Blasto: A little yeast spoils the loaf
Blastomycosis, frequently shortened to simply "blasto," is a fungal disease caused by the organism Blastomyces dermatitides
By Ben J. CharacterWe all know how important our dog's noses are to their (and our) success while afield, but what you may not know is that the nose is the route for acquiring a very deadly fungal infection called blastomycosis.
What is blasto?
Blastomycosis, frequently shortened to simply "blasto," is a fungal disease caused by the organism Blastomyces dermatitides. In nature Blastomyces lives in the soil in the fungal form, but when it is inhaled into the warmer temperature of a body cavity (dog's or man's) it changes into a yeast form. It is this yeast that is so deadly.
The blasto fungus is found in geographical areas that promote moist soil. Deltas, swamps and marshes are common areas, but so are those areas with pothole ponds, nearby rivers, and especially humid climates that promote high soil moisture contents. Specifically the major river valleys of the country (Mississippi, Ohio, etc), Mid-Atlantic States and the Canadian provinces of Quebec, Manitoba, and Ontario, are all considered enzootic for the disease. Of course, the more time spent sniffing around such ground the higher the chance of infection as well.
How blasto effects dog
Blastomycosis is almost always acquired due to inhalation of the spores. Once inside the respiratory passages, the lungs are usually the first organ system to become infected but after this the organism seldom just simply enjoys this success. Next, it may spread to other organ systems including the skin, eyes, bones, lymph nodes, subcutaneous tissues, nose, brain, and testes.
Dogs with blastomycosis usually, but not always have a fever, and/or a cough. These coughs are often dry to begin with, and may have been present for months if not severe enough to concern an owner immediately. Usually involved to some degree, the lymph nodes become enlarged and affected dogs often experience weight loss to the point of emaciation. Involvement in other areas exhibit complementary symptoms.
Diagnosis
The only 100% positive way to diagnose blasto is to find the organism in the body. This can be done by taking needle samples (called "aspirates"), finding it in discharge from the skin or respiratory system, or from biopsies.
Other tests that frequently will suggest a diagnosis include x-rays or blood tests. If there is a current pneumonia, X-rays of the chest will usually show changes of inflammation in the lungs that are frequently described as a "snowstorm" in appearance. Bone x-rays may show bone destruction and repair attempts, as may nasal films.
Although blood tests are available, they are not as good or as accurate as finding the organism. In fact, many dogs with no current infection my test positive because of previous successful immune responses to the organism. On the other hand, many dogs with full-blown infections have negative blood tests specifically because they are not mounting an adequate immune response. The best a blood test can tell you is that the dog has been exposed to blasto and that it is, or has, mounted an immune response to it.
Treatments
| About Ben Character | |
|
Dr. Character is a freelance writer and private veterinary practitioner
concentrating on sporting dog issues. He has practiced large and small animal medicine and surgery since graduating from Auburn University. Recently, he went on to complete post-doctoral studies at Mississippi State University. Dr. Character is a certified PennHIP member and writes for magazines such as Retriever Journal and Pointing Dog Journal. He is an avid outdoorsman who resides in Union, Alabama, south of Tuscaloosa, with his wife and two children. |
Because a blasto is a fungal disease, clinical symptoms do not resolve with routine antibiotic treatment.
Successful treatment involves using anti-fungal drugs that are sometimes toxic themselves, making blasto treatment a serious decision. Several drugs are available to treat fungal disease like blasto. The most effective, easiest, and most importantly, safest treatment to use is the drug Itraconazole. Although more expensive, this newer drug is much safer than older drugs like ketoconazole or amphotericin-B that were formally used to treat blasto.
When caught early the chance of curing a case of blast is relatively good. However, even the safest choice of treatment is not without potential to actually make the condition worse rather than better. This happens when in the process of killing the organism, the resulting inflammatory response causes too much damage to the organ involved. The most common form of "treatment death" is when an infection in the lung tissues is treated resulting in such a massive pneumonia that the patient dies from respiratory failure. This usually happens during the first week of treatment if it is going to occur.
Long-term effects on performance
For the bird dog hunter or trainer, or other performance dog owner, the long-term implications of a blasto infection should be considered. There aren't many areas that blasto effects that are not detrimental to the performance dog.
Prevention
Currently, there is no specific prevention for blastomycosis except awareness of the disease in your area and prompt medical attention if clinical signs develop. If you have dog that contracts the disease, remember that your dog picked up the infection from the soil — therefore, your dog, or others in the pack, may be exposed again.
