Blastomyces dermatitidis, or "blasto" for short, is a disease-causing fungus that can infect the skin and respiratory system of dogs, people, and occasionally cats. This organism is naturally occurring in the environment, especially in the acidic soils of the Midwest and central south. The fungus exists as a mold in the environment and becomes a yeast at body temperature.
According to Dr. Karen Campbell, a veterinarian at the University of Illinois Veterinary Teaching Hospital in Urbana who is board certified in both internal medicine and dermatology, animals can get infected only by direct contact with mold spores, which may be inhaled or may enter through broken skin when a person or animal touches contaminated soil. An infected animal is not at high risk of spreading the disease, since the organism is not shed in urine, saliva, or feces.
Signs of a blasto infection depend on the body system infected. The three forms of blastomycosis—cutaneous (skin), respiratory, and disseminated (spread to other organ systems)—often occur at the same time.
Cutaneous infection appears as sores on the skin. The sores are often "weepy," with pus draining from them. Although these infections can stay contained, according to Dr. Campbell, they can seriously damage nearby muscle and bone tissue if untreated.
The most common—and most life-threatening—form of blasto is pneumonia, since respiratory infection, if left untreated, can lead to severe inflammation of the lungs and eventual death. As with other respiratory diseases, infected dogs often cough, lose their appetite, become lethargic, and have difficulty breathing.
In some individuals, especially those with weakened immunity, the respiratory infection can spread to the kidneys, eyes, or skin, and occasionally to the spinal cord and brain.
Blastomycosis is very treatable with antifungal drugs, and improvement is usually seen within a few days, but the treatment can take a long time—up to six months—and gets expensive. Treatment is most effective when the disease is caught early, however, so proper treatment requires that the correct diagnosis is made early in the course of the disease.
When an animal with blasto is misdiagnosed with a bacterial infection and receives antibiotics, the fungal infection is allowed to progress, and by the time the blasto diagnosis occurs, it may be too late, especially in pneumonia cases.
Diagnosis of blasto is done by identifying blastomyces organisms in the body. Discharge from a skin wound can be swabbed, the trachea or lungs can be rinsed with saline, or fluid from organs such as lymph nodes can be extracted with a needle; these fluids can be then examined under a microscope to identify blasto yeast cells.
Blasto is more common in larger dogs, males, young dogs, and sporting and hunting breeds, since these dogs may spend more time outdoors, sniffing soil. Disease signs may not appear until 5 to 12 weeks after exposure to blasto. While blasto infection is virtually impossible to prevent since the fungus exists in the environment, blastomycosis can be overcome if diagnosed and treated early.
For more information about blastomycosis, consult your local veterinarian.
An archive of Pet Columns from the University of Illinois College of Veterinary Medicine is available online at http://vetmed.illinois.edu/petcolumns/. Requests for reprints of this article may be directed to Chris Beuoy, firstname.lastname@example.org.
Veterinary Extension/Office of Public Engagement