if treatment is working.
Your vet would send the urine sample out to MiraVista Diagnostics, which is the center for human and animal fungal testing in North America. The antigen test, if positive, will yield a number. The number of antigens helps show the severity of the infection. Dogs with higher antigen levels and greater lung or brain involvement have a lower survival rate.
About 4% of infected dogs will have a negative urine test but a positive blood serum test. So, if a veterinarian suspects a dog has blastomycosis, but the urine test is negative, a serum antigen test would be the next step. Leo’s urine antigen test score was off the charts, which isn’t an uncommon reading at first diagnosis.
How Is Blastomycosis Treated?
Treatment for blastomycosis often starts before the test results are in, as time may be critical. It may be too risky to wait for a confirmed diagnosis. Dogs are often very sick with advanced infection by the time they’re diagnosed.
Treatment is a long-term commitment — usually 6 months to a year, or longer. The first week or two is especially critical. In life-threatening cases, the drug amphotericin B may be recommended as a first course of treatment, but it has many side effects. If the fungal load is large, the dying fungus from antifungal drugs could cause inflammation. When the inflammation affects the lungs, dogs can die. Dogs may be given steroids during these first weeks to decrease inflammation.
Several antifungal drugs are available, including amphotericin B, itraconazole, fluconazole and terbinafine.
Itraconazole Forms
The drug of choice for blastomycosis is generally itraconazole. It comes in a brand-name product, “Sporonox,” as well as a generic form. Both are equally effective, but capsules should contain the pellet, not powdered, form of itraconazole. There’s a reason for this, notes Dr. Jennifer M. Reinhart, DVM, PhD, DACVIM (SAIM), DACVCP, a researcher at the University of Illinois College of Veterinary Medicine.
Dr. Reinhart says that Itraconazole doesn’t dissolve well in water, so it’s hard for the gut to absorb it. “To overcome this problem, the company who originally developed itraconazole used tiny sugar pellets and coated them with the itraconazole powder. This creates a lot of surface area from which the itraconazole can mix with water and dissolve, which will then allow the gut cells to absorb the drug,” Dr. Reinhart says. “A tablet or a gel cap filled with powder is essentially useless because these will just form a clump in the gut and not mix in with the water, so the drug can’t be absorbed.”
Monitoring Itraconazole Levels
Itraconazole levels are monitored through blood samples. It’s important to keep a close eye on these levels. There needs to be enough itraconazole to kill the fungus, but not too much. “Itraconazole is very effective for treating blastomycosis, but only if the drug levels are in the therapeutic range, kind of like finding a ‘sweet spot,'” Dr. Reinhart explains. Too much of the drug can cause side effects like upset stomach and liver damage.
This “sweet spot” in the blood levels is different for each dog. “Frustratingly, we don’t exactly know why different dogs have such different levels of itraconazole,” Dr. Reinhart says. “The two main factors are how well the dog’s gut absorbs the drug and how quickly the liver processes the drug and eliminates it from the body.” She says that different dogs have different abilities to absorb the drug from their intestines. Some dog’s livers process the drug faster than others. That’s why it’s important to monitor dogs’ individual levels.
Leo’s initial blood tests looked like he was in that sweet spot. But suddenly, his blood test indicated the itraconazole was at toxic levels. He was pulled from all medication while his liver recovered. When he resumed taking medication, it was with a lower dosage of itraconazole. His blood tests continued throughout his treatment and stayed at a safe level from then on.
Repeatedly measuring itraconazole levels is important, but it’s expensive and time-consuming. At this time, nobody knows how often it should be done. In an AKC Canine Health Foundation-funded project, Dr. Reinhart is studying blood levels of itraconazole that are repeatedly tested throughout therapy. “If we find that dogs’ drug levels are bouncing around a lot, that would mean we should be checking the levels more frequently,” Dr. Reinhart says. “We can adjust the dose to keep the levels in the target range.”
Antigen Monitoring
Another thing to monitor is the antigen levels of blastomycosis. This is done through urine tests every few weeks. When Leo was first diagnosed, his antigen levels were near the top of the scale. A few weeks later, these levels were lower again, but then stalled. Test after test showing the same level, likely an active blastomycosis infection. Finally, after a few months his antigen levels began to creep downward.
Is There a Cure for Blastomycosis?
A dog is considered cured of blastomycosis if they meet the following criteria:
- No clinical signs of the disease. They need to have had at least six months of treatment
- At least 6 months of treatment
- At least two consecutive antigen readings of 0 (zero)
When Leo reached his first zero reading, it was cause for celebration! But the next month his reading was again high. It would take several more months to achieve the two-in-a-row zero readings. Then, they went to check-ups every few months to make sure it stayed at zero.
Who Can I Turn To?
A dog’s blastomycosis diagnosis can be overwhelming. Progress is slow, expenses can be high, and worry can be even higher. But you’re not alone.
The Facebook group Blastomycosis Awareness Forum–Canine has more than 350,000 members. Many know what you’re going through. They’ve compiled information, lists of blastomycosis-savvy veterinarians, and drug sources, Most of all, they’re there to give advice and compassion.
“It was amazing to see so many other people and dogs going through what Leo and I were going through,” recalls Rehberg. “The success stories gave me hope”
Two years later, Leo appears completely cured. He adjusted to his missing eye very soon after the surgery, and hasn’t relapsed. In fact, he went on to finish his AKC conformation championship. He even won a specialty Best of Breed.
“That missing eye saved his life. Without the vet student noticing the sore on his foot, and without the ophthalmologist putting it all together, we’d have never known anything was wrong until it might have been too late,” says Rehberg. “That missing eye reminds me every day just how lucky we are.”