Emmy's first relapse was a judgement error, in that a spot on her lung xray was thought to be scar tissue--not uncommon, and treatment was stopped. She relapsed within a few weeks.
The second treatment was just over five months, no symptoms remained other than the swelling that was above where the initial lesions were excised. This appeared during treatments and was also thought to be scar tissue/drug side-effect, which is also common to see in the leg area after high dose anti-fungal treatment. Due to the potential for organ damage from long term high dose use of anti-fungals and because Xrays were now normal both of the leg and lungs we stopped treatment. She relapsed a week short of seven months later with lympatic system bumps on her chest above the affected leg. Biopsies of both areas came back positive for blasto.
Although the vets here treat blasto fairly often in dogs and occasionally cats they did not have many that relapsed after treatments, and their standard treatment was between 2-6 months in successful cases. Now that I have learned about it, we realize Emmy was a severe case that should have had at least six months of initial treatment, but hindsight isn't going to help us now. We have all learned from this, unfortunately at Emmy's expense which brings us to where we are now.
In regard to how the antifungals work, my understanding is the fungal spores once inhaled or introduced via punctures produce a budding yeast, and it is actually the yeast itself that is kiilled by the drug. The initial kill of the yeast causes the autoimmune reaction that some dogs simply cannot survive. This yeast infection becomes systemic and as it is killed off you see improvement in the lung snowstorm. I surmise that in most cases the actual fungal spores reach a point where they cannot survive when they are rendered completely unable to reproduce from treatment, which cures the infection, or 100% of the spores became active and the resulting yeast is all killed off by the drug resulting in a cure. However, if some spores survive, then a relapse occurs. Then there is the theory that the spores can actuallly seed in some cases in organs and bone, and stay dormant. This is considered a remission period. I was shocked to see that in one study it could be up to three years, which means that the dog has not re-infected but actually relapsed. If you look at the one article I have handy at this link on page 3 it discusses this latent period.
http://www.miravistalabs.com/Files/pdf/BlastomycosisinDogs2007.pdfThis is dis-heartening to say the least, but it certainly mirrors Dr Stack's article regarding using prophylactic long term treatment for relapse cases like Emmy because basically you have no way to determine what situation you are dealing with. There is no way to know 100% if blasto is gone or dormant only time will tell. Each case is different. If you have relapses, it is more likely that you are dealing with seeding. Each relapse causes more damage so the risk of long term side-effects of the drug outweigh the ongoing damage from relapses. Remember that spores are nature's way of insuring survival......they have been around for thousands of years and are designed to be dormant until ideal conditions exist to activate. In my readings, I have found more references to humans that must remain on long term low dose therapy for blastomycosis which I assume can be the same for dogs from what we are seeing with Emmy.
To address whether our dogs are still exposed to blasto, there is no way to know where it is, but to assume it is everywhere, so yes they are. We live on an island in Lake Huron, so we know we have a higher risk area here. However, on a lighter note, I have a lady in my agility class which is in a mainland town located 2 hours from here, and not known as a blasto area. She tells me that 20 years ago she lost a dog to blasto. She has lived and exercised her dogs in the same woods and areas since and has never had another case. At the kennel where I take my dogs for boarding which is located on the mainland 2 hours in the opposite direction, the staff have only known people with the infection, mostly hunters. All of our other dogs were in the same area at the time Emmy was infected, and are all fine. But that's a whole other topic as well. Our vets mostly see successful cases. I believe that early diagnosis and length of initial treatment is the key to successful cases.
Yesterday I was speaking to a retired arborist that worked in various areas for Ontario Hydro. He was taught that blasto was basically everywhere, and was taught what to look for in forestry areas that would provide ideal conditions for it to grow in order to take respiratory precautions. He did have some interesting stuff to say about mulch, if I can get it from him I will post it on the mulch topic.
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Topic: Blastomycosis Prophylaxis (Read 1038 times)