University of Wisconsin - Madison, Canine Blastomycosis

Frequently Asked Questions

My dog has blastomycosis. Is it contagious to me or other members of my family?

No, blastomycosis in dogs cannot be directly transmitted to people or other dogs. The infection is acquired by inhalation of spores from the environment, not by direct transfer of the yeast from one animal to another or to humans. The yeast form of the organism is too large to be inhaled into the lung, and hence cannot initiate the pulmonary infection that is required for systemic blastomycosis. One should be careful when handling exudate material from dogs, since direct inoculation of this into the skin could result in a local infection. However, this is quite rare and does not present a common hazard to those in contact with infected dogs.

We don't live in a highly endemic area for blastomycosis, yet our friend's dog developed severe blastomycosis and died. How can this be?

Infection can be acquired at various times during an animal or person's life. Epidemiologic evidence suggests that there may be brief periods of time in which the organism is present in the environment, and people or animals encountering it will be infected. These encounters might occur on vacations, or even brief outings, such as a hike through a marshland or wooded area, when the spores of the fungus were present. Thus, clinicians should inquire as to the recent history of patients and consider the possibility that blastomycosis might have been acquired while on an outing or vacation, if that individual does not reside in an area where the disease commonly occurs.

How do you diagnosis blastomycosis?

Diagnosis of blastomycosis can be made on a variety of evidence. The clinical signs and presentation of the animal or person can lead to suspicion of blastomycosis. Cytological examination of exudate material, biopsy specimens, or a transtracheal lavage fluid from dogs, should be examined microscopically to visualize the characteristic thick walled broad based budding yeasts of Blastomyces dermatitidis. There are serological tests available to detect an antibody response to the cell wall antigens of B. dermatitidis. Some of these tests are commercially available, and are based on either agar gel immunodiffusion (AGID) or complement fixation. Experimental studies have developed ELISA assays for crude or defined antigens of Blastomyces dermatitidis. These might be developed in the future to provide better diagnostic tests. The mold form of Blastomyces dermatitidis can be isolated from clinical specimens following inoculation onto mycological media, such as brain heart infusion agar supplemented with cycloheximide and cyclophosphamide (which inhibit saprophytic fungi and bacteria). However, B. dermatitidis cannot always be recovered from clinical specimens. When growing in its mold phase, B. dermatitidis presents a biohazard to laboratory personnel. Culture of B. dermatitidis, therefore, should not be performed unless one has well trained personnel and a certified biosafety cabinet in which the mold phase of the fungus can be safely manipulated.

For additional information on diagnosis of blastomycosis in dogs, please contact Dr. Pete MacWilliams, at the University of Wisconsin-Madison School of Veterinary Medicine.

Why is therapy of blastomycosis so long and expensive? Why not just give the dog or person common antibiotics?

Blastomyces dermatitidisis a fungus. Fungi have morphological and biochemical characteristics that are far different from the bacteria against which common antibiotics have been devised. Thus, these drugs are ineffective and cannot be used to treat blastomycosis or other fungal infections. In fact, the yeast of Blastomyces dermatitidis bears some biochemical resemblance to the cells of mammals themselves. Thus, one has to be careful in terms of devising drugs to attack these fungi, since some of these might also recognize and have adverse effects on cells of the host. This is best exemplified by the antifungal drug Amphotericin-B, which binds to ergosterol in the fungal membrane, but also binds somewhat to cholesterol in mammalian membranes. As a result, it commonly causes renal toxicity when it is used therapeutically.

There are a limited number of antifungal drugs that are effective against systemic fungal pathogens such as Blastomyces dermatitidis. These fall largely into two classes: 1) The polyene drugs, such as Amphotericin-B, that bind to ergosterol in the fungal cell membrane, and disrupt cytoplastic membrane integrity, leading to fungal cell death, 2) The imidazole and triazole family of drugs, which inhibit synthesis of ergosterol and related compounds in fungi. This family includes intrconazole (Sporanox), fluconazole (Diflucan), and ketoconazole (Nizoral). Because these fungal biochemical pathways are similar to those involved in steroid hormone synthesis in mammalian cells, these drugs can cause hormonal disturbances in the host.

Is there a vaccine against blastomycosis?

At present, there is no available vaccine for blastomycosis in animals or people. Serious clinical disease in humans is not common. For example, there are approximately 50 to 60 cases of human blastomycosis reported each year in Wisconsin. The disease appears to be much more common and severe in dogs, with there being probably 10 to 100 fold more cases each year in dogs than in humans in Wisconsin. Even this figure could be an underestimate, since owners will likely only seek veterinary care when their dogs develop significant pulmonary disease or some other clinical manifestation (eye or skin infection). Thus, subclinical B. dermatitidis infection may go unrecognized and unreported. There are experimental vaccines that have been developed and tested in lab animals. Some of these will protect against experimental challenge in mice, but at present there is no approved vaccine available that will protect against naturally acquired infection in dogs or people.

What is known about the host pathogen interactions in blastomycosis?

We have a limited understanding of the host-pathogen interactions that occur in blastomycosis. Recent work done by Dr. Bruce Klein, of the University of Wisconsin School of Medicine, indicated that a surface antigen on the yeast (WI-1) is an immunodominant antigen that is recognized by antibodies in the serum of infected people and dogs. This WI-1 antigen also serves as a target for a cellular immune response (delayed type hypersensitivity) in infected individuals. In addition, it appears that the WI-1 antigen also binds to adhesion molecules (integrins) on human leukocytes that facilitate adherence of the yeast with those cells. Other information on virulence mechanisms of B. dermatitidis are limited.

Blastomycosis results in a significant inflammatory response in the host. In humans, this is characterized by a granulomatous-type of inflammation in which macrophages and lymphoid cells predominant. Apparently, this is often an effective form of host defense, since mild or subclinical infection in people will sometimes resolve without antifungal therapy. In dogs, blastomycosis typically elicits a pyogranulomatous inflammatory response in which large numbers of neutrophils are present. When exudate material, or transtracheal lavage fluid, is examined microscopically, it is common to see aggregates of neutrophils and other leukocytes surrounding the broad-based budding yeasts of B. dermatitidis. It is apparent that there is considerable interaction going on between the host inflammatory cells and the yeast, but this does not seem to be effective in preventing the multiplication and spread of the infection. What allows the yeast to resist attack by these inflammatory cells, and what inflammatory mediators are released by these cells as the result of their encounter with the fungus, have not been well delineated. These and related questions are the subject of research here at the University of Wisconsin, and elsewhere.

Does infection with HIV virus increase susceptibility to blastomycosis?

Blastomycosis is not one of the more common infections afflicting those who are HIV positive. However, there are documented cases of severe disease in people who were HIV positive, and then subsequently infected with the fungus. The detrimental effects of HIV infection on cellular immunity would be expected to reduce resistance to a pathogen such as B. dermatitidis. However, the infrequent exposure of people to the fungus, particularly if one does not live in a highly endemic area, places it lower on the list of opportunistic infections that are of concern in the HIV population.

Is human blastomycosis a reportable disease?

Blastomycosis is not a required reportable disease at the national level (U.S. Centers for Disease Control). However, certain states (Wisconsin is one) require that cases of blastomycosis be reported to the state Department of Public Health, or State Epidemiologist. This information is important for monitoring outbreaks, unusual disease presentations, new risk factors, treatment failures, etc., that reflect ongoing or new epidemiological trends of the disease at the state level. It was just this sort of information that led to investigation of the Eagle River , Wisconsin outbreak from which the first convincing environmental isolation of B. dermatitidis was obtained.

How do I tell if B. dermatitidis is present in the soil around my residence or vacation home?

Unfortunately there is no practical or reliable method for isolating B. dermatitidis from the soil. Nor is there any means of eliminating it from the soil or any area associated with acquisition of the infection.


Introduction FAQ Gallery Contact Info References Home		Frequently Asked Questions My dog has blastomycosis. Is it contagious to me or other members of my family? No, blastomycosis in dogs cannot be directly transmitted to people or other dogs. The infection is acquired by inhalation of spores from the environment, not by direct transfer of the yeast from one animal to another or to humans. The yeast form of the organism is too large to be inhaled into the lung, and hence cannot initiate the pulmonary infection that is required for systemic blastomycosis. One should be careful when handling exudate material from dogs, since direct inoculation of this into the skin could result in a local infection. However, this is quite rare and does not present a common hazard to those in contact with infected dogs. We don't live in a highly endemic area for blastomycosis, yet our friend's dog developed severe blastomycosis and died. How can this be? Infection can be acquired at various times during an animal or person's life. Epidemiologic evidence suggests that there may be brief periods of time in which the organism is present in the environment, and people or animals encountering it will be infected. These encounters might occur on vacations, or even brief outings, such as a hike through a marshland or wooded area, when the spores of the fungus were present. Thus, clinicians should inquire as to the recent history of patients and consider the possibility that blastomycosis might have been acquired while on an outing or vacation, if that individual does not reside in an area where the disease commonly occurs. How do you diagnosis blastomycosis? Diagnosis of blastomycosis can be made on a variety of evidence. The clinical signs and presentation of the animal or person can lead to suspicion of blastomycosis. Cytological examination of exudate material, biopsy specimens, or a transtracheal lavage fluid from dogs, should be examined microscopically to visualize the characteristic thick walled broad based budding yeasts of Blastomyces dermatitidis. There are serological tests available to detect an antibody response to the cell wall antigens of B. dermatitidis. Some of these tests are commercially available, and are based on either agar gel immunodiffusion (AGID) or complement fixation. Experimental studies have developed ELISA assays for crude or defined antigens of Blastomyces dermatitidis. These might be developed in the future to provide better diagnostic tests. The mold form of Blastomyces dermatitidis can be isolated from clinical specimens following inoculation onto mycological media, such as brain heart infusion agar supplemented with cycloheximide and cyclophosphamide (which inhibit saprophytic fungi and bacteria). However, B. dermatitidis cannot always be recovered from clinical specimens. When growing in its mold phase, B. dermatitidis presents a biohazard to laboratory personnel. Culture of B. dermatitidis, therefore, should not be performed unless one has well trained personnel and a certified biosafety cabinet in which the mold phase of the fungus can be safely manipulated. For additional information on diagnosis of blastomycosis in dogs, please contact Dr. Pete MacWilliams, at the University of Wisconsin-Madison School of Veterinary Medicine. Why is therapy of blastomycosis so long and expensive? Why not just give the dog or person common antibiotics? Blastomyces dermatitidisis a fungus. Fungi have morphological and biochemical characteristics that are far different from the bacteria against which common antibiotics have been devised. Thus, these drugs are ineffective and cannot be used to treat blastomycosis or other fungal infections. In fact, the yeast of Blastomyces dermatitidis bears some biochemical resemblance to the cells of mammals themselves. Thus, one has to be careful in terms of devising drugs to attack these fungi, since some of these might also recognize and have adverse effects on cells of the host. This is best exemplified by the antifungal drug Amphotericin-B, which binds to ergosterol in the fungal membrane, but also binds somewhat to cholesterol in mammalian membranes. As a result, it commonly causes renal toxicity when it is used therapeutically. There are a limited number of antifungal drugs that are effective against systemic fungal pathogens such as Blastomyces dermatitidis. These fall largely into two classes: 1) The polyene drugs, such as Amphotericin-B, that bind to ergosterol in the fungal cell membrane, and disrupt cytoplastic membrane integrity, leading to fungal cell death, 2) The imidazole and triazole family of drugs, which inhibit synthesis of ergosterol and related compounds in fungi. This family includes intrconazole (Sporanox), fluconazole (Diflucan), and ketoconazole (Nizoral). Because these fungal biochemical pathways are similar to those involved in steroid hormone synthesis in mammalian cells, these drugs can cause hormonal disturbances in the host. Is there a vaccine against blastomycosis? At present, there is no available vaccine for blastomycosis in animals or people. Serious clinical disease in humans is not common. For example, there are approximately 50 to 60 cases of human blastomycosis reported each year in Wisconsin. The disease appears to be much more common and severe in dogs, with there being probably 10 to 100 fold more cases each year in dogs than in humans in Wisconsin. Even this figure could be an underestimate, since owners will likely only seek veterinary care when their dogs develop significant pulmonary disease or some other clinical manifestation (eye or skin infection). Thus, subclinical B. dermatitidis infection may go unrecognized and unreported. There are experimental vaccines that have been developed and tested in lab animals. Some of these will protect against experimental challenge in mice, but at present there is no approved vaccine available that will protect against naturally acquired infection in dogs or people. What is known about the host pathogen interactions in blastomycosis? We have a limited understanding of the host-pathogen interactions that occur in blastomycosis. Recent work done by Dr. Bruce Klein, of the University of Wisconsin School of Medicine, indicated that a surface antigen on the yeast (WI-1) is an immunodominant antigen that is recognized by antibodies in the serum of infected people and dogs. This WI-1 antigen also serves as a target for a cellular immune response (delayed type hypersensitivity) in infected individuals. In addition, it appears that the WI-1 antigen also binds to adhesion molecules (integrins) on human leukocytes that facilitate adherence of the yeast with those cells. Other information on virulence mechanisms of B. dermatitidis are limited. Blastomycosis results in a significant inflammatory response in the host. In humans, this is characterized by a granulomatous-type of inflammation in which macrophages and lymphoid cells predominant. Apparently, this is often an effective form of host defense, since mild or subclinical infection in people will sometimes resolve without antifungal therapy. In dogs, blastomycosis typically elicits a pyogranulomatous inflammatory response in which large numbers of neutrophils are present. When exudate material, or transtracheal lavage fluid, is examined microscopically, it is common to see aggregates of neutrophils and other leukocytes surrounding the broad-based budding yeasts of B. dermatitidis. It is apparent that there is considerable interaction going on between the host inflammatory cells and the yeast, but this does not seem to be effective in preventing the multiplication and spread of the infection. What allows the yeast to resist attack by these inflammatory cells, and what inflammatory mediators are released by these cells as the result of their encounter with the fungus, have not been well delineated. These and related questions are the subject of research here at the University of Wisconsin, and elsewhere. Does infection with HIV virus increase susceptibility to blastomycosis? Blastomycosis is not one of the more common infections afflicting those who are HIV positive. However, there are documented cases of severe disease in people who were HIV positive, and then subsequently infected with the fungus. The detrimental effects of HIV infection on cellular immunity would be expected to reduce resistance to a pathogen such as B. dermatitidis. However, the infrequent exposure of people to the fungus, particularly if one does not live in a highly endemic area, places it lower on the list of opportunistic infections that are of concern in the HIV population. Is human blastomycosis a reportable disease? Blastomycosis is not a required reportable disease at the national level (U.S. Centers for Disease Control). However, certain states (Wisconsin is one) require that cases of blastomycosis be reported to the state Department of Public Health, or State Epidemiologist. This information is important for monitoring outbreaks, unusual disease presentations, new risk factors, treatment failures, etc., that reflect ongoing or new epidemiological trends of the disease at the state level. It was just this sort of information that led to investigation of the Eagle River , Wisconsin outbreak from which the first convincing environmental isolation of B. dermatitidis was obtained. How do I tell if B. dermatitidis is present in the soil around my residence or vacation home? Unfortunately there is no practical or reliable method for isolating B. dermatitidis from the soil. Nor is there any means of eliminating it from the soil or any area associated with acquisition of the infection.