What is Blastomycosis?

Blastomycosis is an infection caused by Blastomyces dermatitidis, a type of fungus. This fungus is naturally occurring as mould in soil, but when it is exposed to body temperatures it can develop into yeast.

Which dogs get Blastomycosis?

All dogs can get Blastomycosis, and so can humans and cats. Some dogs are however more prone to this disease than other. Hunting and sporting dogs, as well as any other dog that spends a lot of time in soil in wet areas, are more at risk, since Blastomyces dermatitidis lives in sandy, acid rich soil – typically near waterways. Blastomycosis is more common in adult dogs, since puppies and old dogs are less likely to be sent out in wet soil. Veterinarians still don’t know why, but male dogs contract Blastomycosis more often than female dogs. A majority of the Blastomycosis infected dogs are 2-4 year old intact male dogs weighing 50-75 pounds.

Blastomycosis symptoms in dogs

Blastomycosis is usually transmitted to dogs by inhaled spores. These spores causes an infection of the lungs, but this type of infection is often self-limiting. If spores manages to penetrate damaged skin, they can cause a local skin infection. The most serious form of Blastomycosis is the generalized or disseminated form where Blastomyces dermatitidis have managed to spread from its original point of entry via the bloodstream of lymphatic system of the dog. This type of Blastomycosis can cause symptoms from the skin, subcutaneous tissues, eyes, bones, urogenital organs, and the brain. The exact symptoms varies depending on which organs that have been affected. Among the general symptoms that can be hard to pinpoint to a specific organ are loss of appetite, weight loss, gloominess and weakness, shortness of breath, a decreased ability to exercise, coughing, eye problems, and a fever that goes up to 103 degrees F or even higher and doesn’t decrease even though the dog is given normal antibiotics against bacteria. An infected dog can also develop skin lesions that produced pus or bloody material. 

Blastomycosis treatment for dogs

A very efficient way of treating Blastomycosis in dogs is to give Amphotericin B in the form of intravenous injections. The vet can either give your dog a slow IV drip over the course of several hours, or opt for fast IV bolus injections that are given 1-3 times per week until the dog has received its maximal cumulative dose. Amphotericin B used to be the standard therapy for Blastomycosis in dogs, but the problem with this drug is the risk for problematic side effects. The risk is even greater when the alternative with fast IV bolus injections is used. Today, Amphotericin B is therefore usually reserved for acute, life-threatening Blastomycosis infections in dogs. Even severely affected dogs normally show improvement within 3-5 days of Amphotericin B treatment. It is important to remember that Amphotericin B has a toxic effect on the dog's kidneys. Sometimes a veterinarian will have to delay the administration of the medication to give the kidneys a chance to recover.

Today, milder drugs have replaced the Amphotericin B therapy for milder cases of Blastomycosis in dogs. One commonly used medication is Ketoconazole, which can be given to the dog orally. In most cases, the dog should receive two doses per day instead of one big one. The problem with Ketoconazole is that it can take up to 10-14 days before any improvement is noticed in the dog, and Ketoconazole also have a lower curing rate than Amphotericin B. The positive thing is that it is much less damaging for the kidneys, and it can be administered even to dogs with compromised kidney function. In many cases, the vet will decide to combine Ketoconazole with Amphotericin B. This makes it possible to reduce the amount of Amphotericin B, thereby lowering the risk of kidney damage. Ketoconazole is however still somewhat liver toxic and the dog can start suffering from nausea, loss of appetite, and vomiting. It can also affect the fertility of male dogs and is not recommended for pregnant bitches.  

During recent years, more and more vets have begun using Itraconazole to treat dogs infected with Blastomycosis. This dog is given orally, and takes effect much more rapidly than Ketoconazole. In most cases, Itraconazole is administered two times per day to begin with, and then once day for 2-3 months. Itraconazole has the same cure rate as a combination of Amphotericin and Ketoconazole, but it is more expensive. In the United States, the owner of a 40 pound dog should be prepared to pay around US$10 per day for this medication, and heavier dogs will need even more Itraconazole, making it a really expensive option for big breeds. The side effects of Itraconazole are related to liver toxicity, just like with Ketoconazole treatment, but high doses of Itraconazole can also cause swelling of the legs and skin lesions.

Fungal Infections in dogs: (click for more info)
Blastomycosis in dogs
Cryptococcosis in dogs
Histoplasmosis in dogs
Phycomycosis in dogs
Pythiosis in dogs
Ringworm in dogs
Sporotrichosis in dogs